No More Punctures, Please!

“I have had three punctures on my Brompton since Christmas.The first in the front Marathon, the second in the rear Brompton tyre, prompting me to change it for a Marathon.The third was in the front Marathon again, causing me to regret spending on the rear tyre change. Just to make it worse, Mosquito Bikes fitted a 5/8in (16mm) Schwalbe 4a AV tube that is supposed to stretch to 13/8in (37mm). When it’s stretched that thin, how long will it last?

What BSI tests, if any, apply to kevlar-reinforced tyres? If there are none, what are the closest applicable to motorcycle tyres?”

Mike Hargaden, London

Punctures are a big problem for some people, under some conditions, while others hardly get to see a flat tyre these days. In general, any solution that prevents foreign bodies penetrating the tube (and there are many) will increase rolling resistance, because tough or springy extra layers don’t like to flex, as a tyre must.They obviously increase weight too, and extra weight in the tyre can result in a less sprightly ride and slower response, making the bike feel turgid and heavy. So, even when they work, it’s not all good news.

As for 16-inch (349mm) tyres, the A to B readers’ tyre survey (see A to B 40) suggests that the standard Brompton tyre punctures about every thousand miles, the ‘Green Flash’ kevlar-banded Brompton tyre a little more frequently, and the kevlar-banded Marathon about every 860 miles.This tends to back up my own observations, so taking weight, price and poor rolling resistance into account, I simply wouldn’t recommend kevlar tyres. It may well be that certain types of band perform better than others, but I have yet to see published research on the matter.

Puncture-proof, at a terrible cost, are the so-called ‘solid’ tyres.These may be just tolerable on a 26-inch wheel, but at 16-inch the high rolling resistance and ‘wooden’ feel make these things more trouble than they’re worth.The same goes for ‘solid’ foam inner tubes, about which the less said the better.

Raleigh extra-thick Puncture-Resistant inner tubes provide a good low-tech compromise, but these may no longer be available in small sizes. I fitted a pair to a Brompton two years ago and I’m still waiting for the tyres to deflate. Schwalbe uses a similar technique on its Marathon Plus tyre, which has a 5mm thick flexible india rubber belt under the tread. These tyres are heavy and only produced down to 20- inch (47x406mm), but a 349mm variant should be available soon. I am currently testing a pair of 20-inch examples and will release data in future issues.

Schwalbe Marathon Plus - the thick rubber band prevents penetration

Many proprietory tyre liners are available, but if wrongly fitted these can cause more trouble than they’re worth. As for the tube, Schwalbe does indeed offer a simplified line- up, with typically four or five similar tyres sharing the same tube. However, you should have been offered the 4AV, which is designed to stretch from 28mm to 37mm. I can find no record of the 16mm Schwalbe 4a, which sounds very tiny, and would be quite unsuitable for stretching to 37mm.

Motorcycles do, indeed, puncture less frequently than bicycles, but they also have a lot more power available to roll the tyres, which can thus be made a lot thicker. As minimum horsepower machines, bicycles will always require lightweight and thus vulnerable tyres.

The subject of tyre technology comes up rather frequently on these pages, mainly because their inherently higher rolling resistance tends to put small-wheelers at the cutting edge.

In the mid-1990s, small tyres were at a considerable disadvantage against their bigger cousins in terms of rolling efficiency, but this was much reduced with the arrival of the Primo and Brompton tyres, whose paper-thin sidewalls flexed more easily as the tyre rolled, reducing rolling resistance. Ever since, the boffins have been burning the midnight oil searching for further gains, with the primary work being carried out at Greenspeed, the Australian recumbent manufacturer, and Brompton. Folding bikes need small wheels for reasons of folded size, of course, but recumbent designers are showing an interest in the same tyres, primarily looking for a small frontal area and reduced wind resistance. As we saw in A to B 39, Greenspeed is starting to adopt the 16-inch (more correctly 349mm) tyre on its recumbent trikes for just these reasons, and I am indebted to the company for access to its latest research in reducing the already small rolling penalty inherent with these tyres.

The Theory

Why does a tyre experience rolling resistance? Most of the energy is absorbed around the contact patch, the crucial zone where the doughnut-shaped tyre and inner tube mould themselves briefly to the flat road surface. If tyres were 100% springy, this wouldn’t matter (although the rider would probably fly off on the first bump), but rubber exhibits a useful self-damping characteristic known as ‘hysteresis’, which effectively means that not all the deformation energy is recovered when the tyre resumes its shape. This damping effect turns motion into heat, and the process takes place continuously as a tyre rolls. In really bad cases, the tyre will feel warm after a hard ride. Small tyres offer greater resistance than larger ones, because the more sharply curved tyre has to bend more acutely to become flat, and visa-versa when reassuming the curve.

As every cyclist, motorcyclist, and indeed motorist, should be aware, the easiest way to reduce the size of the contact patch, and thus the rolling resistance, is to put more air pressure in the tyres.This seems to work in two ways – firstly by reducing the circumference of the contact patch – the ‘battle front’ of rubber doing the work – and secondly by reducing the angle through which the rubber has to flex when it hits the road. Watch an old chap ride past on a Raleigh Shopper with half-inflated tyres, and you will see all the negative factors at work: a small diameter tyre, large contact patch and extreme angles of flex. One is sometimes tempted to offer a few pump-fulls of air.

There is, however, a limit to the improvement that can be made through air pressure alone, particularly on a bicycle without suspension. Pneumatic rubber tyres have been so very successful because they absorb lumps, bumps and vibrations from the road surface. Inflate a tyre really hard and it begins to act like a rigid disc, which would only be good news if the road were as flat and smooth as a mirror. In practice, roads are more or less corrugated, and a solid tyre will pass these surface irregularities to the vehicle and rider. This is not only uncomfortable, but wasteful, because energy is thrown away as the bike vibrates – effectively lifting and dropping the mass of the bike and rider.

Wider Tyres

Greenspeed 40mm tyres on the Brompton - note the slick tread and very tight clearance around the rear tyre

Tyre shape seems to be worth looking at. Conventional orthodoxy has it that a narrow high-pressure tyre rolls better than a wider low-pressure example.We need only compare the performance of the original Moulton, with its narrow high- pressure tyres, and the frightful Raleigh RSW, equipped with wide low- pressure tyres. Narrow tyres do have advantages – low weight primarily, plus reduced frontal area (and thus wind resistance) – but do they really roll better than wide tyres?

Whatever theoretical disadvantages wide tyres might have, it seems that when we compare like with like (the Raleigh tyres were not only low-pressure, but had heavy, stiff sidewalls) they actually perform rather well. Regular readers may recall my slight disappointment with the narrow high-pressure Schwalbe Stelvio, launched in the 349mm size in early 2003.This 28mm wide tyre rolled slightly worse than the ‘cooking’ 37mm Brompton tyre and gave an inferior ride. In that case, might a wider tyre not roll even better?

Observing that wide tyres, even cheap ones, sometimes rolled better than narrow tyres, Ian Sims of Greenspeed decided to develop his own. Like the Primo and Brompton, the tyre has thin, supple sidewalls, but with a completely slick tread and a width of 40mm (against 37mm).Weight is 280g, against 200-250g for the 37mm tyres.

Greenspeed was kind enough to supply a pair of these new ‘Scorchers’, which I fitted to a Brompton – easy enough on the front, but a rather complex operation on the back, due to the tight clearances. After a period of running-in, the tyres proved surprisingly fast on my standard roll-down test, beating the Primo and Brompton tyres by a small but identifiable margin. Intriguingly, they were also more comfortable than the narrow tyres, under identical conditions.Why?

Some Experiments

At the same pressure and carrying the same load, the contact patches are of near identical length, but the width varies broadly in proportion to the width of the tyre

It is widely assumed that – for a given tyre pressure, loading and wheel diameter – the area of the contact patch will always be the same, irrespective of tyre width: a long and thin patch on a narrow tyre, and a short fat one on a wide tyre. As the crucial dimension is generally assumed to be the patch circumference, it seemed to make sense to aim for a round contact patch, with the shortest possible circumference. Hence the move towards wider tyres.

Perhaps surprisingly, this turns out not to be case, or at least, not with tyres of conventional construction in the 16- inch size. Comparing the 28mm Schwalbe Stelvio, 37mm Primo Comet and 40mm Greenspeed Scorcher, with the same loading and tyre pressure, I found the length of the tyre contact patch to be a function of tyre diameter, irrespective of tyre width. But the width of the contact patch varied according to the tyre width.Thus, the most free rolling 349mm tyres have the greatest contact patch circumference and tyre/road contact area, and those with the highest rolling resistance have the shortest circumference and smallest contact area.

That the wide tyres should be more comfortable seems easy to explain.The extra width is bound to ‘average out’ the pits and bumps in the road, and we now know that the ‘point pressure’ is less with the broader tyres, presumably allowing the tyre to mould itself around obstacles, rather than deflecting. And as all the tyres share the same aspect (ie, height to width) ratio, the broader tyre is also taller, putting a greater expanse of rubber between the road and rim. All these factors might be expected to iron out bumps, but they don’t really explain the improved rolling performance.

Two possible answers spring to mind. Looking again at the illustration, it’s clear that the narrow tyre comes almost to a point at front and rear, suggesting a fairly acute degree of flexure at the front and rear of the contact patch as the tyre assumes the flat shape then springs back. On the wide tyre, the more gently rounded tyre shoulder suggests that the rubber is bending more easily to assume the flat contact patch. As one observer commented on seeing the illustration, the wider tyre displays a ‘cleaner’ ellipse, and this cleaner shape results in lower hysteresis. Presumably too, the improved shock absorption of the wide tyre reduces vibration, and thus rolling resistance.

Whatever the explanation, it looks as though a new generation of small tyres is on the way. Can we expect to see broad, slick designs on everyday bikes? Another widely held belief is that tread somehow improves grip. Obviously, this is true enough on soft or loose surfaces, but on tarmac, a slick tyre can be expected to grip better, roll better, and shrug off debris, reducing punctures, compared to a similar treaded tyre.Whether slicks gain widespread acceptance with the general public remains to be seen.

Unfortunately, most small-wheeled machines are designed for narrow tyres, and weight is important too, so it’s unlikely that wider (and taller) designs will be adopted, unless a considerable performance advantage can be demonstrated. For recumbents, on the other hand, the only downside seems to be the slightly increased frontal area.

Tubeless Tyres

Experimental tubeless tyre - note the cut inner tube protruding around the tyre. This surplus can be trimmed off when inflated

As we have seen with the Primo (see Folders 17 & 18), another solution is to make the tyre sidewalls more flexible, thus reducing the effort needed to overcome rolling resistance without compromising (probably improving) the shock absorbing characteristics of the tyre. But where do we go next? One long overlooked solution is to eliminate the inner-tube.There’s little point in fitting a tyre with paper-thin sidewalls backed up by a stiff, inflexible inner-tube. In practice, most good quality tubes flex quite well, but Greenspeed rig tests have found a reduction in rolling resistance of around 20% by eliminating the tube, so in theory, it’s well worth doing.

State-of-the-art. Running tubeless, the Greenspeed tyre rolls well - better than most 20-inch and some 26-inch tyres

If you want to experiment yourself, simply slice open an old inner-tube around the circumference, splay the tube out flat and fit it to a wheel, followed by a tyre. Inflate as usual (not easy) and trim off any excess tube. Provided the tyre is in good condition (you may need to add some sealing gunge), this home-made solution should work well enough.

Tubeless bicycle tyres are not a new idea, although most designs have required a special rim and/or tyre profile, none of which have caught on.The advantages include easy puncture repair (a soft pencil of rubber can be inserted into a hole from the outside, without disturbing the wheel or tyre), lower weight and lower rolling resistance. On the negative side, tubeless tyres are probably more prone to puncture, more difficult to inflate when off the rim, and they require some sort of sealing system Black Primo Comet around the spoke holes.

But what of the future? Greenspeed is currently fine- tuning the composition of the Scorcher tyre, a process that will no doubt yield another small performance gain.The first production examples should be available early in 2005.

Further information from Greenspeed

“The current issue of Modern Railways magazine has an interesting article by Roger Ford on car, train and plane energy efficiency (June 2004, pp30-31). Ford’s analysis, ‘suggests, and I expect that this will generate some howls of protest, that a family of four going by car is about as environmentally friendly as you can get’. He has obviously forgotten the bicycle, but then he is talking about long distance journeys. Given that in theory ‘nothing can equal the steel wheel on steel rail for environmentally friendly transport’, what has gone wrong? A new state-of-the- art Virgin Super Voyager weighs 40% more per seat than an Intercity 125. Second, faster trains use a lot more energy – cutting the London-Edinburgh time by 30 minutes increases energy consumption by one half. Is half an hour worth it? Third, new trains are badly engineered.The new Pendolino intercity trains use 14 times as much energy for lighting as the trains they replace. How can this be?”

Dr Tim Leunig (daily commuter)
Surbiton

There’s no doubt that energy efficiency has been largely ignored by the railways since privatisation. Some of the last British Rail commuter trains were designed to use 20% less power than their (already efficient) predecessors, through lightweight construction, and by using AC motors, which can more easily provide ‘regenerative braking’ – putting electricity back into the supply when slowing down. For various reasons, this system was never made operational, and conventional brakes remain in use today. Meanwhile, the railway power supply is being completely revamped in the southeast to allow even more power-hungry German machines to enter service. Another odd modern practice is the tendency to put a diesel loco at either end of a train, because it’s cheaper than paying Network Rail to operate the points for the locomotive to run round to the front on branch lines! And although I have not seen the figures, I don’t doubt that the new Virgin Voyager is less fuel-efficient than the wonderful Intercity 125 trains (another British Rail achievement, incidentally). As with cars, extra weight through increased crash-worthiness, power-hungry air-conditioning, and greater acceleration are beginning to make inroads into the inherent efficiency of rail vehicles, although as we shall see, the figures stubbornly indicate that both modes are becoming more fuel-efficient.

When comparing road with rail, we must try not to lose sight of the bigger transport picture. Road transport has indeed become slightly more fuel-efficient in recent years: average vehicle consumption improving slightly, from 25.2mpg in 1993 to 28.2mpg in 2002, largely because of the introduction of fuel-efficient small diesels. Incidentally, these figures are drawn from total vehicle mileage and total fuel consumption, so they include buses and HGVs, which might sound unfair. On the other hand, only 5.8% of traffic is HGV, and the figures also include mopeds and motorcycles. Cars and light vans account for an astonishing 92% of total mileage.

In broad terms, the fuel consumption of road vehicles has hardly changed in 80 years because the increase in efficiency has been obscured by increased weight, bigger engines and so on. Only in North America have cars genuinely become more economic (from a very low base, of course).Throughout the developed world, vehicle efficiency is thought to be on the fall again – presumably because of the recent growth in gas-guzzling 4-wheel- drives, and as a side-effect of increasing congestion. And irrespective of the fuel efficiency of individual vehicles, the growth in UK vehicle mileage has caused an increase in overall consumption, from 39.5 million tonnes (petroleum equivalent) in 1993 to 41.5 million tonnes in 2002.

Virgin’s new Pendolino (left). Is it really less fuel-efficient than it’s predecessor (right)? PHOTO : www.the-siding.co.uk

Meanwhile, the amount of fuel consumed by the railway industry (mainly diesel fuel and electricity) has fallen dramatically, from 0.93 million tonnes to 0.72 million tonnes (petroleum equivalent) in the same period, even though rail passenger/miles have increased by almost a quarter.There are many reasons why this might be so – scrapping of older thirstier freight locomotives, reduction of heavy coal traffic, and (hopefully) better vehicle utilisation, being the obvious ones.

If we look more closely at the 2002 figures and remove the fuel used to move freight (about 10% of the total), we find that passenger rail vehicles consumed some 648,000 tonnes of fuel and covered 443 million train/km.This could be expressed as 684 km/tonne or .581 km/litre, or even more conveniently, as 1.7 miles per gallon. As the average passenger loading in 2002 was 89.6, we can deduce a rough figure of 148 mpg/passenger for rail.

Yes, passenger rail vehicles are getting heavier, thirstier and faster, and they’re doing more miles, but because they’re faster, they’re attracting a lot more passengers, which helps to explain why the mpg/passenger figure is holding up so well.

Roger Ford suggests that a family of four can travel long distances more efficiently by road. In theory – provided their vehicle was a little more efficient than average – this would be possible, but as we all know, the problem with road transport is a passenger loading per car that hovers frustratingly around one. In other words, cars are usually carrying one person to work, or worse still, undertaking ‘positioning moves’; running driver-only to pick up passengers howells ac. In ‘cradle to grave’ terms, intensively-used rail vehicles do much better. As always, the answer is to make better use of public transport.

But, as Tim rightly observes, rail could do better and could make more effort to build on its many other environmental advantages.With the right technology, reduced track congestion and even better vehicle loadings, an improvement to 300mpg/passenger or more would be quite achievable.

Which brake system?

“A to B 41 was interesting, as always, but I’m a bit confused by Martin Fillan’s comment (Letters, A to B 40) about grease leaking onto brake drum linings and his suggestion about using a roller brake.What exactly is a roller brake? Is it better than a drum? And is it easier to replace? I can’t find one in the Sturmey catalogue, so whose is it and how much extra will it weigh?”

John Burnett
Swindon

Brakes are a fascinating subject, long neglected by this august publication. Broadly speaking, the problem faced by engineers since the invention of the wheel has been to produce a simple, tough device capable of transposing a large but weak hand or foot movement into a small but powerful force to push against a rotating body and slow its progress.The brake then needs to dissipate the considerable amount of heat generated – something that few bicycle brakes are very good at.The following devices are all available today to retard the progress of bicycles… Some more successfully than others:

1. Caliper brake

The Alhonga dual-pivot caliper. More complex than some, but the principle is the same - two arms, one attached to the brake cable and the other to the cable sleeve.The wheel rim is clamped between the two brake shoes

Long outmoded on motor vehicles, a caliper brake (sometimes called a side-pull) consists of a pair of curved arms or calipers pivoting somewhere beneath the headset bearings, with ‘blocks’ of friction material at their lower extremities. By the action of a pull rod, push bar, or more usually a flexible cable these days, the friction blocks are moved towards each other, squeezing the two outer faces of the wheel rim in the process.

The caliper is light and cheap, because the rotating element is already in place, but being completely exposed to the elements, it is badly effected by rain, grease, oil and grit. Different calipers and brake blocks are affected in different ways, but the most important element is the frictional co-efficient of the wheel rim material. Chromed steel lasts for ever, and works very well when dry, but loses most of its stopping ability in the wet. Aluminium is less effective in the dry, but relatively good in the wet, making it a safer material overall. Unfortunately, aluminium rims can wear away quite fast, especially on small-wheeled bikes.

The quality of the brake ‘feel’ depends largely on the friction material and the construction of the caliper. Poor calipers bend and distort when the brake is applied, giving a rubbery feel at the lever and/or judder or squeal.

Calipers are notoriously difficult to centre correctly, which can leave one brake block rubbing against the rim, and a wobbly rim will cause one or both blocks to rub intermittently. Generally, the rim disposes of heat quite successfully, but heat build-up can be a problem on long descents, particularly for heavily-laden or small-wheeled bikes. Excessive heat in the rim can cause tube failure and a catastrophic blow-out.

2. Band brake

Band brake principles. Friction between the tethered band and rotating drum tends to slow the drum’s progress

A long-outmoded Edwardian technology, the band brake is nevertheless worth mentioning because these devices do still turn up in the rear wheels of Chinese bicycles once in a while. A band brake utilises a flexible band of friction material, firmly fastened at one end and wrapped loosely round a rotating steel drum.When the band is pulled tight by a lever, it wraps tightly around the drum, slowing its progress.This tendency for the brake to apply itself without undue effort from the rider is known as ‘self servo’.The bad news is that the effect usually disappears in reverse, so a band brake will not stop you running backwards down a hill…

Band brakes are cheap, low-tech devices, but the negative aspects go on forever.With the drum inside the band, there’s nowhere for heat to go, and being difficult to protect from the elements, water can slosh straight in, resulting in a near total loss of braking effort. Brake bind, shriek and squeal can be a problem too, especially after a good soaking.

3. Drum or hub brakes

More correctly an ‘internal expanding shoe’ brake.This was the standard motorcar and motorcycle brake for most of this century until superseded by cheap reliable discs, and remains a favourite on hard-used and/or heavy bicycles. The general layout is two curved aluminium blocks or ‘shoes’ faced with friction material, both pivoting at the same point, and pushed outward at the other end by a cam of some kind, to make contact with a metal (usually steel) drum. Like the band brake, drums exhibit a self servo action – the leading shoe tending to be drawn harder into contact with the drum, whilst the trailing shoe tends to be pushed away, and visa versa in reverse. A variant common on older motorcycles and cars was known as ‘twin leading shoe’ – much more effective going forwards, but virtually useless in reverse (see band brake).

Drums can be heavy, although much of the weight penalty is negated where the brake is combined with a hub gear, and modern manufacturing techniques can reduce the weight significantly.The shoes are largely immune from contamination, but internal and external sealing arrangements can be a bit crude. Sealing problems between the gear and brake components of a hub can result in grease contamination, which can ruin the shoes, and poor external sealing can allow water in, although this generally requires total immersion.Wet friction shoes lose most of their effect, and as they start to dry, a violent self-servo action can result in brake snatch and squeal.

Hub brakes are not good at dissipating heat, but they make do by transferring it into the substantial mass of the hub in the short term, where it can safely radiate away when the descent is over. If a good quality drum does overheat, it should gently ‘fade’, or become less effective until cooled. Adjustment is rarely required once the shoes have bedded in, and the progressive action and ‘feel’ of a hub brake beats most other types.

Drum brake exploded diagram. Left to right: back plate (fixed pivot above, moving pivot and lever below), brake shoes faced with friction material and steel drum.This is the Sturmey Archer ‘BR’ of 1932 – it survived, effectively unchanged, for 70 years

4. Back-pedal or coaster

Simplified coaster brake diagram. Left to right: brake arm and hub dust cap (fixed to bicycle frame), brake shoe segments, brake actuator, rotating hub shell. Back pedalling drives the actuator into the shoes, forcing them against the inside of the hub shell

Rare in Britain, but common elsewhere, the coaster is usually combined with a hub gear. Pedal backwards and a metal cone slides through the hub, pushing metal brake segments against the rotating hub shell. Operation can be a bit insensitive, with a lack of feel, although hubs vary. Being grease filled, a coaster brake is more or less immune from contamination. It also has no exposed levers and cables to go wrong, requires no adjustment, and lasts more or less for ever. Like the drum brake, heat dissipation relies on warming the hub on a descent, then allowing the heat to escape. In extremis, localised heating from the metal-on-metal contact can boil away the grease or even weld parts together, although I have never heard of this on a bicycle.

5. Cantilever and V-brake

Similar rim-squeezing action to the caliper, but the force is provided by two vertical arms, pivoting at the bottom and brought together by a cable pulling the top of the arms together.The only real difference between the cantilever and V- is in the way the cable pulls the arms. In both types, the brake blocks are mounted some way down the arms in order to gain a degree of mechanical advantage.

V-brakes have become the braking system of choice because they’re light and crudely effective in operation. Problems are as for the caliper brake – water and oil contamination, rim wear, difficulty with centring and heat build-up on long descents. Cheap V-brakes can be unpredictably fierce in operation, so many feature pressure limiting devices of various kinds (usually fitted in the cable) to prevent the front wheel from locking up. Other problems include squeal on cheaper units, judder, and frame or fork distortion when the brake is applied. On the positive side,V-brakes are simple to maintain.

6. Roller brake

Diagrammatic view of Nexus roller brake. Force from the brake lever is applied through the operating lever (top) to the central cam.The cam pushes the rollers out against brake shoe segments, forcing them into contact with a rotating drum, integral (in some designs) with a cooling disc

Like so much else in the bicycle world, the roller brake is a Shimano invention, or re-invention. Combining elements of the drum, coaster and disc brake, the friction effect comes from steel rollers which are forced outward by a cam, pushing metal shoes against a rotating steel drum. Heat build-up can be a problem, but most designs incorporate a cooling disc, just like a ‘proper’ disc brake. Brake feel can be unpleasantly ‘woolly’ and vague compared to other types, and the shoes can make nasty metal-on-metal noises unless well greased.That’s also the good news, because water and oil won’t make much headway into a grease-packed unit.

7. Disc brake

The Hope Mono Mini bicycle disc brake. High pressure fluid pushes a piston against a friction pad, forcing it into the disc. Most brake assemblies contain two (or more) opposing pistons, but here the caliper ‘floats’, allowing a fixed friction pad to contact the back of the disc

This brake generally utilises a pair of friction pads, which are forced against opposite sides of a steel disc. Heat does build up in the disc (they can glow cherry red on a hard-driven racing car, or after stopping a high speed train), but the disc is well exposed, so heat is rapidly dissipated and fade is rare. Disc brakes have become the preferred means of de-acceleration on just about every wheeled vehicle, from aircraft to trains, cars and motorcycles. Progress in the bicycle world has been limited, mainly because the disc brake lends itself to hydraulic operation, which can add weight and complication. Pads may also bind slightly in the ‘off’ position, which can be frustrating on a fractional horsepower vehicle. Early bicycle discs were heavy, ineffective in the wet and noisy, but these problems have been largely eliminated by reducing the disc to a delicate tracery of struts.

In answer to the question, it isn’t easy to convert a bicycle to roller brakes because the Shimano Nexus system will fit only a Shimano hub. But if you have a Sturmey Archer or SRAM-equipped bike, there’s really no need – an upgrade to hub brakes is generally quite easy (not on smaller bikes like the Brompton, unfortunately). In practice, few roller, drum, coaster or disc brakes work badly enough to be worth changing.

Heart rate versus effective road speed for different crank lengths. Cadence was adjusted to suit each crank length: ie at 15mph, 175mm were spun at at 79rpm, 125mm and 100mm at 89rpm. Peak power of 780 watts was recorded with 175mm cranks, but both 155mm and 125mm managed 770 watts, and 110mm, 705 watts.

I too used to belief firmly that 150mm cranks were only for kids, or adults with very short legs. In fact, after much experimentation, I came to the conclusion that extra-long 185mm cranks suited me best, and that the formula put forward by Kirby Palm [see www.nettally.com/palmk/crankset.html] was correct.

Then two of my customers, Rob Hague, and Mark Mueller started experimenting with short cranks. Rob found an improvement in his race times by going from 170mm to 150mm, even though he has long legs! Mark found that after training for a month with 110mm cranks, he was back to the same performance he was getting with 170mm cranks. My son Paul tried 100mm cranks on his trike and found so much improvement over normal length cranks, that there was no way he was ever going back to normal ones.

Then a customer, Irene, who had hired a trike with 165mm cranks for three months, came to take delivery of her new trike. I measured her legs against the formula, and discovered that according to Palm, she needed 150mm, so I fitted a pair of 150s for her.

After a few days I got rave emails from her saying how smooth the trike felt, and how much better than the demo it was.This seemed rather puzzling to me, as the hire trike was a little lighter.Then she told me that with the new trike, she did not get leg cramps any more, which had been a problem for her with the old trike.Then the penny dropped. It was the cranks which had made the difference.

Next, Paul built a trike to race at the 24hr Pedal Prix at Wonthaggi.Without time to train all the team on 100mm cranks it was decided to use 150mm cranks. Despite losing a few laps following the collapse of an experiment wheel which had been fitted by mistake, they won the race by three laps! Paul then did some tests on our new Computrainer machine and came up with the following results. In all it seems than the higher cadence gained by using short cranks, has no negative effect on power output, and gives an improved leg function, with reduced stress.

On a recumbent, short cranks also help to get a 69rpm, 155mm more efficient aerodynamic were spun at fairing over the rider’s legs.

“I was interested to see the solar electric recumbent in A to B 38. It occurred to me that if you could power a recumbent tricycle with two solar panels, one could probably power an electric rickshaw with three or four such panels?”

Felicity Wright
Redditch

With the oil supply/demand crisis on the way, this may well become a fascinating question. At present, rickshaws are being replaced by internal combustion machines of various kinds, and that will have to change. But is a solar-powered rickshaw viable? We have all the data we need from past A to B magazines – issue 37, on solar power, and issue 39 featuring an electric-assist rickshaw.

As a rule of thumb, the sun supplies around one kilowatt of energy per square metre, which just happens to be the roof area of a typical rickshaw. Unfortunately, another rather more depressing rule of thumb suggests that commercial panel efficiency is somewhere in the region of 10%, reducing peak power to 100 watts. In practice, our Unisolar flexible panels did even worse with British solar radiation, achieving a peak output equivalent to 65 watts per square metre, or 390watt/hours (or Wh) per day.

Cycles Maximus solar- powered pedicab

The roof of the Cycles Maximus rickshaw featured in A to B 39, measures approximately 100cm by 110cm, giving a practical collection area of about 1.1 square metres, or 7.2 times the size of the panels in our previous experiment.Thus, provided our rickshaw was always in the open – something hard to arrange in a cityscape, for example – we could reasonably expect to see peak power of 72 watts, and daily output of 430Wh.

…future developments will depend on the price and availability of oil…

One immediate problem – in UK climes at least – is that our roof-mounted panels were angled towards the south at 20 degrees because at our latitude, a horizontal panel would never be fully effective. Another problem is cloud cover – even in June, the average panel output was cut almost by half, to 36.6watt/hours per day.Taking these factors into account, it’s unlikely that our rickshaw would generate more than 200Wh per day in fine weather, and virtually nothing on an overcast winters day.

The powerful Lynch motor on the Cycles Maximus rickshaw had a battery of 828Wh, giving about two hours power-assistance, well loaded in hilly country. So again, rather depressingly, we are brought to the conclusion that four days, or 40 hours, constant charging in mid-summer would give only two hour’s use…With the less power- hungry Heinzmann motor, the equations become a little more favourable – somewhere in the region of ten hours charging per motor/hour.

Of course, the power consumed depends on the terrain. In a relatively flat city, an hour’s power-assistance per day might well be sufficient, but in this case, we are really looking at a human-powered vehicle with occasional motor assistance, rather than the other way around!

Naturally, once we get close to the equator, we have a great deal more sunlight to play with.With more powerful solar radiation and no cloud cover, we could reasonably expect to generate peak power of up to 100 watts, or perhaps 600Wh per day, giving some three hours motor-assistance.There are other incidental advantages – the solar panels would help to keep the occupants cool by absorbing (and reflecting) solar radiation, and although a battery would be required to deal with the peaks and troughs of production and use, it could be quite small, itself reducing the weight of the machine.

Several experimental solar rickshaws have been trialled in India, one impractical monster weighing 300kg, or nearly three times the weight of the British-designed Maximus! Some have been built with access to prodigious overseas aid, such as the rickshaw claiming to carry panels with an output of 850 watts – clearly either satellite- grade technology, or a surface area of a great deal more than one square metre…There are also a number of ‘exhibition’ solar machines around, but these are a long way from earning a living day-to-day. As with so many other things, future developments will depend on the price and availability of oil. State of the art panels, with an efficiency of 30% or more, would make a lightweight solar vehicle perfectly viable, but only in a sunny area!

“I think A to B should do a review of existing options for solar powered bicycle lights. I found one at www.energycapture.co.uk and the Alternative Energy Centre in Wales [www.cat.org.uk] sells a solar-powered 6 LED red emergency light which is sold with a bracket to attach to a bicycle.”

Jonathan Pattison
Leeds

Clearly, in this case, we’re looking at a very much smaller power requirement, from a correspondingly small solar panel. First let’s look a bit more closely at the power demands of a bicycle front light. A typical conventional or halogen filament bulb for a bicycle front lamp consumes two watts.That’s manageable, but realistically, few people would want to carry around a solar panel large enough to provide that sort of power, so we need slightly cleverer technology to reduce the energy demand. Fortunately, as regular readers will be aware, Light Emitting Diodes are advancing very rapidly and can now provide an adequate light output with much lower power consumption.

The only front LED lamp currently available to German (and by default, British) standards is the Cateye EL300G, although the situation is changing rapidly, so this may already be out of date.When we tested its predecessor, the EL300 (A to B 33), we found power consumption of 0.58 – 0.89 watts, depending on battery voltage. Consumption is claimed to have fallen since, so we’ll generously base our calculations on the lower figure.

“…the solid-state LED solar torch is perfectly viable and will no doubt be available soon…”

To provide 0.58 watts for, let us say, two hours each evening would require 0.58 watts x 2 hours = 1.16 watt/hours. If we reckon on twelve hours charging time each day in summer, the charge rate would thus need to be 1.16 watt/hours divided by 12 = 0.097 watts.With peak power of 65 watts per square metre of solar panel (see above), each square centimetre will provide 0.0065 watts, so a panel of 15 square centimetres would more than cover our requirement of 0.097 watts.

This raw data suggests that a panel measuring just four square centimetres would provide two hours of light output per day – if only it were thus! The problem, of course, is that our panels provide a peak output of 65 watts per square metre. In reality, the mean figure over the course of a bright sunny day is about half this, increasing the panel requirement to 30 square centimetres.

The Cateye EL300 is one of the few cycle lights efficient enough to run from solar power

Unfortunately, even in June, the sun is often partially or completely overcast, and during my experiments last summer I recorded an even lower mean figure over a 16-day period of 20 watts per square metre, giving a panel size of nearly 50 square centimetres to work our low-consumption front light.

Nevertheless, the figures suggest that a square panel measuring just 7cms across would provide up to two hours light each night throughout a typical English summer, and a panel of double that size would be physically possible, making a light of this kind practical for most of the spring and autumn too. One proviso – the panel must be angled towards direct sunlight throughout most of the day, something that’s hard to arrange in practice, as we discovered during our experiments.

But what of the Energy Capture cycle light Jonathan found on the internet? Armed with our raw data, we can tell quite a lot:The solar panel measures a reasonable 88 square centimetres, and is rather optimistically claimed to have a 1.1 watt output.That may be attainable in a test lab, but working on our 20 watts/square metre average figure, I would suggest 0.17 watts in practice.That would certainly power an LED front light, but unfortunately the Solar Light is fitted with a filament bulb drawing four times as much power as the Cateye EL300!

For occasional use (say 30 minutes per day) a lamp of this kind might suffice, but for nearly £50 you really would be better off buying a conventional light with rechargeable batteries, and recharging a spare set each day by mounting a small solar panel on a south- facing window sill. However, the solid-state LED solar torch is perfectly viable and will no doubt be available soon. Regrettably, it seems Energy Capture has ceased trading, demonstrating that this example might have been an idea ahead of its time.

“I would like to query the basis of the electric bike range statistics you quote. I realise that you are ‘A to B’, but for many people, their use of such a bike for leisure purposes would be ‘A to A’; that is to say starting and finishing at the same location. If one assumes a hilly terrain, and ignores any flat areas, at the completion of a journey the uphill sections will have equalled the downhill. If therefore, one only used the electric-assist on the uphill sections, and turned the motor off on the downhill sections to freewheel, would the ranges you quote notionally be doubled?”

Michael Bartlett, Shoreham-by-Sea

Unfortunately, life is rarely that simple. For one thing, where a bike has the capability, the A to B testers usually opt for speed over range, which is why tests always quote the average speed.To keep speed up, the motor is often used for long periods on the flat, as well as climbing hills. Secondly, you never get back all the energy expended climbing a hill going down the other side! This is partly because motors tend to be inefficient when climbing at low speed, but primarily because most of the energy is dissipated in fighting the wind.This effect is barely noticeable at low speed, but descending a hill at 30mph will scrub off much of the kinetic energy stored on the climb…This is why ‘regenerative’ braking (recharging a battery or other storage device on a descent) is hardly worthwhile on a bicycle.

Think of the hill as a battery:Whether you ride a conventional or power-assisted bicycle, you store kinetic energy on the way up, and discharge it on the way down. A heavy freight train crossing the Swiss Alps will store a great deal of energy, which can usefully be returned to the electricity grid going down the other side, but a bicycle stores a tiny amount, and on such a small lightweight vehicle, wind resistance has a comparatively large effect. On a switchback road, the stored energy may enable you to get half way up the other side, so it can be useful, but in most cases, mechanical or electrical storage devices would be of little help. Now, where were we?

The A to B 17.6 mile test route starts and finishes at about the same elevation, but climbs and falls almost continuously in between, so the motor tends to be used for a high proportion of the ride.The figures published in the magazine are always lower than the maximum achievable, although they seem to equate fairly well to the sort of range a typical rider might expect, making shorter trips in heavier stop-start traffic.

In terms of maximum range, in level country, you might expect to exceed the A to B figures by 40% or more, even when using the motor much of the time. For example, the Powabyke or Ezee Forza can manage 50 miles relatively easily on the flat.

Most bikes complete the test course in 75-80 minutes, but the Forza did the run in 62 minutes – exactly 17mph. How can a bicycle limited to 15mph maintain such a high speed? The reason is that the more powerful machines cruise at close to 15mph and rarely fall below 10mph on hills.Add a few downhill bursts, and the average speed can exceed the maximum assisted speed…This is why electric bikes work so well in hilly areas.

“Can you tell us how to deal with or prevent punctures? I don’t mean sticking a patch on, but what is the best strategy? I believe that the hassle of punctures really does put people off using a bike regularly for important journeys. In Peterborough the cycleways are edged with thorn bushes like pyracantha.”

James Haugh
Peterborough

Astonishingly, some local authorities continue to plant thorn bushes next to cycle paths and have no policy for sweeping debris from paths – something normally done by motor traffic on the road. Not surprisingly, cycle path usage continues to languish in these places.

James is quite right, of course.The (often irrational) fear of punctures does put many people off cycling, but these days the threat can be largely eliminated.With the right equipment and some basic preparation, roadside disasters should become rare events.

1. QUALITY

Choose good quality tyres and tubes, and replace them before they’re life- expired. Cheap and/or worn tyres are much more likely to puncture.The range of tyre brands is bewildering, and some are only suited to particular uses, so I can only give a few pointers: I’m not convinced that kevlar-banded tyres really do give much protection, but many swear otherwise.They certainly increase rolling resistance, as do puncture-proof liners, which can also cause tube failure if incorrectly fitted. An interesting, but heavier, option (as yet untested by A to B) is Schwalbe’s Marathon Plus, constructed with a special spongy lining to ‘bounce’ objects back out of the tyre.This is now available in the 47- 406mm (20-inch) size, with 18″ and 16″ on the way.

Surprisingly enough, slick and lightly-treaded tyres often work quite well, presumably because they are less likely to trap and hold road debris. But paradoxically, you shouldn’t write off treaded tyres either, because some are very puncture resistant. As a second line of defence, thick puncture-resistant inner tubes seem to help, at the expense of increased rolling resistance.

For a given bike/tyre size, ask regular users what they’d recommend. Much of the advice will be pure hearsay, but you should begin to get a picture of what works and, more importantly, the brands to avoid.

2. PREVENTION

Keep the tyres correctly inflated. Under-inflated tyres are good at picking up debris and can also suffer ‘pinch punctures’ on bumps and kerbs. It seems reasonable to assume that over-inflated tyres might be vulnerable too, although I have no specific evidence for this. A simple rule of thumb is to inspect the tyres with the bike loaded.They should bulge slightly around the road contact patch: No bulge, or too pronounced a bulge, and you’re asking for trouble.

Secondly, it might seem obvious, but if you can avoid thorns, roadside debris or glass, you will more or less eliminate punctures.Try to stick to the well-swept part of the road – wobbling along in the gutter is a recipe for tyre failure. If in doubt, jump off and push – or even carry – the bike through. Once back on a clear stretch of road, check the tyres quickly for foreign bodies and decide whether to remove them. If an object has barely begun to penetrate the tyre, remove it. If in doubt, break it off flush with the tyre and carry on – the inner tube will sometimes grasp and seal an object with very little loss of air. If you hear or feel a rhythmic bump, always stop and investigate.This sort of procedure takes seconds, but can save hours of unpleasantness.

Traditional cycle tourists use all sorts of clever tricks to prevent debris penetrating the tyre, including blades positioned close to the tread to knock objects off.These sort of things are best left to the experts, because they can cause more harm than good if poorly fitted or adjusted. However, it’s probably worth pouring in one of the proprietary leak sealants, but don’t forget those regular inspections.

3. REPAIR

Some cyclists take pride in their instantaneous roadside repairs, but a large proportion of mine seem to fail, particularly in miserable weather.These days, I very rarely bother to carry a puncture repair kit, following instead a few simple rules:

a) Holts Tyre Weld is a mixture of sealant foam and compressed gas that repairs smaller punctures and re-inflates the tyre. Designed to inflate one tubeless car tyre,Tyre Weld is arguably more effective with bicycle tyres, providing up to a dozen repairs, depending on the canister and tyre sizes.This product will usually get you home, and can even be treated as a permanent repair if you’re lucky. It won’t work in every case, but it seems to be wholly or partially effective in about 75% of punctures in my experience.

b) If sealant doesn’t work, it may be possible to pump the tyre up, ride on, re-inflate, ride on, and so forth, especially with front tyres, where less pressure is required. It’s not much fun, but easier than wrestling with the tyre, tube and glue by the roadside. Sealant foam can take a few minutes to work, so this technique may gradually provide a cure.

c) Ride a folding bike! If the worst happens, you can complete your journey or reach a cycle shop by train, bus, taxi or hitching a lift.This last resort is rare, but a folder does give peace of mind that you will be able to get home quickly and easily by other means.

I’ve been trying to locate a rear LED light incorporating a brake light.The only ones I have seen recently are those gimmicky types with built-in indicator lights. I’ve managed to find a few products on the internet, such as Mavic, whose ML-273EZ seems to fit the bill.

Gethin Sheppard
Cowbridge, South Glamorgan

The Mavic design shows two LEDs in rear light mode, but five under braking, which would certainly prove visible at dusk, or during the night. Surprisingly though, the system is activated by a rather crude switch looped over the rear V-brake. Useless if your machine doesn’t happen to feature V-brakes, and rather dubious if it does.The gimmick sounds like the B-Seen, a rather expensive lighting, indicator and brake light set widely advertised in the UK cycling press in the last few months.

However, a light weight and effective brake light system utilising ultra-bright red LEDs is perfectly feasible these days and could be made to function automatically using a ‘tilt switch’.With all the componentry inside the rear lamp housing, there would be no wires, no switches and very little extra weight over a conventional rear lamp. Sensitivity would not be as good as a wired system, but probably adequate. I believe there is no legal difficulty with fitting a brake light in the UK, but I don’t think a device of this kind is currently on sale. If anyone knows better, please do get in touch.