For some time we’ve been predicting that the winners and losers from the next generation of folding bikes will be judged in terms of weight. On a conventional bike, light weight is little more than a good talking point, but a folder has to be carryable. We’ve lost count of the strapping great fellows who’ve told us they can’t understand our enthusiasm for lightweight folders. And if you too can run the length of Clapham Junction with a 15kg bike, or heave it over the sill of a car boot, you won’t really be interested either. For the rest of us, lightweight folding bikes are the future.

…our demo bike was sold before we could grab it. Clearly there was a demand…

Every gram counts, but once you get into exotic materials, the cost can rise rapidly.When we built our lightweight Brompton back in 1998, some changes were easy and cheap, but others cost 50p or more, per gram saved. Our fully-equipped bike ending up weighing 10.4kg and costing £687 (including purchase cost) – figures that look respectable even today.

Back to conventional off-the-shelf technology in 2004, and a typical Dahon or Brompton will weigh 12 or 13kg and cost around £500. But start stripping weight off, and the price rises rapidly. Birdy market a couple of bikes in the 11kg region for around a thousand pounds, and Bike Friday will sell you an even lighter machine, but it’ll cost well into four-figures in the UK. At the ultra-light end, there are a few single-speed, titanium oddities, such as the 6.5kg Panasonic Traincle, but that’s more or less priceless here, and a bit of a quirky thing to ride.

Dahon launched its assault on the ‘quality end’ last year with the limited edition Helios XX, which weighed a claimed 7.8kg without pedals, and cost £1,000.We say ‘claimed’ because our long-promised demo bike was sold (by a shop that must remain nameless) before we could grab it. Clearly there was a demand.

The XX utilised all sorts of expensive bits, but after some careful cost/benefit calculations, Dahon introduced the ‘budget’ Helios SL for the summer 2004 season.This bike costs a relatively slimline £800 and weighs 8.65kg on our scales, or precisely 19lb in real units.That’s far and away the lightest bike we’ve tested (if we ignore the Traincle), and one of a very select group of sub-10kg bikes – certainly the only one costing under the magic grand. Congratu- lations to Dahon for converting a relatively conventional aluminium bike (our last Helios weighed 12.2kg) into a super- lightweight racer. How was it done?

The Knowledge

The basis for this machine is the Helios 20-inch wheel bicycle, reviewed in more conventional form in A to B 31. Centrepiece of the conversion to SL spec are a pair of beautiful and ultra-light Rolf wheels, with 14 radial spokes on the front and 16 more conventionally-strung spokes at the rear.The spokes are noticeably ‘waisted’ to save weight (double-butted in engineering terms) and the wheel rims are the deep racy kind.Tyres are a super-lightweight version of the Schwalbe Stelvio we tested last year in 16-inch form.

…a wheel/tyre combination making all the right noises and transmitting all the right vibrations…

We judged the conventional Stelvio to have similar rolling resistance to the Brompton or Primo, which was slightly disappointing, but it weighed a few grams less, and was better suited to narrow rims. At 172g, the new ‘Light’ version fitted to the SL is probably the lightest production 406mm tyre in the world. It’s hard to believe that not so long ago, the 260g Primo Comet was considered a world-beater…The Light Stelvio rolls well too, reaching an excellent roll-down speed of 15mph on our test-hill, but in this respect, it’s still narrowly beaten by the Primo. Schwalbe has launched the tyre as a ‘Dahon Special Edition’ in snazzy orange and black, although a mass-market version is expected in the autumn.

Pair the Light Stelvio with inner tubes weighing only 74g apiece, and wheels weighing 500g, and you get an idea where much of the weight has been taken off. As any Formula One designer will tell you, if you’re removing weight from a machine the wheels are a good place to start, because lighter rotating bits react faster and more precisely to power input, plus cornering and braking forces. This certainly holds true for the SL, which goes far better than you might expect from a bike/rider combination that’s only 5% lighter than the cooking model.The bike storms away from the lights, leans hard through sweeping curves and brakes smoothly and consistently. Of course, much of the performance comes from the enthusiasm of the rider, and nothing generates enthusiasm more than a highly strung wheel/tyre combination making all the right sporty noises and transmitting all the right vibrations.

The gear system (presumably chosen on weight grounds) is SRAM X-7, which is actually an 8-speed, just to confuse the innocent consumer. It’s very pretty to look at and seems to do all the proper gear things as and when expected, although the change is not quite on a par with the very best. According to SRAM, the 7-series features ‘speed release spool detent shifting’, whatever that might mean, if indeed it means anything. In practice, most changes are satisfyingly crisp and clunky, rather than sewing machine slick.Very Germanic.

As compromises go, the ratios are more or less perfect.The 34-inch bottom gear should get the Helios up most gradients without too much huffing and blowing, and the top gear of 88-inches is tall enough to nip along on the flat with a following breeze, but not high enough for spinning down long gradual descents. Power transmission is wonderfully direct and there’s very little flex from the rear of the bike, so the Helios SL tends to encourage you to work hard and reward you with the desired forward motion. Standing out of the saddle is less satisfactory, because there’s quite a lot of flex in the front of the frame and the handlebar stem, which feels too frail for grunty, sweaty riding. Whether this is enough of a problem to put off the more seriously athletic types remains to be seen. A Bike Friday is certainly tauter, and thus almost certainly a little faster, but within the slightly flexy limitations of the Helios frame, the SL runs a surprisingly close second. And don’t forget how much money you’ve saved.

Elsewhere it’s hard to see where the weight has been shaved off.The handlebars look like carbon fibre and are called Carbonlite, but seem to be made of aluminium. No matter, they’re clearly very light and they look the part. Speaking of looks, the orange and black tyres, black frame, black stem and orange/yellow saddle may not be your cup of tea, but the general effect is suitably striking. As evidence for this, the hot wheels elicited a nod and grunt from a passing racer – a rare occurrence with a small-wheeler.

Opinions differ over the riding position.The saddle starts as-low-as-you-like and goes up to 100cm from the ground, while the bars are adjustable between a lowish 92.5cm and a giant 112cm. Not surprisingly, big people had mostly nice things to say, but those with a shorter torso and arms complained that although the saddle was in the right place, the handlebars were a bit of a stretch. Adjusting the height doesn’t cure the reach problem.

Folding

Typical Dahon, and easier than most.The handlebars fold down using the same mechanism we took a dislike to on the Presto in A to B 36. It does seem better on this example, but we know from experience that play can develop with use, which is something you really don’t want on a sportier bike like this. No complaint in that department with the mainframe hinge, which was horribly tight, producing a nasty groan whenever we forced it to perform. It got more cheerful after a bit of lubrication, but don’t we all? Nice tight engineering tolerances are no bad thing in hinges, but when you come to fold your beautiful new SL in front of an appreciative crowd, they’re liable to fall about laughing.

Folded size is adequate rather than stunning: 40cm wide, 68cm tall and 80cm long. That’s taller and wider than the standard Helios, but shorter, because the SL has slightly smaller tyres and no mudguards. Folded volume ‘as it comes’ is a reasonable 218 litres (7.8 cu ft), but remove the seat pillar and stow it between the wheels and the volume reduces to a much more presentable 180 litres (6.4 cu ft).Various fiddlings with handlebars will reduce the width below 40cm, but it’s hardly worth the trouble unless you expect to be travelling on a very packed train, for example.The bike comes with a velcro band to tie the wheels together, but as nearly always happens, we lost it within ten minutes. Fortunately – provided the bits are all properly secured – this is an easy bike to carry.You can’t argue with 8.7kg.

The folding process is aided by a pair of MKS Promenade demountable pedals. If you haven’t seen these before, fitting and removal involves pulling back a little spring-loaded collar on the pedal stem, which allows the pedal to slip out, leaving just the 20mm collar. Weighing only 175g apiece, these are the lightest ‘folding’ pedals around, with only the Brompton pedal leaving a smaller folded projection or more efficient folded/unfolded size ratio (6:1 against 4.3:1 for the MKS). Our only criticism is that you have to double check that the collars have seated properly before riding off. One of ours was a bit sticky, resulting in a loose pedal on a couple of occasions.When removed, the pedals have gooey greasy stubs. Dahon provides a little bag to put ‘em in, which solves the grease problem, but leave the bag on the train, and you’re completely stuck.You’ll also be £60 poorer (see Letters). Incidentally, with the pedals stowed elsewhere (‘Is that an MKS Promenade in your pocket, or are you just glad to see me?’), the rest of the bike weighs only 8.37kg. A small, but significant bonus.

Accessories

A short paragraph this one.The SL has no mudguards, no pump, no lights, no rack and no stand. But it’s a standard Helios frame, with standard fitting lugs, so you can bolt most of them on if you want.The only thing we’d demand if we were using the bike on a regular basis would be lightweight mudguards of some kind – there must be such a thing?

Speaking of accessories, the Rolf wheels do not take kindly to reflectors, which are, of course, a legal requirement in the UK and almost everywhere else.We found the reflectors supplied with the bike fitted the front wheel (albeit rather close to the hub) but wouldn’t play ball with the rear spokes. If some clown knocks you off your SL at dusk, a quick-witted lawyer may pick up on this, so would-be purchasers need to find a BS- approved reflector that fits.

Conclusion

Rather to our surprise, we found ourselves using the SL for all sorts of journeys, the light weight more than making up for the large folded size for rail trips. On the open road, the low rolling resistance and crisp gear change were much appreciated too.

We think the SL is worth every penny of that eight hundred quid, and even if it wasn’t, it has the lightweight market all to itself. If you’ve bought A to B with the intention of spending a few pounds on a car-boot bike for Sunday afternoons in the park, we insist you think again. If you can live with the lurid orange/black colour scheme, this is a bike you will learn to love – it rolls well and it’s a dream to carry.

The real market, one assumes, is amongst younger, trendier, more serious riders, and the SL bursts straight into Airnimal/Bike Friday territory, breaking all the weight records by a considerable margin. Add some basic mudguards and a pair of LED lights, and you could build a practical super-commuter weighing less than 9kg – a sensational figure. If you would prefer to put those few precious grams into full suspension, Dahon also produce the 9kg Jetstream XP.

Specification

Dahon Helios SL . £800 . Weight 8.65kg (19lb) . Gears SRAM X-7 8spd . Ratios 34″ – 88″ Folded Dimensions W40cm H68cm L80cm . Folded Volume 218 litres (7.8cu ft) .Folded Dimensions Saddle stem removed W40cm H56cm L80cm . Folded volume Saddle stem removed 180 litres 6.4cu ft . Manufacturer Dahon web www.dahon.com . UK distributor Cyclemotion tel 0800 585405 mail sales@cyclemotion.co.uk web www.dahon.co.uk