Small wheels play an important role in the alternative transport world, enabling recumbents and fared HPVs to be built sleeker and lower, and folding bikes smaller.
Twenty years ago, most small (ie, sub 24-inch) tyres absorbed energy like a sponge, handled badly, tended to puncture and generally caused frustration and annoyance to all who came across them.Today, thanks to a liberal dose of cutting edge technology, the picture is completely different.Tyre life and general performance is broadly similar to the traditional big-wheel jobs, and rolling resistance is much improved, but there’s a price to pay: vibration. Much of the reduction in rolling resistance is due to more compliant tyre sidewalls, but the rest comes from increased tyre pressures. In the 349mm and 406mm sizes, tyre pressures of 90 and 100psi are now the norm, with the new Stelvio pointing the way to 120psi and beyond. Run a small tyre at this sort of pressure on a bike without suspension and pea-sized road irregularities become pot-holes, and pot-holes gaping, bike- shattering chasms. And, as Professor Pivot notes on page 16, high tyre pressures can actually be counterproductive on some surfaces. All these matters come to a head on the Brompton, which has useful suspension at the rear, but nothing at the front.With rising tyre pressures, this lack of suspension is becoming a problem.
Enter the Pantour hub. Motorcycle enthusiasts may have seen this sort of technology before, in the sprung rear hubs that came briefly into vogue during the 1940s and early ‘50s before swinging arms became commonplace.
How does it work?
The Pantour is a simple device.The slightly oversize hub shell contains two axles held rigidly together and secured to the forks by end caps. In use, the hub rotates around the lower shaft (A), while the upper shaft (B) rests against a polymer block, which gives the springing effect The outer shell of the hub rotates on sealed needle-roller bearings.
The travel of only 12mm is quite small, which is fortunate, because – as eagle-eyed readers may already have spotted – if the hub lifts up, the wheel rims will move relative to the brake blocks. If it moves too far, the blocks may miss the rim altogether. In practice, this isn’t a great problem, because of the way the hub (and thus the rim) rotates rearwards as well as upwards, although obviously the brake blocks need to be set with extra care.
Shafts A and B are fixed rigidly to the fork drop-outs – the quick-release skewer running through A. At rest (left), the primary polymer pushes the hub shell down until the rebound polymer rests against the shell. Under load (right), the hub shell rotates rearwards and upwards, forcing shaft B against the primary polymer.
Despite the limited travel, the Pantour hub offers a number of advantages.Weight is a tiny fraction of any alternative suspension design, the hub adding only 50g against the very light Brompton hub. At 35mm or so in diameter and – more importantly – 100mm between fork drop-outs, it’s bigger than the Brompton hub (it could easily be made narrower, of course), but even though this means fitting wider forks, there is little effect on the folded size of the bike.Where the design really scores is in the rather esoteric field of ‘unsprung weight’. If you think about it, the aim of suspension is to reduce the amount of weight forced to deflect sharply on hitting an obstacle, reducing shock forces to the frame and causing the load (that’s you) to deflect in a more comfortable and dignified manner.The lower the ‘unsprung’ element in the equation, the faster and more precisely the suspension will work. If you fit a Pantour hub to a bicycle, the only unsprung elements will be the tyre, rim, spokes and part of the hub, and you can’t get much lighter than that. Most suspension designs not only add more weight to the bike, but add it in the form of unsprung weight, which is generally counter productive.
Fitting requires replacement stretched forks (supplied as a kit by UK importer Kinetics of Glasgow), a quick-release skewer, repositioned mudguard (37mm tyres can contact the stay as the suspension flexes, but not the new 28mm Stelvio), and fine-tuning of the Brompton lower stop mechanism to keep the bike folding properly.The Pantour can be set in the forks at one of three angles, effecting the degree of verticality of the motion (and thus the relative hardness), and the hub comes with a choice of two grades of polymer.We chose the softest and the most vertical action, which suited the Brompton well, although other bikes (or heavy luggage) might require different settings.
…the suspension feels nicely damped, exhibiting little or no ‘po-go’ effect on hills…
How does it perform?
With suspension movement of only 12mm, you won’t turn your Brompton into a downhill racer, but that’s not the point.What the hub will do is more or less eliminate tiresome high frequency vibration, no matter how high the tyre pressure. Pot-holes are little changed, but – perhaps surprisingly – rocky tracks and trails are noticeably easier to negotiate.The overall effect, with a rider of typical weight, is a slightly softer feel than the standard rear suspension.
The suspension feels nicely damped, exhibiting little or no ‘po-go’ effect on hills.You’ll be pressed to find any side-effects – the rearward movement seems to introduce a tiny rearward shimmy under some conditions, but that’s about it.
Longevity is hard to judge. In winter use, the shell is bound to fill with water and grit, but there isn’t much to go wrong inside. Our only long-term worry would be the ‘sealed for life’ roller bearing assembly, which looks expensive.
At first glance, the Pantour is prohibitively expensive – £135 for the basic hub, plus £35 for wheel building, and a further £45 should replacement forks be needed (yours can be modified free of charge, on an exchange basis). But on the other hand, this is the only practical way to build suspension into the front of a small-wheeled machine, and fitting takes less than a couple of hours.
The Pantour is one of those rare bolt-on accessories that leave you wondering how you survived without it. At first sight, the ride and performance of the bike are not radically transformed, but in practice – particularly on longer rides – higher tyre pressures and subtle suspension compliance work together to produce a taughter, more sophisticated, and – according to Professor Pivot – freer-running machine. If you ride any distance on an unsuspended small-wheeled bike, this device could be worth every penny.
Incidentally, it’s possible that the vertical wheel movement would have a beneficial effect on rim life, although no-one yet seems to have measured this. If nothing else, the movement between rim and brake blocks will help spread wear over a greater rim area, but it might also reduce the tendency for deep tram-lines to form in the alloy surface. That’s quite unproven, we hasten to add, but if true, the Pantour could pay for itself in a few years in rim life alone. Reduced vibration should give spokes, bearings, fingers and luggage an easier time too. Invaluable if you carry a lap-top computer in the front pannier.
We’ve tried the Pantour on a Brompton, because that seemed the most obvious application, but the hub would work equally well on recumbents and other unsprung folders, such as the Bike Friday.The Pantour is obviously designed to fit a conventional bike too – presumably giving the same step change in comfort. Suspension of this kind would be useful anywhere sprung forks would be too heavy or bulky, or where greater suspension travel is simply unnecessary.
Pantour also produces a front disc-brake model offering 25mm of travel, and a rear hub (12mm travel) designed around a standard Shimano 9-speed derailleur system. Long- travel rear suspension is reported to be on the way too.
Pantour 2002 Prolite Suspension Hub £135
Net Weight (against Brompton
hub – less hub nuts, but including quick release assembly) 50g
Polymers (red) rider weight 100-200lb (blue) rider weight 200-300lb
UK Distributor Kinetics web www.kinetics-online.co.uk tel 0141 942 2552 . mail email@example.com
Manufacturer Pantour tel +1 760 739 9058 mail firstname.lastname@example.org web www.pantourhub.com