Belt drives power forward

Al Harley Davidson motorbikes use ‘Poly Chain’ synchronous belt drives made by Gates Corporation, a multi-national power transmission specialist. If motorbikes use them (and have done for many years), why not bicycles? But, of course, they have. In fact, Gates has produced many bicycle belt drives, such as the rubber belt used on the 1980s Strida, wide belt drives for Raleigh, and the Kevlar-corded Poly Chain belt drive used by Errol Drew’s 2004 US commuter bike, the iXi.

These earlier belt drives were fine for the bikes in question but belt drives never made it into mainstream bicycle supply. The carbon-corded Poly Chain by Gates Corporation stands a better chance of acceptance because of greater strength and efficiency. Companies such as Trek, GT, Pacific Cycle, and Whyte have been trialling the latest Poly Chain incarnation since last year.

None have so far gone beyond the prototype stage because belt drives can’t work on derailleur systems and there are frame production problems: a roller chain snaps into place on a frame, bikes need to be built around a one-piece Poly Chain or need a ‘cut and shut’ process on the chain stay or seat stay.

Such problems have not thwarted Orange or Spot Bikes of the US. Orange – introduced to Poly Chains by G-boxx innovator Karl Nicolai – hopes to have a production city bike ready for March, equipped with a low-maintenance, quiet and super-efficient Poly Chain along with a Shimano Alfine internal hub. Orange hasn’t asked Gates for exclusivity, instead it’s hoping for first mover advantage.

However, Spot Bikes of the US has been granted a one year exclusive deal for sale of its singlespeed MTBs in North America.

Orange has been working with Gates since April (the company has a Poly Chain factory in Dumfries) and displayed three working prototypes at Eurobike. Two of the prototypes are based around a standard hardtail offroad frame, the third is based on a 4-inch travel full suspension frame. The technology is based around a Gates Poly Chain, toothed pulleys (made by a small engineering firm close to the Gates factory in Dumfries) and a Shimano Alfine rear 8-speed internal hub. A Rohloff version is being trialled.

As others have found previously, Orange had to tussle with complications in the design of the frames and the drive train.

First, the rear triangle has to be cut to allow the belt to pass through. Production hardtails will have lugged dropouts on the drive side that unscrew to facilitate the building. This is much easier to achieve on a 4-bar rear end as the components of the suspension frame already have the necessary joints. There can be no chain growth, as there is no chain to grow and no idlers or tensioners are currently present in the system. The main pivot therefore has to rotate around the bottom bracket.

Other considerations are the need to have high tension on the belt, to prevent slipping, a perennial problem with belt drives powering high torque but low speed devices such as bicycles.
Orange is working on how far it can reduce tension without slip, as over-tight belts will impact on chainstay fatigue, and limit the use of the technology on svelte chain stays.

Singletrack’s Chipps Chippendale has been riding a singlespeed belt drive Orange for several months, and is impressed: “You expect to feel the ‘give’ in the belt, but there’s none at all. The ride feel is more akin to a track bike with a super tight chain.”

Spinning the cranks backward shows there is some friction to the drive, inherent in the tension of the belt.

It also shows just how clean an idea this is, in terms of city biking without oil stains on your chinos, and in not picking up mud and trail debris. Sling a leg over the hardtail and there is only one gear selector, that works without pedalling, excellent for beginners. Drive is ultra direct and eerily silent.

Stomping on the pedals gives instant movement and feel, not damped by chain take-up, and not masked by worn gear teeth, there is no stretch in the belt. Changing gear too is rather direct, no clunks or having to find pick up pins, just an instant different ratio. Orange says the tension pings stones out, and any collected mud oozes through cog holes due to high tension.

Michael Bonney is the prime mover for belt drives at Orange. He believes the system has a lot of potential. He’d like Shimano to produce an XTR/XT/Saint-level version of the Alfine hub. That would crack longevity issues for off road, no doubt making it more commercially viable, too.

He’d also like a front 5-speed (or anything more than one speed) drive inside a front chain ring mechanism to extend the gear range even more. Other alternatives include a Variable Transmission box (á la DAF), or the lighter Rohloff that still has not surfaced. In fact, Bonney wants all three to tinker with, and anything else that might make a difference.

At Eurobike, ‘MTB Hall of Famer’ Joe Murray, now back at the helm of Voodoo Cycles, took time out to evaluate the Orange belt drive bikes. He liked what he saw and, as a tester for Shimano, he could have some influence on the Japanese company.

Shimano is always interested in widening the appeal of cycling and belt drives could play a part in this broader appeal.
Bonney sees a lot of positives in Poly Chains: “This is the first product I’ve seen in a long time which will bring new riders into cycling, one which lets you focus on riding.

“The transmission on a mountain bike is the last part left over from road bikes. We’ve moved frame design, suspension, brakes forward and yet are stuck with a chain which flexes and wears out. If you had to start MTB design with a clean sheet of paper I’d think the last thing you’d use is a flexing chain, running over a cluster of cogs with a couple of springs lifting it up and down, and at the mercy of the elements.

“We still have a lot of work to do. There are chainline issues, clearance for the wider sprockets, different hub fitments but we’re all confident rapid progress will be made.”