Thanks, Michael. Good ‘n meaty.
There’s also a review here:
Thanks Carlton,I’ve posted this with my full name
Below is a reply I made on Singletrackworld and MTBR back in September in answer to forum posters questions on belts, it probably answers a few similar ones raised here in conjunction with Carlton’s podcast and the BiekBiz thread where it is also posted.
For anyone attending Core bike show i January we’ll have bikes there for people to try.
orginal thread http://www.singletrackworld.com/forum/read.php?f=2...
Date: 28/09/07 18:14
I’ll try and answer what I can, sorry I can’t get into more of a discussion on it but I’ll try and give as full a reply as possible, apologies for the long read.
In no particular order
Efficiency – no-one has accurate data for chain v’s belt efficiency, even chain efficiency varies according to chainline and which size sprockets are selected. There are various documents and studies but a lot of the data does go back to the 1937 Renolds paper which seems to suggest 98% for a clean, well lubricated chain. Few studies have used low power/low RPM scenarios (The HPV one does), most have related to motorbike or other applications with higher revs and more power transmitted. Most of the stuff I’ve seen suggests that belt will be as efficient or better but it does rely upon the tensions used.
TBH for MTB use I question whether its a real issue, MTB chains are usually covered in crap so it would need a totally different study but more importantly we ride around on 2.35 inch super tacky tyres, the small amount of energy loss on a drive chain has got to be fractional compared to that!!
Belt type – yes, there are other belts out there, most are aramid/rubber construction and stretch or are affected by water, Shimano have made special hubs and cranks for Bridgestone and Corratec to allow this type of belt to be used, they needed tensioners in the crank to work. The system we’ve been playing with is actually a poly chain developed by Gates Power Transmission Division, the construction is different to the old technology and its a patented process, I’ve been to the plant and the procedure is kept very secret, all recording devices removed, phones etc as Gates have invested considerable time and money into the development of poly chain. Unfortunately most people see the bikes and call it belt, poly chain as a name is a lot closer to what it actually does.
If you have access to the Audi Channel keep an eye out for a programme called Science in Sport on cycling, there is a short section with an explanation from one of the Gates engineers on what the poly chain is and what it does.
Belt lengths/sprocket diameter – currently the available belt lengths are limited by the molds and tooling available, we’ve used 3 lengths varying from 1200 to almost 1300mm. The sprockets are calculated on a final ratio say 1.8:1, 1.9:1 or whatever suits the hub/use - we vary the sizes to suit chainstay length, ratios and available adjustment, most run 56/30 but it would be easy enough to alter that to say 54/32 if we wanted a lower gearing, it’ll be more difficult just to swap front or back by itself. As demand for polychain grows Gates will invest in more diameters, each mold has a crazy cost (in excess of 60K I believe) so whilst its only us and Spot I don’t think we’ll ever have enough volumes to justify that
Sprocket design – we prefer the cut away sprockets as seen on the bike Singletrack have, these allow mud and grit to be pushed through by the tooth form. The Alfine bikes are a bit more difficult to design sprockets for, the belt width is critical to performance and leaves little clearance so we need to offset the sprocket, the cut away design is done with an undercut but we can’t machine that into an offset sprocket. Rohloff is different offset again as is SRAM i9 and yes, we’ve got versions of all 3 under development, the Rohloff bike hasn’t been seen yet but is based on a Sub Xero. We’ve never had a stone jam in the belt, I’m pretty sure that the reason motorbikes don’t use it off road is that they run with belt tensioners to take up suspension movement, this means a stone can be in the belt and get squashed in, we’ve never seen this happen when we run without a tensioner hence the ful sus concept bike with a BB pivot ( no chain tension change, no tensioner needed), the belt can skip but it actually unships from the point of low tension and jumps at about 7 o clock on the rear sprocket not where the belt is under tension.
Frame design does need altering, not just for the split chain/seat stay but also to take into account the different diameters of front chain wheel and chainline, its also involves different cable stop positions etc etc. Ideally this needs doing with the hub makers which is one of the reasons we are pushing Shimano and SRAM to help.
Snapping – yes, it is possible to snap the belt, this usually happens if the belt has been pinched during fitting ( they don’t like tight radii) Gates know the problems on this, have faced it in motor industry and any assembly company will be briefed on the importance of correct installation.
Belt with link – not possible, it uses thin strips of carbon running around the ful diameter, the clever bit is how Gates join this into one loop and then seal it with the outer material, the material is self lubricating and hard wearing, check the Gates website if you want more info on it. A lot of people who ride the bikes say the poly chain feels different, more smooth and even power transmission, we think it could be the way the load is spread around the carbon cord rather than the energy being passed from link plate/roller to link plate/roller in a chain. I can’t feel it as much as some people do, maybe I’m used to new clean chains
Why??? - I guess I’m like a lot of riders, I hate looking after my bike and if I ride a lot hate having to replace expensive chain/cassette and chainwheels within months of buying a bike IMHO only enthusiasts will put up with that.
I’d quite happily put up with a slightly heavier bike to get rid of that ( although I’d prefer it to be the same weight).
It’ll come down to what individual riders want, I’d think racers, performance junkies will always go for chain/derailleur unless Shimano and SRAM really invest time and energy on good internal hub or gearbox. If anyone has heard or seen any of the interviews I’ve done they’ll know how big an advocate of these systems I am, putting my bike industry hat on I know that as an industry we need to improve our products to appeal to new customers, maybe tempted in to bikes because of congestion charging or fuel prices but the only way we’ll keep them is is we have product that matches their expectations, cars have service intervals at 2 years now, we get less than 3 months on some chain/sprocket/BB combinations, honestly, that isn’t good enough and we need to look at how we make it happen.
The only way the big players (Shmano/SRAM) will respond with better product (XTR/X0 level internal hubs etc etc) is if small companies like Orange and Spot show them there is demand and threads like this are very important to that hence why I’ll spend time writing this rather long reply Even if the big 2 just go down the internal gear route at first the technology they develop for that is quite easy to swap to a gearbox
When – we can make singlespeed bikes fairly quickly, certainly by mid 08, geared versions for city/commuter use should be doable in 08, full suspension with gears might take a lot longer]]>
As Carlton points out there are a number of prototype bikes around from diferent companies, most singlespeed but Orange have worked on geared versions with Alfine and Rohloff up and going and SRAM i9 next on the list and full suspension MTB also under development.]]>
Interestingly, despite both Spot and Orange using Gates’ PolyChains they each use different chain widths. VHS vs Betamax?]]>
And Spot has rolled out a new company, trying to get other bike makers to go with the US version of the technology.]]>