Part I: An Introduction To The Gates Carbon Belt Drive System
By: “c_g”, Grannygear, and Guitar Ted
Welcome to our report on the Gates Carbon Belt Drive System: Twenty Nine Inches has been intensively testing and researching the Gates Carbon Belt Drive System over much of the last half of 2010. In the following reports, we have prepared a look into the belt and what it takes to make it work, how it performs on the trails, and finally, an analysis on the belt versus traditional chain driven bicycles, especially single speed mountain bikes.
In this part, we introduce you to the Gates Carbon Belt Drive with a little history and the peculiarities of its design and integration into a bicycle drive train.
GATES CARBON BELT DRIVE – An Introduction:
Let´s take a look back: It was back in the year 2007 when Gates introduced their first bicycle dedicated belt drive system to the world. Though highly respected for innovation and as a concept, the industry response had been slow. In 2008 only 4 production models were being offered, in 2009 there were already 17 models available, and for 2010 Gates cites a total of 43 models. For 2011 the numbers are anticipated to at least double and these statistics do not include custom builders which seem to have a special favor for the system.
Most of the belt equipped bikes are high end touring or commuting bikes but there are a few real mountain bike brands as well. Here is the short list of the ones known to us that even do a 29”er – mostly smaller companies with flexible productions, but all renowned for their high performance products.
* SPOT BRAND is one that has been promoting the Gates Belt drive from beginning on for their steel tubed Longboard 29”er model.
* VENTANA has been doing a belted option of the El Commandante 29”er.
* RALEIGH is following suit in 2011 with the XXIX in a belt version – shown on test on TNI here (link). This bike does have an interesting position in being the first mass produced “belted” 29”er
Others make belt driven 29″ers on request as well, but we have not listed these companies here.
More focused on the European market there are a few others also:
* NICOLAI, the highly renowned innovation think-tank for suspension designs and new transmission ideas have been doing custom 29”er belted bikes for some time and now are offering a a production 29”er, the Argon 29 (introduced at Eurobike´10 and first shown here) and…
There are others in this market as well that will do a belted 29″er on request.
Peculiarities Of The Belt Drive System
1: The GATES BELT Drive relies on a constant distance from bottom bracket to the rear axle.
This means it does not work for anything but single speed or internally geared bike applications on hard tails (Interestingly, the near-dead “Unified rear triangle” design as used on Trek´s “Y” bikes of old, is one of the only full suspension options that would work in existence).
So forget it if you absolutely want to stick to your current externally geared drive train – here it is CHAIN-ONLY. For Rohloff and other internally geared hub bikes, the GCBD is worth pondering.
2: The belt is a single monocoque structure.
Unlike the muti-piece linked standard chain it cannot be split, or altered in length. This requires some access into the right rear triangle via split-able chain or seat stays for mounting, or by a special split drop out, features that really should be designed into the bike’s concept from drawing on. (why? Read on.)
As has been shown in “c-g”’s intro on the MI-Tech Tyke 29”er all the other parts of the belt drive (only front and rear cogs) are adaptable to existing components, so not much hassle there. Since the belt drive system is rather new, only a hand full of more common cog options and belt lengths are available, but by some wise consideration most riders should be able to achieve the desired ratio and set up. However; a new belt may be needed, along with a different cog in order to change ratios if desired.
Keep in mind that the tooth size in the belt system is smaller than the tooth size in chained drives; the outside diameter of the 46t cog is a bout the same as a standard 38t chain ring, so ground contact is less of an issue than the tooth number would make you think.
3:SENSITIVITY TO WRONG HANDLING: The belt does require some attention and careful handling. It should not be kinked or overly bent when loose and during installation but once mounted and tensioned properly it really can become a tough “mount and forget” item. Gates and the manufacturers interviewed in unison said that 98 % of all belt failures did happen within the first 10 miles of riding and all could be traced back to misuse the belt in the process of installation.
4: BELT TENSIONING: A big part of GATES´ instructions on the belt drive system is dealing with properly tensioning the belt before use. This is said to be the second biggest reason for damaging the belt – by running too low a tension and having it skip on the cogs. (In my experience skipping might still occur when tensioning correctly under high torque– Rohloff has developed a device called a SNUBBER to rule that out – shown in several pictures) Gates does have a tension measuring device available called the “Cricket” which you can use to be certain the belt tension is proper. ( Note: per “c_g”: Several manufacturers and even the Gates Europe folks have said to the cricket is pretty much useless) It should be noted that bicycles supplied with the Gates Carbon Belt Drive often do not come with this tool, so you would need to purchase this item separately.
5: “Belt Line” Must Be Precise: Since a belt has near zero tolerance for out of alignment conditions laterally, a precise “Belt Line” must be maintained to insure proper performance. (Gates new “Center Track” design is said to help alleviate some of this issue) This can be affected by a frame with lateral and torsional flex, which leads us to….
6: Frame Design: Gates has specified frame tolerances for lateral and torsional flex that will be enforced in the future for companies wanting to spec Gates Carbon Belt Drive. This is being pursued in an effort to help frame designers produce designs that will have ultimate stiffness in the chain stay area in particular to avoid issues with flex that can derail a belt, or cause it to skip or otherwise malfunction. While belt drive bikes can be made from chain driven frame designs, this has proven to not be optimal for belt drive performance at the highest level.
Finally, due to the peculiar offset of Gates Carbon Belt Drive cogs, and the larger diameter of the cogs which Gates recommends, frame designs may have to compromise to a degree in terms of chain stay length, (usually longer), and in some cases, tire clearances for the rear tire. Another possible compromise would be in terms of the crank set “Q” factor, where the Gates Cogs would be placed further outboard to avoid some of the frame issues described here. It is also possible that a shorter chain stay length may be possible by careful manipulation of the frame and still retain some modicum of tire clearance, but this is not as common.
Benefits Of Using Belt Drive
NO MAINTENANCE: Of course there is no maintenance involved, no lubing, no cleaning, and no worry about it when getting wet. Besides there is no lube to get on your clothes or disc rotors, spoiling the pads.
LIFE EXPECTANCY: Life expectancy of the belt is said to be roughly double that of a well kept chain. The belt is not prone to stretching but the cogs do wear, reducing interfacing surface and forcing the belt to deform, eventually getting the system to malfunction. There is a caliper available from GATES, to tell when it its time to change the cogs and belt all in unison.
Weight Reductions: The belt and the specific belt cogs are lighter than a chain and traditional chain ring and cog combinations. (However; the specific frame design requirements being placed upon frame designs for belt drive bikes may negate any specific drive train weight savings.)
Other “Benefits”?: Some will point to quieter operation than a chain. However; in real world riding, where tires are bounding over roots, rocks, and spinning over dirt, the sound difference of running a chain versus a belt is probably a non-issue. Perhaps in the paved run up to a trail head one might discern a difference; otherwise we feel this is a moot point. Some will also point out that belts run cleaner than a chain. However; once again, this seems to be a small thing in terms of the realities of riding. We don’t hear about or experience any negatives with “dirty chains” on single speed bikes other than the rare times one might clean their single speed chain. Besides, having a belt does not absolve one from maintaining or cleaning the rest of the bicycle.
Coming Up In Part II: We take a look at a couple of specific belt drive applications and evaluate performance in real world mountain biking scenarios.