The Gates Carbon Drive Timing Belt System:
Incredibly smooth and more efficient power transfer, immediate response and an incredible weight savings of 283 grams/10 ounces (compared to top quality chain and chainrings) makes the Gates Carbon Drive a natural choice for our top race tandems. The Carbon Drive lasts as much as 10 times longer than traditional chain and chainrings, and never needs oil [Note: Gates’ official word is to expect 2-3x normal chain life- we find this very conservative]. Optional on most tandem models, and exclusive to Co-motion Cycles through 2009.
Will The Gates Carbon Drive Fit The Tandem I Have Now?
If you have a Co-Motion tandem manufactured in 2000 or later, chances are good that the Gates Carbon Drive will work on your bike. Most of our tandems made within this time frame have a 28.5” boom tube length- measured from the center of the rear bottom bracket, to the center of the front bottom bracket, disregarding the placement of the eccentric unit.
The Gates Carbon Drive sprockets will replace your chainrings on the timing cranks. The sprockets are made to fit onto a 130mm bolt circle diameter (BCD). Our current FSA Gossamer and FSA SL-K cranks both accept 130 BCD rings. Shimano Ultegra cranks also accept 130 BCD rings. The older Race Face tandem cranks have a 110 BCD, as do many other older tandem cranks. Some cranks, like our current Truvativ Elita cranks have the right 130mm BCD, but have a compatibility problem in that there is inadequate chainring clearance from the chainstay. We do not expect that the Gates Carbon Drive will fit on all tandems.
If your tandem meets these criteria, the Gates Carbon Drive may work for you
28.5”/724mm boom tube length (measure from rear bottom bracket to front bottom bracket)
Tandem crankset with 130mm BCD timing crankarms
Same length bottom bracket spindles front and rear
A way to adjust chainline or “beltline” on front and rear cranksets
Chain and chainrings must be removed from your tandem, and the bottom bracket eccentric unit should be loosened and placed in its shortest effective position. The Gates sprockets will replace the original chainrings. You can re-use the original chainring mounting bolts. Chainline, or in this case, “Beltline” is extremely important. The belt will track straight only when there is excellent lateral alignment from the rear drive sprocket to the front drive sprocket.
Gates Carbon Drive Checklist
How is the Gates Carbon Drive System Installed?
Use a straightedge at least 28.5” long to verify that the sprockets are in plane. A metal yardstick will serve this purpose well. Lateral adjustment of your sprocket placement depends on the type of crankset you have. Some adjustment can be done by sliding your eccentric laterally. Most bottom brackets can be adjusted laterally by repositioning some spacers. It is possible that your crankset will not alow enough lateral movement for the Gates Carbon Drive system to work properly. In this case, the only solution is to replace the crankset with a new FSA Gossamer, FSA SL-K, or other crank with either excellent timing-side alignment, or facility to adjust alignment.
The new FSA Gossamer and SL-K cranksets facilitate lateral alignment using spacers between the crankarm and external bearing mechanism. This means you’re actually changing the lateral position of the crankarm without moving the bottom bracket assembly itself. There is a fixed number of spacers between the crankarms and bearing assembly. The number of spacers cannot be changed, but they can be repositioned from the right side to the left side. Using your straightedge, adjust the lateral position of both sprockets until they’re in perfect alignment. Note: the minimum clearance between the inner edge of the sprocket and frame should be 2mm. This dimension is most important for the rear sprocket when considering clearance with the chainstay.
Once you’re satisfied with the alignment of the sprockets, check to make sure the eccentric is in the position for shortest possible span from front to rear (lobes forward, bore rearward). Next, place the belt onto one sprocket, much as you would place a chain. Then, pull the belt to the opposite ring, checking that the crankarms are synchronized to your preference, and slide the belt laterally onto the second sprocket, do not roll the belt onto the sprocket like a chain as you may risk belt damage. Rotate the cranks 6-8 times forward, then 6-8 times backward times to see that the belt tracks properly.
If your belt is tracking properly, there should be zero to 1/2 millimeter gap between the belt and the outer guard on the sprocket. If you see a gap, this would indicate which direction to reset the lateral alignment of your crankset. You may want to try reversing the direction of the belt before making any changes- if you do so, remember to never derail the belt as you might derail a chain, always loosen the eccentric and slide the belt laterally off of the sprockets. There may be a slight difference in the cut of the belt when its driven direction is reversed, so we have found reversing belt direction to be effective in some cases. If you still see a gap, or the belt derails after reversing the belt, readjust your crankset’s lateral alignment accordingly.
The Carbon Drive’s belt tension should be set tighter than you might be accustomed to running your chain. The concentricity of the sprockets allows for more consistent tension that most chainrings. With about 10 pounds of force, press with your finger against the center of the belt between sprockets- with the belt tensioned properly the belt should deflect no more than 1/2” (12.7mm).
Gates technical info and FAQ is posted here