RichardT

Hi all

the one who knows an answer on this one is my hero

I'm building a new road tandem. Lightning cranks are coming and I would like to try the Gates belt system. Got my doubts about it but if you don't try, you don't know.
The Centrer Track sysem is build for a boom lenght of 720 mm, standard for Cannondale, Co-Motion and Calfee I guess.
My new tandem will have a boom lenght of 700 mm, center-bracket / center bracket.
Does anyone know if the belt will be long enough with the 74T beltrings? Can I still adjust the belt a bit or will my excenter already be turned all the way? I'm receiving different answers sofar. The Gates distributor in Europe says, it should work out. Gates USA though says the belt will probably to long.
So, who knows the answer on this question?
Is the Gates belt for the tandem a specific belt, specific widht or will for example a car belt fit as will since those are availbable in different sizes.
I have been asking Gates USA if bigger beltrings excist (for example a 76 or 78) but sofar not.....

Those of you with Gates experience should know the answer on tis question.
By the way, does a Gates belt stretch lots like a chain?

Richard

Artmo 

I only know the answer to your last question: no, it doesn't stretch like a chain, in my experience of 2000+ miles, and it will last much longer.

RichardT

Okay, thanks
the distributor in Europe told me too, it will last 2 or 3 times longer but with a chain I already do 10000 km.
so I guess the belt will last longer then I do.....

merlinextraligh

^ The belt lasts longer. The rings, however, may well wear much quicker than chain rings.

I was surprised by how fast the rings wore out on the original system. Haven't had the center drive system long enough to know how it will wear.

twocicle

I'm in the same boat, new CT install but no miles yet.

Other than environmental factors such as dirt, I think the belt system wear can be largely effected by install alignment. Even though the CT system seems to tollerate fairly large ring misalignment, when rotating the cranks there is definite noise feedback can indicate excess belt rub. Dialing in the alignment virtually silences the belt setup and over heavier usage time should prove to reduce wear too.

To the OP, the Gates USA response is incorrect. 74T rings are designed to accomodate a shorter bottom tube such as provided with Santana (sub 700mm). If your bottom tube is 700mm, the belt + 74T rings may be a little too tight if anything. I forget exactly what the Santana tube length is, but if you find that info then extrapolate to yours.

tandemdr

The Gates CDC and CDX 69T cog systems are designed for the 724mm center-to-center boom lengths. In my experience the eccentric must be able to reduce the bottom bracket c-c distance to 720mm for the CDC installation and 722mm for the CDX installation. The tension point for the 69T system is 726mm, which should cause the bb to land mostly in line with the seattube, i.e., rotated forward slightly compared to bottom dead center.

The Gates CDC and CDX 74T cog systems are designed for ~704mm center to center boom lengths. The tension point for this system is 706mm. With a 700mm boom distance there will be no problem getting the belt on but that length may not permit full tensioning of the belt. It will be close and I would predict that if it did tension that the eccentric would be nearly all the way forward if not right there. And that changes one's fit considerably, too. Please post your results should you give the belt a try.

In the real world, many stated boom lengths of finished products seem to vary and come up short more often than long. Call it manufacturer's tolerance I suppose. If by chance your builder errs on the longish side, you should be good to go with the 74T system.

For future reference and updates, most of this dimensional information can be found in our on-line catalog under "Belt Drive - Timing"
https://www.precisiontandems.com/cata....htm#beltdrive

Hope this helps.....

merlinextraligh

In our case, I don't think it was allignment as much as the pressure put on the stoker's ring by the captain.

Looking at the pictures below, the wear appears to be pretty symmetrical on the stoker's ring, starting from the middle and going outward (hence my thought that it wasn't allignment)

And the wear on the stoker's ring was much more pronounced than the captain's.

twocicle

^^^ Merlin, I understand your points about the CDC ring wear. That appeared to be a design issue of the belt nubs and ring teeth. Given that you had symmetrical wear, that seems to prove you had good alignment - which is an absolute requirement of that version.

My comments were oriented more for the CT (CDX) setup and simply to point out that while it can tollerate more ring misalignment without the belt coming off, it is very noticable audibly if the belt and rings are not meshing cleanly. Assuming higher noise = increased wear.

Our new frame has a Bushnell style EBB installed, and while that can be moved side-to-side, I prefer to leave my captain's cranks centered and not offset to one side (asymmetrical). To achieve timing ring alignment I added 2mm chainring spacers (and used longer bolts) between the Ultegra front spider and the CT rings. Hopefully it all works out ok.

RichardT

Thanks gusy for all the feedback.
I'll think I'll just try the 74T.
But, can somebody explain me the difference in the two systems? CDC and CDX?

Richard

Chris_W

About ring wear on the original system - we took ours off after about 10-12,000 km and there was barely any sign of wear, certainly nothing like shown in merlin's photos. We've done some major Alpine passes on the bike, and some loaded touring, so it had it's fair share of power going through it (the captain rides over 10,000 km per year on various bikes, with LOTS of climbing) but maybe not as much power as merlin puts out.

Our main reason for changing to the CenterTrack was because we had the original 71 tooth rings that they sold in the first batch, until reducing these to a more appropriate 69 teeth. On a stock 2008 Co-Motion Speedster, the belt barely fit on these larger rings even with the eccentric all the way back, and it never seemed to stretch over time (it was always equally hard to mount it every time).

merlinextraligh

^ My hoypothesis on the wear on our system was not so much the amount of power, but the difference in power between Captain and stoker. I'm both substantially stronger, and heavier than my stoker.

If you look at the 2 rings there is little wear on the captain's ring in relation to the stoker's. Thus, I'm thinking that it's my weight/power pulling forward on the belt against her ring that caused the wear.

waynesulak

I don't see it that way. The force transmitted from the belt to the stokers ring must first be transmitted from the captain's ring to the belt. In both cases friction would be created between the ring teeth and the belt. Maybe their are properties of belts that make the direction of the force transmission an issue (ring to belt vs belt to ring) ?

Looigi

Theory: The bottom run of belt has its teeth facing up and may be holding grit and debris kicked up by the front wheel as it feeds onto the stoker ring. The belt teeth are facing downward along the top run before it feeds onto the captains ring so perhaps there's less grit on the belt.

waynesulak

Sounds like a possibility.

twocicle

CDC = original "Mudport" belt system with side flange on rings.
CDX = new "CenterTrack" system with a center ridge on the rings and a center slot on the belt.

see: ProductListAug2012_sm.pdf

witgen01

We ride our speedster year round in Michigan. Im thinking of switch to the belt drive to relieve the rusting timing chain from road salt spray off the front tire. Would the center track have any excess wear issues?

twocicle

I am not aware of any data concerning salt corrosion on the belt system (especially the rings). Give Gates support a call, they are very helpful. https://www.carbondrivesystems.com

witgen01

Thanks. I contacted Gates and they said that there should be no issue with road salt. He did recommend a spray bottle rinse after riding to reduce buildup and help with sprocket wear.

merlinextraligh

In our experience, the CenterTrack system works much better.

1) you can see the wear issue above with the old system,

2) the old system would skip under heavy loads for us,

3) the old system started walking off the rings on our bike.

So far, we've had none of these issues with the CenterTrack, and we can run the CenterTrack with lower belt tension, which presumably equals less drag.

waynesulak

I believe you have mentioned before that you were running about the same tension as a chain. Has that worked out well or have you adjusted the tension?

merlinextraligh

We haven't been able to make it skip. So so far so good.

Chris_W

We accidentally ran the ultimate test of how well the CenterTrack belt works under very low tension.

After taking our de-coupled tandem on a small charter plane during our New Zealand tour (we were going from the end of one dead-end road to another - they don't put roads over every mountain range there like they do in Europe), we hurriedly put the bike back together at the grass airstrip to ride the couple of miles to the campground in the nearby village. The next day, we rode out to do a hike in the afternoon, and I noticed that something felt a bit funny with the belt - there was a slight lag whenever going from coasting to putting the power down. I didn't check it until we got back to the campground at the end of the afternoon, when I discovered that the belt had been almost completely slack, I believe for about 20 km of riding, including up some really steep pitches on a dirt road.

It appeared that despite the lack of tension and the power I must have put through it at times, there was no skipping, as shown by the pedals still being 90 degrees out of phase, as I had set them initially. At the time I didn't think to check the pedal phase too precisely to know whether or not it had skipped one or two teeth because I was too busy rectifying my foolish mistake, but I certainly hadn't felt any sudden skips, so I don't believe it had moved at all.

This happened because when putting the bike back together, I had played with the eccentric to get it to the right tension (using the iPod Touch App), and when doing so I only ever bother to half-tighten one of the four bolts on the eccentric before checking the tension each time (it normally takes a few attempts before getting it right). When I'd got the tension right, I forgot to go back and tighten the eccentric properly because I was in a hurry. The eccentric had therefore quickly moved into the loosest position.

I was a bit surprised that apart from losing the feeling of direct connectedness between the cranks, there didn't seem to be any other effects of having run the belt totally loose. After I tensioned it properly, it performed flawlessly for another 800 km of touring. Even so, I don't plan to run this experiment again, and I'll try to keep the belt at the advised tension, ignoring the fact that this might be robbing us of 1 or 2 watts of power.

RichardT

about the tension of the belt.
Chris, you have been writing abou tan APP?
What should be the tension of the belt? WIth the chain I always guess and feel a bit.
I can do the same with the belt?

Richard

texasdiver

Gates has put out an iPhone app that helps you adjust the tension of Gates Drive belts. I haven't tried it yet and just downloaded it to my phone. It allows you to adjust tension by plucking the belt. The phone mic measures the frequency of the twang when you pluck the belt and you tighten or loosen as appropriate just like tuning a guitar. There's also a gear ratio calculator and other reference material in the app. Here it is:

https://itunes.apple.com/us/app/carb...438346486?mt=8

As for these belts wearing out? The technology has been ported over from auto applications. A similarly made toothed engine timing belt is good for 100,000 miles of driving. I should hope that a bicycle belt is good for at least 1/10th of that.

DubT

I use the app and it works great!