Bent In El Paso

I'm happy with the performance of our belt drive system, no need to call Gates.

Once I figured out how to properly tension the belt so it will remain centered on the pulleys, it has worked fine. It is interesting though that the belt tension seems critical on some setups and not on others. We have friends who ride with the same setup and the tension seems much less critical for them. Our bike was delivered from Co-Motion with the belt drive so I know it is not a design problem. The pulleys are in perfect alignment with the eccentric centered in the bottom bracket. I think it has more to do with the belt/pulley interface.

The bike shop that built our tandem did put the stoker's pulley on backwards. We rode the bike that way for probably 2K miles before I discovered (through this forum) that it was installed incorrectly. Co-Motion replaced the belt (at Gate's recommendation) but would not replace the pulleys. I wonder if running that pulley backwards for 2K miles may have worn it in a way that makes our system more sensitive to belt tension? If and when I upgrade, I will most likely go with the new center-track system so I will probably never know for sure.

sixtiescycles

First of all, yes, Gates is coming out with a 66T CenterTrack tandem (8 mm pitch) sprocket in June of this year. Second, it's not necessarily just for Calfee and Cannondale, as we could get them, too, if we wanted. Which brings me to my third point, that being I don't think we'll want to design a new frame just for an additional 12 mm (1/2") of boom tube length, so 29" instead of 28.5" (approx.). That's right: the 66T sprockets only increase the boom tube length by one half of an inch; not worth the effort, IMO.

It's likely that the 66T sprockets are in response to a particular OEM application where they have enough volume to justify tooling up another (at this point unique) size sprocket. C'dale is the likely suspect, IMO. But why would they bother with 29" boom tube instead of the informal tandem standard (for belt drive, anyway) of 28.5"?

twocicle

Do you have the older CDC belt system and not the newer CDX (CenterTrack)? The latter is a piece of cake to setup as the center track keeps the belt from wandering off to the side.

The CDC system is more particular to alignment and belt tension. You should note that with the CDC rings (or CDX for that matter) it does not matter which way you mount them. Retaining ring in, ring out, whatever... no diff. In fact, in some cases people prefer to mix the ring orientation... one ring in, one ring out for various reasons.

If you continue to have issues with the CDC setup, the CenterTrack system should alleviate problems you may have had with the old system.

Ritterview

Well, duh... like you haven't heard of the growing popularity of 29ers?


Surge in 29er Sales Points to Market Shift

Bent In El Paso

Actually I have a CDX system on the way.

When I spoke to Gates a couple of years ago about the CDC stoker sprocket installed backwards, they told me that it would cause the belt and sprockets to wear improperly. Since we had a couple thousand miles on the components, their recommendation was to replace the belt and both sprockets. Co-Motion agreed to replace the belt but did not want to replace the sprockets.

We have put over 10K miles on the CDC system. I'm ready to move on to what is hopefully a better system.

TandemGeek

Just getting back on line after being incommunicado for a few days.

I agree on the net length supported by the 66t sprockets being closer to 29" not 30" and believe Steve at Gates simply gave me some incorrect info on belt compatibility. It's a simple calculation that I'd already ran and that yielded a need for a 60t sprocket... not 66t. My only error was not remembering that the standard drive systems used 11 pitch instead of 8 pitch, noting there was an 11-pitch 60t sprocket.

Not sure why I chose to ignore the math and assumed there was some fairy dust floating around that would "solve" the math gap. It sort of dawned on me while as we were riding our motorcycles to Key West on Monday. This was the first chance that I had to log-on other than a quick visit to address a private message yesterday. I've also sent off a note to Steve P. at Gates just to follow-up.

Our friend Bob Thompson could provide a 60t solution using some custom sprockets that would use the Gates 250t/2000mm belt and that would bolt-up to our daVinci cranks so I may mull that over a bit.

twocicle

Yea, understood what you said the first time. Still, whoever told you that you couldn't mount the CDC rings "backward" did not know what they were talking about... even if it was somebody from Gates.

twocicle

Great article. It really clarifies what has been confusing to me about the reasons for using either 29er or 26er. "Trail riders want 29er trail bikes. For us, it’s an up valley trail rider or down valley hardtail customer”. WTF? I must be lingo challenged

Bent In El Paso

Thanks.

It's good to know someone out there has all of the answers.

twocicle

Was that a snipe or a joke?

You have a collection of people on this forum that have gathered information and some that have used this product more or less successfully for years. Conversely, larger companies such as Gates have people who have never used their own product. I do know for fact that when I have called them, the support/tech person has never ridden a tandem let alone used a gates belt-timing ring setup.

jnbrown

Is there a CDX system that fits the original 71 tooth chain rings?
I believe that is what fits our Calfee.
I don't see anybody selling Tandem CDX parts online, where do you buy them?

Bent In El Paso

Gates website shows a 69T and a 74T centertrack pulley for tandems. Some discussions earlier in this thread indicate a 66T will be available this summer.

I think most of the tandem shops either stock or can get the CDX system. I purchased a 69T system for our CoMo from House of Tandems earlier this week. Tandems East and Precision Tandems also advertise the system.

Before purchasing from HoT, I did a google search for Gates Tandem CDX. The "shopping" results showed several belts and pulleys that were advertised to be CDX but the pictures did not look like CDX components.

One example is this pulley from bikepartsexpress.com. It shows the CDX label on the side but it does not look like a CDX pulley. It looks more like the pulley for the CDC belt drive system that we have on our bike now. I decided to play it safe and purchase my system from one of the reputable tandem shops.

DubT

If the center to center distance between your bottom brackets is 28.5 inches you will be able to use the new 69 tooth rings and the 250 tooth belt. The kit is available directly from Gates and I believe most of the tandem speciality shops such as Tanems East, House of Tandems, Precision Tandems etc. I bought ours directly from Gates and have had it installed since early October of 2012, it has around 2,500 miles on it with no problems, no wear that I can see, quiet and clean.

Wayne

twocicle

"71 tooth chain rings" is something of a misnomer, since there is no chain involved with the CDX setup.

71T CDC rings were made and you may be lucky to still find some laying around. Check with Calfee direct.

As far as CDX 71T rings, you can't. At least not from Gates and presently no 3rd party either. I had inquired last year because our 2007 Calfee was in the same boat - it would need 71T rings due to the BB spacing. Gates stated they will not produce any 71T CenterTrack rings, ever. From 2008 onward, Calfee tweeked the BB spacing which then conformed to the Gates belt requirement and from then onward uses the 69T rings on their standard sized frames.

Maybe the same people that will be producing the 66T CDX could be persuaded to make a 71T too. That would let a bunch of people into the game, but something of a deadend as those frames needing a 71T ring are no longer made.

akexpress 

We have been using the CDC belt system for at least 10k miles without issues. However when we first sent our frame to have it installed along with painting we wanted done Calfee had issues with it walking off. they investigated the problem and found that when our bike was jigged intially somehow our bottom brackets were not parallel by about 2 degrees. They redid one of them and actually made a tool at that time the assured all other tandem BB's would be absolutely parallel. We can run our belt well below the recommended tension with out problems. So the lack of parallelism may be the cause of many of the belt problems. We were early belt drive adopters and paid the high initial price. At this point I see no reason to go to the CDX system

uspspro

I love Calfees, but that is totally lame. Imagine if you have ordered with a chain drive, they may have not discovered this. My front water bottle mounts are crooked. One day I will bring the frame back to fix it.... but still that kind of stuff should not happen.

sinkr8

Hi Folks,
I'm new on the list, and have read a lot!
I'm trying to update our 2009 Cdale. Co-Motion has/had a sale to close out the Gates CDC system. I thought, "what the heck" and purchased. Now I am having some difficulties with install...of course I'm hoping someone will set me straight.
Equipment:
FSA Gossamar cranks
FSA MegaExo BB.
Cannondale dual-wedge ECC

First question: I am using the iPhone app for tension. I tested with the cranks in various positions to see what the range is and expect some differential in tension. I am getting a 15hz variation i.e 50hz in one position vs. 65 in another. That seems significant to me especially since the Gates App indicates a 5hz variation between "lightweight" and "big and powerful" for tandems.
I have repositioned the front pulley on the spider to see if it changed, it didn't have a noticeable impact.
What kind of hz ranges are others getting with this App?

Second question: Alignment. If I can rotate the cranks forward and backwards without the belt walking off, is that considered aligned? I believe I can hear the belt rubbing against the flange of the pulley but I currently have the system "aligned" such that the belt will not walk off while on the stand but have not ridden it.
I ask this question after investing a significant amount of time trying to attain alignment. I am using the ECC to attain aligment though I do have some option with shims. Once I get the alignment set I have to rotate (using a pin spanner) the ECC for tension, the ECC "walks" in the BB which throws off the alignment. If I'm lucky and get the tension acceptable (see above) and the alignment is still good, I have the challenge of tightening the ECC which again may cause the alignment to shift ever so slightly...and the belt will wander.
Am I the only one pulling my hair out? - technically not my 3rd question...
Any insight appreciated!

akexpress 

My experience over 4+ years on a CDC system is you can run it with much lower tension than specs recommend if the alignment is good. I no longer use the app or the kricket but just do it by feel. I can actually put it on be sliding it on from the inside without moving the eccentric. YRMV but I would try riding it a much lower tension and see if it walks. My experience if it stays on pedaling backwards on the stand it will ride just fine. We recently climbed many ascents in New Zealand with grades up to 17% without skipping at the low tension.

twocicle

You are correct that ring positioning on the spider is key to obtaining a consistent tension. That said, it is doubtful you will get it perfect. At least the CDC rings have a crank bolt head recess which should help you with the ring positioning.

Our belt tension varies somewhat depending on the crank positions, but as it is neither binding nor terribly loose, it appears to otherwise run fine. I do not use the app. I gave our CDX ring positioning my "best effort" and then left it at that without fretting too much. With the CDX rings it is best to rely on the sleaves of the crank nuts to provide the best concentric position.

If your ECC insists on centering itself, then perhaps you should resort to using chain ring spacers (aka washers) instead. Likely you can use 1-2mm without any issue, but more may require longer chainring bolts/nuts (which can be surprisingly expensive, especially if you need 10 of them. Problem Solvers packets of 5 at ~$16/ea).

DubT

I chose to wait for the CDX system so that I would not have any of the issues that you are describing. I hope that you saved a lot of money. I would pack the whole thing up and send it back and spend the extra money for the redesigned system. Engineers redesign for a reason.

Wayne, retired engineer!

twocicle

If you subscribe to the school of Dilbert, you would know it is marketing that drives product development

I'm just glad this kit now costs less than half of what people originally paid (>$500) for the CDC setup.

sinkr8

Amen. Just because they designed a new system that will stay on the pulleys doesn't mean they addressed alignment issues specific to the frame and cranks! That's the beauty of chain drive, its very tolerant!

Turbotandem

I agree with those saying tension can vary. I'd set it to proper tension at the point the belt feels tightest, such that it is a bit less tension at certain points in the rotation. IMHO I would not slack it all the way down below spec.

I think you are trying too hard. In my experience, the belt will ride against or rub the inside flange of one of the CDC sprockets, and that's OK. It won't catch and run off. But that's why the CDC has a flange is so the belt can't walk off. If it means one sprocket is a couple mm outbord of the other that's OK too. That is, if when riding under load, which is the importnant metric, and the belt tends to walk off to the inside under the stoker, you can move the captains sprocket out a mm. In an ideal world the bottom tube, cranks, spiders, axles all have so little flex that aligmnet in the bike stand is the same as on the road. But short of that ideal, it takes a bit of nuance to set up alignment, especially on a retrofit tandem. Thus the release of the CDX to solve this problem.
I would also say that back pedaling may lead to differnt results; if it walks off while pedaling backwards, don't pedal backwards. I've seen belts walk over if you pedal backwards a whole bunch. But why would you? If you pedal backwards just to get the stokers cleats in and your own, a couple pedal strokes is not going to throw the belt.

sinkr8

Thanks Turbo,
That is what I needed to hear.
On a couple occasions I did manage to get it aligned perfectly such that it was not rubbing on either flange at which time it was very quiet and smooth! Alas, the alignment was not quite right and it would walk off the stokers pulley. On this CDale there is only about 2mm clearance between the stoker pulley and the chain stay so it really cannot walk off but is can rub if misaligned. My back pedaling comment was driven off of what i read on the Co-Motion FAQ's page and another comment I read which indicated a perfect alignment would allow both forward and back rotation but maybe that is pie in the sky...
As an additional comment on the tension challenge, I find it amazing the either the belt or the pulleys cannot be manufactured (economically?) to a higher tolerance such that the variation is minimized.
I will get things aligned and tensioned and give a report back.
Thanks again.

Krenovian

For those of you that are finding the tension on the Gates Belt changes as you rotate the cranks you might try the following. After setting the initial tension on the belt, back off the chainring bolts holding the Gates sprockets on both timing side spyders so they are still snug but not tight. Now rotate the captain's crankset through several full rotations then re-torque the chain ring bolts. If the sprockets were not concentric with the bottom bracket axle initially, causing variable tension as the cranks are rotated, this may improve the concentricity.

After initially installing the Gates CDX system on our bike equipped with a DaVinci crankset I found quite a bit of variation in tension as the cranks went through one full rotation. After I had carried out the above procedure I couldn't detect that difference any longer. This should apply to bikes equipped with the CDC system as well. Regarding the tensioning of the CDX belt, I found quite a bit or rotational resistance when the belt was tensioned near the recommended level. When I backed this tension off there seemed to be a lot less resistance, as a result I now run the belt with relatively low tension.

Curtis