yes, very true. Flipping the belt starts a new wear surface

I used the app and it just seems way to tight.

Interesting solution. I never would have thought that the CT belt was compatible with the old CDC rings.

I imagine you considered each of these, so maybe you could comment on them and why they didn't work out:
- drill your own bolt recesses in the CDX ring
- look for chainring bolts that have a flatter/thinner head
- spacing the Lightning cranks differently to provide a bit more clearance room on the drive side

It is tempting to do a test ride at some point to find the loosest setting the belt can run without skipping. Assuming loose = best, all things being considered like BB wear and friction.

We are currently running the CT belt with more like 1" deflection rather than 1/2" and it is working just fine at that looser tension. Our setup is using a more standard crossover/timing ring configuration with the 2012 Ultegra R601/603 tandem cranks. So far, we have not detected any flex in our new S&S Calfee frame, so having a super stable inter-BB span may aid in maintaining tension uniformity under load.

With the belt being perfectly quiet and no vibration as I always felt with tha timing chain, our impression of the Gates CT is very much thumbs up. Bonus I don't have to clean or oil the sucker either :)

Twocicle, I also backed mine off to about what you set yours at and I think I'm happier with that tension. But the real test will be when we get out on the road with it.
http://i497.photobucket.com/albums/r...ps2049b0e2.jpg

I see you mounted the ring on the inside of the spider. To do that on our setup would require cheating the crank spacing to the timing side, and the drive side chainline would have suffered. With the chainline set at 50mm, there wasn't enough room for mounting the CDX ring on the inside. On the front, I added 2mm chainring spacers (and 9mm bolts) to move the ring further out and align it with the rear, without requiring offsetting the captain's cranks to the timing side.

Pretty nice & new cranks there :) I can't tell if it's the carbon weave or protective tape in your photo. If they don't have some kind of "frame-saver" tape on the crank arms yet, you might want to add that to keep scuffs off. I use: ISC Helicopter-OG Surface Guard Tape (8 mil Outdoor Grade)

pushing the middle of the belt down should be no more than 1/2" deflection under pretty good force. Yes, very tight. For the teeth to interact with the sprocket correctly it needs to be tight. If the teeth squirm up in the sproket they wear incorrectly. The teeth of the belt are not meant to ride high on the sproket as they would under low tension.

Reducing the tension does not help. The tension from the captains pedal stroke is higher than 60psi, so you are not really inducing any more load on the frame by running the belt at the proper tension.

The belt teeth and ring sprockets are quite different between the new CDX and the earlier CDC. The CDC does not work well at all when the belt tension was not tight up to spec, whereas the new system does appear to work fine with less. This seems to indicate a substantial tollerance difference between the two systems. We aren't talking about running with a very loose CT belt to the point where it is sagging - which would be extreme, but suggesting that a little less than spec may be sufficient and perhaps preferable to getting it too tight which would induce excess wear on other components.

Do you have photos, data or other information that proves the CT/CDX system would wear improperly when less tension is used?

The Gates Belt App calls for 60-65hz, where did you see 83hz as a setting?

According to the following doc, 60-65hz is for "a Lightweight Speedster". Does your team fall into that category?
see: http://www.carbondrivesystems.com/im...endations1.pdf

Also, from the Gates FAQ section, they indicate approximately 1/2" deflection with 5-10lbs of force. To me this indicates there is a window of tollerance. Absent sufficient reason otherwise, I choose to run on the "less force" side.

The app has the same catagories listed, but also lists a tandem catagory:

Tandem Drives
Lightweight Speedster: 60hz
Big and Powerful: 65hz

What isn't clear from the Nov/11 doc I cited, is whether or not the CDC and newer CDX systems have different tensioning ranges. That doc is from Nov/11 which means it predates the CDX system.

I picked up the phone and called Gates (720-524-7206)... again, to discuss all this with their tech guy "Ian". Unfortunately they do not have any docs or FAQS discussing the possible installation differences between the CDX vs CDC (the latter may require the higher tension to prevent the belt from walking), or between single bikes vs tandem setups.

Ian confirmed that although the CDX/CT system can be tensioned up to 85hz (even higher than 83hz), there is no requirement to do so. He also confirmed that "less tension is always better because there is less friction", and that there is no wear issue that would be caused by running a looser tension - logically the reverse would be true.

Final recommendation point is to run the system just tight enough to prevent the belt from slipping/jumping sprocket teeth.

I just got off of the phone with the Sales guy, Steve, who I bought my system from. His comment is that twocicle may have loosely interpreted what Ian said. The issue is that if you do run the belt too loose and it skips, you can damage the fiber in the belts. He said there is not a good reason to run the belt loose. So there you have it! LOL I will run mine at around 50hz.

Wayne

My post here was not a lame interpretation of the earlier conversation and although I do not have an actual transcript it pretty much quoted what was said on that call. FWIW, my wife sitting in the same room heard the entire thing too.

Perhaps Steve misinterpreted what I said, or didn't actually participate in the call (bingo!). Nobody said to run the belt so loose that it would skip, but that it may not be necessary to run it at the top end of the tension specification. If Gates is worried people will start riding around with floppy loose belts and poke their eye out (A Christmas Story), then that is quite laughable.

50hz sounds (pun) about right, Wayne. Glad you got the gist of it, unlike Steve.

You know how sales guys can be! LOL

Hitting the 60-65 Hz range is not so easy when you're on tour, reassembling the bike in a coach parking lot or beside a grass airstrip, and don't have a nice pin spanner to rotate the eccentric precisely, and are instead relying on the needle-nose pliers from a Leatherman multi-tool braced against the crank (which I became quite adept at). In addition, the tension varies a little with the position of the two cranks since the belt rings are not perfectly centered on the crank axles, which for us results in a variation of about 5 to 8 Hz between the loosest and tightest spots in the cranks' rotation.

Therefore, if there is no point in the crank rotation that gives a reading below 50 Hz or above 65 Hz, then I am happy enough, and I lock it in place there (hopefully, as long as I remember this final step). So I'd certainly agree on the guidelines that others above have given.

Perhaps some of the schwagoholics here might consider bagging a titanium mouth harp (PC name) if one were available in the correct pitch to use as a belt tuning aid. Having a Ti harp in your seatbag would be oh so cool. Gates, you missed out on selling at least one of those trinkets. LOL.

A recess could be drilled. Pretty touchy work to get the recess centered on the existing holes. We have a shop that could do it. But in the mean time, odd that Gates included them on the CDC and not on the CDX. There is no real down side to the CDC on the rear.

The chain ring bolts are a specialty item, very long to get this configuration. I didn't procure them, but I suspect options are limited in this length. If I could those bolts would be ti, but they are not available in the length needed.

I did not do the assembly, but I know Dave worked the configuration over and over again including shim options with the Lightning cranks. He was not happy with any of those configurations. He's thinking about chain line as well as keeping the belt center close to the bottom tube center which makes the tandem ride more stiff/responsive.

For now, the solution is to use the CDC ring. For the day when CDC rings are no longer supported or available, we'll have to work another solution. Gates says they will continue to support and manufacture the CDC, but in case not there are solutions as you suggest.

Makes sense. I agree it seems odd Gates did not provide bolt recesses in these new rings.

I looked at putting our rear CDX ring on the inside of the spider, but that would leave only about 1mm clearance to the chainstay with the belt on. That is a bit too close for my comfort level and I didn't want to mess up the chainline by shifting the rear Ultegra cranks more to the timing side. These cranks have a fairly low Q-factor (159mm), but along with that comes less wiggle room for spacers, etc. So, I stayed with outboard ring mountings for now, until I come up with something better.

If you go with the inboard mounting you will gain some stiffeness / responsiveness in the frame bottom tube. The closer to the centerline of the frame the less bending stresses are induced. If you have only 1mm, the sprocket and axle do deflect a bit so it is tight. I would put one of those clear 8mm protective film/dots on the stay right where the belt might rub, just in case.

PS. When I used the term "inboard" in prior posts to refer to our bike, that is to mean inboard of the chain rings. A few makers have attempeted a belt installation outboard of the chain rings, but this induces so much bending in the frame so far from the center line. Better to put the belt on the left than to put it outboard of the chainrings on the right.

DONE, well, sort of.

I tweeked our rear Ultegra R603 crank alignment to allow the timing ring enough space + mud gap (more on this below) from the chainstay. However, our front Ultegra R601 crank timing alignment seems to be somewhere either left or right of the rear timing ring no matter which orientation (in or out), so I ended up with the front timing ring on the outside and then shifting the EBB a couple mm inward to achieve a close alignment with the rear ring. Having the rear timing ring mounted on the inside of the spider is probably the more important of the two, so mission accomplished there.

Mud:
Initial ride with the rear ring on the inner side was last weekend when road conditions were wet and very gritty. With only 1mm or so of chainstay clearance, accumulated muck on the chainstay was rubbing the side of the belt. Having now increased the clearance to +2mm I'm hoping that will be sufficient to avoid problems in mucky conditions. Should we encounter that problem again, stoker has been instructed to squirt the chainstay with water. Also, having framesaver tape at that spot proved very worthwhile.

New observation about chainring bolts and no recesses in the CDX rings:
The Ultegra chainring bolts supplied have a backing nut depth of only 4mm, while the CDX ring + Ultegra spider totals 7mm thick. As the CDX rings do not have a bolt head recess, the rings tend to float on the spider because the ring holes are much bigger than the bolt thread width and the nut is not long enough to reach through and hold the ring in place. If these rings had head recesses, that would help hold the rings in place, but without the recess the rings move around a lot until you tighten the bolts. With the rings floating around, trying to get them perfectly centered is a real hassle.

Solutions:
1) Flip the bolt/nut around so the nut (now on the outside) will hold the ring in a centered position (or if you mount the ring on the inside you can leave the bolt/nut in the normal orientation)
or
2) use longer chainring nuts. ie: for the Ultegra spiders, 5-6mm nuts in normal orientation will reach the timing ring and hold it in place.


Your setup may vary. My comments above are based on experience with the Ultegra R601/603 cranks.

Where are the pictures? And why did you do this?

Reason for inner mounting the rear timing ring per comments from Turbotandem above. FWIW, it's also explained in the PR info for the Paketa Vr2 (possibly the original source?) regarding advantages of moving the timing setup as far inward as possible.

On our 2013 Calfee, alignment seems to work out better with the rear ring in and the front out. It was either mount the rings in this fashion, or else the original/normal mounting on the outside of the spider required addition of 2mm chainring spacers on the front ring to get the front/back alignment close enough.

Gates made the ring holes far too large for typical chainring bolts to hold the rings firmly in place without a bolt head recess like most chainrings have, but a nut sleave will hold them fine when placed directly against the ring (or if you have sleaves long enough to reach through the spider arm. Here's a couple snaps of our CDX rings...

First, is the rear ring on the inside of spider with bolt/nut in normal orientation:
https://lh3.googleusercontent.com/-L...Large%2529.JPG


Next is the front ring mounted on outside of spider but with the bolt/nut reversed to hold the ring in place better:
https://lh3.googleusercontent.com/-v...Large%2529.JPG

Wayne, if your crank nuts are 4mm like mine, and you mounted your rings on the outside with normal bolt orientation, then you can test this out... just loosen your ring bolts and see how much the ring moves. You'll see that it moves a lot. Then, flip the bolts/nuts around and do the same test. The ring should be much more stable on the spider arms because the nut sleave is just long enough to go through the ring plus catch the spider arm. I believe this helps get and keep the ring centered and shear torque is applied more to the nut sleaves rather than the bolt thread area.

-

BTW, moving the rear timing ring to the inside has another minor advantage (when either belt or chain is used)... clearance is improved for a stoker crank mounted computer magnet.

I was able to mount both front and back rings on the inside on my Co-Motion Speedster

Without more information, that is like saying "I have tires on my bike".

1. Ring alignment. did your rings align perfectly OOTB, or how did you configure to achieve it?

2. Crank symmetry. ie: how close are your cranks to being of equal distance from the BB center?

but I do have tires on my bike! LOL

Ring alignment: I installed a new set of FSA SL-K Light cranksets with the both Bottom Brackets installed centered with one Bottom Bracket spacer installed on each side. I did have to cheat the eccentric about 2cm to the right to align the Rings.

Crank Symmetry: The Belt Rings are about 4.5cm from the center of the bottom bracket shell. The belt sits about 2cm from the chain stay.

Crap...

After seeing the black CenterTrack sprockets on a Calfee and a few other tandems at the Tandems East Expo two weeks ago, being pinged by brother USPSPRO on the results of our custom Gates belt test from a few year back, and then spending way too much time analyzing the drive train noise coming off our sync chain & rings during a Saturday ride this past weekend my interest in fiddling with the belts was piqued once again.

Worse yet, I made the mistake of building a little spreadsheet-based table to figure out what size sprockets would be needed on our tandem to work with the 250t / 2000mm Gates CarbonDrive tandem sync belt. Son-of-a-Gun, if my math is correct it would appear 60t CDX sprockets would support a nearly perfect fit on our 30" boom tube.

I've got questions into Gates as well as da Vinci to see if all of the various bits and pieces I'd need are available and if there's any past experience in mounting CDX sprockets to the da Vinci cranks to know if there would be any interference issues, i.e., can the sprockets be mounted either in-board or out-board on the da Vinci spiders.

Debbie's gonna slap me up side the head if I mess with "her" tandem again.... but sometimes I just can't help myself. Inquiring minds 'need' to have answers to esoteric things such as the power of FARKLE.

I'm thinking of having some davinci 130mm BCD 5-arm spiders machined, that would allow for any standard 130mm rings including the belt drive setup.

Actually.... doesn't the main stoker spider have the same spline pattern as the timing gears? I could just order two of those from Davinci.

Shame... I just got done drawing this to be CNC machined (note I didn't measure the square spline yet... it was just a placeholder).

http://farm9.staticflickr.com/8239/8...29d50a91df.jpg

Yeah, you answered your own question regarding the da Vinci spiders. They have all of the key configurations and dimensions covered: Four Arm 104mm - 64mm, Standard 110mm - 74mm, and - Road 130mm (with 74mm triple option) in the Five Arm variety that bolt up to either drive or timing side cranks. In fact, I converted a set of 130mm BCD road cranks into 104mm off-road cranks for our Ventana back in 2002 using the interchangeable spiders. daVinci makes some really cool (and super light) stuff... and all of this stuff has been around since the mid-90s!

If it were not for the square taper BBs, I'd be on board for the DV cranks.

I'm curious if Todd or anyone else tested using a 24mm HTII/Mega style axle that threads into the drive crank instead of being permanently pressed in as those two mfr do? That way you could simply swap axle lengths to whatever you needed and still have the advantage of using outboard bearings and a much bigger/stiffer (and lighter?) axle.

As far as CenterTrack feedback, it has been a "set it and forget it" experience. The belt is performing quietly and smoothly. After the expected install tweeking / learning curve, we have had no issues. Belt tensioning is a snap to do with external HTII BB cups, as rotating the EBB by hand is simple even without a pin spanner tool. For the most part, I haven't bothered with precise tensioning and just going by feel and plucking the belt to hear the tension pitch. Plus, not having to clean & lube a long timing chain has been a real pleasure.