merlinextraligh

Just ordered the CDX system. It's only available with 69 tooth rings.

The rep at Gates asked if there was something about the Tandem CDX drive online somewhere because it's only out this week, and they're getting lots of orders.

I told him I thought this thread might be driving it.

twocicle

CenterTrack 69T & 74T rings are listed in a few places and confirmed by rep the other day. No size diffs from 2011 offerings from Gates. One such source:
https://www.carbondrivesystems.com/do...Aug2012_sm.pdf

For others seeking more info, here's a nice belt drive info article:
https://cyclingabout.com/index.php/20...-need-to-know/

Interesting feedback that "The Centertrack belt is very picky in terms of chainline" at least for installs with rear sprockets (ie: single speeds). Tandem installs TBD.

For those who neglect to clean their bikes, you'll be pleased to see this operational allowance:

ct-vt-trekker

Is there a listing somewhere with either what Tandems would allow the use of the CenterTrack system or the range of dimensions of the spread between center of captain bottom bracket to center of stoker bottom bracket?
I get that the different tooth rings allow for different spreads but what are those ranges?

twocicle

Available rings:
69T is for current standard 28.5"/724mm bottom tube lengths
74T is for Santana's current bottom tube length of use 27.75"/705mm (ie: their bottom tubes are shorter, requiring a larger timing ring).

For a good description, see: https://www.precisiontandems.com/cat_...e_comotion.htm

DubT

The new Gates Center track belt drive came today. It took less than an hour to install it and tension the belt using the iPhone app.


The Wipperman 8 speed chain weighed 426 grams and the Shimano chainrings each weighed 43 grams for a total of 512 grams. The new belt weighs 108 grams and the new chainrings each weigh 86 grams for a total of 280 grams.


The total weight reduction is 232 grams / .51 pounds / 8.16 ounces. The new belt is 1/2 inch wide.

Weight reduction is just a side benefit, the main reason formthe upgrade was for cleanliness and hopefully less maintenance.

Wayne

twocicle

Looking forward to your first ride reports, re: load noise, tracking, etc.

Photos?

While the CT belt is wider (12mm), the new system is supposed to require less clearance. What is your impression of that?

DubT

the first ride should occur tomorrow, i was raining here today, so the tandem stayedin the garage. There is plenty of clearance with the chainstay.

i have photos on my phone that I need to email myself so I can put themin photo bucket.

DubT

Here are a couple of pictures of the installation, first ride should occur this afternoon.

DubT

It was in the upper 40's/low 50's with a NW wind but we bundled up and took a short 16.7 mile ride. We were both amazed at two things about the belt drive. It is very quiet and it is very smooth, I would not have believed it if I had not just experienced it. It is supposed to be warmer tomorrow so we get a longer ride in.

wayne

waynesulak

Great looking Bebop pedals!

DubT

They are the standard pedals with titanium spindles. They were much less expensive that way and we both like them, the secret to the Bebop's is to keep the cleat clean and lubed.

twocicle

To clarify about the Bebops, I think what DubT means is he bought the cromo then swapped the spindles. see: https://weightweenies.starbike.com/fo...hp?f=3&t=87081

For those with a near perfect natural biomechanic pedal stroke, the Bebop float wouldn't be an issue. We (both stoker and I) use Speedplay Zeros because we can dial in the our shoe angles then narrow down the float to provide rotational limits outside our normal stoke range. I've tried riding with these opened up in a "float" setup but do not like the lack of stability - especially when standing for climbs and sprints. In fact, years ago I had the X pedals which I hated for that float, plus that the round springs wore out very quickly due to my natural shoe movement. A long time ago I read a report from a knee Dr. who indicated some rotational support is best, otherwise the "ice cube" effect could overwork the knee/ankle, so you'd have to experiment to see if unlimited float would work for you.

DubT, about the Gates CT setup, your eccentric appears to be in or very close to the full forward position (at max tension limit). Is my observation correct?

DubT

Thanks for the clarification on the pedals. I have used floating pedals for years, even in my racing days (Samson Stratics, I still have them on my Trek SC, I had a pair on the tandem for awhile but wanted a double sided pedal, so went with the Bebops) I have no issues with the float even standing and sprinting, I think it is what you get used to.

There is still some adjustment left in the eccentric, if the belt functions as it is supposed to I should not need much more. Proper installation requires that the belt be placed on the chain ring not forced on as you can sometimes do the chain. I think this is why the belt length is so long. I actually had the front chain (belt) ring off and inserted it into the belt and the. Attached it to the crank, very easy install.

My position on the bike is changed, the cranks are further forward. I talked to my fitter and he said to ride it and see how I like it before making any changes.

wayne

twocicle

The last point is something a lot of tandemers overlook... how moving the eccentric orientation directly effects your position over the BB. I have very specific rider/bike position setup measurements that I always reproduce on all my road bikes. Moving the eccentric around can force me to adjust my saddle fore/aft/height, plus the stem length/height. If a fitter has any specific setup in mind, then the "see how you like it" response would not be acceptable IMO. You will find the most notable effects while you are using the drops.

I wouldn't recommend installing a timing ring with a belt (or chain) already in place, regardless of the amount of tension at that time. Doing so with any external pressure to the ring could potentially result in the ring being slightly off center and thus an oblong rotation in the timing circle.

Chris_W

I agree with both of twocicle's points: First, I'm very surprised that the professional bike fitter has not encouraged you to alter the saddle position to compensate for the BB moving. Second, installing a belt or chain ring with the belt/chain mounted normally results in off-center placement, which will cause the belt/chain tension to vary as the crank is rotated - a more constant tension is preferable, so you should check for this.

DubT

There was 0 tension on the belt, it was very loose so there is not an issue with the chain rings being off center. I installed all of the fixing bolts before I tightened the belt. After setting the tension using the iPhone app I checked the tension in several spots and it is within 2 hz every where that I checked. I will use this method in the future as it worked so well!

We now have right at 50 miles on the setup and I thnk I like the location of the cranks, it actually feels very good. We are due a follow up with our fitter so I will make an appointment to get everything checked out in the near future.

twocicle

Great! We just try to contribute to progress and it's not intended as critisism

I suspect your new saddle->BB relationship has your seated position further back. This position will increase the utilization of glute muscles and hamstrings. Finding a good balance between that and using too much quad muscle is a key point.

Especially when in the drops, it can have the downside of pinching the gap between your diaphragm and legs which reduces peak load efficiency due to lowered lung volume, plus it can increase your hamstring and IT tension to the point where cronic soreness develops. It can also result in a sore lower back as it makes the hips want to sag back instead of keeping a rolled forward tilt. You won't notice these possible downsides much until you are in the drops for longer and harder durations.

merlinextraligh

Installed ours yesterday, and went for a short ride. So far it's great. We did several all out sprinting efforts trying to make it skip, and couldn't even from a standing start in the 53/11. (which we could do with the original belt system).

From what I've read, you can run the new system at lower tension, so I've got it set up with less tension than the original belt, (albeit still a bit tighter than a timing chain) which should help with efficency and wear.

No trouble with it walking off ( which was happening with the second belt we had).

It also has much better clearence around the chainstay than the previous belt. Even though it's wider, the nature of the design moves the belt further out. On the lod system, I had to fabricate 2mm shims for the chain ring bolts. New system has more clearance with no shims.

DubT

What method did you use to set the tension. I used the iPhone app.

merlinextraligh

^ Just feel. Tried for half inch deflection with what felt like 5-10lbs of pressure.

Admittedly its not very precise. But it spins freely, and it doesn't skip. As long as it doesn't skip, I'm not going to bother with the app

twocicle

At risk of starting a flame war, gotta respond to your sig...

Chris_W

I'm interested in the width of the new center track version. I had thought that it was slightly narrower than the old version. Is it the belt that is wider, the rings, or both?

I'm asking because we're currently running the old version of the belt in a single-side drive setup, with the belt and rings in the outside position of two single-bike triple cranksets (Shimano 105, 5603, the belt-rings are flipped to make mounting possible without any spacers). There is barely enough room for the old rings to fit behind the crankarms; looking at the centertrack system, it looked like it would be slightly narrower, so can someone please confirm the exact dimensions of the center track belt and rings, please?

We currently have the 71 tooth rings, but I want to change to a 69-tooth setup to get rid of our belt tension problem, but I now need to choose between the center track version and the old version, and width is the main consideration for us.

DubT

The belt is 12 mm wide.

twocicle

For visual reference, view the top-down photo from DubT, above in post #58 this thread.

The new CenterTrack CDX sprockets are 11mm wide and sit completely within the edges of the 12mm wide belt, unlike the older CDC system in which the sprockets are wide enough to have the 10mm belt sit within the outer rims. According to this doc: (https://www.carbondrivesystems.com/do...ifications.pdf) the CDC sprocket (aka timing ring) width is 13.1mm, so there is not a large overall difference (1.1mm) in width between the two systems.

In your case for same-side-drive, an issue you may encounter with the CT sprockets is the difference in sprocket offset. The CT setup is more centered over the spider arms, whereas the CDC sprockets have a much larger offset to one side. The offset specs are in the doc above. You probably can overcome the CT sprocket offset difference by adjusting the mounting with chainring spacers.

---

The naming of parts for these two systems varies depending on the Gates docs you read. Some call the tandem timing rings pulleys and other docs call them sprockets. ie:, the link above uses the term "front pulley", but the 2012 catalog calls them sprockets as in:
CDC MudPort Tandem Components / CDC MudPort Tandem Sprockets
CDX CenterTrack Tandem Components / CDX CenterTrack Tandem Sprockets

merlinextraligh

Net effect appears to be something around 4mm more clearance between the ring and the chainstay with the CDX system. With the original system, I had to use 2mm spacers, and the ring just barely cleared the chain stay. With the CDX, no spacers, and there's a couple of mm of clearance.