Doh! I forgot the tandem CarbonDrive / sync drive system and the regular Gates CarbonDrive / drive-side systems use belts and sprockets that have a different pitch: 8mm for the tandem application and 11mm for the drive-side.

However, timing is everything -- no pun intended -- and it turns out Gates was already working to bring a 66t sprocket system to market this summer for Calfee & Cannondale that will work with a 30" boom tube dimension. So, I'll have to cool my jets until June when they become available via Gates or Calfee.

I'm also told "no worries" on the daVinci cranks + 130 bcd spider + Gates sprockets; they work fine together. There has been some talk but no movement as of yet on a spiderless CDX sprocket for da Vinci. Wouldn't that be nice.

I have no qualms about using square taper BB's. The day I / we can generate enough wattage or torque to bring BB axle deflection into play as a concern is the day I quit my day job and begin training for the Nationals & sign-on for the TransRocky challenge. I've only had one rear bottom bracket -- a very, very light Erickson Ti BB -- ever show clear signs of axle deflection. Never a hint of it with Shimano UN72s, UN73s, UN52s, Race Face TaperLock or our Phil Wood SS or Ti BB's. Being a lightweight, recreational team apparently has its advantages. Don't get me wrong, I like the simplicity of the MegaEXO, GigaPipe, Hollowtech and other crank interface systems, but I really get tired of hearing creaky tandems with under-torqued BB bolts or stories of chewed up BB bearings due to alignment or low-torque issues.

Just my narrow view... as I look forward to June and some additional FARKLE for our tandem.

I totally agree the belt is great, set it and forget it, I did use the iPhone app to set the tension. We just returned from a 3,000 mile road trip (tandem in the back of the Odyssey) and it was so nice not having to worry about a bag or suitcase toucing the tandem chain. The belt is clean!

That sounds somewhat similar to Cannondale's Hollowgram cranks and axle - they have the bigger axle that is separable from both cranks. However, the bearings are internal and fit BB30 frames only. I've head of the system being referred to as "ISIS on steroids" - there are some similarities to ISIS, but with the axle and bearings way oversized and all separable.

I wonder how BB deflection compares on a tandem, versus a single, at least for the captain. The last square taper BB I had was on a single steel bike. I could definitely flex it to the point of inducing chain rub. However, my bet is that was more flex in the frame than the BB itself.

My understanding is that one of the advantages of newer BB configurations is the larger BB shell, allowing designers to stiffen the frame around the BB.

With a tandem, you've already got a large BB shell for the eccentric. Thus, my bet that the difference between square faced spindles, and newer systems doesn't result in much if any change in flex of the entire system.


Also , old sqaure taper BB's still have about the lowest friction of anything available.

You're on the right track, at least by my way of thinking as it pertains to tandems. Of course, I could be completely out of mind too.

Here's the deal: If someone has never done so, it's very eye-opening to put your tandem on a rear-wheel resistance trainer with the front wheel in a wheel chock and then to observe the left-to-right, back & forth movement of the entire front crank/eccentric bottom bracket assembly. It's rather significant and it makes perfect sense why there's that much movement: it's the most unsupported part of the frame in terms of lateral bracing with contributions to the overall amount of deflection you see coming from axle-to-axle contributors, such as the tires, wheels fork/rear stays + frame.

So, given that deflection will come from the weakest links in the chain, what are the chances that it's that short, very stiff axle that's bending when pedal loads go into the cranks?

The rear bottom bracket is a different story altogether since the rear bottom bracket axle on a cross-over crankset tandem is being pushed and pulled in four different directions; two directions per side and always in opposing directions left vs. right. Right side drive becomes more attractive here because at least the fore/aft forces have a bit of a cancelling effect.

My wife's single bike has the last model of Record Triple cranks and a Record square taper BB. That thing spins like butter. They are also very durable.

http://1.bp.blogspot.com/_atrK-jBKJK...e+Crankset.jpg

I broke down and purchased the Gates Carbon Drive Krikit Tension Gauge. I want to compare it's measurement against the iPhone App.

Since I started using the app, I have never resorted back to the Krikit. I find the app to be much more repeatable. The whole key is to find the spot in the belt with the most tension and take the measurement in that same spot every time. Since I started using the app, my belt worries have been nonexistent. I set the tension to about 75 Hz and forget about it.

Periodically the belt will begin to creak under pressure. That is when I know it is time to wipe it and the pulleys down with a wet rag. Since our riding is exclusively in arid climates, I think the dust and sand collects in the grooves of the belt where it is "packed" in as the belt goes over the pulley. Without moisture on the roads to periodically "wash" the belt during rides, this dust and sand just continues to accumulate until the belt gets noisy. If it gets real annoying during a ride, I will give it a squirt out of a water bottle and that will quiet it down for 10 miles or so.

We had one super gritty, wet ride where maybe every moving part on the bike started making ugly noises, so I can't say if the belt was contributing or not.

Maybe a belt treatment spray would help... silicone or something. Call Gates support and ask, then report back here.

Y'all just need to brush your teeth once in a while! :thumb:

We saw (OK, heard) the same thing during our small-pulley testing. A soft bristle brush with soapy wash water did the trick.

[QUOTE=TandemGeek;15459733]... it turns out Gates was already working to bring a 66t sprocket system to market this summer fora 30" boom tube dimension.[QUOTE]

Note that as the sproket gets smaller the tension in the belt goes up and therefore the deflection induced in the bottom tube. I don't know how to calculate the percent differnce between, say, 74t, 69t and 66t.

I have no qualms about using square taper BB's. The day I / we can generate enough wattage or torque to bring BB axle deflection into play as a concern is the day I quit my day job and begin training for the Nationals & sign-on for the TransRocky challenge. [QUOTE]

I knew a strong team once that swisted the stokers square taper axle from the captains power. Saw the result myself.

I use a dry film silicone spray meant for timing belts in a car engine. Works very well. Spray liberally once every month or two if I get any squeeks from belt squirm.

Our CenterTrack timing belt makes some noise after each extended section of dirt road. A couple of quick squirts from the water bottle doesn't quiet it down. Some continuous squirts from a full 750 ml water bottle while back-pedalling until the bottle is empty always does the trick (but I have to wait until we find a water fountain to do this so that we don't waste a valuable bottle of water). This is fine on a road/touring bike that only occasionally encounters dirt roads, but it makes me wonder how mountain bikers cope who are using the system - they must have an almost-permanently noisy drivetrain!

For those following sprokets here but not reading the di2 thread, I'll repost here:

Below is the production version of Paketa's proprietary, 69 gram, adaptor. This is hot off the CNC line for mating a right side belt drive 130bcd gates sproket with a 110bcd compact crank, and a 52t and 34t chainrings in our case. At NAHBS 2013 the protoype was revealed as an option for the V2r. I'd previously posted a picture of that prototype in use on our bike, but it was hard to appreciate without removing the crank. And the final version now looks much more refined. It adds a lot of flexibility even if a team didn't want 34t inner ring, the adaptor works for any 110bcd set up, say 54-38, or 52-34 as we have. I don't think any other builders have solved a right side belt, so the details of the adaptor are not something most will need. But is is a beautifully solved bit of engineering, and the machining is sweet. Chaulk up another point for the custom world of high performance tandems where few things are off-the-shelf. Both normal chainring nut and bolts, and 12mm chainring bolts are involved in the assembly. Here, the adaptor is mating a CDC sproket, but it is also designed to propery space with a CDX sprocket. Since the belt for CDC and CDX is the same just with a groove, the front cranks use a CDX sproket to manage the drift of the belt(not pictured)

http://bikeforums.net/attachment.php...hmentid=308693
http://bikeforums.net/attachment.php...hmentid=308692

It can happen to any axle: (this is a DA 7900)
http://www.roadgrime.com.au/file/bro...e_crank_61.jpg

Worn/failed bearings are big contributors to axle damage.

Yes, it does and we have a little bit of experience with running very small sprockets & belts on our Calfee.

http://tandemgeek.files.wordpress.co...lt_s.jpg?w=600

They ultimately proved to be too small to be practical and were a bit problematic given the force they generated on the bottom bracket axles. But, that's in part what the experiment was investigating; how small is too small.

http://tandemgeek.files.wordpress.co...hain.jpg?w=600

66t sprockets would be even a bit larger in diameter than the 34t da Vinci timing rings we've been using on all of our road tandems since 1998 and on two different Ventana off-road tandems since 2000. Given that we've never had any issues running 34t timing rings relative to excessive deflection at the boom tube or accelerated wear and tear of the bottom brackets (square taper on all five of the tandems that have used the daVinci cranks & 34t rings), I have no concerns about the 66t sprocket coming out this summer. 100% static tension is another issue altogether and only time will tell what the long-term effects might be, but that would be the same for any tandem riding a sync belt. Again, as for driven loads generated by a belt system I don't see them being any higher than an equivalent diameter chain system as I'm convinced the sync belts are performing more-or-less like a chain where the upper run carries most of the load vs. a true synchronous drive belt system where it distributes the load on both / all spans. Harley's aren't all that different under hard acceleration as you can see their lower belt runs flopping around.

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.

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"?

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.

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


Surge in 29er Sales Points to Market Shift

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.

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.

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.

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 ;)

Thanks.

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

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.

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?

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.


http://bikeforums.net/attachment.php...hmentid=309811

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

"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.

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