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Tandem Cycling A bicycle built for two. Want to find out more about this wonderful world of tandems? Check out this forum to talk with other tandem enthusiasts. Captains and stokers welcome!

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Old 04-19-09, 05:11 PM   #1
merlinextraligh
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Carbon Timing Belt System

Put the Gates Carbon Timing belt on our 2008 Robusta today.

The installation was pretty easy. The only significant problem was clearence between the stoker's timing ring, and the chainstay. (The chainrings used for this system are wider than a conventional chainring.) Web Cyclery has a good piece on their website, on retrofitting the Gates system on Co-Motion Tandems http://webcyclery.com/pages.php?pageid=72. They recommend a 2mm chainring bolt spacer.

Being an impatient sort, not wanting to wait to get chainring spacers delivered on line, I bought 3/8 inch washers at the hardware store, dremeled down one side to make them fit, and they worked fine (and saved $10 in the process).

According to Gates, chain line is critical to this setup. I was able to fine tune the chainline by sliding the eccentric sideways, and with a few mintues playing around pretty much had it dialed in.

We road it afterwards for about an hour, and tested it out, with some hard efforts standiing out of the saddle, and some high rpm sprints, with no problems.

It definitely is lighter. Claimed weight reduction is 10 ounces. I didn't put the parts on a scale, but it is clear that is lighter. The Gates' rings are slightly heavier than conventional chaing rings. However the belt is dramatically lighter than a timing chain.

This is getting long, so I'll save riding impressions for another post.




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Old 04-19-09, 05:44 PM   #2
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These are said to require the latest iteration of the FSA cranks.

Quote:
NOTE: These are only recommended for use with the new FSA adjustable chain-line cranks. If you're running the newest FSA tandem cranks these will bolt right on in place of your current timing rings. Ask us if you have questions regarding compatibility.
There is more detail at the Co-Motion site:

Quote:
The new FSA Gossamer and SL-K cranksets facilitate lateral alignment using spacers between the crankarm and external bearing mechanism. This means you're actually changing the lateral position of the crankarm without moving the bottom bracket assembly itself. There is a fixed number of spacers between the crankarms and bearing assembly. The number of spacers cannot be changed, but they can be repositioned from the right side to the left side. Using your straightedge, adjust the lateral position of both sprockets until they're in perfect alignment. Note: the minimum clearance between the inner edge of the sprocket and frame should be 2mm. This dimension is most important for the rear sprocket when considering clearance with the chainstay.
What is this lateral chainline alignment all about? Is the FSA solution something that could be readily applied on other external bearing cranksets? A photo of this spacer business would be nice, but dang, you've already got your cranksets installed!
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Old 04-19-09, 05:52 PM   #3
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Rode a prototype several years ago (not on a Co-Motion); our impressions were similar to yours.
Asides from weight savings, there's no chain tattoo issue. But those innovations come at a price, especially when retrofitting. So your wallet will dictate!
Pedal on TWOgether!
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Old 04-19-09, 06:13 PM   #4
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These are said to require the latest iteration of the FSA cranks.


Yeah, I read all that, and looked at the FSA website for tech info on the Gossamer tandem cranks,and honestly I'm not really sure what they're talking about.

We have FSA Gossamer crank spec'd on a 2008 bike. I'm not aware of any changes since 2008.

There are essentially 3 issues in setting up the Gates system:

1) the correct spacing linearly between the 2 cranks, which is not an issue to my knoweldge for recent C0-Motion tandems, or other custom tandmes built to the same spec.

2) Clearence for the stoker's timing ring and the chain stay. The timing ring is wider, and our bike without adjustment would have struck the chainstay. I did look at the spacer issue, but didn't see an obvious answer. Also, I didn't want to mess up the chain line on the dirve side, so I lef the stoker's BB alone, and resloved the clearence issue with spacers as suggested by Web Cyclery.

If I undertand correctly, 2009 Co-Motions have dimpled chainstays which largely adress this issue.

3) Chainline for the timing chain. To keep the belt centered, it does appear you need to have the chain line dialed in. This was pretty easy to do simply by sliding the eccentric laterally.

So far, so good.
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Old 04-19-09, 06:14 PM   #5
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^ the above poster types atrouciously.
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Old 04-20-09, 05:35 AM   #6
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Originally Posted by merlinextraligh View Post
3) Chainline for the timing chain. To keep the belt centered, it does appear you need to have the chain line dialed in. This was pretty easy to do simply by sliding the eccentric laterally.
How far did you need to move it?
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Old 04-20-09, 06:41 AM   #7
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1-2mm, basically making up for the width of the spacers moving out the stoker's chainring.
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Old 04-20-09, 07:08 AM   #8
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I'm not sure how far off centerline you would have to move the eccentric before it caused biomechanical issues with your legs/hips/knees due to the lack of symetry. I'm guessing more than 2 mm. Regardless, is there any reason that you couldn't also shim the captains chainring to allow you to center the eccentric?
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Old 04-20-09, 07:36 AM   #9
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I'm not sure how far off centerline you would have to move the eccentric before it caused biomechanical issues with your legs/hips/knees due to the lack of symetry. I'm guessing more than 2 mm. Regardless, is there any reason that you couldn't also shim the captains chainring to allow you to center the eccentric?

True, you could shim the captain's chainrings as well, but it would be either $12 for the parts, or more time with the dremel making my homemade spacers.

And we're talking the width of approximately a dime here. To visualize this in the last picture you can see how close the ring is to chain stay. Before I put in the washers, the ring barely touched the chain stay. So the distance shown in the pic is the distance the chain line moved left.

Even if you shimmed the captain's chain ring you'd still have to fiddle with sliding the eccentric to get it just right.

I'm sure that I've moved the eccentric laterally more than a mm just in the process of adjusting the timing chain, without paying any attention to it. It's just with the Carbon Belt system, that lateral adjustment actually matters, where a mm or two with a conventional chain is likely to go unnoticed.
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Old 04-20-09, 07:48 AM   #10
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Can you tell if it is quieter?
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Old 04-20-09, 08:13 AM   #11
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Can you tell if it is quieter?

It is noticebly quieter. I think this is more noticeable by the Captain because you're farther removed from the drive chain. I cleaned and lubed the drive chain when I installed the belt, and it was amazing how quiet the bike was.

In fact, a persistent creak in the captain's seat and/or captain's bb, is now more noticeable, and is going to drive me crazy, with less noise to drown it out.
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Old 04-20-09, 09:53 AM   #12
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I'm no expert by any means, but I remember reading somewhere that chain drive was almost 99% efficient and that belt drive was only 90-95% efficient.

Has this changed with claims of the belt drive being more efficient? I'm curious why that would be for a timing chain/belt on a tandem, but for motorcycles its known that belt drive is slightly less efficient?

At any rate the belt drive looks amazing.
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Old 04-20-09, 10:21 AM   #13
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The data I've seen suggests that a tandem with conventional chains is about 93% efficient for the Captain.

Gates claims that the tooth pitch, and sprocket profile makes their system as efficient as a chain.
http://www.carbondrivesystems.com/overview.php

Without a power meter, and with only one ride, I can't say whether there's any efficiency difference.

One reason I was interested in the belt system was anecdotal reports that it made the bike accelerate more crisply because you run the belt drive at higher tension, and there's no slack to be taken out in the timing chain when you sprint. One guy posted about racing in the CCTR with the belt system and was quite impressed in that regard. Now, how much of that is marketing and/or plecebo I don't know.

I can say doing sprints yesterday that it felt very crisp accelerating, and we hit the highest speed we ever have doing the same drill we've done before.

Of course you always run faster in your new tennis shoes.
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Old 04-20-09, 12:14 PM   #14
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Xtralight,

How practicle to you think the carbon drive is on a travel tandem? i.e remove and reinstall on a frequent basis.
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Old 04-20-09, 12:25 PM   #15
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Xtralight,

How practicle to you think the carbon drive is on a travel tandem? i.e remove and reinstall on a frequent basis.
Once you get the rings on, and the chainline set it's not a big deal to get the belt on.

You can't just roll it on however. (Gates warns you that will damage the belt.) So each time you reinstalled it, you would need to loosen and tighten the eccentric. Doing it that way is maybe a 5 minute job.


Unlesss the frame breaks apart in a way that allows you to shorten the distance between the 2 timing rings, pop the chain on, and then lenghten the distance between the 2 rings.
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Old 04-28-09, 01:41 PM   #16
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Update. We've ridden with the timing belt a few times now, including a competitive group ride with some sprints. The most notable thing is how quiet the belt is.

I can't say I notice any difference in how quickly the bike accelerates (one of the claimed advantages).

My other observation is that the system is absurdly expensive at $520. A carbon belt for a single speed can be had for $50 (http://www.bikeman.com/CH8000.html?u...ign=GoogleBase) And the belts system is finding its way on commuter bikes where the whole bike is below $1,000

I think the price for the tandem system is the result of the limited market, and the price you pay to be the first kids on the block. I would expect the price of this to drop significantly over time if the idea takes off.
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Old 04-28-09, 03:59 PM   #17
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Originally Posted by merlinextraligh View Post
My other observation is that the system is absurdly expensive at $520. A carbon belt for a single speed can be had for $50 (http://www.bikeman.com/CH8000.html?u...ign=GoogleBase) And the belts system is finding its way on commuter bikes where the whole bike is below $1,000
That's my biggest problem with even considering this retrofit on our CoMo. From a functional standpoint i'm sure I could make it work - but I can't fathom paying north of $500 for it.

I think your right they can overcharge for it - simply because they are the only ones out there.
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Old 04-28-09, 04:14 PM   #18
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Merxli, Thanks a lot for your report, and pics!

You've cited some advantages of the Gates Carbon Drive, as have others. I've listed some of the advantages. Could you rank or designate these for us using your experience thus far?

Example designation:
(1) Hugely important
(2) Important
(3) Somewhat important
(4) Minor import
(5) Not a factor

Alleged advantages:
Connectedness, acceleration quickness
Tidiness (e.g no chain tattoos).
Quietude
Weight reduction
Drive efficiency
Esthetics and coolness
No maintenance, reliability, durability.
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Old 04-28-09, 04:15 PM   #19
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My other observation is that the system is absurdly expensive at $520.
Hmmmm. This sounds ripe for a separate topic....

The absurdly expensive bike sh*t thread.
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Old 04-28-09, 05:38 PM   #20
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How many miles do you get on a conventional timing chain? I would think reliability for this chain would be excellent. It's handling just the captain's power, "perfectly" aligned and running on relatively large gears.
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Old 04-28-09, 06:07 PM   #21
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...but I can't fathom paying north of $500 for it.

I think your right they can overcharge for it - simply because they are the only ones out there.
It is possible that Gates is using one of their myriad of off-the-shelf belts that they sell elsewhere for less than $20. This example appears close, but is 8 mm thick, not 6 mm.

Quote:


Metric V-Belt, XPZ Belt Type, RMA Belt Number XPZ2000, Length 2000 mm, Width 10 mm, 8 mm Thickness, Raw Edge Molded Notch Construction, -30F - 140F Temp Range
Price (ea.) $17.83
The dimensions of the Gates Carbon Drive belt:

Length: 2000 mm
Width: 10 mm
Depth: 6 mm
Pitch: 8 mm (distance between teeth)

I've looked for it at the Gates Search by Specification page, but cannot find a 2000 mm belt less than 12 mm width. Maybe if we could get the part # off the belt or packaging, we might find a $20 match.

That which comes closest is the Poly Chain GT Carbon Model 92740250, but this has a 12mm not 10 mm width.

Quote:
Attributes.................. Values
Product Number......... 92740250
Product Name......... Poly Chain GT Carbon
Profile................... GT
Pitch............... 8 mm
Number of Teeth......... 250
Top Belt Width per strand......... (inch) 0.47
Top Belt Width per strand......... (mm) 12
Length (inch).............. 78.74
Length (mm)............. 2000
Core Material............ Polyurethane
Tensile Cord............ Carbon
Fabric Cover............ Blue Nylon
Weight (lbs)............. 0.95 [430 grams]
The weight of the tandem Gates belt is only 105 grams. So though this belt looks close, the tandem belt must be much different.

Last edited by Ritterview; 04-28-09 at 06:24 PM.
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Old 04-28-09, 06:51 PM   #22
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Been riding our Supremo 2 yrs. now, 2-3 times a week, 150 miles a week and we still run the stock chain. I thought this bike was quiet, can't imagine it being silent. belts last a long time, the belts on my chevy have 150,000 miles on them. Belt drive clutches on Brit bikes last 20-30,000. Adjustment is critical. As far as sprinting goes, we could use something faster, and the bling factor! 10oz. lighter, try losing 10oz. on a 8600$ tandem. I need these parts!
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Old 04-28-09, 06:58 PM   #23
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Originally Posted by Ritterview View Post
Merxli, Thanks a lot for your report, and pics!

You've cited some advantages of the Gates Carbon Drive, as have others. I've listed some of the advantages. Could you rank or designate these for us using your experience thus far?

Example designation:
(1) Hugely important
(2) Important
(3) Somewhat important
(4) Minor import
(5) Not a factor

Alleged advantages:
Connectedness, acceleration quickness
Tidiness (e.g no chain tattoos).
Quietude
Weight reduction
Drive efficiency
Esthetics and coolness
No maintenance, reliability, durability.
Acceleration/ Connectiveness-- Minor, so far we just haven't perceived a significant difference.

Tideness-- Somewhat important. It definitely is cleaner. I think this would be a huge advantage on a single speed, or internally geared hub, but on the tandem you still have a regular drive chain so its still got the tatoo potential. It is going to keep the inside of our truck cleaner, given that there is now a "clean side" to face downward.

Quitetude-- Somewhat important. It is definitely quieter, particularly for the captain who's farther from the drive chain, but again it only eliminates half of the chain related issue.

Drive efficiency-- Not a factor, possibly a negative factor. Without power meters I can't quantify, but subjecively I can't perceive any loss or gain in efficiency.

Weight Reduction-- Hugely important. The belt is dramatically lighter. Didn't put it on a scale, but I'd believe it is the full 10 ounces lighter. I think you have to be a weight weenie to justify the current price.

Aesthetics/ Coolness. IMHO, aesthetics are not a factor, to a negative factor. The slightly wider rings and belt look clunky to the uniniated. The Coolness factor is nice , but only affects those that are clued in.

Maintence, Reliabilty Durabilty. Somewhat important. Not enough experience yet for areal informed opinion. However if it works as claimed this would be a major advantage. But again, given that you still have a drive chain to maintain it tempers the value of the partial solution.

Overall, I'd say if you really want the lightest tandem, and/or like having the latest toy, go for it.

Otherwise wait a bit and see if the price drops.
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Old 04-28-09, 08:21 PM   #24
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To summarize then:

Hugely important:
  • Weight reduction
Somewhat important:
  • Tidiness
  • Quietude
Not a factor:
  • Drive efficiency
  • Aesthetics/Bling
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Old 04-28-09, 09:26 PM   #25
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Originally Posted by merlinextraligh View Post
2) Clearence for the stoker's timing ring and the chain stay. The timing ring is wider, and our bike without adjustment would have struck the chainstay. I did look at the spacer issue, but didn't see an obvious answer. Also, I didn't want to mess up the chain line on the dirve side, so I lef the stoker's BB alone, and resloved the clearence issue with spacers as suggested by Web Cyclery.

If I undertand correctly, 2009 Co-Motions have dimpled chainstays which largely adress this issue.
Looked at what it would take to mount this system on our Calfee yesterday, think I am going to need 4mm or even 5mm spacers for the stoker "belt-ring" to clear the chainstay. Ordered spacers and some longer bolts for both captain and stoker, we'll see ...
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