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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 07-17-13, 04:46 AM   #1
GCBikefit
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Track Cogs

Having been through a fair bit of gear failure on our road tandem, we eventually got it right, and dont have major dramas any more. (thanks to Chris king hubs, and a gates Belt). But the Fun is restarting again with our track bike. Im reaching out for help with Track Cogs, and anyones experiences so far.
We are generally using 100inch gear (48x13) but up to 112inch is common. The problem is keeping all 13 teeth on the rear!
The cogs that we have damaged so far are
Shimano 7600
Gebhardt 7075 Alu
Titanium CBC machined

Using both KMC Kool chain and Izumi SuperV chains.

Do I need to run much bigger chainrings and a 14 or 15 tooth cog?
At what point will the chainrings start to fail? (I am a big Gebhardt fan, and would be surprised if they failed)
Is there a better cog option that isnt likley to fail??

Thanks for sharing your experiences
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Old 07-17-13, 06:23 AM   #2
mkane77g
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Bigger is better.
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Old 07-19-13, 01:11 PM   #3
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the more teeth, the less stress on the cog; 1st order it is proportional to the number of teeth, until you get past something around 30 teeth (beyond concern here).

The downside is increased weight.

If you continue breaking cogs, get some made of heat treated 4130 or 4140.
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Old 07-19-13, 05:51 PM   #4
Dean V
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Get a bigger chainring. 100"+ is a big gear to push on the track isn't it? That is more than any of the single bikes use and although I don't know anything about your team I wouldn't of thought you would be faster than the fast solo riders.
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Old 07-21-13, 06:01 AM   #5
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More teeth do equal less stress. However I suspect that it will get increasingly difficult to find big enough chainrings. Some quick maths makes me think that with a 15T cog you'd be looking at between 56T for 100" and up to 62T for the 112".

Actually for this team who are no slouches I think they'd be disappointed with only being as fast as a fast solo rider. I think that the aero advantage of a tandem would be best highlighted by track TT events so I'd expect their 4km time to be somewhere between a fast individual and a fast team.


Cheers,

Cameron
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Old 07-22-13, 03:06 AM   #6
GCBikefit
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Quote:
Originally Posted by Dean V View Post
Get a bigger chainring. 100"+ is a big gear to push on the track isn't it? That is more than any of the single bikes use and although I don't know anything about your team I wouldn't of thought you would be faster than the fast solo riders.
It has little to do with straight line speed, but the torque of moving double the mass from the start. If you look up The Orange Tandem on Facebook, you can see some photos of what used to be cogs...
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Old 07-22-13, 03:11 AM   #7
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Thank you for your responses, Particularly on the Material suggestions. We have a Titanium set of cogs, that have been offerd to us for testing, and GarsidePedeler Fabrications have machined us some pretty special Chainrings to be able to use 13 and 14 cogs dominantly. If need be we can move to a 15, but not likley at this point.
Now we are having Crank issues!!! We just rounded a square taper on the crank side (stoker NDS) and have moved to a FSA Road Crank for the bigger axle attatchment. We are joking about starting a thread about "what part did you break today"...
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