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1x di2 Time trial/triathlon setup

by Nicholas dew
Tue, Aug 11, 2020 10:26
8

Hello everyone, I was wondering what problems I should look out for if I were to set up a tt bike with: a single 50t chain ring a shimano grx long cage derailleur with an 11-40 cassette.

Just thinking I could do this with an older tt frame I had and could save some money and weight on shifters and derailleurs.

Is this crazy or doable. Would I worry about the rear derailleur next to the spokes or would the grx derailleur cope with it?

Many thanks in advance

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8 comments

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CXR94Di2 | 4 years ago
2 likes

Ive done this to my Planter X EXO 2 TT bike.  It had 50/34 crankset 11-25 cassette.  I swapped the double chainring for carbon 58T single and 11-28 cassette. 

It improves chain line where I mostly have my gearing set on the 13-14t cassette

I was initially getting dropped chains on bumpy roads, so added a custom made chain guide where the front derailleur was mounted.  There is no real weight advantage, but slimmer bike profile (a little) and positve gear changes.

Not done any TT this year ,so ;(

 

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BBB | 4 years ago
1 like

With a GRX mech (clutch) you could probably get away with any standard chainring but running a narrow wide one would give you almost 100% certainty of not dropping the chain on some choppy tarmac downhill sections. Chainrings with an offset like SRAM X-Sync also improve the chainline. Other than that, there is really nothing else go consider.

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Nicholas dew replied to BBB | 4 years ago
0 likes

I would definitely run a narrow wide.

Thanks

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njblackadder | 4 years ago
0 likes

This is a serious question, I'm not being facetious. Why on Earth do you want a gear so low on a TT bike? It would need a mountain course to require anything bigger than a 25t sprocket with a 50t ring. If you are planning on riding events where low gears are going to be necessary, my advice would be to get yourself a couple of different cassettes and use the closest ratios you can get away with in each particular race.

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Nicholas dew replied to njblackadder | 4 years ago
1 like

More for covering IM triathlon and training 50k plus rides. No way I could get away with 25 and 50 I'd be grinding big time up even a half a mile climb.

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njblackadder replied to Nicholas dew | 4 years ago
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Hello Nicholas. Fair enough. Afraid I can't help you with the original technical aspects of your question though. Alongside the requirement for the lower gears you wish to use when necessary, I would strongly advise looking into the possibility of having a choice of cassettes for 'flatter' courses. In my experience, closer ratios are a good thing for time trials, when feasible. Good luck with it.

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Nicholas dew replied to njblackadder | 4 years ago
1 like

That's a good idea I take it a di2 derailleur doesn't really care what cassette is on the back. Would I need to worry about chain length if I had multiple cassettes.

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njblackadder replied to Nicholas dew | 4 years ago
0 likes

As long as the chain is sufficient for the 'worst case', i.e. cassette with largest sprockets, then there would be no problem. You are effectively using sprockets that could be somehwre in the middle of your widest range cassette!

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