10s crankset on 7 speed

FelaKuti
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10s crankset on 7 speed

Postby FelaKuti » Wed Jun 13, 2018 1:30 pm

I want to replace the crankset on a 1980s steel touring bike with a 10 speed 105 triple. At the back I have a 7 speed freewheel, the shifters are RSX 7 speed sti, and I think I'll use probably a 9s Tiagra FD. Is this combination likely to work together?

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find_bruce
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Re: 10s crankset on 7 speed

Postby find_bruce » Wed Jun 13, 2018 2:35 pm

Front cranks are pretty much interchangeable as long as you have a suitable bottom bracket. IIRC RSX 7 speed had a triple crank so your shifters will be fine, as will 9s Tiagra FC (or most other road triple FDs).

What rear deraileur will you be using ? Is the body long enough to cope with the maximum rear cog size, is the cage long enough to cope with the maximum chain wrap.

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10speedsemiracer
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Re: 10s crankset on 7 speed

Postby 10speedsemiracer » Wed Jun 13, 2018 2:59 pm

A skinny 10sp chain on a 7sp cassette may not shift nicely. The reverse, a 7sp chain on 10sp chainrings will have similar issues, but at the front. The combination may be noisy and shifting may be crappy. Am hoping your Tiagra FD is a triple..

Try it and see but I think that would be a noisy, unco-operative shifting experience.

Furthest I've gone is 9sp chain and cassette on 7sp 52/42 BioPace rings, worked really well.
Mmm, SunTour

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find_bruce
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Re: 10s crankset on 7 speed

Postby find_bruce » Wed Jun 13, 2018 4:24 pm

10speedsemiracer wrote:A skinny 10sp chain on a 7sp cassette may not shift nicely. The reverse, a 7sp chain on 10sp chainrings will have similar issues, but at the front. The combination may be noisy and shifting may be crappy. Am hoping your Tiagra FD is a triple..

Try it and see but I think that would be a noisy, unco-operative shifting experience.

Furthest I've gone is 9sp chain and cassette on 7sp 52/42 BioPace rings, worked really well.

Nope - stick with a 7 speed chain which will run just fine on "10 speed" chainrings - every bike I have is 8 speed (identical chain to 7 speed) & I am running "11speed" cranks (shimano 5800) on my road bike - zero noise & the smoothest shifting cranks I have. The 10speed cranks on my commuter are 2nd best shifting.

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Re: 10s crankset on 7 speed

Postby Duck! » Wed Jun 13, 2018 7:22 pm

find_bruce wrote:
10speedsemiracer wrote:A skinny 10sp chain on a 7sp cassette may not shift nicely. The reverse, a 7sp chain on 10sp chainrings will have similar issues, but at the front. The combination may be noisy and shifting may be crappy. Am hoping your Tiagra FD is a triple..

Try it and see but I think that would be a noisy, unco-operative shifting experience.

Furthest I've gone is 9sp chain and cassette on 7sp 52/42 BioPace rings, worked really well.

Nope - stick with a 7 speed chain which will run just fine on "10 speed" chainrings - every bike I have is 8 speed (identical chain to 7 speed) & I am running "11speed" cranks (shimano 5800) on my road bike - zero noise & the smoothest shifting cranks I have. The 10speed cranks on my commuter are 2nd best shifting.

+1. Match the chain to the cassette, the crankset is the least fussy part of the equation, although there are some little things to watch with newer stuff. In contrast to cassettes, chainring spacing has actually increased with the widening of cassetes, and particularly the advent of compact cranksets. That said, it's less applicable to triples, particularly given that the total difference between big & small rings has decreased by a couple of teeth (20T down from 22T, and more notably, the middle-small difference had dropped from 12T to 9T).

From what I can tell, the RSX left shifter is 3x-compatible, but you will need to ensure the front derailleur is for a triple (it has a deeper cage to accommodate the additional smaller ring) and that you have a long (or medium, same thing in road context) cage rear derailleur to carry the necessary chain length.
I had a thought, but it got run over as it crossed my mind.

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Re: 10s crankset on 7 speed

Postby FelaKuti » Fri Jun 15, 2018 12:49 pm

Thanks for the comments. I'll definitely be using a Tiagra triple FD, and the RSX shifters are triple. RD is a XT long cage. I'll start with a 7/8 speed chain, and if that is not shifting well on the front, I'll try a 9 speed chain. My concern is that the front triple shifter will be shifting the chain further than the chainrings at each shift as 7 speed rings are further apart than 10 speed.

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Re: 10s crankset on 7 speed

Postby find_bruce » Fri Jun 15, 2018 2:57 pm

FelaKuti wrote:My concern is that the front triple shifter will be shifting the chain further than the chainrings at each shift as 7 speed rings are further apart than 10 speed.
I don't think that is correct - while Shimano changed the rear spacing, I don't think the front spacing changed until going slightly wider for 11 speed doubles. I have an RSX triple at home that I could check

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Re: 10s crankset on 7 speed

Postby Duck! » Fri Jun 15, 2018 4:21 pm

Exactly what I wrote three posts up.... ;-)
I had a thought, but it got run over as it crossed my mind.

FelaKuti
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Re: 10s crankset on 7 speed

Postby FelaKuti » Sat Jun 16, 2018 1:15 pm

In contrast to cassettes, chainring spacing has actually increased with the widening of cassetes, and particularly the advent of compact cranksets.

I don't think that is correct - while Shimano changed the rear spacing, I don't think the front spacing changed until going slightly wider for 11 speed doubles.


Thanks for this information. I think this set up will work well enough as it's only for touring. I have one more question about this project which I'll start in a new thread.

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