Cable tension?

Schoie81

Could/does the air temperature effect the cable tension on gears? I cycled 30miles a couple of weeks ago in the sun one evening, shade temperature probably around 16deg, warmer than that in the sun and everything was running nicely. Next morning, out on the bike again early morning before the sun was up and it was about 3deg air temperature - started having problems with the gears, skipping in the middle of the cassette. Nothing had been adjusted overnight, but something seemed to have changed.

My limited memory of physics at school tells me that things tend to expand when they get warm and contract when they get cold - so could a 13deg shift in air temperature cause the tension in the cable to tighten up on the cold ride and affect the gear changes?

John.T

It should not make any difference as the frame also gets a 13 deg change in temp. Carbon or alloy frames will expand more than steel but I have never noticed any problems.

arlowood

More likely to be some grot in the shifter or somewhere along the length of the cable. (grot getting more gungy at lower temps??)

Sounds like a classic case of the inner cable being fouled in some way and causing the indexing to go out at a specific point on the cassette.

I would advise releasing the inner at the rear derailleur and pulling the cable through at the shifter enough to give you something to work with. Then spray cable and shifter with lubricant and work it back and forward to spread the lubricant along as much of the outer as possible.

Monty Dog

13 degrees C temp change is about 0.5% in absolute terms and therefore negligible - as said, more likely to be dirt or water ingress in your cables

Schoie81

Thanks guys - was a nice theory while it lasted!! Maybe its the bike's way of telling me to stay in bed when its cold!?!?

bernithebiker

Could be the cable is starting to fray.

I've just been through this. What shifters are you using? DA9000 are known to eat cables.

darkhairedlord

could be the lower temperature causing increased viscosity of the lube in your cables and shifters.

mr_evil

I think this thread could do with some quantification. According to Wikipedia, stainless steel has a linear thermal expansion coefficient of 17e-6K^-1 (It doesn't speciy the type, but I doubt it varies much), The change in temperature was 13K, and let's assume that a rear gear cable is 2m long. That gives a change in length of 0.4mm.

For comparison, a barrel adjuster has a thread pitch of 0.8mm, so the thermal expansion is equivalent to half a turn. That's not a lot, but might be enough to make a difference.

John.T

But the cable is fastened to and housed in things that are not temperature neutral.