Odd drivetrain problem

lemuppet

I have an odd problem in that as I pedal harder it seems as though someone is pulling the rear brake on, the harder I pedal the worse it seems to get. Everything is ok when spinning easily but it feels like I'm on the turbo trainer when I put some power down and it is hard to get to over 30kph.

I have stripped and cleaned all the transmission, adjusted the hubs and loosened off the rear brake so that there is no chance of brake rub but the problem still persists.

I'm running Chorus compact 11 speed with a 12/27 cassette and Ksyrium elites, wheels are true and the whole setup has done about 1500kms.

Anyone any idea what the problem could be as it has me baffled?

centimani

First thing i'd think of was rear wheel flex. I'm not saying i'm right and don't even know whether the wheelsets prone to flex, but i'd open out my rear caliper, get the pads away from the wheels and see if that improves it.
Or on the same principle...rear triangle flex causing the same pads to catch the rims.

rafletcher

As above - try opening the quick release on the brakes and testing results on a flat and quiet bit of road!

lemuppet

Hi, thanks for the replies.

As I said, I've loosened off the rear brake so there's no chance of brake rub, there's a good 10mm of clearance between pad and rim. I've also tried with another rear wheel and the problem is still there which what makes me think it is something in the transmission.

centimani

lemuppet wrote:

Hi, thanks for the replies.

As I said, I've loosened off the rear brake so there's no chance of brake rub, there's a good 10mm of clearance between pad and rim. I've also tried with another rear wheel and the problem is still there which what makes me think it is something in the transmission.

You've got to start isolating various bits of the transmission then.
Firstly though, stating the obvious, the rear wheel is secured tight in the frame and centred properly (obvious i know, but easily overlooked, even less likely mind bearing in mind the fact you've tried a different wheel)
I'd start with chain off, then have a real good feel of the BB, any play ? any resistance ?

Twostage

I've had this sensation a few times, I've got off my bike to check the wheels and pedals spin ok and everything seems fine. I'd come to the conclusion that it was me imagining it. I had a similar thing on Friday when I changed from the big sprocket to the middle one it seemed to get harder to pedal rather than easier. Again I thought I was just imagining it. I'm now wondering if it's a knackered bottom bracket.

centimani

Just re-read the OP...does this JUST happen on your turbo or have you been out on the road and had the same problem ?
Don't discount the fact it could be your turbo...

freehub

I've had the same thing, on a day where if I was pushing it home I could average up to 23mph, and this particular day I'd be struggling to get over 20 it would feel like something is pulling me back, just ends up to be me, eventually it goes away.

lemuppet

It happens out on the road, the sensation is as though someone is increasing the resistance on a turbo as I pedal harder.

I've stripped down all the drivetrain, removed the cranks, checked for any play or resistance in the BB and then rebuilt it all with a spotless chain, cassette etc. The wheel is centered in the frame, I've adjusted the bearings as per the advice on the Mavic site, the tyres are at 110 psi and the wheels are true.

Like Twostage, I'm beginning to feel it is in my head myself as I can't figure out what might be causing it!

freehub

Have a couple days rest and try again.

centimani

Although i said it's can be easy to miss the obvious...perhaps it is you !!!
I always think the body's a finely tuned instrument...any slight change in health up or down easily shows itself. Some days you fly and you don't know why, some days (sometimes more) it's just plain hard work. Perhaps this is the reason !!!