Ghost Shifting

beams87

Extract:

http://www.superclydesdale.com/?p=627

A splash of cold water on this long crank fantasy may be this — I have noticed a  potential red flag:  frame flex on my aluminum frame when using the 180mm crankset.  When I get up out of the saddle and really hammer it, I’ve been experiencing “ghost shifting” on all three of my test rides.   The bike shifts beautifully, even on steep climbs, but when I really crank hard for a rapid acceleration, it will shift around on the cassette. 

This explains a lot....

I have witnessed this phenomenon a few times, and before reading the above article, I had not been able to pin it!

Even when IN the saddle hammering it away from lights, I am hopping gears up and down on the cassette as I grind a large gear! Lets not even talk abut when I am out of the saddle.... Its horrible. Now, I am considering upping my crank size from 175 to 180, but now I am worried (as per above) that this will only exaggerate the problem!

Has anyone else experienced this, and can anyone share their views in how to eradicate this problem? Should I be looking at a stiffer framed bike, or an oversized bottom bracket on a new bike?

A bit of bio, I am 6ft 7 and ride an entry level Orbea, 60cms.

Thanks in advance.

Beams

cycleclinic

One don't grind/mash gears it is not efficient pedaling. Lower gear and higher cadance is normally better. Standing up if fine for sprinting in a race but is not efficient. That wobble from side to side wastes energy. The really fast riders in the club I ride with all sit down all the time.

Ghost shifting is normally caused by other issues rather than cranks flexing. If cranks flex causes shifting then the rings must be flexing. Given the chain has lateral flex in it any chain ring flex an be acomadated.

Ghost shifting at the back is normally caused by a worn chain misbehaving under load and or a worn cassette a bent hanger may influane this as might a bent deraileur cage. Flex in the rear cassette sprockets themselves, the hub and rear dropouts can also contribute to ghost shifting.

Crank flex is not the first place I would look.

beams87

Hi Cycle Clinic,

Thanks for the reply.

I do understand the benefits of efficient higher cadance peddaling, and I do try to employ this method when possible. Just invested in a bike computer to track cadance.

Interestingly I do not stand to sprint, even when tackling hills. It has been said that I have a "hoy-esque" sprint in the saddle, so I naturally I assumed the frame was flexing under load.

So, it could be my rear cassette, or the hub ... I would rule out the chain being worn, it is pretty new (bike is less than 6 months old)

I naturally assumed it was too much torque in the pedals skewing the frame? If that is so, should I be safer with longer cranks?

Appreciate your advice, thanks.
Beams

Rodders30

If I push too hard on the right hand crank (when sitting), I can get the chaing to rub the front mech. High cadence, low load it doesnt. If I stand up, the whole bike creaks, but I only ever do this on one short steep hill.
Alloy frame too. But I dont get any ghost shifting.
Im also a little heavy (110kg) so that probably dosent help.

amaferanga

thecycleclinic wrote:

One don't grind/mash gears it is not efficient pedaling. Lower gear and higher cadance is normally better. Standing up if fine for sprinting in a race but is not efficient. That wobble from side to side wastes energy. The really fast riders in the club I ride with all sit down all the time.

Less efficient? Perhaps, marginally.

If those really fast riders in your club race then I guarantee they don't stay in the saddle all the time and only get out the saddle to sprint.

beams87

Rodders30 wrote:

Im also a little heavy (110kg) so that probably dosent help.

I am about 100 and my bike doesn't creak when I'm out the saddle - what do you ride? Maybe get the bike looked at?

Patient turns doctor...

Rodders30

Trek 1.5T

Changed BB the other day as old one worn. Did it before and still does. Cranks are tight. Will have to investigate more. Thought it was just cause im fat.