Shorter cranks = bouncing up and down?

Hi folks,

I have a cycling question completely unrelated to Wahoo (at least I hope so), but thought I’d post here as you’re such a lovely bunch…

I just changed my road bike from 172.5 mm cranks to 165 mm cranks (as I was upgrading anyway, and I have legs like a corgi) and also pushed the saddle up by 7.5 mm to compensate. Riding with them is fine, but… whenever I get up above 95 - 100 rpm I bounce up and down in the saddle like I used to at 130 rpm on the longer cranks. I can’t figure it out, it’s really weird.

Maybe saddle height/position is now off, maybe I just have terrible pedal action which is now getting exposed, maybe I have inordinately long shins and shouldn’t be on the shorter cranks after all, I dunno, it’s just weird…

Anyone any thoughts?

1 Like

I did the same (after a bikefit) and they also put my saddle back a few mm too. Don’t know if that would cause / fix it, but might be worth a try?

Also, I found putting it up by 7.5mm (or whatever the difference between your cranks is), was slightly too much. About 5mm for me was the sweet spot. :ok_hand:

Hope that helps.


Hey there.

(Have done much the same on more than one bike, 172.5 to 167.5 then 165 or 170 to 165 etc).

The bike fit almost needs done again after touce adapted to the change. As your body is now doing something quite different. But ideally after you’ve got used to it.

With the circumference of your pedal stroke being smaller, you have the bottom of the pedal stroke in the same position as before (as you’ve matched that by the 7.5mm saddle height increase, but the top of your pedal stroke is now 15mm lower than you were used to.

This will be opening up the hip angle at the top of each pedal stroke and changing your dynamics a fair bit as you adjust over time. That may mean you’re getting better leverage at one part of the pedal stroke and maybe (guessing) you’re losing stability at that point (focus on core, practice cadence drills for a few weeks - usual stuff that I suspect you do anyway)

Choices: focus on keeping the bottom of that role in the same place and adjust to the top being different.
Or go half way. Some people have tried leaving the saddle where it is and that means at the bottom of the pedal stroke you’re now 7.5mm closer (therefore and effective saddle height drop for the bottom of the stroke) but it means the top of the stroke is only changed by 7.5mm too.

Choice number 3 is to pick a variable number inbetween :slight_smile:

Without a bike fit (once you’ve adapted a bit) it’s a bit of trial and error.

I know when I was only adjusting 5mm to begin with I tried matching the bottom of the pedal stroke to begin with. Over time I think I’ve ended up with my saddle pretty much where it was and happier still having a more open hip angle at the top and a bit more flex at the bottom.

Everyone’s different though.

What I would suggest:
Don’t do another bike fit until you’ve adapted a bit.
Start with one position and try it for a few rides before you try another one. Ideally long enough where you’ve stopped noticing the difference as much. It often isn’t an instant thing and chopping and changing daily may be counterproductive.


@Edd @Martin great advice! The only thing I would add is to keep your rides at a lower intensity during the adjustment period to prevent injury. The adjustment period can be 1 week to 2 weeks, as this depends on the frequency of your rides. Stretching and yoga/mobility should help your body adjust to the new position.

As mentioned, cadence work will help smoothing out your pedal stroke. I recommend these specific workouts. The Systems Check within Elements of Style can be very beneficial.

Cadence builds
Cadence builds and holds
Cadence drills with single leg
Elements of Style
Power Station

Happy Training!


That’s awesome advice, everyone, many thanks. I’ve only done one ride with the shorter cranks, so yeah, still getting used to them. Cadence work is a good idea. Will try with the saddle height and maybe back a bit (though my cool and neat recessed seatpost bolt is a pain to adjust on the fly).

Will let you know how it goes… Cheers!


Changing saddle height on the fly might get a bit confusing for what your body is trying to subconsciously do - maybe different if it was a few mm because of an in ride issue or small changes and so on but with changes like this it might be good to just try that change for a few hours then try a different one ….

But who know. Maybe it’s worth a try for instant feedback … these recessed posts eh … just carry whatever tool you need for now on every ride :rofl:

(Now have an image of someone biking with a full DIY kit strapped to their bike)

True. Just thinking if I only discover a new saddle position is aggravatingly bad after 1 hour away from home…

I just need to carry this small tool :wink:


Ahahahaha. Leave the hammer behind …

Ps. That are tiny wee ‘straight’ wrenches with tiny handles that can be got I think that’ll help with that in the fly type thing.

Hope it all levels out


You don’t necessarily need to put the saddle up when you put on shorter cranks, one of the benefits can actually be that the shorter crank at the top of the stroke removes some hip impingement, allowing you to lower the saddle and therefore bring your entire body down, closer to the bike and this can allow for a more aerodynamic position.

Also, bear in mind that while changing crank length changes the height of the top and bottom of the stroke, it doesn’t change the median point of the stroke (relative to your knee) without moving the saddle. You might find you’re simply in a position that you don’t deal nicely with.

It’s best when changing anything to understand why and then why you want to make further changes, if going to a shorter crank was a guess (even if founded on having short legs) you should probably have left your saddle where it was initially and then adapted from there.
A bike fit would absolutely be the best option, but initially I’d just put the saddle back where it was.


Just to add to @Jon 's thread. I went from 170s on my old bike to 172.5 on my new bike (it came with them - TCR Medium) and it killed my knees, back, hips. After/during physio I went down to 165mm cranks and they are awesome. But… the break in period takes a while as does finding a suitable seat height. I did exactly the same and put my saddle up the amount of difference in length of the cranks and after a couple of rides ended up putting it down a few mm. Trial and error to get the right seat height, but you will get it. I assume if you are bouncing at high rpm then it may be a little high. It took me a couple of weeks of minor adjustments to get it there, but I never regretted the shorter cranks they are awesome. Good luck, you will get there.


More great advice - thank you! Yeah, think I will “reset” my saddle back to where it was and start from there. Cheers.


One thing you may find is you may actually want to LOWER your saddle as the top of the stroke is now lower by 1/2 the change and you are opening your hip too much. As others suggested, now is the time for a professional bike fit.


Talking of professional bike fit, I had one done for my son who is 15 and races in U17 here in Belgium. He was having pain in his back and it was difficult for me to fit him having size 44 feet.

I got him a professional bike fit and it made a dramatic difference. Funnily enough the stem was slammed, saddle further forward and nose dipped ±2 % but it worked. He felt so much more comfortable. And it looked fast and is indeed fast. If you are more comfortable you’ll be able to get the power down.

It was amazing watching the guy use the Cyclofit equipment and software too. I may have a bikefit one day, but at the moment the spare cash is going on my son’s racing, it is not a cheap hobby.


You’re a good dad! :+1:


Cheers. Proud dad too. He got 2nd place on Sunday in a U17 here in Belgium. I screamed my lungs out when he burst out the peloton. It was Mother’s Day here on Sunday so he won Mama a nice bunch of flowers





So… I put the saddle back to where it was, IE 7mm down, and… no change. Still bobbing at high (100 rpm) cadence. Think it must be my (lack of) style. Will try to focus on a smoother pedal stroke. Apart from that the shorter cranks feel fine, no better or worse than the old, longer ones tbh.


Try a bike fit if you get funds. It proved awesome for my son. Also do cadence builds and work up to cadence builds and holds. It takes time to adapt to higher cadences. I remember one of my old clubs used to have bottom gear races when everyone had 39x23 for the bottom gear.