Leg pain after switching to shorter cranks

[choochoo]

I recently switched from 172.5mm cranks to 165mm.
I've done a couple of 30 miles rides since the switch and i've been experiencing some knee soreness at about the 20 mile mark. Yesterday, I was on the trainer for 30 minutes and I was getting some knee soreness and also some pain in a muscle above my quads. I wonder if my knees are coming up that 7.5mm higher is causing this.
I'm generally not that flexible of a person. I should be stretching more. I should go for a bike fit too since my bike is fairly new to me. But has anyone ever experienced this with going to shorter cranks? I haven't changed any other positions. I might raise my seat a little to see if that helps.

[RacerJRP]

If you changed to shorter cranks, your knee should be hitting a TDC point that is not as high as before - so the opposite of what you stated. Can we assume you moved you saddle down the 7.5mm to compensate? Did you also move it back to account for STA?

[choochoo]

Ahhhh. You're right. My knee is not coming up as high. I didnt change anything else...

[Spdntrxi]

you should be raising your saddle for what it is worth and pushing it forward

[fa63]

Correct; you should raise your saddle 7.5mm because the shorter cranks don't go down as low at the bottom of the pedal stroke. You would also slide your saddle forward slightly to maintain the same saddle setback, but that is a much more marginal difference.

Originally Posted by Spdntrxi

you should be raising your saddle for what it is worth and pushing it forward

[sheepdog84]

Originally Posted by Spdntrxi

you should be raising your saddle for what it is worth and pushing it forward

Raising the saddle, and moving it back should be the correct adjustment here. Mostly on the grounds that, as the crank length shortens, your pelvis’s relation to the cranks needs to change as well.

@OP - I would recommend taking many rides to get used to this new position. I have a hard time with the whole whole shorter = better, philosophy but I think its definitely a worthy experiment if you experience hip or knee pain with longer cranks. For myself, I’m about 6’, i tried 165’s coming from 172.5’s and just couldn’t get comfortable. Always had excessive weight on the front end, and didn’t like the feeling of winding up the cranks to get the power out.

My solution was to move my feet wider apart and stick with the 172.5’s - which seemed to match my physiology better.

[Spdntrxi]

Originally Posted by sheepdog84

Raising the saddle, and moving it back should be the correct adjustment here. Mostly on the grounds that, as the crank length shortens, your pelvis’s relation to the cranks needs to change as well.

@OP - I would recommend taking many rides to get used to this new position. I have a hard time with the whole whole shorter = better, philosophy but I think its definitely a worthy experiment if you experience hip or knee pain with longer cranks. For myself, I’m about 6’, i tried 165’s coming from 172.5’s and just couldn’t get comfortable. Always had excessive weight on the front end, and didn’t like the feeling of winding up the cranks to get the power out.

My solution was to move my feet wider apart and stick with the 172.5’s - which seemed to match my physiology better.

forward, because raising the saddle will automatically move the saddle back because of the STA..unless you have a very weird STA.

[benb]

It depends on what you're sensitive to.

If you're sensitive to your knee getting ahead of the pedal you might need to move it back in addition to up.

But yes, moving it up to get your knee angles back in the correct range does move it back.

On a 73 degree STA moving the saddle up 7.5mm to compensate for the shorter cranks increases the the vertical height by about 7.1mm and increases setback from the BB by only 2.2mm.

So you have essentially still got your foot 5mm further back under your knee when the pedal is at 3 o'clock and you're pushing hardest... you might need to push it back if you're sensitive to the ball of your foot being back behind the knee and your starting position was fairly far forward.

I did an experiment when I was racing and I was slower even with just 2.5mm shorter cranks. It's not like I was doing TT or Triathlon where I could have taken advantage of some aero benefit though. For crits and road races the loss of some of that leverage didn't help me for whatever reason. 7.5mm all at once seems huge and I think it'd take me a long time to get used to how that felt.

[robt57]

Errr.. shorter arm = move saddle up, not down.

Originally Posted by RacerJRP

If you changed to shorter cranks, your knee should be hitting a TDC point that is not as high as before - so the opposite of what you stated. Can we assume you moved you saddle down the 7.5mm to compensate? Did you also move it back to account for STA?

[choochoo]

Roger that. I'm going to try to move the saddle up a few millimeters to see how that feels.

[tv_vt]

You might want to think about just going to 170mm cranks from the 172.5 you were using.

But in regards to your original complaint, you have to adjust your saddle height for any crank length change. Otherwise, your knees are going to get wrecked, assuming you had the proper saddle height to begin with. Shorter crank - saddle goes up same amount as the change in crank length, in your example, 7.5mm. Conversely, going to longer cranks means you need to lower the saddle same amount.

One of the arguments for shorter cranks has to do with having a higher saddle height in relation to the handlebars and how 'open' your hips are. With a shorter crank, at the 12 position, your knees aren't as high and the angle of your leg to upper body is not as cramped as it would be with longer cranks.

[benb]

I thought I had originally mentioned 7.5mm change is a big change all at once too. I must have edited that out.

Shorter cranks + higher seat versus longer cranks + lower seat on top of changing your torso angle also reduces how much your hip angle closes down.

To a certain extent you might need to move bars around too, and some of us might get a better combination of all the angles with different length cranks compared to the typical recommendations.

My leg:torso ratio seems to skew towards more leg. Longer cranks + lower seat help me control my torso angle, which is pretty extreme even with relatively high bars. But that setup makes it more likely I close my hip down too far and hit the end of ROM on my hip at the top of the pedal stroke.

The longer cranks mean I can run the seat further forward though, which helps out with all those angle issues.

I've never tried cranks longer than 175mm since they aren't that common. I suspect they would have had nice benefits for me.

[robt57]

FWIW;

I have 167.5 to 180 cranks. Inseam is 34.25", pedal to top of saddle very similar on all close depending on pedal/cleat stack.

I can say the longer arms are used for off road and lower cadence overall. Or to negate a higher BB a little...

For JRA on road bike 172.5 seem most fluid in my minds eye or actually maybe even.

[choochoo]

I switched to 170mm on my old bike for about a 9 months or so before i sold the bike. I notice no difference between 172.5mm and 170mm.

As I said previously, I'll make adjustments to the saddle height just havent had the chance to ride this week.....

[Flinch]

I was having major issues with pelvic tilt, my right side was down, yet my right foot 'floated' on the pedal at lowest extension. Also had R knee aches after the rides, not during. This on two mountain bikes that I rode mostly on the road for training. No, not much leg length discrepancy. I went from 175 to 170mm, and it helped a bit. Then went to 165mm. I also effectively lowered my saddle, actually did not raise it to account for the shorter cranks, and that helped. For example, I used to be at 748mm saddle height for 175mm cranks, and now am at 730 with the 165mm. Yes I tried a lower height with the 175/172.5mm cranks, and no bueno.

End result is that 165mm seems the sweet spot. I experienced my fastest times for standard routes on the shorter cranks. Lowering the seat also helped.

My only issue is that with the two most recent road bikes, Campy equipped, they have 172.5 cranks, so will wait and see.

Oh, and all of this on my own after a $450 bike fit (two bikes) that was worthless!