I have bad knees. Hockey and biking are two of the few sports remaining that my Dr has not nixed. I think you will find that changing your crank length will not make your knees feel better. If your knees are hurting after riding your bike, odds are that you are mashing and not spinning. You should not be getting knee pain with nice smooth low or no impact peddling. Changing the diameter of your pedal stroke by 2 CM is not even going to be noticeable. If you find yourself out of the saddle on climbs, try and shift sooner and keep your cadence up. I had to give up my single speed for just this reason. With a single speed, you are either mashing like mad or spinning at mach 2, good for building strong legs and lungs, and super fun, but hard on the knees. Another thing to consider if you are not running one now is a dropper post. Unless you are a weight weenie XC guy, it can be nice to change your leg extension a bit during a ride. I have found that on a long grinding climb i prefer to have full extension on my legs and even a little ankle extension, then back down an inch or so on the flats, then dropped fully for descents. All that bike fitting is great on road bike where you are clipped in and and your seat does not move, but for a mountain bike with flats, and a dropper post about all there is is seat tilt and stem reach, neither is going to give you sore knees.

quote:

Originally posted by konata88:

I've been wondering if I could just tap in new holes. Just didn't know who to ask. Can I just go to any bike shop if they deal with a machine shop? Any machine shop? Or are their specialists?

Thanks for the offer. I may take you up on it if I can't find someone local to do it. (if I need to go this route).

It is a simple task. Just about any machine shop should be able to do it. If you can't find anyone, feel free to contact me.

The problem with tapping crank arms is that one side is an odd ball left hand thread. That and how critical it is to get the hole square.

Any good machinist can make the tapped holes correctly.

I would think the alignment to be important as to not be perceivable while in use.

Here's a place that does it:

http://bikesmithdesign.com/Short_Cranks/index.html

A couple of posts mentioned better bike fitting and adjustments as being very important. Obviously very true. Shorter cranks can also help with the overall comfort by reducing hip rocking side to side for people with shorter legs. Unless you get a custom made bike, you can only adjust them so much. Shorter cranks can help.

There isn't a commercially available bike that fits my body proportions.

Thanks guys.

I'm going to revisit my fit but I think I'm pretty close. I've done it a couple of times on my 26" and once on my 29" and generally rides pretty well.

The problem I think is going up hill, especially suddenly (blind curve) and I'm feeling a little strong, trying to keep momentum and probably not in the ideal gear. I'm not a spring chicken anymore (at least not physically) so my mind is probably thinking I can do things that my body just can't handle.

If this is the case, I can probably avoid issues if I just downshift immediately and regardless. I just thought that shorter crank arms would be easy and cheap. Sounds like I'll just make do with my current arms, recheck fit and when in doubt, downshift.

Downshifting is highly underrated.

Note that even Tour de France champions now use very low gears when going uphill. Basically, if you can't spin at least 70 RPM, you are just fooling yourself and need lower gears. Cadences in the 80-90 range would be more efficient.

So that can be a rough guide. It feels like pushing harder will make you go faster, and it will...but for only a few pedal strokes, and at the cost of knee pain and potential damage. It is really all "how much oxygenated blood can my heart pump to my legs?"

More than distance or speed, I wonder if I should get some sort of cadence computer. I can get the feel of 70+ rpm but maybe it wouldn't hurt to have an explicit reminder.

Even with downshifting, my knees may still be at some risk if the crank arms are really too long for me. But probably the risk is less if I downshift low enough.

Computers with cadence are dirt cheap now.

Or you can find a popular song that you can remember and mentally tap out a cadence with. Not quite as accurate, but if you pick one that would definitely feel like it was "dragging" at 70 (BPM) you would now when it is time to downshift more.

quote:

Originally posted by TRIO:
If the cranks are somewhat solid, it would be an easy mod to have new crank holes added.

I can do this if you're interested.

Are you also going to re temper them and how do explain the stress riser you just made... sorry Ive seen this, it’s not a good idea at all. Even in old school Shimano XT cranks, it will fail.

Im coming from 12+ years professional bike shop fit work. Based on size cycle method and serrotta fit school, yada yada bike fit training and years of cleat adjustments. So as you already read there are a multitude of possibilities that could cause your aches and pains.

Gearing and fit are crucial with any weekly mile stacking. Knowing your limits is important as well.

Get a fitting. Then make your purchases.

Sometimes however your going to get bullshit advice from rookie “fit specialists”, And it could cause more issues than you bargained for.
So yes a second opinion and an experienced set of eyes watching you actually ride, are the best ways to get real time feed back.

Have your fitter go for a ride with you.


Or Ride while video taping your self stationary is ok but real time is ideal. Then review for cadence inconsistencies and pedaling rotation. It’s cheap. No whiz bang tech to buy. Just use your eyes.

Happy trails.