My only muni is a 26" Oracle with 165s that came standard with it. Last spring I bought Qu-Ax 145s from someone on the MB. I don’t know why but I didn’t try them until today. Once I was mounted and rode 50 yards, I knew they were easier to use than the 165s. Here are the immediate improvements.
Greatly reduced wobble
Less wobble means I can hang on to the saddle easier
Can use brake easier
Better steering
My ass didn’t hurt as much
Improved freemounts
My hill climbing was about the same. I did make an uphill switchback that I have never made before. The only downside was I did notice a little more strain on the tops of my thighs on significant uphills.
I ride 165s on my Nimbus 26" for off road trails without any problem. On some of the short steep hills where I ride I have to give it everything I have to make it up.
That being said, if I am riding the road or a very flat trail I switch out to a set of 114s. Since I don’t need all the leverage, the 165s end up seeming lanky. Its much easier to keep a faster pace on the shorter cranks. Slowing down took some getting used to but I was able to adjust. Mainly you just have to plan ahead since you don’t have the instant stopping power you have with 165s. I could maybe go one size down from 114 but I think at that point I would need a break to make sure I could hold back on some of the down hills.
I have only tried these two sizes but they work perfect for the riding I do.
If its not too terribly steep 150s will do fine. Even shorter cranks will do even better on flats. I just dont like them for the really really steep stuffs that I climb for 3 hours, and besides my Oregon likes that extra leverage. For me, on the zero q Qx cranks, ive gotten used it. They’re not twitchy or wobbly to me. I tried the Truvative Hussefelt 175’s the other day. Lenght was fine, just hated the wide Q on it. It was terribly wobbly going down on it. If there were 175 zero Q I would buy it!
I’ve been slowly adapting to shorter and shorter cranks for both road and muni.
The advantages of shorter cranks have pretty much been listed:
easier to spin and less wobble, so much faster
smoother going uphill, so better for climbing up to a certain steepness (this increases as you get better)
But this comes with the following disadvantages:
harder to mount (especially b/c of higher seat on larger wheels, e.g. 36)
less slow-speed control (gets better with practice)
less leverage for steep climbs where you almost stop between pedal strokes.
A few months ago I was riding:
150s on my 26 for muni,
165s on my 36 for muni and
127s on my 36 for the road.
In the last few months, I have improved a lot and have been riding:
127s on my 26 for muni,
150s, then 137s, then 127s on my 36 for muni, and
100s and 114s on my 36 for the road.
As you go shorter it helps to have a brake for the downhill. The mounting and slow-speed control really improve with practice - actually it’s amazing how much. Just a few months ago I found the 36er hard to control on moderate downhills with 165, and now I have a lot more control with 127s on the same downhills and even ones twice as steep!
Beyond the technical/control, the other main factor about shorter cranks is that you go a lot faster and as a result the whole experience is way more tiring. On my last few 3 hour 36er muni rides with 127s and 137s I was totally beat at the end and wiped out for 2 days afterwards.
Oh, as far as being hard on the knees, thus far I think it’s a matter of slowly building up the muscles as well as ligaments and tendons (they take even longer to build up). That said, I think a brake is a good idea for steep downhills with short cranks as otherwise it can really tax the legs/knees.
