Helderberg

So this is how it all ended up. These are 165 mm cranks and the new Ultegra BB. The FD is also a Sora that was on the bike when I bought it. The rear cogs have been swapped out for 11-36 and the rear D was changed also. Went for three rides with the new crankset and have been pain-free. I was able to remove the knee savers and the shorter cranks have made it easier to keep my knees over the peddles. It is a better ride now that I have made the change and am looking at possibly doing the same to my Topstone. This has been a very good change and I could not be happier that I have made it. Now I have to sort out the seat height and setback. Be safe all.

freeranger

Good to hear it's working for ya! Looks good to boot.

canklecat

I'm considering that as a replacement for the 175 Ultegra crankset on one of my bikes. Technically my legs are long enough for 175 cranks, but with age my knees, hips and lower back prefer shorter cranks. I don't want to buy another Ultegra or DA crankset if I'm not sure about the crank arm length, but Sora is priced about right.

Helderberg

What I have found is that with the shorter cranks I have a seat height that allows my knees to not bind, for lack of a better word, at the top of the rotation. With the 175's that were on the bike, I realize now that I was splaying my knees away from the bike, out, and not correcting it on the downstroke. That was putting my knee at an odd angle and causing pain in my knee, oddly, only my left knee, but now there is none. I was also able to remove the spacers, sometimes referred to as knee savers, on the peddles which along with the shorter cranks gives me a few more degrees of lean while peddling on curves. Granted, nothing is going to make up for 72 years for the abuse my knees have taken but this is a welcome relief that will hopefully give me a few more years on a bike. It is not obvious if there is a noticeable difference in the leverage, actual or perceived, in the stroke. It has been very windy here for my rides so I can not judge the stretch of road, speed, effort, compared to the 175's but it sure feels good no matter what. Looking to do the same to my Topstone in the near future but that will be the GRX as I want to keep the 46-30 chainring. Thanks for the reply.
Frank.

Retro Grouch 

So you went from 175mm cranks to 165mm? That's not quite 1/2 inch. Assuming your seat height was right initially, I'd expect you to have to raise your saddle the by same amount. That way your leg extension at the bottom of the stroke will be the same, but your knee flexion at the top of the stroke will be less and you'll probably not find yourself sticking your knee out to the side so much.

That leverage thing is something that people like to ponder over but it's really just another gearing factor that you automatically adjust for by spinning in a slightly smaller gear. I wouldn't expect you to find any speed difference in real life.

wphamilton

People are going to disagree, but the shorter cranks likely do help a small amount, provided you've adapted to them. I say "help" vaguely because the measurements I've seen were in terms of metabolic efficiency and we tend to assume that efficiency leads ultimately to a tiny bit faster. Maybe not but it's plausible.

Not because of leverage or cadence. As has already been noted those are red herrings in this case. It makes sense though that moving your legs in a smaller arc just has less energy overhead.

These are very small effects and IMO would reasonably be secondary to other considerations regarding crank length.

Helderberg

From what I can tell the lesser angle of my knees at the top of the peddle stroke seems to be the biggest improvement. I am not a physiotherapist but I do know that today I have no pain and that is a real improvement that I can feel.
Be safe, Frank.

Bill Kapaun

I made a post about switching to 165's a BUNCH of years ago.
It was a Godsend.
My range of motion was simply not adequate and I was basically "carrying" one knee over the top by pushing the the other pedal. That's fighting yourself energywise.
At the time, 175's gave chronic knee pain, 170's I'd have some 2-3x/wk and 165's allowed my to ride about 3X the miles pretty much painless. It allowed me to do 70 miles at age 65 on my hybrid.
A year ago, I had my grocery getter stolen and w/175's my knees were hurting before I got the shifting tuned.
Another 10 years of wear & tear on the knees and 175's were brutal.
EDIT:
Forgot to add- My cadence went from a barely 60 to 72- 75 RPM. Lower gear, spin faster.
My stamina nearly doubled. 15/mi./day would wear me out. In a matter of a few weeks I was doing 25...30...40. I was able to improve my conditioning because I was able to ride a lot more miles.

Joe F

Interesting discussion. I had considered going from 175 to 165 after the earlier thread, but thought the difference in length to be so small it wouldn't make enough difference to be worth the investment. Might have to find someone around here with a 165 and give it a spin. My knees have taken a lot of abuse over the years between sports injuries and motorcycle wrecks, not to mention the occasional crash out on the mountain bike trails. Not in need of replacements yet or anything, but I can tell they aren't what they once were in mobility and strength.

Helderberg

I have a Topstone that has 172.5, not a huge difference from the Quicks 175, but enough to show me that I was on the right track. I borrowed my daughter's Quick, a women's medium, that has 170's and that was enough for me to close the deal. I realized that the body position on the gravel bike was very different from the Hybrid but it was just a starting point for me. I would not have made the change without having ridden my daughter's bike as it was the same basic geometry but again different. Not inexpensive but the swap was definitely worth it for me.
Thanks for the post, Frank.

Bill Kapaun

The effect is 2X.
You raise the seat another 10mm, when in the 6 o'clock because of the shorter crank.
When at 12 o'clock, the pedal is another 10mm closer to the ground then it was before.
Therefore, you sit 20mm higher then the top of the pedal stroke.
Late Edit-
I also tried some 160mm cranks, but they were too short for me. I couldn't really improve the cadence and it was "less comfortable" trying. It was like the acceleration/deceleration occurred too rapidly for my ratty, chubby knees to follow "smoothly". Like being on a kids trike.

jppe

I’m glad it’s helping you out! Knee pain can keep the fun out of riding.

My one experience with shorter cranks didn’t go well. I ride 175’s and usually spin around 85-90 rpm. So I’m not really mashing or pushing harder gears but doing more spinning. I used a friends bike with 170 cranks and I just didn’t seem to be able to generate the same amount of power as the 175s. I had a much harder time staying with the group I rode with using the shorter cranks. It wasn’t a great experiment since it was on different bike but it left me with the impression shorter cranks weren’t for me. But if I were having joint issues I couldn’t resolve I’d certainly look at trying shorter cranks again.

wphamilton

If I were going to experiment with a shorter crank, I'd want to try 160 or even 155. The key in my mind would be training for the same cadence which means lower foot-speed. The amount of torque needed would be adjusted by gear selection, as usual.

The reason being, shorter even than the standards is optimal per some old studies, and if it helps with the knee angles then even shorter could help more. If you can adapt to it.

Helderberg

That is why I went with 165's and they have been what I needed for the sake of my knees. I was not as concerned with loss of possible speed as I am about the pain I was experiencing. I am not saying this is the magic pill but it has been good for me.
Thanks all for all of the responses and I welcome all your advice.
Frank.

OldBrokeReCycle

I bought an older 54 cm Specialized Secteur a couple of years ago as my California bike. I am (or was, I don't think I can stand that straight anymore) 5'7", so it barely fits and the 175 cranks were a bit much, so I spent 1/3 of the cost of the bike on 165 cranks. It's probably because it was one of my few Frankenbike mods that actually seem to have accomplished something, but I really like it. I still spin at what most people grind at, but it seems to be a lot easier and more comfortable, and I do think I can go farther, if not faster. 170-175 seems to be one of those standards because standards are cheaper things. Especially for the young at heart vertically challenged, I would recommend it.

BlazingPedals

Quite a few recumbent riders use short cranks. And by "short" I mean 155mm or less. Buying a set of 165mm cranks hardly seems worth the cost for the 0.2" reduction in radius. Reduced knee flex seems to be the primary motivation, although like a lot of things recumbent riders say, they tend to over-proselytize about it even to other 'bent riders. One thing that's acknowledged, you should increase cadence to compensate for the smaller pedal circle. This usually means running a gear or two lower. You want foot speed along the pedal circle to stay the same in spite of the faster cadence.

Personally, I tried them and didn't see any advantage for me. I can see the advantage for someone who is very short, or has reduced knee flexion. Bionic knees come to mind as one application.

Lazyass

Greg Lemond had an interesting take about crank length.

Greg LeMond Fans - Questions for Greg.