Going from 170mm cranks to 172.5mm?

[shinomaster]

I have been thinking of doing this for years, but haven't for several reasons. The first being that I have weak knees and I have read that longer cranks strees the knees more. Second All my bikes have 170's and it would be expensive to switch all my bikes, and I am a destitute artist. Third, I am lazy.
I am asking because cross season is quickly approaching and I think I could crank through the mud at a slow cadence better in a low gear with longer arms. I ued to ride a MTB with 175's many moons ago. Is there time to make the switch? Some like the Jerkobtuse would say no, it would seem. Would 2.5mm make any difference? Or should I just train harder?

Much Love,

Shino

[Too Tall]

Ride you bike, keep your $$ in ze wallet and eyes on the road.

Won't make any diff.

[sailorboy]

I have gone back and forth on this myself since most of the 'formulas' tell me that I need a 170 with my short inseam despite being 5-9, but had ridden longer cranks for many years. I have basically compromised by using 170s on one or two bikes, and 172.5 on another. I typically ride the 170s on flats or days when I will try to sit in on most of the climbing, such as early in the season when I want to spin more. As the knees get stronger during the season, or in races, I tend to ride the 172s. Some days the 170s just feel better, but when I'm standing up on shorter climbs and need to power over, I feel the 172 offer a slight advantage with more leverage. Otherwise, the difference is debatable IMO, and I have no problems switching bikes day to day.

[Keith A]

Shino,

I'm sure you will get a number of opinions on this subject and would expect there to be valid points for either option. So let me share my experience of having been there and done that. To start off, I'm just under 5' 10" with longish femurs. I'm also a spinner and like to keep my cadence between 95 to 105.

When I started out cycling, I rode 170's cause that is what came on my first road bike. My second bike came with 172.5's and I first I didn't like them because I couldn't spin as well with the 170's -- I know there is only 2.5mm difference, but I could really tell the difference. I talked to my friend a the LBS and he suggested that I give my body a chance to adjust to the 172.5's, before giving up on them -- and he was right. Once I could spin these smoothly again, I really like them better than the 170's. When I ride 170's now, it feels like don't have as much power.

I haven't done any power meter comparisons or even a TT test to see if I my perception has any real data to back it up -- but I really do like the feel of the 172.5's better. BTW, I've ACL reconstruction on one of my knees and I haven't had any problems using the 172.5's.

[martianbait]

Shino,

I am 5 ft. 9 in. with a 30-inch inseam. According to the calculators, I could go either way with a 170 or a 172.5 crank. I have two road bikes, one with a 170 crank arm and the other with a 172.5. In all other ways, they are pretty much the same. I can't say I'm as tuned in to the subtle differences as other posters have noted....but maybe that's a good thing. I don't notice the difference. And it's not a factor that I use to select one bike over the other when I go out to ride. If it's nice weather, I take the Land Shark...if it's not, I take the Seven (well, OK, sometimes I take the Seven even when it's nice. But I like the Shark.)

[Samster]

having ridden 165, 170, 172.5, i don't think it makes that much of a difference. as someone else said, save your money--unless you're experiencing some kind of irregular pain (as opposed to what? regular pain?) i'd leave well enough alone...

[DarrenCT]

i went from 175 cranks to 172.5 on my scott cr1. i have nfc if it makes a difference but i figure what the hell. my csi, legend st, crown jewel and madone have 172.5 so i figured i'd keep it consistent.

i think its more mental than anything ;)

have a good ride!

[stevep]

put on the 172s and dump the 53 t ring. put on a 52 or a 50
much better for general use and much, much better for your knees.
50-12 is a big enough gear for anyone who does not race. and big enough for a lot who do race.

[Tailwinds]

Shino, I am 5'7" w/a 32.25" inseam, and I have ridden both 170's and 172.5's. I felt like it was a little harder to get on top of the gear w/quick accelerations w/the 172.5's -- I am a spinner -- so I went back to the 170's. I was riding in flat FL at the time. I wonder now how 172.5's would feel in CO...

[Louis]

John,

FWIW, here's my experience:

I'm 6' and ride 60 ST frames.

My original bike (which I think was a 62 and way too big for me) came with 170 cranks. I didn't know any better, but in hindsight, those cranks were way to short for a frame of that size. I used the 170's for years and was none the wiser. The original frame broke and I moved the components to a 69 ST frame that fit me much better. As I started to learn more about fit I realized that 170 cranks were to short so I went to 172.5. I noticed very little difference. After a while I decided to try 175. I immediately noticed a significant difference on the rolling hills that form the majority of my riding.

With the longer cranks it was easier to crest some of the smaller rollers without downshifting. I'm a pretty horrible climber, but felt noticeably stronger on the rollers. As best I could tell, there was little impact to my spinning.

My recommendation: Buy a used/inexpensive set of longer cranks for a frame you ride a lot and are very familiar with. See if you like them. If so, great. If not, you haven't wasted too much money.

Louis

[shinomaster]

Thank's to all for the free advice. Louis, that is a good idea...I'm borderline...I'm just a hair under 5'10", and have been told I could both. It is really hilly here so I probably could use the extra leverage. The only reason I never switched was that I heard it can borther knees.