12/11/19 8:18 AM

When i first started riding in the early 90's, I bought a used road bike with 170 crankarms. I got the fever and started upgrading parts and after reading the infinite internet writings of drankarm length, I got a 175mm crankset. Legs were sore and stayed sore for a month or 2. I kept all bikes at 175 but I'm not sure it ever helped me and I'm not sure that the economy of motion/energy of the shorter cranks outweighs the increased leverage of the 175's.

I'm thinking about a new Campy crank and tempted to go 172.5. I've found that going shorter is an easy transition but longer takes much more adaptation. I'd leave my trainer bike at 175 but change my gravel bike to 172.5. Anybody have experience with this?

I know I'm not very adaptable because I don't ride very well when I get on a different bike with very minor changes in position, based on when I had 5-7 bikes. I ride better when I ride the same bike everytime so I'm down to 1 bike,a blessing. Don't want anymore.

12/11/19 6:24 PM

I have settled into 172.5 favored over 175, for road. At this point, I'd go 170 before 175 from the 172.5 sweet spot/road. My inseam is 34.25" FWIW.

Off road, MTB, gravel 175 or my 29er has 180. But I am at lower RPM overall by a decent margin non road.

And I have recently put a 167.5 set on my old Strong to try out after a few months on the Computrainer junker. I liked those, and wanted to see if on the road would make me feel differently. So far I like them on the road too. Makes me think I may be on 170 eventually on all road bikes.

So really when avg RPM is higher, shorter is working for me, and visa versa. I am surprised the 167.5 are not too far. But only done a few 12-20 mile rides with them. But after about a year of Computrainer use. But weather allows me to get out off season here and the CT does not get the use it once did.

12/11/19 7:50 PM

I'm 5'11", generally ride 59cm or 61cm frames in old money, and I've always used either 165mm or 170mm cranks. I really don't notice the difference when swapping from a bike with 170s to one with 165s. It's probably pretty close to a 50/50 split on the two lengths across my fleet.

But I have one friend I ride with who absolutely refuses to countenance anything but 172.5mm cranks...

12/12/19 9:55 AM

I came of age when the only real choice was 170 mm. TA cranks were readily available in many different lengths but few chose other than 170. I think it was Indurain who "popularize" 175 mm cranks for time trials and that was combined with the use of longer cranks on MTBs. After 30 years on 170 mm, I followed the wave and went to 175 mm for 17 years. The result was a small reduction in cadence and nothing else that I could discern. 5 years ago a new bike resulted in a new choice so I went back to 170 mm. Slight increase in cadence and nothing else.

It's just quite possible that the reason 170 mm is so common goes beyond the obvious convenience for the manufacturers, distributors, and retailers is that it is a length that works for most people. Not everybody, but most. I'm pretty sure I'll be on 170 mm for the rest of my riding career.

12/13/19 7:01 AM

If there's anyone out there looking to go the other direction, I have some 177.5s, formerly ridden by ex-pro Ted King!

12/13/19 8:18 AM

like everyone, started with 170s back in the day. in the first 3-4 years i gradually moved 172.5 and settled on 175 for the last +30 years. common guidance suggested 175 was "right" for my 35.5" inseam.

however, i feel like i was a better sprinter with the 170s. maybe it's because i was 20 years old and riding 300 miles/week, but still!

Last edited by walter on 12/13/19 11:02 AM; edited 1 time in total

12/13/19 9:46 AM

I think I started with 170, went to 172.5, 175, 177.5, back to 175. Rented bikes with 172.5, didn't notice much difference.

After I spec'd my Checkpoint, I realized I forgot to specify crank length. Since I didn't feel strongly about it, I figured I'd just ride the bike and worry about it if it felt wrong. I loved the bike right away, so I haven't even checked the crank and don't know what length it is.

Doubt I'd do well on a blind test....

12/14/19 9:03 AM

When you get right down to it, the changes we're making are really small. Going from 170 to 175 is only a 3% increase. It's no wonder that there isn't a huge difference in feel.

I briefly rode the 177.5s before switching cranks to get better gearing, and I can't say that I felt any real difference. The fact that it was a new bike completely masked the crank length difference, assuming that I would actually have been able to feel it, which is questionable.

12/14/19 9:21 AM

Two bikes I have are almost identical except for crank length (170 vs 172.5). I’m definitely not a spinner but started monitoring cadence trying to increase. I noticed over a year or so a slight difference of 2-3 rpm between the two. But it might be all mental too.

12/14/19 11:15 AM

Side note: As all will recall I busted my right knee in 2006. There was some tendons that got tweaked as well. Post injury I had 177.5 cranks on a road bike. It made mt right knee sore and tender after a long ride.

Of course, no knee deficiency, no issue? Left leg was fine with it.

But I will get some soreness 'that night' road bike 175mm I don't seem to on shorter. It takes a 50+ mile ride to get sore enough I take anti inflams FWIW.

So deficiency aside, not matter really?? ;)

New question as part of this. Some folks pedals toes down with lots of ankling, me more flat footed.
What might this bring to the equation