Corben

What difference will there be if I swap out my 170 crank with a 175?
I see only a little difference in length.

Brannigan

Careful. When pedaling through turns it is a drag to clip a pedal, 5mm is a big change when leaning into a turn.

xenologer

you'll find it harder to spin, think circumference, not just 5mm

fietsbob

Not spinning , I've got 170, 172,5 175 and 180 cranks on various bikes .

the 180 give the illusion of more saddle setback..

It depends too on the BB drop.

hint: dont pedal thru a corner ..

165 get used on the track , somewhat, to not hit the track bank high side..

GamblerGORD53

You will find it 3% easier on hills. All gears will shift at lower speed. It feels like 3 GI less.
I went from wussie 165s to stump pulling 180s for my SA 5w. I Don't even need less than 40s GI.

Retro Grouch 

How tall are you?

Unless you're unusually tall or unusually short I doubt you'll notice a difference. You might feel the need to lower your seat 1/4 inch.

A couple of years ago I broke my hip (actually my femur). After it healed I didn't have the same range of motion and switched to 152 mm cranks. My most recent ride was on a bike that had 175 mm cranks and I didn't even think about it so I guess that I'm back. Thanks for the reminder.

Myosmith

While a few mm can make a difference, I think people vastly over estimate the effect that 5mm in crank length has. The difference in circumference of the pedal stroke between 170 and 175 mm cranks is only 31.4mm or about a 3% increase (from 1,067.6 mm to 1099.0 mm). As far as pedal strike, the 175 mm crank decreases clearance by just a bit less than 1/5 of an inch. A difference, yes, but in all honesty, if you took two otherwise identical bikes and equipped one with a 170 mm crank and the other with a 175 mm and had riders try each bike without telling them what the difference was, I doubt that 95% of the riders would be able to pick out the difference.

MichaelW

Both are good for medium-sized riders. If you are on the shorter side they will be too long. If you are on the taller side they will be better.
Most bikes are dimensioned to take 175mm cranks so pedal clip is not such a big issue.
Crank length does alter the transmission but riders automatically compensate by selecting a different cog ratio.
You will find high cadence pedaling harder on longer cranks.

skidder

My situation's probably unique, but I went from 175mm to 170mm cranks, and it made a world of difference in comfort. I've got joint problems developing from many years of distance running on hard pavement, and the smaller diameter rotation just made the aches and pains go away. Due to my mom's medical issues I'm somewhat paranoid about joint replacement so I'm doing everything to avoid it/put it off as long as possilbe. I haven't tried 165mm cranks, but if I find one cheap in a square-taper format I might swap it onto one of my bikes.

Retro Grouch 

While I was recovering from my broken hip I converted my recumbents to short (158/162 mm) cranks. Recumbents aren't known for climbing prowess so I worried about how I'd be able to handle climbs. As it turned out, my worry was baseless. I climb just as well (or as slowly) as I ever did.

My diamond frame bikes have 172.5 or 175 mm cranks, but i haven't felt any urging to reconvert my recumbents to longer cranks.

DataJunkie

I built up my cross bike with 170mm cranks and cannot tell a difference between that and my FG with 165 and my roadie with 172.5.
My thought at the time was to have a tad bit more room on off camber slopes and ruts.

devianb

My bike came with 175 so that is what I was used to. I switched over to 170 and couldn't tell the difference except for slightly higher cadence, but I would have to be riding fairly fast to notice.

Mobile 155

worth reading, may be interesting maybe not. https://www.cobbcycling.com/articles/...ng-full-circle

Sixty Fiver

There really is not much of a difference between 170 and 175 mm cranks.

Really long cranks tend to be used for people with really long legs and proportionately longer femur lengths to maintain proper position when a shorter crank would push them farther back and require more setback on the seatpost / saddle.

I ride 170, 172.5, and 175 mm cranks... I spin like a gerbil on crack regardless of the crank length and the change in leverage is pretty negligible, gearing choices make more of a difference.

PompeyMonkey

I have always ridden 170mm cranks. This year I bought a bike with 175mm cranks as part of the package to get a bargain. Rode it twice and really, really didn't get on with it and ended up changing to 170's*

From my reading, it seems that some people don't notice while others really have a problem adapting to different lengths. It might just be a case of "suck it and see".

*The bike was still a bargain!

PS - First post! Hello everybody!