JGAN

Hey cyclists,
My road bike fixie conversion needs new cranks and BB. I took it to a LBS to see what they had, and they said I currently have 170mm cranks. Looking at what they sell, I'm trying to decide between 165mm Retrospec and 170mm Origin-8 crankset. The Retrospecs are a lot cheaper, so I'm considering switching but want to know how much of a difference I will feel?

The frame is a tad big on me, but I like the way it lets me ride. Also, I don't really have problems with pedal strike right now, and I don't feel like riding is difficult with the 170mm really. However, I did a lot of reading, and it seems to be going a lot between the kinesiology and physics of riding (like body build vs leverage). I'm 5'6", average build, but I used to run and know I'm built as a sprinter. I have a short stride length and can accelerate on the (running ) track in a heartbeat. Would I benefit from having a shorter crank or will the difference be negligible?

Thanks,
JGAN

Dannihilator

Sounds like 167.5 is in your future. Seriously though, it's personal preference.

europa

Makes stuff all difference except to the frequency of pedal strike, and not a lot then. From your comments, go with what you like but seeing it's a road frame, if you really really really can't make a choice, go for the shorter set.

headloss 

5mm difference in crank length yields a 5mm difference in saddle height, changes the balance of the bike, how far your knee rises relative to the top-tube, etc. Things to think about in determining the best size. Most likely, you won't notice a difference one way or the other.

darkarcher

Personally, I think the rate of diminishing returns for crank length increases under 170mm. I have run 170, 172.5, and 175. I have a 30" inseam and I like all three lengths equally but for different reasons. Depending on how heavy my bike is, and if I have been good on my diet determines my favorite. If you are around a 28" inseam then 165 may be in your range but depending on how much weight your pushing I would try before you buy. For me 170mm is definitely as low as I want to go.

JGAN

Thanks guys. I ended up going for the 165mm, we will see how it goes!

SquidPuppet

Are you a masher or a spinner?

50voltphantom

One thing not to be over looked is the additional leverage afforded with longer cranks. Larger gear-inches benefit from longer cranks. I spun 180's comfortably in my BMX days.

mihlbach

Yeah I race with 180s, but you don't spin a bmx bike for more than a few seconds at at time in a race. With a fixed gear if your are riding, you are spinning. No one wants to spin 180s for hours on end.

Bakersb

I'd agree as well for the 165mm. I'm 5'6 too, and I have 170mm length cranks at the moment. Definitely wished I had 165's; I miss my old cranks. I think crankarm length is less about sizing and more about preference (as mentioned, more or less leverage/spin vs mash)

UltraManDan

I'm 5'10" on a 56cm frame and just dropped from 175mm cranks to 165mm and I love it. Much more of a compact rotation and prevents bouncing in the saddle at high rpm's

TejanoTrackie 

I'm 5'-3" with a 28" inseam, and have ridden 165mm cranks on both road and track bikes all my life with the exception of a few bikes I bought complete, mostly mtbs, that came with 170mm cranks. I can definitely feel the difference in the length when I'm spinning a high cadence.

T13

You probably wont even notice the difference.

UltraManDan

That's a pretty bold statement.

To the OP, here is a pretty informative article that helped me decide. Crank Length: Coming Full Circle

T13

According to the OP, the bike shop told him that he had 170mm cranks. If he didn't even know what length cranks he had, then i'm guessing, it's probably not gonna make a whole big difference(maybe placebo effect) if he goes 5mm smaller. I mean, there are always gonna be cork sniffing, elbow patch wearing people out there that swear by this and that, and some of it may even be proven by "men of science" who write informative articles. I used to swear by 165s, but I'm riding some 170 Campys and they feel fine, to me.

UltraManDan

Fair enough

RoyIII

I have 165s on my fixed bike and 170s on the SS and Geared bikes. I've been riding all my life and I cannot tell the difference.

Huffandstuff

My everyday bike has 165s, track bike has 167.5s and cross bike has 172.5s. I can spin 170+ on all of them, I've never really noticed it except sometime I try to clip into the 172.5s and the pedals aren't where I thought they'd be.

cruiserhead

same here
love the spin on 165s and it just doesn't quite feel the same with 172.5s

I do fear pedal strike so i'll never do 172.5s again

bro

i had 170's and a heavier gear ratio, which worked great, and when i geared down, i was spinning way more and i didnt like the 170s anymore and switched to 165s, which made a huge difference for me. i'm kind of a little dude though so it might be different for someone with a longer cycling inseam