yeyo999

hey guys...i am deciding on wether to go with a 165 mm or a 170 mm. I have a 32-33 in inseam. I want to build a a fast bike. I'm going with a 46/15 for freewheel and 46/17 for normal day use. I have small hills to get around on campus. there not that bad...i just want to build a fast bike. I search, read a couple of articles. But i'm still somewhat confused by reading both sides of the arguement. What do you guys think

xxxfattonyxxx

You'll have better corner clearance with 165's. That's about all I can tell you. I haven't used 170's

Wake

I've got 172.5 cranks on my Sputnik and I'm glad. It gives me some extra torque to push over the hills and against the wind. At 64 I need everything I can get. I, too, have about a 32" inseam. I would go for the 170. It used to be standard on multi-speed bikes - not sure if that's still the case with 20+ speeds.

Shorter cranks will let you spin faster but longer ones let you come off the line quicker.

yeyo999

yea, thats what i am thinking, cause i've hit some corners on my 12 speed with 170mm crankarms and they do hit the ground when when i pedal through the corners in order for speed

Yaktizzle417

I've only ridden 165's and I like them a lot.

elTwitcho

If you're worried about clearance, go clipless

tFUnK

i run 175s for mtb and went with 172.5s on my fixies. i sort of wish i had 170s or even 165s to help with the spinning and pedal strike issues, but wonder how much more punishment the hills will be.

Dannihilator

I run 172.5's on the fixed gear and 170's on the mtb. Just remember, when changing crank length, you may feel a change in body positioning on the bike.

Yaktizzle417

I've ridden both cages and clipless and I don't see how going clipless makes a bit of difference? Assuming the rider is always in the cages (the way it should be) then the cages will not scrape the ground...

adriano 

ive got 160mm crank arms. its a shame that i cant turn back.

tmh657

started with 170's, went to 172.5, now I have 175's.
I have no pedal strike issue and love the way I can crank up hills. My geared bike had 170's and I changed then to 175's.
Try a longer crank and see what you think.

I know it's hard to do a real scientific comparison. You would need 2 bikes set up exactly the same but with different crank lengths.

look at this and scroll down to crank length.....
https://www.peterwhitecycles.com/fitting.htm

dilzymCcarver

a 5mm difference is going to help more with clearance issues than torque... but if ur really worried, get a bottom bracket with a shorter spindle length. thatll help even more.

droobieinop

There are some charts out there for figureing out the "proper" crank length, but I can't remember where I put them. Here is what I've got going on, my geared bikes have all turned out to be 175s I believe, I have one fixie with 165s (I built it that way) and one with 170s. Both are conversions, but the first had a welded trple and the 170s are original campy, and for me at 5'9"ish with a 30ish inseam these work great.

The short crank thing was explained to me by an ex NYC messenger who said the shorter cranks were easier to get spun up to speed and would be less likely to cause pedal strike. I'm going on 5 mts and so far so good.

adriano 

picture yourself with shorter legs and a fever for spin.

planyourfate

If you have pedal strike on your 12 speed then you should measure from the ground up to the bottom of your 12 speed bottom bracket shell and the ground up to your fixed gear bottom bracket shell. If your fixed gear has a higher bottom bracket shell then 170's might be ok. If it's lower you might want to consider shorter crank arms. If you "just want to build a fast bike" then you may want to consider your shortest option for crankarms that way you can really crank through corners.

dookie

you said 'freewheel', implying not fixed-gear. if indeed you meant that, go for the longer cranks and coast through the tightest corners...the bike will be far more stable and speed loss minimal. it doesn't sound like you're racing...

elTwitcho

Pedal strike isn't an issue if your cages scrape the ground. Pedal strike is an issue if your pedals strike the ground.

That said, the narrowest pedals on the market designed for straps are going to be at minimum twice as wide as nearly every clipless pedal (excepting those built into a platform) on the market.

cyrano138

I'm not trying to start a fight or anything, but there's something I've never understood about this argument. I get the clearance thing, because I'm sure any little bit helps, though, for the record I have 170's on my fuji track and I've NEVER struck even after cornering pretty damned fast. I think I read somewhere that the fuji track has a nice higher bottom bracket.

But the idea that it's going to produce any noticeable difference in torque is absurd, if I remember my physics correctly. Torque is directly proportional to the distance (from the center of rotation) from which it's applied, which in this case is the crank arm. So you're talking about a 2.94% decrease from 170's to 165's.

Correct me if I'm wrong, but maybe this is just another case of people trying to sell you **** you don't need?

Ken Cox

I ride 175mm cranks on my fixed gear mountain bike and 170mm cranks on my fixed gear street bike.

With an appropriately high bottom bracket, as one finds on dedicated fixed gear bikes, pedal strike does not pose a problem.

With a converted bike, though, 170mm cranks can hit, with disastrous results.

You can ride with 170mm cranks on a conversion if you remember you have cornering limits.

As for the effect of the length on spin, my 170mm cranks spin so much better than my 175mm, but my 175mm cranks give me easy torque for very slow speeds on uneven ground.

For a street bike, the shorter the cranks the better.

The rider's leg length has almost nothing to do with crank length.

Rather, as one goes shorter in length, one trades off torque for spin; and, as one goes longer in length, one trades off spin for torque.

Shorter cranks spin much faster than one would expect from 5mm increments.

I'd rather have spin than torque, and so I gear down a little and spin much faster.

I have stayed with 170mm cranks on my street bike only because I had my bike professionally fitted with 170mm cranks; otherwise, I'd go with 165mm.

I ride with 175mm cranks on my mountain bike only because no one makes short cranks for mountain bike bottom brackets.

JohnDThompson 

I assume you mean "toe clips" where you've written "cages." The word cages has a different sense in the context of pedals.

From Sheldon Brown's glossary:

#4. The outer part of a conventional pedal, the part that comes into contact with the rider's shoe.

dookie

have you tried different arm lengths on an otherwise identical bicycle? if not, your post is absurd. i assure you, the differences described by mr. cox are plenty apparent.

yeyo999

your right...but i love option.. 15 cog, have fun with buddies : freewheel-cruise on the beach and get around the city to take pictures. The 17 cog for dailiy use on campus and up and down hills. around campus i want to get around on a fix gear. It help me build up endurance. When, eventually, I've build enough endurance, i'll lower the gears again...i'm sorry if i'm not at your level yet...just messing with you buddy

i'm personally looking for clearence, however, regarding your physics, it true but when you work with gears/ratios, things change, but you are somewhat right.

schnee

That's assuming people are biomechanically set up to produce proportional torque at different leg extensions in relation to the circle described by the arc of the crank. We're not. Once you take the whole system into account, it's far more complex than just a single torque number on one pivot.

Mr.Huffer

If you "want to build a fast bike" then go for bigger gear inches and throw a front brake on. Also dump the freewheel and use the fixed cog. Coasting won't build up your endurance and the rotational inertia will give you a little help on the hills.

cyrano138

Your argument is absolutely watertight. I mean, there's no way it could seem easier unless it actually was easier, right?

Sheldon Brown's site seemed to indicate that more work is required when the legs are closer to the center of rotation (in his section on saddle height), which runs counter to the argument. Again, correct me if I'm wrong.