Singlespeed & Fixed Gear - 165mm vs 170 mm Crank Arms

I'm looking to upgrade my crankset and I want someone to explain the benefits/disadvantages of having a shorter crank arm set up. I have 170mm now, but I found a good 165 crankset with a 46t chain ring (I have a 46t chain ring with 170mm arms). My gear ratio is 46/17 fixed. Thanks.

Shorter cranks give less chance of a pedal strike with the ground, and they're a bit easier to spin at high cadence. If you're riding on the street, 165 is generally a better choice.

Leg length also plays apart check out this dandy little chart: http://nl.tinypic.com/view.php?pic=315mwqt&s=5

1. reduces overlap
2. reduces the occurrence of pedal strike

I read sheldon saying a 175 gives 3% more gear in. than a 170. So, I would believe that a 170 is the same regarding a 165. As for the pedal strike, I don't see it being a problem w/ a 170. I have used a 175 and struck it. I think the real issue w/ striking is how wide your pedals are.

I am 6'1" with a 34" inseam.
I have used 165mm, 170mm, 172,5mm. I now have 175mm Dura Ace track cranks which are 175mm. I got those because they were a smokin deal on CL. I have less pedal strike issue with these cranks than with 170mm Sugino RD's because the crank arms are closer to the frame than the RD's. They go almost straight from the BB and spider but the RD's have a curve out to them.

You will generate more torque with longer arms but can't spin as efficiently. There are tons of threads about it.

Gotta remember that BB clearance is the other factor in pedal strike. A conversion will most likely have a lower BB than a track frame.
My 2¢ worth.
BTW I love my DA cranks. 49t and 17t

1. reduces overlap
2. reduces the occurrence of pedal strike

Why is it that people consistently ignore point number 3.


3. Reduces leverage on the chainring and requires more torque to pedal.


170s are noticeably easier to pedal (plug in the different crank lengths in a gear inches calculator) than 165s IME. This is slightly offset by the smaller circumference of the pedal stroke but personally, I think 165s suck.

Why is it that people consistently ignore point number 3.


3. Reduces leverage on the chainring and requires more torque to pedal.


170s are noticeably easier to pedal (plug in the different crank lengths in a gear inches calculator) than 165s IME. This is slightly offset by the smaller circumference of the pedal stroke but personally, I think 165s suck.

Most fit sites actually (like the one above, for example) suggest 165s for my inseam. Anyway, couldn't you just compensate for the difference with a different size cog and/or chainring?

I use 165 since I ride a smallish frame. Lack of torque isn't that noticeable to me when riding, but it does seem to make skidding a bit more difficult.

Most fit sites actually (like the one above, for example) suggest 165s for my inseam. Anyway, couldn't you just compensate for the difference with a different size cog and/or chainring?

Yes, you can compensate for the gearing difference. However, there's still some leverage advantage in a longer crank, which comes at the expense of a smoother spin. I imagine most folks here ride under conditions where pedal strike is more of a concern than leverage, but obviously that's not going to be true across the board.

Most fit sites actually (like the one above, for example) suggest 165s for my inseam. Anyway, couldn't you just compensate for the difference with a different size cog and/or chainring?

Not exactly. You can compensate with a step up in a cog, but then for instance (and these numbers are pulled from the air just to explain the example) you'd be running 48-19 so that it FELT like running 48-18. But you'd only be going 48-19 speed. So really, you end up going slower for what feels like the same effort.

That said, if you're more comfortable riding 165s as an issue of bike fit, ride 165s. Personally, having given them both a spin (165s and 170s) I hate the shorter cranks. Personal preferrence is everything though, ride what makes you happy. I'm just saying it bears pointing out that 165s are going to require more torque to move the bike.

Not exactly. You can compensate with a step up in a cog, but then for instance (and these numbers are pulled from the air just to explain the example) you'd be running 48-19 so that it FELT like running 48-18. But you'd only be going 48-19 speed. So really, you end up going slower for what feels like the same effort.

That said, if you're more comfortable riding 165s as an issue of bike fit, ride 165s. Personally, having given them both a spin (165s and 170s) I hate the shorter cranks. Personal preferrence is everything though, ride what makes you happy. I'm just saying it bears pointing out that 165s are going to require more torque to move the bike.

Shorter cranks don't fundamentally move you any more slowly for the same amount of effort -- they shorten the path your foot takes in rotating the cranks. You can get back the same effective ratio (Sheldon calls this the "gain ratio") by increasing the cog size. You don't end up going any more slowly for your effort, you just end up doing a little more rotation along a shorter path than with the longer crank. The radius is tighter with shorter cranks, and from a biomechanical perspective, certain lengths will work better with certain legs, and it's a matter of finding the sweet spot in the middle.

Shorter cranks don't fundamentally move you any more slowly for the same amount of effort -- they shorten the path your foot takes in rotating the cranks. You can get back the same effective ratio (Sheldon calls this the "gain ratio") by increasing the cog size. You don't end up going any more slowly for your effort, you just end up doing a little more rotation along a shorter path than with the longer crank. The radius is tighter with shorter cranks, and from a biomechanical perspective, certain lengths will work better with certain legs, and it's a matter of finding the sweet spot in the middle.

It depends on what you define as "amount of effort". You can't get back the same "effective" ratio by changing cogs out. 48x18 will always move a given amount per pedal rotation, regardless of whether you're running 175 cranks or 165 cranks. However,

48x18 with 165 cranks will require more torque in a given rotation than 48x18 with 170 cranks to move the exact same speed. The tradeoff is that the circumference of your pedal stroke is shorter. What's defined as "effort" is arbitrary though so there's no objectively correct answer either which way.

If you are short, get 165's.

If you are tall, get 170's.

If you are cheap, you get whatever you can take.

It's really not that hard on track bikes.

48x18 with 165 cranks will require more torque in a given rotation than 48x18 with 170 cranks to move the exact same speed.

not to be picky or anything, but the torque is also identical. T = F*r, where F is your leg pushing the pedal ('effort'), and r is crank length. keep T (ie: gear inches) constant...if r goes up, F goes down. which is the whole point...longer cranks provide more leverage ant the expense of pedal strike and/or lack of spin.

I'm looking to upgrade my crankset and I want someone to explain the benefits/disadvantages of having a shorter crank arm set up. I have 170mm now, but I found a good 165 crankset with a 46t chain ring (I have a 46t chain ring with 170mm arms). My gear ratio is 46/17 fixed. Thanks.
You have less chance of pedal strike with shorter arms, so you can take corners faster. This is particularly an issue if you're riding a road bike conversion, as road frames tend to have more bottom bracket drop than track frames.

You get more leverage with longer arms which makes it easier to mash gears.

If you are short, get 165's.

If you are tall, get 170's.

If you are cheap, you get whatever you can take.

It's really not that hard on track bikes.

True dat.

It depends on:
- Your bike's geometry. If it has a low BB then pedal strike (your pedal hitting the ground when turning a corner) is a concern. If your pedal strikes when in the turn, you will likely go down.
- Your shoe size. Big feet make toe overlap (touching the front tire during turns) an issue
- Your gear ratio. Shorter arms make tougher pushing. You will notice the difference during starts and stops.


So, weigh the benefits of the shorter arms with the cons being that they will be harder to push and you won't get the full stroke of power from your legs (if you are a taller rider).

im pumped to try out my 160s!

im pumped to try out my 160s!

Man, that's REALLY short. Unless you are a shorter dude with a small bike, it's gonna feel like you are pedaling a tricycle.

Man, that's REALLY short. Unless you are a shorter dude with a small bike, it's gonna feel like you are pedaling a tricycle.

ive got a 47cm and a big heart.

Guys, does 5mm reallly make that much of a difference? Take out your ruler and look at it. That's less than a 1/4 of an inch. I bet if I put two cranks out on a table (not next to each other) and have you look at them, you're going to be able to tell the difference.

If it didn't make a difference then why do cranks come in 2.5mm increments?

Heck, why are bike components measured in millimeters in general?


...because it does matter.

Guys, does 5mm reallly make that much of a difference? Take out your ruler and look at it. That's less than a 1/4 of an inch. I bet if I put two cranks out on a table (not next to each other) and have you look at them, you're going to be able to tell the difference.

I can't tell the difference between a tire inflated to 130psi and one inflated to 90psi just by looking at it either. You can tell subtle differences in your components when you actually use them though

I'm looking to upgrade my crankset and I want someone to explain the benefits/disadvantages of having a shorter crank arm set up. I have 170mm now, but I found a good 165 crankset with a 46t chain ring (I have a 46t chain ring with 170mm arms). My gear ratio is 46/17 fixed. Thanks.

Have a look here: http://www.cptips.com/crnklth.htm

Guys, does 5mm reallly make that much of a difference? Take out your ruler and look at it. That's less than a 1/4 of an inch. I bet if I put two cranks out on a table (not next to each other) and have you look at them, you're going to be able to tell the difference.

Yeah, it does make "that much" of a difference.

Hey, a difference in frame size is only what, an inch? Why bother getting a frame that fits you correctly?

will your legs really feel that tiny difference? Anyone have experiences with two similar bikes with different crank arm lengths?


Yes and yes. It's not a huge difference, but it's definately noticeable.

Yes and yes. It's not a huge difference, but it's definately noticeable.

+1. absolutely. try it.

i've been on 165-180mm arms on different bikes, 165-170mm and 175-180 on otherwise identical bikes. there is a difference. 2.5mm is fairly subtle, but 5mm is immediately apparent.

Unless I have a SRAM crank or a Power Meter my results aren't going to mean anything.

it is a noticeable difference, and it will **** with your seat height too. I run 172.5s on my roadie, and when i tried 165s on my fixed gear, i can take pretty much any corner at full speed, but get no leverage, and just feel too constricted. that said, i am 6'2" or a bit more, so it makes zero sense for me to be rocking 165. Just learn to rock the bike as you turn (lifting the inside pedal as you turn), get a bike with a higher bottom bracket, or take turns more slowly
effectively: it makes it more difficult to climb, but will give you easier time with high cadences, and corners

im 6.2 with 170mm with 47/18 feels nice but im going to downsize my cog to 16t so im a bit less spinny going downhills full speed. I had a 52t with 165 and cant really tell the difference esept for the ratio change. Not pedal issues tho

I switched from 175 to 170's, am 5'10" 32" inseam, weigh 152, and run a 45x16. It made a pretty big difference in my pedal stroke. I ride SS and not FG, but when pedaling it makes no difference.

I actually have a higher top end with the 170's because I can spin faster and smoother. I spun out at about 30-31mph. I now spin out at about 33mph at a full sprint.

On big hills I can also feel the effects of a shorter crank.... I climb slower now, but where I live, I have to look for hills to climb so its not a huge issue for me.

I did not think 5mm would make that much diff either, but for me it was very noticable.

Guys, does 5mm reallly make that much of a difference? Take out your ruler and look at it. That's less than a 1/4 of an inch. I bet if I put two cranks out on a table (not next to each other) and have you look at them, you're going to be able to tell the difference.
It doesn't make a large difference in pedaling effort, but it does make a significant difference in how far you can lean in corners.

So after going through these comments, I'm going to pass on moving down to 165's just to get a good deal. I like the way my bike rides now, so I'm sticking with what I've got. Still going to upgrade soon, but staying at 170. Thanks for the input. Of course, don't let me stop any of you that still need to get involved.

in terms of proper form, the shorter cranks lessen the amount of bend at the knee at the top of the pedalstroke, which is good. seat height can achieve that too, but relying on that adjustment alone means you're leg is further extended at the bottom of your stroke, which isn't so good.

the trade off is, as others pointed out, the amount of torque and leverage you get. 5mm is noticeable, but its not like switching to 165s is going to make your dreams come true.

I have two bikes: one with a 170mm crank and the other with a 175mm crank.

Whether it matters or not, I have a 32" inseam.

My 170mm crank spins so much nicer than my 175mm crank, especially out of the saddle.

I'd like to try a 165mm crank, and I think I will, soon.

167.5

is there a measurement to determine optimal crank fit?
I should consult my zinn book.

is there a measurement to determine optimal crank fit?
I should consult my zinn book.

the rule of thumb is:

165mm.
170mm if you think youre tall.

the rule of thumb doesnt work.

is there a measurement to determine optimal crank fit?
I should consult my zinn book.

Peter White Cycles has a calculation that worked well for me.
"...18.5% of the distance from the top of the femur to the floor in bare feet should be the crank length. ..."

Here's a link to his bike fit article:
http://www.peterwhitecycles.com/fitting.htm

I just moved from a 175mm to 160mm and it feels great.

theres always some odd balls, but does the ratio between the length of leg above the knee and below the knee vary much in the majority of the population?

According to this site:
http://www.makemetaller.info/index.php?topic=293.0

"The femur/ tibia percentage ratio from individual to individual normally falls from 52:48 UP to 56:44."

I'm not sure which way having a high/low ratio would change the equation. Any experts out there?

ok this is what zinn has to say:

"generally, road crankarms come in 2.5mm length increments from 165mm to 180mm - although 167.5 is often hard to find. Longer than 175mm can usually only be found on high-end cranks, and Campagnolo has stopped making crankarms longer than 175mm in any model. It is possible to find 185mm and even 200mm and longer or 160mm or shorter from some small manufacturers.

Given that there is no consensus on ideal crank length, I will give you a simple selection method that works well when buying stock-sized bikes and cranks.

frame size:

less than 46 = 165 or shorter
47-49 = 167.5
50-53 = 170
54-57 = 172.5
58-60 = 175
61-63 = 177.5
64 or larger = 180 or longer

If your riding is focused on time trials, triathlons, or hill climbing, try 2.5mm longer than the recommendations give here.

I have done numerous crank-length tests for VeloNews, and the results show that 1) there is no one crank length that works for a given body size and 2) standard stock crank lengths are arbitrary. It is worth experimenting to see what you like."

So, according to zinn, I should be using a 172.5mm crank. But according to peter white, I should use a 170mm crank.

it seems that the most acute knee angle for most at 6' 0" and taller with even 175mm is markedly more obtuse than someone sub 5' 6" with 165mm.

...So, according to zinn, I should be using a 172.5mm crank. But according to peter white, I should use a 170mm crank.

in conclusion, your results may vary and use what feels best.

Yep. I'd say if you feel like your legs are taking a trip around the world every spin, get shorter cranks. Or if you feel like you're riding a circus bike get longer cranks.

It'd be nice if it was easy to try out various sizes and then pick the best one. But that's not going to happen at most LBSs.

theres always some odd balls, but does the ratio between the length of leg above the knee and below the knee vary much in the majority of the population?

In short: Yes

In short: Yes

i imagine it changes as height changes, but how much? give me the long version and the data!

i imagine it changes as height changes, but how much? give me the long version and the data!

Now WHERE the h*ll am I gonna get that data from? WHY the h*ll would spend hours researching it for you?

I'll put it to you this way, if road bike manufacturers could get away with making S/M/L/XL bikes like MTB manufacturers do then they would totally do it. It's much easier and cheaper to design, manufacture, and sell 4 sizes of a bike than 8 (ex: 48, 50, 52, 54, 56, 58, 60, 63cm).

Now WHERE the h*ll am I gonna get that data from? WHY the h*ll would spend hours researching it for you?

I'll put it to you this way, if road bike manufacturers could get away with making S/M/L/XL bikes like MTB manufacturers do then they would totally do it. It's much easier and cheaper to design, manufacture, and sell 4 sizes of a bike than 8 (ex: 48, 50, 52, 54, 56, 58, 60, 63cm).

since you said you had a short version, i assumed you had a long version with some sort of elaboration on 'yes' with some sort of evidence or experience. how does frame size relate to the ratio in question?

since you said you had a short version, i assumed you had a long version with some sort of elaboration on 'yes' with some sort of evidence or experience. how does frame size relate to the ratio in question?

I'm too tired to argue with the internet tonight.


You win, internet. You win.

I'm too tired to argue with the internet tonight.


You win, internet. You win.

in short, if you know anything, sleep and come back around!