Not being very savvy at physics, I was wondering what sort of difference it makes going from 165 cranks to 175. Obviously the 175s will make for a larger stroke (if that's even the right term), but what else? It affects the gear inches as well, right?

I switched and after 30 minutes I had no idea anything was different... I haven't had a pedal scrape yet on my 165, but that could also be because I switched to clipless at the same time...

all i know is that it creates a very small difference in your gain ratio. the difference is extremely slight and i don't think you'd notice much of a difference.

the avoidance of pedal-strike whilst cornering.

thanks guys. i know pedal strike will be an issue, but it sounds like not much else will change.

Going to a longer crank arm will change your ability to spin at high RPMS. You might not notice much of a difference at low RPMs but when you get above 90RPMs you'll feel it....all of that will require you to basically rebuild your pedal stroke from the hips.

That being said it's a biomechanic thing. Without knowing your inseam length, bike fit/setup, experience who can say.

Pedal strike will probably be the biggest issue.

i recently went from 170 to 165. i'm pretty short - hovering between 5'5" and 5'6". 165s were much more comfortable. i did not notice the little bit of leverage that you lose with shorter cranks, but i did notice that it's easier and more comfortable to spin, especially when down in drops.

there's a tiny bit less movement in your legs, since you're moving your feet in a smaller circle.

I've heard that you will notice when cranks are too long, you won't notice if they are too short.

Please assimilate this advice as you would any from a stranger on the internet.

it changes your ratio not one bit. that is dictated by the gears. a longer crank will let you produce more torque and possibly have an easier time turning a large ratio at slower speeds. but the trade off is having to move through a bigger circle (possibly more slowly).

i like 175's, and i notice a difference over 170's. i have one of each on my two bikes now, and im hunting around to get 175's on the campus bike so they will both be the same again.

I changed from 165s to 175s, because I got a good deal on them. I was kind of suprised I prefer them. I don't have to put the seat all the way back to be comfortable & I still haven't had pedal strike. Now on 165s I feel like a bear on a tiny circus bike.

If you're going to correct someone, make sure you're correct.

Gain ratio most certainly does change with crank length.

(wheel radius / crank length) x (front gear / rear gear) = gain ratio

i'd argue that it doesn't change your gear inches. one chainring rotation equals so many inches of wheel rotation. the crank arm length provides torque; a longer arm will produce more torque but rotate slower. it won't effect the gear inches part of your ratio but it will have an effect.

Longer cranks make hill climbing easier at the expense of easier spinning on the flats.

Why does the truth make me laugh?

Huh?

=====

A friend has a very nice fixie conversion.

He got pedal strike with 175mm cranks.

A frame designed for fixed gear has a much higher bottom bracket, and this reduces the probability of pedal strike almost to zero.

Let's see.

Yesterday, Pi Day.

3/14

What did we learn from Pi Day?

A 175mm crank has a diameter of 350mm and a 165mm crank has a diameter of 330mm (did that in my head...better check it).

350 X 3.141592 equals a larger number than 330 X 3.141592.

What else?

Distance equals Time times Rate.

D = TR.

In one case, the pedal and the foot on the pedal must travel 350 X 3.141592 every time the crank goes around, and, in the other case, the pedal and the foot on the pedal must travel 330 X 3.141592 every time the crank goes around.

If the crank must go around in its circle 120 times in a minute in order for the bicycle to go as fast as the rider wants it to go, how much further will the foot on the 175mm crank travel in a minute than will the foot on a 165mm crank in the same minute?

Or, given that the foot on the pedal can only travel so far in a minute, how many more revolutions per minute would a 165mm crank make, for the same foot speed, than would a 175mm crank?

summed up the whole thread right here. that's the biggest thing i've noticed. i went from 175 to 170 and haven't noticed much, but when i'd go from 175 to 165 on my friend's bike, it'd be a fairly noticeable difference. i'm happy with the 170 right now though it is true at higher cadences, a smaller arm could but a little more comfortable, but i definitely like the leverage for hills.

if my city were flat though, there'd be no question about going 165 or even 160 if i could find it.

Have 165 on fixed, and on road bikes have 170 & 172.5 (on my climbing bike)

As Boson Fixed said it is easier to spin at high cadence with shorter cranks--no problem spinning on the fixed (maybe I'm being pulled along) and picking up the cadence when the speed ups, but on my 172.5 bike I usually have the slowest cadence in the group but can stand and torque on hill ciimbs, and ride a big gear.

I went to Sheldon Brown's online gear calculator and ran the gear inches with a 165mm, 170mm and 175mm crank.

If the online gear calculator worked correctly, changing the crank arm didn't change the gear inches.

https://sheldonbrown.com/gears/

how could it possibly cgange your gear inches
?

Yeah, the distance a bike goes after one revolution of the crank or chanring is the same no matter the length of your cranks.

because as you increase the radius of the circle being made by the crank arms, the distance that your leg travels increases.

The increased leverage you get from the longer cranks is countered by the bigger diameter circles you must pedal on the downhill spin. But as already mentioned, the increased chances of a pedal strike in the turns makes them a dubious choice. Gerry

whoops whoops whoops, I was talking about gain ratios. my bad.