170mm cranks vs 175mm...
- Thread starter bergsnj
- Start date
JerseyPete
Well-Known Member
https://www.mtbnj.com/forum/threads/inseam-to-crank-arm-length.18860/
I wonder the same thing, can 5mm really make a difference?
I wonder the same thing, can 5mm really make a difference?
Karate Monkey
Well-Known Member
Go big [small] or go home.
02camaro
Well-Known Member
ive been riding 170 for the past 3 years. my sb5.5 which came with 175 got immediately switched to 170 because of to many random strikes. im sure you could adapt your riding style with 175 but there doesnt seem to be a benefit to riding 175s.
when holding the two cranks side by side there is nearly a 1/4in difference but when riding it seemed to make a huge difference
when holding the two cranks side by side there is nearly a 1/4in difference but when riding it seemed to make a huge difference
That is a 1/4" difference in length, so the seat goes up 1/4". At the top, the knee doesn't come up as far (if i'm picturing it right,
it is 1/2" less) - On my fatbike, this might be more comfortable because i'm running the seat a bit low because no dropper.
mechanical advantage is reduced - not sure 3% makes a difference.
Never thought about the pedal strikes - i just thew a few extra psi in the shock to reduce sag.
it is 1/2" less) - On my fatbike, this might be more comfortable because i'm running the seat a bit low because no dropper.
mechanical advantage is reduced - not sure 3% makes a difference.
Never thought about the pedal strikes - i just thew a few extra psi in the shock to reduce sag.
pkovo
Well-Known Member
I run 170mm on one bike, 175mm on all the others and although it's only 5mm, I can feel the difference from a pedaling perspective. I have relatively short legs and the 170 feels slightly more natural. It's definitely not a huge deal and not enough to make me swap out my 175 cranks.
I don't know for sure if I would notice the 5mm difference with rock strikes, because I've not swapped the different sizes on the same bike, however I suspect I might. I say that because fairly recently I tried to run 27.5 plus wheels/tires on my hardtail and the increased rock strikes were quite noticeable. I measured the BB drop, but can't remember exactly what it was. I believe it was more in the ballpark of 10mm or even slightly more, but still I remember being annoyed and surprised at how noticeable a relatively slight drop was. So....from that I would deduce 175 to 165 would definitely be noticeable to me, and 175 to 170 might be.
I may have adjusted to it eventually, but it gave me an excuse to build a new bike around the 27.5 wheels, rather than just selling them like a normal person.
I don't know for sure if I would notice the 5mm difference with rock strikes, because I've not swapped the different sizes on the same bike, however I suspect I might. I say that because fairly recently I tried to run 27.5 plus wheels/tires on my hardtail and the increased rock strikes were quite noticeable. I measured the BB drop, but can't remember exactly what it was. I believe it was more in the ballpark of 10mm or even slightly more, but still I remember being annoyed and surprised at how noticeable a relatively slight drop was. So....from that I would deduce 175 to 165 would definitely be noticeable to me, and 175 to 170 might be.
I may have adjusted to it eventually, but it gave me an excuse to build a new bike around the 27.5 wheels, rather than just selling them like a normal person.
Lol'ed at adding pressure to reduce pedal strikes.
i am switching from 175 to 170 tonight.
serviceguy
Well-Known Member
You're picturing it wrong. The knee comes up only 5mm less (1/4" is a about 6.25 mm).
A Potted Plant
Honorary Sod
I'm going 170 on my current build long low and slack needs that
but if i move the bottom up, then move the saddle up to maintain an optimum bottom location, then isn't the result at the top 1/2" ?
if i didn't move the seat to adjust the bottom, then sure. but then again, i might have to move the seat forward a bit if there is more post sticking out....
so that changes stuff too....ugh. anyway - i'll give it a try on the next round of stupid purchases.
bergsnj
Well-Known Member
yea thats what i'm thinking, i have 175mm cranks on an SB150 and I'm thinking i should swap them for 170's. These bikes come stock now with 170 cranks (2020 model year) but mine is a 2019 built up with the cranks from my previous bike.
serviceguy
Well-Known Member
If you reference the bottom of the pedal stroke yes because your total displacement is now 340mm instead of 350mm. I thought you referred to the bike frame or BB.
jklett
Well-Known Member
I thought that's how you go blind or am I mixing it up with something else?
TimBay
Well-Known Member
I think it's the bottom bracket that tends to sag with wear.
There has to be a mechanical advantage or disadvantage, length of lever and stuff.
Pat?
@Blk06CompIRL had 165’s on his new build and it felt like a hamster wheel. You couldn’t generate any power on a punchy “up” move. He swapped them out for longer but was also running a tiny front ring which also was changed. So I’m not sure which was ultimately the main reason for the odd feel.
Pat?
@Blk06CompIRL had 165’s on his new build and it felt like a hamster wheel. You couldn’t generate any power on a punchy “up” move. He swapped them out for longer but was also running a tiny front ring which also was changed. So I’m not sure which was ultimately the main reason for the odd feel.
shorter is a disadvantage, but can be made up with the chainring (or any other gear). It is a class 2 lever, ratio of the arm to length to the radius of the chainring.
i've been thinking about this a bit more - probably need to talk to the bike fit gurus - there has to be an optimum high and low position (or bend angle?) for the knee.
Might be different for each person? does that mean some sort of ftp test to optimize?
I'd think i'd opt for more power/efficiency, and better form/technique, than just shortening the crank arms to avoid strikes.