[Closed] smaller cranks: you'll never notice the difference

I think its one of those things some folk notice and others do not.  Some of my bikes are 175 and some 170 and I cannot tell the difference

Yes. Its all in yer bonce.
Or stop skipping leg day.
Or your cassette is 11/34.😀

Yes I noticed the difference even when going to a smaller chainring at the same time as fitting the shorter cranks. But I definately missed leg day!

I notice the difference, but the shorter crank for me makes it easier rather than harder.

I do have an 11-51 cassette and a 32 chainring, but will be looking at a 34 chainring soon.

It's a real thing.

Get a smaller chainring and you'll be fine.

I'm on a 11-46 cassette.
Last summer I was ok on a 34 chain ring ( though it always felt a little too big) - and 175 cranks.
Now its a 32 chainring - the shorter cranks are to stop pedal strikes - that seems to no longer be an issue but long uphills seem much harder ( or it may just have been the very strong South Easterly I was cycling into.

It's just physics. Going from 175 to 165 you need to switch from 32 to 30 to keep the same mechanical advantage. You don't lose any power though because the shorter cranks increase your max comfortable rpm. You also have to raise your saddle slightly - if you didn't then that'll have lost you a bit more torque, seated anyway.

I have 165 and 170. I can feel the difference when going 170 to 165 but not  really when moving 165 to 170. I've ridden 175 in the past and while ok off road my knees didn't like them for long sections sat in the saddle on roads.

avdave2

I have 165 and 170. I can feel the difference when going 170 to 165 but not really when moving 165 to 170

If you're anything like me, that's:

165-170 - "I feel fit today, nothing to do with those cranks"

170-i65 - "Hard going today, must be those bloody cranks"

It’s just physics. Going from 175 to 165 you need to switch from 32 to 30 to keep the same mechanical advantage. You don’t lose any power though because the shorter cranks increase your max comfortable rpm. You also have to raise your saddle slightly – if you didn’t then that’ll have lost you a bit more torque, seated anyway.

Saddle raised, as you are effectively losing 10mm of stroke.
Going down to 30 kind of seems counter productive... I can / would do. But I do understand the physics - you have lost about 7-8% of mechanical advantage
It wasn't the intention in going to 165mm.. I was hoping it would be small enough not to notice.

Or if I ride for a few rides, will I just re calibrate ?

All depends...

If the new cranks are XTR then yes you will notice the difference for ages, it will really bug you you are best off selling them to me as I am still bitter about missing the PSA on them last year 😉

If they were XT or SLX then .... frankly just get on with it. ( I've already got 165mmm SLX cranks and am perfectly happy with them (apart from the weight) so dont want to buy yours.

Leaving that aside, when I bought the 165mm cranks I also got a 28t chain ring to go with the 51t cassette. Love it to bits and cannot understand how people manage with 30 or even 32t

Means I now only have 11 gears, but I don't care as one of them is sooooooo low 🥰😍🤩

I don't really feel any difference in gearing- I guess because I'm not a "do this in 3rd gear" sort of a person, I just use whatever gear feels appropriate. OTOH one of my bikes is right on the margin for dropper post length and I think it might just be enough to push me over.

I do probably crash a bit less though.

I had 160s on an old dh bike- very short and I liked to pedal it up hills, and kept kneeing the fork crowns. They felt really weird, at the time, not for pedalling but for the short stance in the attack position.

“ Going down to 30 kind of seems counter productive… ”

It isn’t. Once you’re used to the shorter cranks you’ll realise your natural cadence is proportionately faster and your max cadence likewise.

I put Eagle GX 165 on my ECR and I felt kind of flat and powerless all the time. I then swapped them for a pair of NX 170s on and the whole thing felts loads better. That’s wasn’t what I expected as I was quite happy moving from 175 to 170s in the past.

Pedal circumference on 165mm. is around 104 cm as opposed to 110 cm for 175mm. cranks.
Faster cadence to match the bigger crank. Force x distance = work done.

I notice the difference, but the shorter crank for me makes it easier rather than harder.

This. I can certainly tell the difference, especially in the very lowest gear cranking up a steep hill. With 165s I can just keep going. 170s and up I run out of power.

I only notice it in the 46 tooth rear - when if feels like I am pushing too much load, soo I can't spin - and then I just want to give up. It is a huge difference to me - and makes me feel a bit pathetic.
I have slow been trying to push bigger gears, trying o get fitter. Last year was mainly done on the same set up but with a 34 ring.
28 ring will mean I spin out too much on the flatter or down hill sections.

I guess it is out to buy 30 tooth chain rings, swap back the old cranks - or buy a larger cassette ( but finding one is a challenge)

I've just dropped from 175 to 165

The only difference I've noticed is less pedal strikes and needing to raise my saddle a bit

I'm currently on 170mm/32T, have 165mm and 30T waiting to be fitted. First bought the 30T 'cause at the end of a long hilly ride I'm struggling on tricky bits that need a bit of momentum (I live in a flat area so don't get used to it). Then thought 165mm would be nice to have a few less pedal strike scares, but that's going to cancel out my smaller chainring.

Wondering if I should go straight to 165mm/30T, or try just the 30T first.

I went from 172.5 to 165 on my gravel bike, few months ago. I did notice the difference at first, wasn’t a negative, if anything it felt slightly quicker uphill. But I did got to slightly bigger rings at the same time, so it might’ve been a combination of the 2 changes. Probably was come to think of it.

One thing is, it can be pretty unintuitive- like, a lot of us like to mash a higher gear, right? It's generally the wrong thing to do, unless you're a massive diesel engine of a rider, but it feels strong, all whooomph whoomph whoomph. Whereas spinny spinny generally feels soft and low impact but is generally better. So you could easily make a change that actually works better, but feels worse, or vice versa

I would always go for a 165mm where I can/have the choice. The biggest problem is that most shops don't actually stock them and some manufacturers don't even offer them.

Saddle raised, as you are effectively losing 10mm of stroke.

'We're all different' disclaimer.. I use 170 and 175, have tried 165s and have 2 bikes with EBBs so maybe I'm just past caring about 5mm changes here, but fwiw I think I care more about my saddle to pedal relationship X-Y at the 3pm position, when I'm pushing hardest. At the bottom of the stroke it doesn't matter so much to me. So shorter cranks = a slightly further back saddle on a road bike, which also adds to saddle top to BB distance a little anyway. On the MTB I go between 175 and 170 w/o change of saddle to BB axle. If it were 175 to 165, maybe a similar move to the road bike, back a bit + up a bit if needed.

As mentioned earlier shorter cranks = shorter lever.
Torque (NM) = force X distance

Shorter cranks = shorter distance

As also mentioned earlier a smaller chain ring will help as the diameter of the chain ring also has an effect on lever length.

Actually that might make a good maths/ mechanical principles assignment question ......

The reason to choose a shorter crank is physiological, we're not all 6'+ with identically proportioned limbs are we..

I know My knees get along better with the slightly reduced range of motion a 170mm or shorter crank requires.

It also helps if you're more of a spinner than a masher...

As mentioned earlier shorter cranks = shorter lever.
Torque (NM) = force X distance

Shorter cranks = shorter distance

As also mentioned earlier a smaller chain ring will help as the diameter of the chain ring also has an effect on lever length.

Actually that might make a good maths/ mechanical principles assignment question ……

Sure - basic physics.
I will try a smaller chain ring - but hope as the spring comes my enthusiasm will also mean that the differences will lessen.

28 ring will mean I spin out too much on the flatter or down hill sections.

I have 165mm cranks and 10-46t cassettes on all my MTBs.

The heavier, enduro-y bikes have 28t rings and the lighter trail bike has a 30t ring.

I never really spin out on the flat, but I do have one less tooth on my small cog compared to you.

I have slow been trying to push bigger gears, trying o get fitter. Last year was mainly done on the same set up but with a 34 ring.

Pushing bigger gears in itself doesn't make you fitter, you need to be doing more total work as well. Going faster in other words.

(Pushing bigger gears can work for specific training sessions and to meet specific needs, but doesn't sound like it in this case!)

I’m currently on 170mm/32T, have 165mm and 30T waiting to be fitted. First bought the 30T ’cause at the end of a long hilly ride I’m struggling on tricky bits that need a bit of momentum

I think you've said something slightly different to what you meant. ( if you keep the cassette size the same) having a smaller ring will give you less momentum not more. Small ring is great for keeping going very slowly up very steep hills and/ or at the end of the day. They're bad for stuff that needs momentum as you don't build up that momentum past a certain speed.

I love my 28/51 to bits, but know full well if there's a gnagery momentum section coming up then I need to move to a higher gear.

crank length is clearly an important part of bike fit.

but let's not pretend that the usual range of 175-170-165 comes close to offering a suitable fit for the usual range of leg lengths.

the reason that lots of people don't notice much difference between 175-170-165 is because it's about a 5% difference - about the same as between an 20" frame and a 19" frame.

fwiw, i've got the longest legs in the world : 36", and i use 165's.

MsWife uses 140's, i'd need 230mm cranks to see how bad 165's must feel for her.

I think you’ve said something slightly different to what you meant

Quite possibly... yes I see now. I'm not sure how leg tiredness works but when my legs (not whole body) are tired I feel I could sustainably achieve more momentum by spinning an easier gear faster, or the same for less effort.

“ Going down to 30 kind of seems counter productive… ”

In what way?

FWIW I put 165mm cranks on at Christmas as I was getting a lot of pedal strikes (probably because I put a -2 headset on early last year 🙂 ).

I also dropped to a 30t front ring, based on 'losing' some torque.

No issues whatsoever and while I was a bit concerned of losing the top end, running SRAM & a 10t smallest cog means it's rare I'm in top. And it did mean yesterday I could still climb over for the last descent with 5000ft done.

^
a) Not running SRAM - but Shimano - 11-46
b) two 30 chain rings ordered to cover both bikes
c) then found I had a 11-50 SunRace cassette - so that could have solved the problem. That will go on one of the bike today

So shorter cranks are actually more efficient

https://www.pinkbike.com/news/why-shorter-cranks-are-better-according-to-science.html

A shorter crank means less leverage, but less movement might be more efficient. I prefer a longer crank even though I have short legs. My experience of shorter cranks is much like the OP's.

It depends on the length of your leg as well, the calculator in the Pinkbike article suggests I should run a 180mm crank so my actual 175 could be deemed short. I work on the basis that I've never had an issue with 175, if it ain't broke

30 rings on ...
Let see how that works !
Will report back later this week ...