170mm v 175mm Cranks
Discussion
tjdixon911 said:
I need some new Cranks on my 29er, currently its running 175mm cranks but I have seen the equivalent in 170mm for a bargain price.
Whats the difference apart from 5mm?
is one more suited to a taller rider than the other or is it just personal preference?
In theory, longer cranks are more suited to longer legs. Also, shorter cranks means fewer pedal strikes if you've got a particularly low bottom bracket. Lastly, thanks to the rules of physics, you'll have to pedal slightly harder for the same output with shorter cranks.Whats the difference apart from 5mm?
is one more suited to a taller rider than the other or is it just personal preference?
I'm not sure how much difference 5mm is going to make though?
Most cranks are 170, 172.5 or 175. Larger bikes sizes, broadly, get longer cranks.
You'll either produce the same power or will gain a bit. You'll be a bit more aero and also gain ground clearance.
Shorter riders or people with knee, hip or general flexibility problems can benefit from shorter cranks.
You will have to adjust your saddle a bit after changing.
You'll either produce the same power or will gain a bit. You'll be a bit more aero and also gain ground clearance.
Shorter riders or people with knee, hip or general flexibility problems can benefit from shorter cranks.
You will have to adjust your saddle a bit after changing.
E65Ross said:
It can play a very large role in ergonomics. If you've been riding 175mm I wouldn't drop to 170mm. saddle height would have to change, that then effects aerodynamics, handlebar reach, drops etc.
Someone has to be the one to point this out Ross, and I'm ever so sorry, but...The OP is talking about a 29er. No real issues with aerodynamics to worry about deep in the woods, no drops (unless the rider has gone totally nuts and retro-fitted them?) and a drop of 5mm in saddle height equates to something like 2mm to 3mm in terms of reach.
So long as the shorter cranks don't affect him comfort-wise, and I doubt 5mm will affect the position all that much, being as how you spend a lot of time out of the saddle anyway on a MTB, then there may be some slight improvements over the original cranks. Lower saddle height (even just 5mm) brings your 'as ridden' CoG down slightly, the shorter crank means the pedal is now 5mm further from the ground at the bottom of the stroke, increasing clearance. And who's to say that the bigger cranks are the right size for the rider anyway? So many people fanny about with upgrades of wheels, handlebars, stems, seatposts etc that are aimed solely at reducing weight, yet they blindly accept the "one size fits all" approach that manufacturers apply to important ergonomic components like the cranks. He may well find that the shorter cranks are a better fit for him, besides which, there's not so much of a 'fitting industry' with MTBs. Yes, if I take a road bike to a 'fitter' they will be able to recommend crank length for me, but there just aren't as many fitters claiming to know the 'secret' to a good MTB fit, because MTBers move about on the bike so much more than when they are riding road bikes.
OP, if the price is right, buy the smaller cranks. Seriously. Get a tape measure out, and remind yourself just how small a measurement 5mm is. Compensating for such a change is literally a 2 second task with your seatpost QR lever, and I doubt you'll even notice a difference if you ride 'proper' MTB trails. Think about how much time you spend in one single solid position off road. You shouldn't, because you shift your weight about a lot more to control the bike. Completely different to time spent trying to develop a static, solid position on a road bike.
yellowjack said:
Magic919 said:
Saddle would go up, not down.
Really? I'd assumed that shorter cranks would increase the distance between saddle and pedal. This would leave the OP needing to find longer legs, or knocking his saddle down to compensate, no?Banana Boy said:
There's an interesting article in this week's Cycling Weekly about this very subject that suggests shorter cranks are better for power output!
Going back to the roots. Old school rules dictated that 170 was right for almost everyone. I'd only deviate if you have long femurs.scherzkeks said:
Banana Boy said:
There's an interesting article in this week's Cycling Weekly about this very subject that suggests shorter cranks are better for power output!
Going back to the roots. Old school rules dictated that 170 was right for almost everyone. I'd only deviate if you have long femurs.Tbh shorter cranks actually makes more sense than initially considered when you stop thinking about whats going on through the wheel and gears and think more about yourself as an engine! When you think, most high performance engines are large bore and short stroke it starts to make sense - after reading that article, I wouldn't be scared of 165mm cranks! (Although at only 5' 5&3/4" tall with a 29" inside leg I am already a short stroke motor!
)Sorry for mixing units. IMHO................
If you are 5foot 8in and over, (29in inside leg for trousers) - 172.5 cranks should be considered.
When British (Christian) units ruled the waves, the standard crank length was 6-3/4 inches, which works out at 171.5mm. So 172.5 matches.
Originally, our continental friends established 170mm as their standard, but introduced 172.5 later on.
Sadly their does not appear to be much choice in the way of crank lengths today.
If you are 5foot 8in and over, (29in inside leg for trousers) - 172.5 cranks should be considered.
When British (Christian) units ruled the waves, the standard crank length was 6-3/4 inches, which works out at 171.5mm. So 172.5 matches.
Originally, our continental friends established 170mm as their standard, but introduced 172.5 later on.
Sadly their does not appear to be much choice in the way of crank lengths today.
I'm really not convinced there's too much in it!
When I built up my lad's bike, I bought a set of 165mm Shimano Zee cranks on Pinkbike. When I went to pick them up, it turned out they were actually 170mm, but given that they were at a very good price and I was working to a set budget, I figured he'd just have to grow into them.
He's 4'5", and shows absolutely no signs whatsoever of being uncomfortable on 170mm cranks. No rocking or anything, and I've proudly watched him clear climbs going through the middle of adults who've stopped to walk, so it doesn't seem to be holding him back at all.
When I built up my lad's bike, I bought a set of 165mm Shimano Zee cranks on Pinkbike. When I went to pick them up, it turned out they were actually 170mm, but given that they were at a very good price and I was working to a set budget, I figured he'd just have to grow into them.
He's 4'5", and shows absolutely no signs whatsoever of being uncomfortable on 170mm cranks. No rocking or anything, and I've proudly watched him clear climbs going through the middle of adults who've stopped to walk, so it doesn't seem to be holding him back at all.
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