Crank arm length - would a novice notice a difference?
Discussion
I found a bargain 175 crankset and pondered this point for a while replacing the 172.5 I had before. Aft adjusting the saddle height I don't notice the difference.
To reinforce that, I was amazed to discover that I already had a 175 on another bike I recently stripped down but only found out when I took the crankset off and saw the markings.
The conclusion is that you would struggle to tell the difference if you knew, if you didn't know you likely wouldn't be able to tell. 2.5 mm isn't a lot when you think about the differences you might encounter when changing shoes, pedals, socks etc. anyway.
To reinforce that, I was amazed to discover that I already had a 175 on another bike I recently stripped down but only found out when I took the crankset off and saw the markings.
The conclusion is that you would struggle to tell the difference if you knew, if you didn't know you likely wouldn't be able to tell. 2.5 mm isn't a lot when you think about the differences you might encounter when changing shoes, pedals, socks etc. anyway.
Double the difference - each crank arm is 2.5mm different - so in theory your saddle would go up 2.5mm, and your foot will be 5mm lower relative to your body/other foot at the top of the stroke.
It's more likely to cause problems going to a longer crank as it means you have to bend your hip/knee more. Shorter cranks are a thing for some when it comes to getting more 'aero'. As to whether you'll notice the difference, maybe, maybe not, depends on you. Personally I'm a big fan of shorter cranks, ymmv.
It's more likely to cause problems going to a longer crank as it means you have to bend your hip/knee more. Shorter cranks are a thing for some when it comes to getting more 'aero'. As to whether you'll notice the difference, maybe, maybe not, depends on you. Personally I'm a big fan of shorter cranks, ymmv.
I'm also interested in knowing how people find this, I'm current running a 170mm crankset, although I'll be ordering a new bike within the next few months and my bike fitter has advised I opt for a 165mm crank (I am only 5ft 6in, mind!). But I do a fair bit of riding (circa 9 hours a week) and so I even notice a few mm difference in saddle height when I changed shoes which had a different sole thickness!
A novice might notice the difference but, after adjustments, that would be dealt with and she could ride just as she did before
A serious cyclist would more likely notice the difference and, after adjustments might notice differences in the effect the different crank length has. Those differences could net out to zero, or could be sufficient enough to make the difference between a PB and not a PB on any particular ride
The serious cyclist is likely to seek advice on such changes from people that know about these things and experiment to find the optimum. For the novice, there are probably bigger priorities
A serious cyclist would more likely notice the difference and, after adjustments might notice differences in the effect the different crank length has. Those differences could net out to zero, or could be sufficient enough to make the difference between a PB and not a PB on any particular ride
The serious cyclist is likely to seek advice on such changes from people that know about these things and experiment to find the optimum. For the novice, there are probably bigger priorities
ferrisbueller said:
Looking at replacing the crank set on a bike. Currently have 172.5mm arms on it. Would I notice going to 170mm? The shorter ones appear more plentiful and therefore a good bit cheaper.
You'll climb better in the seat with the longer arms. I've currently got 175 on the chain side and 170 on the left but I'm weird...Of course there's a Sheldon article all about this in which he discusses mixing lengths and the impact on gearing... longer levers = lower gear.
https://www.sheldonbrown.com/cranks.html
https://www.sheldonbrown.com/cranks.html
WinstonWolf said:
ferrisbueller said:
Looking at replacing the crank set on a bike. Currently have 172.5mm arms on it. Would I notice going to 170mm? The shorter ones appear more plentiful and therefore a good bit cheaper.
You'll climb better in the seat with the longer arms. I've currently got 175 on the chain side and 170 on the left but I'm weird...
.WinstonWolf said:
You'll climb better in the seat with the longer arms. I've currently got 175 on the chain side and 170 on the left but I'm weird...
Would that not apply either in or out of the saddle ? Bigger torque on a longer lever but as stated above you may suffer on cadence. I suppose it will depend on how much climbing and the ratios available. I'm thinking of a longer crank and bigger chainring for those odd occasions I run out of gears down hill (currently 50/11 max ratio giving about 80kph) however retaining the ability to remain on the larger chainring on the flatter sections. I used to run a 58/42 chainring in the 1980s but I'm not longer that fit !There has been loads of research into this; I have only found stuff saying that shorter cranks are more beneficial. I went down to 170 from 172.5 and found that my average speed went up.
The thinking behind it is that because your lower leg is not going as far down (by 2.5 mm), your seat can go up slightly (2.5mm) to maintain the same leg extension. Because your seat is higher, your back is flatter. The second order of effects are that a shorter crank means that your knee is not pushed up towards your chest as far at the top of pedal stroke, meaning that (for those of us less flexible) power generation is easier.
Shorter crank > Higher seat > Flatter back > More open 'V' between thigh and chest at top of stroke > Faster and more comfortable for me.
The thinking behind it is that because your lower leg is not going as far down (by 2.5 mm), your seat can go up slightly (2.5mm) to maintain the same leg extension. Because your seat is higher, your back is flatter. The second order of effects are that a shorter crank means that your knee is not pushed up towards your chest as far at the top of pedal stroke, meaning that (for those of us less flexible) power generation is easier.
Shorter crank > Higher seat > Flatter back > More open 'V' between thigh and chest at top of stroke > Faster and more comfortable for me.
ferrisbueller said:
WinstonWolf said:
ferrisbueller said:
Looking at replacing the crank set on a bike. Currently have 172.5mm arms on it. Would I notice going to 170mm? The shorter ones appear more plentiful and therefore a good bit cheaper.
You'll climb better in the seat with the longer arms. I've currently got 175 on the chain side and 170 on the left but I'm weird....Bob the Planner said:
WinstonWolf said:
You'll climb better in the seat with the longer arms. I've currently got 175 on the chain side and 170 on the left but I'm weird...
Would that not apply either in or out of the saddle ? Bigger torque on a longer lever but as stated above you may suffer on cadence. I suppose it will depend on how much climbing and the ratios available. I'm thinking of a longer crank and bigger chainring for those odd occasions I run out of gears down hill (currently 50/11 max ratio giving about 80kph) however retaining the ability to remain on the larger chainring on the flatter sections. I used to run a 58/42 chainring in the 1980s but I'm not longer that fit !I'm extremely atypical though...
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