crank arm lengths

[Profpointy]

how about a compromise?
...one of each

 

[ColinJ]

how about a compromise?
...one of each

Works for me!

 

[boydj]

Umm, you and numbnuts are are reporting the notion that trauma on knees over time will be reduced if a shorter crank is used. This is obviously good, so is it the case that cyclists should use a crank as short as possible to prevent injury later in life, given their physical measurements??

I previously thought that the longer the crank the better as the extra length allows extra mechanical advantage when driving the cranks hard to achieve more speed.

I think i favour being kinder to my knees, but by having shorter cranks, would i not then need to put greater physical effort on driving the crank to achieve movement.... it then follows, would i then not still be causing trauma to the knees but in a different way?

Cycling does not cause 'trauma' to the knees - as a form of exercise, it's relatively kind to the knees. My main point is that over time shorter cranks will result in slightly less wear and tear in knee and hip joints by a small reduction in the range of movement. In my opinion, 170mm is not short enough for people under about 5'7".

As for reduced mechanical advantage, all that happens is that you change gear at slightly different speeds, so the only impact is at the top and bottom of the gear range.

 

[Profpointy]

to boyd & 139....

You may not be disagreeing necessarily though you are saying different things as it were.

Obviously for a given set of cogs, smaller cranks will be more force on the knees - possibly straining a touch more, but if you change gear so force is the same, but twiddle em round more, as you can with smaller cranks, then similar effort but less force.
Gearing overall needs to be "equalised" so to speak for a fair comparison

 

[Profpointy]

Works for me!

I meant on the same bike !
And yes, I was being silly

 

[ColinJ]

I meant on the same bike !
And yes, I was being silly

Follow my link - mine are on the same bike!

When I tripleise my other bike, I will have a spare 175 mm crank so I will swap out the shorter one from the bike in question.

 

[Kins]

I went from 175mm to 165mm crank lengths and felt the difference on my main rode bike. 45, 6ft and buggered up knees from football.

 

[shouldbeinbed]

Ah, not our esteemed Cambridge correspondent at the swimming baths then

 

[simon.r]

I'm 6'2" and use 165mm cranks because I have an arthritic knee that I am unable to bend fully (the result of a motorbike crash years ago). The difference between 165mm and 175mm cranks is very noticeable to me.

 

[bigjim]

You do know that at least 50% of the population and probably more have one leg shorter than the other? But they never notice.

 

[ColinJ]

You do know that at least 50% of the population and probably more have one leg shorter than the other? But they never notice.

100% of people have one leg shorter than the other! (Unless you believe that some people have legs matched to the exact number of atoms ...)

My left leg is about 2 cm shorter than the right. My pelvis is noticeably tilted when I try to stand up straight, and my shoulders lean one way, and my head the other to try to compensate.

I used to put shims under my left Look cleat to make up half the difference, but that doesn't really work as well for SPD shoes because the metal cleat then sticks out.

 

[simon.r]

100% of people have one leg shorter than the other! (Unless you believe that some people have legs matched to the exact number of atoms ...)

My left leg is about 2 cm shorter than the right. My pelvis is noticeably tilted when I try to stand up straight, and my shoulders lean one way, and my head the other to try to compensate.

I used to put shims under my left Look cleat to make up half the difference, but that doesn't really work as well for SPD shoes because the metal cleat then sticks out.

@ColinJ I'm in a similar position (no pun intended!) and a couple of years ago was referred to the orthotic department of my local hospital. They sorted me out a pair custom insoles, deigned to compensate for the difference in leg length and also for my poor posture bought on by a natural tendency to try and compensate for the difference over the last 30 years.

The insoles have made a world of difference - less knee pain and a much better natural posture (to the extent that people are asking me how come I've got taller at the age of 50). (The insoles add about 2mm of height, so it's not down to them).

I think I've posted similar before, but I'd really recommend anyone with mild physical deformities (to use what is probably an old fashioned and non PC phrase) to sort our an appointment with their local orthotic department.

 

[bigjim]

Wikipedia told me 50% but whatever. Just makes me wonder then how much difference crank length makes. I don't think I know the crank lengths on my bikes.

 

[winjim]

Wikipedia told me 50% but whatever. Just makes me wonder then how much difference crank length makes. I don't think I know the crank lengths on my bikes.

I think I see where your confusion lies. 50% of people have one leg shorter than the other. The remaining 50% have one leg longer than the other.

 

[ColinJ]

@ColinJ I'm in a similar position (no pun intended!) and a couple of years ago was referred to the orthotic department of my local hospital. They sorted me out a pair custom insoles, deigned to compensate for the difference in leg length and also for my poor posture bought on by a natural tendency to try and compensate for the difference over the last 30 years.

The insoles have made a world of difference - less knee pain and a much better natural posture (to the extent that people are asking me how come I've got taller at the age of 50). (The insoles add about 2mm of height, so it's not down to them).

I think I've posted similar before, but I'd really recommend anyone with mild physical deformities (to use what is probably an old fashioned and non PC phrase) to sort our an appointment with their local orthotic department.

Hmm ... I might check that out.

I can see how a heel lift could sort out the pelvic tilt when standing or walking, but I would have thought that a cyclist needs the front of the foot lifting because that is what contacts the pedal. The trouble is that there isn't that much spare room above my toes in my shoes.