Crank Length?

[Kins]

I understadn it is related to spin rate. IIRC you can spin a shorter length crank faster so going up hill should be easier, if you can spin it all the way that is. - though it could be the opposite way around, can't really remember!

They use longer on mountains/hilly stages and shorter on flat on the tour if I read the article correctly.

 

[Ningishzidda]

When you climb a hill, your bodyweight is not in kg. Its in Newtons. You can’t easily ( except for taking everything out of your seatpack and putting it in your back pocket ) increase your bodyweight, but if you choose a longer crank length, you apply more Newton metres torque.
Its gonna be a slow cadence up the hill, so there’s no problem with pedalling speed, so more Nm and the same rpm gives more power.

 

[SatNavSaysStraightOn]

They use longer on mountains/hilly stages and shorter on flat on the tour if I read the article correctly.

yep - memory is not what it used to be yesterday. knackered from little sleep after too much exercise yesterday...

found this

Indicators your cranks are too long.
You are the first to get out of the saddle when climbing in a group.
You feel your upper body ‘bobbing’ vertically when spinning fast and lightly loaded.
Your transmission occasionally ‘clangs’ as you hit a dead spot at the top of the stroke.
Your knees / hips hurt.
Your knees come uncomfortably close to your chest when on the drops or tri bars.

Indicators your cranks are too short.
You feel strong on hills but seem to struggle on the flats.

Could be where I am going wrong at the moment. lousy on hills and my Triban 3 has 175mm cranks on it. don't know what my MTB has and my tourer has 170mm on and I was fine uphills with it... left me thinking I might go and look at the mtb - but that means washing it down first!

 

[simon.r]

I'm 6'2" and use 165mm cranks, because the amount I can bend one knee is restricted (the result of a motorbike accident years ago). I recently bought a new bike with 175mm cranks fitted and rode a few miles on it, but my knee protested and 165mm cranks went on the bike - no problems since.

 

[tyred]

I did once come across an elderly rider (70+) with dodgy knees who had drilled and tapped his cranks to move the pedals and shorten the cranks by 1.5" and spinning very low gears at high cadence. He reckoned it made a big difference and allowed him to keep riding.

 

[billy1561]

So where is the measurement taken from? Interested in this.

 

[Kins]

Rough idea use this : http://www.machinehead-software.co.uk/bike/cranks/cyclist_crank_length_calculator.html and inside leg measurement. That worked mine out as 166mm and I am 6ft. Every bike I have has 175mm except one which I have just changed to 165mm and see if knee pain recedes.

If you mean to measure your cranks, its from centre of each bolt hole.

 

[billy1561]

Yeah the actual crank size sorry. Thanks Kins

 

[SatNavSaysStraightOn]

summary - 175mm on my road bike & struggle up hills
170mm on touring bike, fine up hills
170mm on mountain bike and also fine up hills...

think i can see a potential change happening... (also have one the other indicators that crank arms may be too long, but not covering that one... little too embarrasing! )

 

[simon.r]

I can recommend these cranks as a cheap-ish way for anyone who's looking to trial different lengths (assuming your existing BB and rings are compatible). Available in 160mm - 175mm:

http://www.spacycles.co.uk/products.php?plid=m2b0s109p2003

Also worth looking at http://www.highpath.net/ for other solutions.

 

[Rob3rt]

When you climb a hill, your bodyweight is not in kg. Its in Newtons. You can’t easily ( except for taking everything out of your seatpack and putting it in your back pocket ) increase your bodyweight, but if you choose a longer crank length, you apply more Newton metres torque.
Its gonna be a slow cadence up the hill, so there’s no problem with pedalling speed, so more Nm and the same rpm gives more power.

Your bodyweight is still measured in a unit relating to mass regardless of what you are doing. Newtons is a unit of force, kg is a unit of mass, they describe different things.