Cadence & crank length for a big lad?

Bullet1

When I started riding a few years ago and first bought my Garmin with cadence sensor I was averaging typically 70 rpm. Taking on board the 'magic' 80-100 rpm target as the best balance between cardiovascular tiredness (at higher RPMs) and muscle tiredness (lower RPMs) I have since increased my cadence to now average 90rpm and I believe its now much easier and feels more effiecient.

I'm 6'5" and currently running a 175mm crank on an off the peg bike (which if I bought crank only I'd guess I'd move to a 177.5mm or 180mm).

So this got me thinking, given my size and hence the mechanincs of my pedalling stroke would someone who is taller in theory have a higher or lower average cadence to maintain the efficiency.

simonj

Crank length can be calculated based on inside leg length. Saw this calc, whihc says inside leg in inches x 5.48 equals ideal crank length in mm. I'm 31" which gives 169.88mm, so I presume my ideal is 170mm. Most bikes I buy fo my height give me 172.5mm, when I built one I put a 170mm on there, but to be hinest I can't tell the difference. I to am trying to improve my cadence.

MichaelW

The OP is a big lad, not an average sized person. Working out your proportional crank length according to one or other of the methods will probably give you longer than 180mm.
Long cranks have longer pedalling circles and can generate more torque (at the BB) so the style of pedalling is slower revs and higher gears. The power output, pedalling force and resulting speed don't change. You big legs will be turning a proportionate circle, much like taking longer strides.

For a medium sized rider top go from 170 to 172.5 is insignificant and barely noticeable. Both are med sized. For a big rider, 175mm is a very short crank.

sub55

This is why those who continually spout on about the ideal cadence are talking out of their arse.
I too am a big fella, 6ft 6inches and ride with 180 cranks , if i put my lg length through the calculations , should be on something like 190`s. Anyway, think in the terms of circumference i.e foot speed as apposed to radius and rpm. Switch to 180 cranks , expect to have a slightly lower cadence but thats not to say ,your feet aren't going just as quickly.

Bobbinogs

Here is a very interesting article on the subject which pretty much concludes that crank length is very subjective!

http://bikedynamics.co.uk/FitGuidecranks.htm

MichaelW

sub55 wrote:

This is why those who continually spout on about the ideal cadence are talking out of their ars*.
I too am a big fella, 6ft 6inches and ride with 180 cranks , if i put my lg length through the calculations , should be on something like 190`s.

So you should be on 190's; what is wrong with that. Only that crank manufacturers don't make them and big bikes are not designed for them. If you could get them and a bike to fit them, you would be able to see if they were any good.