More on Crank Lengths

Question: How will it affect the performance changing from 172.5mm to 175mm crank arms?
Will the effect be directly adverse switching from 172.5mm to 170mm arms?
Anything special to consider in each of these swaps?
Regards
T.

Hi Terje,

The answer to your very interesting question is quite simple, really. The correct length of crank depends on the length of your thigh, the longer the thigh the longer the crank. Also it depends on your pedaling style, if you are a fast peddler then you can handle shorter cranks, but if you push a big gear then longer cranks can help as you have more leverage.

Finding the correct crank length can be a case of trial and error, which is an expensive method. The best way to find out what is your perfect crank length is to be measured up on a bike fitting jig. This will give you all your measurements, from frame to handle bar size and crank length.

Normally mountain bikes come fitted with 175 mm cranks, this is for the leverage needed for climbing, track bikes have shorter 165 mm cranks, this is because tracks can have steep banking and you don't want to hit the track with the pedal. It is also because with the fixed gear you need to be able to pedal at high revs and this is easier with shorter cranks. The important thing is to find which length suits your leg measurement, your riding style and which kind of cycling you do.

If your cranks are too long then you're pedaling feels dead and heavy. If they are short then you feel as though you are spinning out and tend not to have the power to push a big gear. The crank length is quite important, if you think of the pistons in a car engine or the push rods on an old fashioned steam train, the way they turn the wheels is the same way that your legs turn the chain ring, which of course turns your wheels, if the measurements are wrong then it wont work properly. I hope this answers your questions?