Tuesday, 8 July 2014

Choosing New Cranks

Having busted my previous pair of cranks two days ago, it is time to get a new pair.

The busted pair are 170mm cranks, because that is what came with the bike - like many riders, I don't have an infinite budget, and I tend to use what I have, unless I have a very good reason to change something.

How long should I get?
A quick peek on the internet came up with a reasonable sounding set of three basic answers:
Method 1: 65 cm + (Inseam (in cm) x 1.25)
Method 2: Rider height x 0.095
Method 3: Consult a crank manufacturer's tables

A fuller critique of the three methods, with sources where they are from, as well as a lot of discussion of ergonomics and basics is also on the site (Bike Dynamics)

So, enough generalisations.
How do the "numbers" work out for me.
I am about 6 foot 2 or 6 foot 3 tall
I have a 34 inch inseam.
I have roughly average proportions (I think!) between my head/neck, torso, and legs.
Using method 1 gives an answer of 173mm
Using method 2 gives an answer of 178.5mm to 181mm
Using method 3 (using the link in the Bike Dynamics website) gives an answer of 172.5mm to 175mm.

So a bit longer on the cranks could be beneficial, and as I have to buy new cranks anyway ...

For interest, Bike Dynamics has it's own recommendations, and they come out with a 175mm.

A quick look at the cost of cranks suggests that there are many 170mm cranksets available at all price levels, with 175mm cranksets available at all but the very cheapest end.
180mm cranks, however, see a significant jump in the price!

So for a combination of crank length analysis, and cost-efficiency, it looks like I'll be getting a new set of 175mm cranks.

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