Cranks?

edschof

What is the difference between the different ratios?

34/50 - 12-28 170mm cassette
34/50 - 12-28 175mm cassette
34/50 - 11-25 175mm cassette

What does it mean?

Pross

The 170 or 175mm is the length of the crank arm and in my experience makes little difference.

34 / 50 relates to the number of teeth on the front chainrings i.e. the inner chain ring has 34 teeth and the outer has 50 teeth (this is a compact chainset to make climbing easier, traditional chainsets would have something like 53 / 39). The final number is the number of teeth on the biggest and smallest sprockets of the rear cassette. If the biggest sprocket has more teeth it makes climbing easier but you will have a marginally bigger jump somewhere in the intermediate sprockets. Basically the smaller the gap between the size of the front chainring and rear sprocket the easier it is to go uphill so if you are a novice then the 34 / 50 and 12-28 is likely to be the best option. Rear cassettes are easily changed in the future. Both have the same highest gear of 50 front 12 rear for when you are going flat out.

edschof

Thanks very much that was very helpful!

Know it's nothing to do with this but how the hell do you set a signature, starting think I'm missing the obvious!

Welsh boy

Crank length makes a big difference and should be selected mainly on the length of your leg (or more accurately your thigh). Under 30-32" inside leg look at 165mm cranks and increase the length as leg length increases. A short (165mm) crank does not give you so much leverage as a long crank but it can help turn a gear at a higher speed because your foot goes around in a smaller circle with a shorter crank. Track riders on indoor (or steep outdoor) tracks use short cranks to increase clearance and reduce the risk of grounding the pedal and to help pedal quickly, big gear pushers and time trialists tend to use longer cranks for extra leverage at the lower pedaling speeds they tend to ride at. Just one issue with what Pross says, if you have too low a gear (and a 34 ring with 28 sprocket is a low gear, you could almost ride your bike upstairs to bed on that) you might find that you ride slower than if you had a slightly bigger gear, unless you live somewhere like the Lake District, 34 by 25 is probably low enough for most people.

Gizmodo

edschof wrote:

Thanks very much that was very helpful!

Know it's nothing to do with this but how the hell do you set a signature, starting think I'm missing the obvious!

User Control Panel, Profile, Edit Signature

MichaelW

Usually you measure cranks by "Gear Inches". This takes account of the chainring and sprocket teeth and the wheel size but not the crank length.
The late Sheldon Brown incorporated the leverage effect of crank length into his "gain ratio"