170 and 175mm crank arms

[Blue Hills]

I've often very casually wondered about cranks being offered in these two alternative lengths, just 5mm apart.

My various bikes all have 170 which is partly coincidence and partly design as I do remember getting a new bike with 170mm as it matched the others.

But now giving it a bit more thought as in my rush to buy a spare crankset for future use (it's being phased out) I ended up getting a 175mm.

Is it likely to cause me any issues switching from 170 to 175?

Just how much difference can 5mm make?

 

[Citius]

About 5mm difference usually

Just lower your saddle by 5mm and carry on...

 

[blackgoff]

Just how much difference can 5mm make?

Quite a lot - you wont spin as fast, and spinning is winning ! you'll push a slower cadence, thus giving you bigger muscles which will slow you uphills...

 

[Citius]

Quite a lot - you wont spin as fast, and spinning is winning ! you'll push a slower cadence, thus giving you bigger muscles which will slow you uphills...

Utter nonsense. Sorry, but it is. 5mm giving you bigger muscles... How exactly?

 

[Milkfloat]

You should go 172.5.

 

[Milkfloat]

Being serious how tall are / inside leg?

 

[Levo-Lon]

Its 10mm from tdc to bdc..on a 5mm longer crank.
i was told to go with 172.5mm ..thats 5mm..and only 200 quid to change with my sram xo Lol

as for will it help ,i doubt it unless your a top rider

 

[PhilDawson8270]

I use a 175mm crank. If I went to 170 I'd have to move saddle back 5mm. My seat is already near the Max rear movement

 

[Blue Hills]

Its 10mm from tdc to bdc..on a 5mm longer crank.
i was told to go with 172.5mm ..thats 5mm.r

Sorry, can you explain this "doubling".
Tdc?
Bdc?

 

[midlife]

The diameter of the circle the 5mm longer cranks transcribe is 10mm longer.

Shaun

 

[JoeyB]

Top dead centre and bottom dead centre.

 

[simongt]

Most mass produced bikes tend to be kitted out with 175mm cranks regardless of the size of the frame they are fitted to. Thus you will get a small framed woman's bike with 175mm cranks; not much fun of you are 5' 2" - ! The general guidance is one relative to leg length unless you have a specific bike for a specific discipline. I think it is 29" inside leg or less, 165mm, 30 - 32", 170mm, 32" +, 175mm. If you happen to be a longshanks, then see a good bikeshop for advice - ! I'm 32" inside leg and all my bikes regardless of type or frame size have 170mm cranks, because that what suits me.

 

[Sharky]

Just to add to the confusion, try googling short cranks. Mine are 145mm and 150mm now!

 

[Citius]

Most mass produced bikes tend to be kitted out with 175mm cranks regardless of the size of the frame they are fitted to.

You must be talking about MTBs - most road bikes come fitted with 170mm as a default.

 

[Blue Hills]

The diameter of the circle the 5mm longer cranks transcribe is 10mm longer.

Shaun

Ah, of course it is - thanks - i have a feeling that i would have known the answer without asking when i was 16