just about to buy myself some deore hollow tech 11 ones but there's 170mm and 175mm ones whats the difference and which one should i go for?

tom

5mm

its the crank arm length… i always have 175, but some companies have the shorter for small bikes and the bigger for med and large frame sizes… track bikes also have smaller ones to get the clearence!

175mm it is then i think on a 20" inbred?

Damn, I wanted to say "about 5mm".

No rider, except the incredibly sensitive, can notice. Go for whichever you like.

170mm if you're short and/or a spinner.
175mm if you're tall and/or a masher.

One of each if you're SFB.

There is a website somewhere on the net (might be on the Sheldon Brown site) that has a calculator that works out what size cranks you need all you have to do is put your inside leg measuremnet in in mm I did it and I need 173 mm cranks looked everywhere and no one sells them

I'm a short spinner – got 175's on my older bike and 170's on my newer bike.

170's more efficient, more comfortable, faster and much, much smoother. Eliminates those 'pedal under the chin' deadspots for the short-legged.

People who say that they can't tell the difference won't be shorties (I'm about 5 foot 6 inches tall) everyone I've spoken to who's made the change will never change back – it's like night and day.

Ms Spanner is about the same height as me but has longer legs – she doesn't like the 170's and prefers the 175's.

you can get 172.5 though Pantsonfire

One of each if you're SFB.

after the kindness of HTTP404 I now have matching length cranks – not that it feels any different :o) According to a sports physio, most men under 6' are better suited by 170mm, particularly if they're long in the torso like me 🙂

Or read another website 🙂

it's like night and day

not to me 🙂

"I now have matching length cranks"

OMG! 😯

Like I said – consistently silly..

SFB – you're awesome! 😀

No rider, except the incredibly sensitive, can notice. Go for whichever you like.
nonsense

I agree. Most riders unless they're entirely devoid of feeling should be able to tell the difference.

I've ridden between 165 and 180.

32-33" legs

can tell the difference between the extremes but it doesn't make a difference

I've got 170mm on my HT and 175mm on my FS, to be honest I can't tell the difference.

I used to have 182.5mm on my race BMX, I noticed the difference changing to 180mm.

can tell the difference between the extremes but it doesn't make a difference

of course it does