Crank Lenths ???

feno46

Looking to change my 53/39 for a compact.

What difference do the various crank lenths make, apart from the obvious.

I have a 170m, ( if I have measured it correctly, from centre of crank bolt to centre of pedal ).

Will a longer one mean moving seat higher, and maybe back, as it will put my knee further forward.

Is there a reason why that size was fitted in the first place. Frame size is 58. (maybe i've just answered my own question)

feno46

BUMP....................any offers on this one before I go and buy the wrong chainset.

Thanks. Pete.

pb21

If you put a longer crankset on you will need to lower your seat by the same amount so that the total extension is the same. I suppose technicaly you will have to move you seat back a bit too, to compensate, but this would be negligible.

170 on a 58 sounds on the samll side I would suggest a 172.5 or a 175.

I dont know if you would notice much diffence though in terms of speed though, more of an ergonomic thing I think, and if you had any trouble with your knees etc.

fast as fupp

how tall are you?

maddog 2

I agree with pb21, 170 sounds short for a 58cm frame.

My guess is you're 6 foot plus, which would suit 175, depending on body shape etc.

ash68

Am I right to think a longer cranklength would aid climbing? Or am I barking up the wrong tree? :oops:

nicklouse

does it not depend on your inside leg length?

and there is a formula to work it out.

Shrews Phil

according to a maintenance dvd I have recently watched, it is 21.5% of your inside leg length

feno46

Thanks for the replies,


I am 6' 2", 32 inside leg.

So its not too critical is what I can gather from the replies.

Thanks , Pete.

andrew_s

I've heard 20% of inside leg (actual leg, not trouser size). It's only a starting point for personal preference, and most people just get used to what they have. Just look at the crank sizes on bikes aimed at 5' 0" women (170mm) and those aimed at 6'5" blokes (175mm).

With longer cranks you get a little more leverage. With shorter cranks you can get the same leverage by using a lower gear, but that means that you spin the cranks a bit faster.
With shorter cranks, it's easier to spin the pedals at high rpm. This is one of the reasons why people on fixies tend to use shorter cranks (the other being pedal strike).

It is possible to get knee damage from too long cranks, but this is normally only an issue if the cranks are considerably too long (the aforementioned 5'0" women, who ought to be on 150mm cranks). The manufacturers rely on the fact that most people don't ride all that far. and those who do mostly know enough to change the cranks.

term1te

Crank length does have an impact on climbing. I switched from a 175 to a 172.5mm and needed an extra gear on my local hill climb. Haven't really noticed any difference at higher cadance, if anything it is a little easier.

Bugly

its all about mech advantage - shorter cranks for people who like to spin, longer for mashers, Im 183cm ride with 175 on a mtb and 170 on road.

fast as fupp

my mates got 180's on his enigma and hes only 5'11"

his pedalling action looks like hes trying to get a 50 kg flywheel turning from scratch!!

i constantly rip the p*ss out of him for it

ARE YOU READING THIS HANS KRANKL???