Changing Crankset (FSA Gossamer)

[NorthernSky]

hi folks
i want to change my crank set. i have the fsa gossamer, 50/34t
i want to change to a 170mm with the same teeth
what style is this? bottom bracket etc
if i change to shimano does everything need changed? would i need special tool to do myself?
would this fit http://www.ebay.co.uk/itm/FSA-Gossa...139298?hash=item2ee9ed4f62:g:deIAAOSwJcZWggav
thanks

 

[Citius]

It's a MegaExo BB. The chainset in the link would also fit, but you would need to fit the ISIS BB supplied with it, as the one fitted currently is different.

 

[NorthernSky]

thanks
do you normally change amount of teeth if going to a smaller crank length?

 

[uclown2002]

Why are you changing?

 

[NorthernSky]

it's too long for me, 175mm currently

 

[Citius]

thanks
do you normally change amount of teeth if going to a smaller crank length?

No - not unless you particularly want to alter your gearing. Don't over-estimate the effect of crank length - it actually makes very little detectable difference in the real world.

 

[ayceejay]

it actually makes very little detectable difference in the real world.
this statement is no doubt anecdotal because I found that it does make a difference in my world

 

[Citius]

Which is also entirely anecdotal...

 

[Sharky]

it's too long for me, 175mm currently

Can you be more specific, why do you think it too long? A change of only 5mm is only a minor change, so will probably not be noticeable. However, if you switch to something a bit shorter, like 145mm, you will notice the difference. I've appreciated the switch to 150mm cranks, with a much more fluid pedal action, less knee bend etc and surprisingly better on hills as you stay seated for longer, but in a lower gear.

It is difficult finding short cranks, but if your cranks are solid and not fluted, they can be re-drilled to 155 or shorter for not much £.

 

[ayceejay]

Which is also entirely anecdotal...

I know citius but so is that and.....
If you say something like 'In my experience it makes very little detectable difference that is quite different from what you said - no?

 

[Strathlubnaig]

for the record, I had FSA on a BB30 and got fed up with the wearing it out too often, fitted a Praxxis Works conversion and now have full Shimano 105, works great.

 

[Globalti]

Changing the crank length will make NO difference to the effort because you will simply choose a gear to suit the conditions and your leg strength and fitness.

However it will make a tiny, probably imperceptible difference to the angles of your leg joints.

 

[Ajax Bay]

do you normally change amount of teeth if going to a smaller crank length?

No. In any (and all) gear, changing from 175mm to 170mm cranks loses you 3% mechanical advantage (leverage). But as @Globalti says, you will simply choose a gear to suit. The next time you change your cassette you may wish to consider a cassette with an extra tooth on the largest sprocket eg from 27t to 28t would give you that will give you a 3.7% shorter gear (as the loss of leverage changing cranks will be felt, if felt at all, only in the shortest gear (ie climbing the steepest hill). But there are physical factors which also come into play and may confound this: I assume you are seeking/expecting to be more efficient by changing the cranks to a length more suited to your leg length.

With regard to your bottom bracket, you may find this thread (the BB bit) worth scanning:
https://www.cyclechat.net/threads/knackered-bearings-after-4-300-miles.194250/

 

[Citius]

I know citius but so is that and.....
If you say something like 'In my experience it makes very little detectable difference that is quite different from what you said - no?

Saying it makes no detectable difference is proven - not anecdotal. Crank length is more a component of bike fit and leg length - there is little - if any - performance benefit in changing crank arm length.

 

[Mo1959]

Saying it makes no detectable difference is proven - not anecdotal. Crank length is more a component of bike fit and leg length - there is little - if any - performance benefit in changing crank arm length.

Would a shorter crank length be any easier on the knees for someone with knee problems?