Crankset change

[sibluenose]

I currently ride a Cervelo S5 VWD with a BBright 53/39 172.5mm crankset.

I want to change to a compact crank. I am pretty sure I shall have to change my chain too. I want to know:

Will I notice a difference in either a 170mm or 175mm set? I will keep the bottom bracket so I am limited to either a Roto or FSA (and prefer to get a K-Force Light) BBright. Will I definitelyneed to change my chain?

 

[raleighnut]

If the chain is newish it will just need shortening, if it is worn then fit a new un.

 

[MisterStan]

I'm not sure if you understand correctly but the compact aspect is the chainring size, not the crank length. If you want smaller rings on the front then a compact is the way to go, the same length as you have now would make sense to me.

The BBright has a 30mm spindle, so any crankset with a 30mm spindle will go in, you can also buy adapters so you can install a 24mm spindle to fit shimano if you wish.

As @raleighnut says, assuming the chain is new, you can just shorten it.

 

[Yellow Saddle]

If you have BB Right on there right now you will need a BB adapter to use any other crank that's not BB Right specific.

 

[ayceejay]

Shortening the existing chain will work: is this the best option? Noticing the difference in crank length is a personal thing so...

 

[Tojo]

If you have BB Right on there right now you will need a BB adapter to use any other crank that's not BB Right specific.

Eh, Have you had a wee tipple, BB's.....?

 

[Sharky]

I currently ride a Cervelo S5 VWD with a BBright 53/39 172.5mm crankset.

I want to change to a compact crank. I am pretty sure I shall have to change my chain too. I want to know:

Will I notice a difference in either a 170mm or 175mm set? I will keep the bottom bracket so I am limited to either a Roto or FSA (and prefer to get a K-Force Light) BBright. Will I definitelyneed to change my chain?

Am always curious when people say they want to switch from/to compact chain sets. What are the issues that are hoped to be resolved? The differences between the two at the extreme ends of the gear ratios are about the same as you would get from one tooth difference on the rear sprocket, so maybe exploring rear cassette options might be a better route?

 

[sibluenose]

I have already changed the rear cassette from an 11/25 to a 12/30. My other bike has a compact crank with an 11/28 on it. This is better for climbing (easier to spin):
Sharky: 30 divided by 28 = 1.07. 39 divided by 30 = 1.3.

My 30 tooth cassette on the 39 gear is the equivalent of a 23 tooth gear on a compact crank (7 teeth difference, not 1). (30/23 = 1.304)
I am generally OK most of the time on my 53/39 set but I am riding some long sustained climbs in June and know I will benefit from the compact set.

I still want to know what difference a 175mm crank length will make to me (there is one on offer at 175mm) when I have only ever ridden with 172.5mm cranks before.

 

[MisterStan]

In theory you'll need to drop your seat and possibly adjust saddle fore/aft. In reality (i've got 175mm instead of 172.5mm on my bike) it doesn't make much difference. Could possibly lead to a bit of toe overlap too.

 

[Citius]

The only real change is going to be the need to raise or lower your saddle by the corresponding 2.5mm, to accommodate the different crank length. You might even be able to use the same chain, and allow the rear mech to take up the (minimal) slack.

 

[raleighnut]

2.5 mill is an 1/8 of an inch, I doubt you will notice the difference

 

[Smokin Joe]

At 6'1" I've gone the other way with crank length, 172.5 down to 170 leaving the set height where it was. Although the total stroke length is only 5mm shorter my pedalling action seems that bit smoother. I wish now I'd gone the whole hog and dropped to 165mm. Various bits of research I've been reading suggest that shorter may be more efficient, though I guess it's a very personal thing.

 

[bpsmith]

I read similar articles also. Posted them a little while back. The usual suspects will be along shortly...

 

[Citius]

It's a popular topic - especially where there's money to be made from bike fits

http://bespokecycling.blogspot.co.uk/2013/02/crank-length-long-and-short-of-it.html

 

[bpsmith]

From that article, and the others I posted before, the gain is getting a smoother ride and a more natural cadence. Helps with hip and/or knee problems also.

Yes, people make money from it, but bike fits are done irrespective of crank length considerations. Therefore why not just build it in to the equation and allow people to decide based on actually riding the fit bike with the actual crank lengths adjusted?