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Shimano Dura-ace left crank on an FSA Gossamer Crankset

Posted: Mon Jan 14, 2019 8:54 pm
by wlbm
Hello, I'm hoping someone here has some experience with this, because google isn't coming up with much of anything...
My wife has a 43cm XS 2015 Giant Liv Avail 1 (https://www.liv-cycling.com/us/avail-1-2015) which comes with an FSA Gossamer Pro CK-C6028 crankset. The specs show the BB as a "Shimano Press-fit". As far I can tell from measuring, the crank length is 165mm. There is no length marking on the crank itself, or on Giant's archive, so I'm going by a measurement from centre of BB to centre of pedal spindle.
I have a chance to buy a cheap 165mm left-hand Stages power meter crank for her, but the model is a Dura-Ace 9000, and I'm unsure as to whether it will be compatible enough to swap out only the one side of the crankset. Will it require the entire crankset to be swapped out with Shimano? Does the BB have to be replaced, too?
Does anyone have experience trying this?
Thanks!

Shimano Dura-ace left crank on an FSA Gossamer Crankset

Posted: Mon Jan 14, 2019 8:54 pm
by Weenie

Re: Shimano Dura-ace left crank on an FSA Gossamer Crankset

Posted: Mon Jan 14, 2019 8:59 pm
by mattr
Whole crank will need replacing, the interface between LH crank and spindle is brand, and in some cases, model specific. So (in this case) you'll need D-A on both sides. Or you can muck around with spacers and do DA LH and Ultegra/105 RH.

Bottom bracket should be ok to leave where it is.

Crank length marking should be on there somewhere, but it might be a bugger to spot. But it's easy enough to measure. And you'll need a whole new crank, so you'll at least have the same length left and right.

Re: Shimano Dura-ace left crank on an FSA Gossamer Crankset

Posted: Tue Jan 15, 2019 12:04 am
by 2lo8
mattr wrote:
Mon Jan 14, 2019 8:59 pm
So (in this case) you'll need D-A on both sides. Or you can muck around with spacers and do DA LH and Ultegra/105 RH.
...
Crank length marking should be on there somewhere, but it might be a bugger to spot. But it's easy enough to measure. And you'll need a whole new crank, so you'll at least have the same length left and right.
What? Shimano lists LH crank arms as B compatible. Also crank length marking is almost always on the back of the crank arm, either at the pedal eye or in rarer cases in the middle of the arm.

Re: Shimano Dura-ace left crank on an FSA Gossamer Crankset

Posted: Tue Jan 15, 2019 4:36 am
by mattr
More than likely, yes. I'm only gong from a half remembered thread from 2+ years ago where sometime fitted the "wrong" crank.

It might even have been D-A to XT.

If Shimano list them all as compatible I'd go with that!

Re: Shimano Dura-ace left crank on an FSA Gossamer Crankset

Posted: Tue Jan 15, 2019 5:37 am
by 2lo8
For road/mtb the spline interface is the same but the Q factor is way off for tire clearance. I'm pretty sure the road ones all all dimentionally pretty similar.

Re: Shimano Dura-ace left crank on an FSA Gossamer Crankset

Posted: Tue Jan 15, 2019 6:17 am
by alcatraz
How about getting a 105 (5800) crank if you want to save some money.

It will fit the same bottom bracket and the pwm will fit it.

/a

Re: Shimano Dura-ace left crank on an FSA Gossamer Crankset

Posted: Tue Jan 15, 2019 6:26 am
by wlbm
Thanks for all the replies!
Yes, the crank length (165mm) was stamped in just below the pedal eye. I just needed the right light (and a kick in the pants) to see it

Sounds like swapping out the full crankset with a mixed Shimano group for a cheap(ish) gen-2 stages is a fools errand and likely to cost me more than just buying a compatible meter.

Honestly we aren't at the point in our training where power data is going to be hugely beneficial, but I didn't want to let a potential chance go to waste.

We'll just continue zone training with HR and cadence.

Thanks again!

Re: Shimano Dura-ace left crank on an FSA Gossamer Crankset

Posted: Tue Jan 15, 2019 12:51 pm
by alcatraz
Fsa have no single sided 24mm spindle power meters. Entry level pwm will always be shimano single sided. That's what is being produced and what you will find most likely.

(Single sided crank power meters can't be fitted to carbon arms (expensive exceptions) or to crank arms that aren't flat on the backside. Most arms out there are not hollow = with a flat backside on which the strain gauges can be mounted to. Fsa has only one called "energy" which explains why they are so rare. Shimano happens to have 99% compatible hollow alloy arms on 105/ultegra/da which makes them perfect to fit an inexpensive pwm onto. This is why 90% of all cheap pwm's are shimano. A pwm is often worth 3-4 times the cost of the bare crank. Switching crank to get a pwm makes sense when you look at the big picture.)

I live in China where the cheap pwm's are made. Even here 165mm isn't a standard size that the national brands stock up on. It's made to order.

So I'm surprised you stumbled across a 165mm pwm. They are quite rare, and often not cheap because of that.

Usually you have to use a spider based pwm solution mounted to 165 arms to make a 165mm pwm crank, and that's a lot more expensive.

Fsa gossamer is basically a Shimano Tiagra level crank. It works fine but it's not worth that much to cling onto. I can find them 2nd hand for 20-30usd. 105 could maybe be 40-50usd 2nd hand.

A da9000 arm fits any shimano hollowtec road crank. Sora/tiagra/105/ultegra.

Re: Shimano Dura-ace left crank on an FSA Gossamer Crankset

Posted: Tue Jan 15, 2019 1:04 pm
by 2lo8
I have 2 Stages MegaExo PMs. The reason you don't see them on the current generation of PMs is that FSA wants to move to BB386 which is their not-quite-BSA30 standard. It's not that they didn't or don't exist.

Re: Shimano Dura-ace left crank on an FSA Gossamer Crankset

Posted: Tue Jan 15, 2019 1:04 pm
by Weenie