gsteinb

ok

tetonrider

it's the same arm for 7800, 7900 and 9000.

shovelhd

Impossible. Left side maybe.

gsteinb

I don't think so. My understanding is that they're not legitimate 7900/9000 but jury rigged versions.

shovelhd

Gotcha.

tetonrider

they're 7800 arms that are specially machined by SRM to work. they started life as 7800s, but they become something more.

Digitalfiend

I have zero experience with other power meters, but my Quarq ELSA is working fine with my Madone 6.9 using Zero series GXP BB conversion set from Enduroforkseals. I even left the SRAM chain rings on it and it works fine with my 7970 Di2. I've been tempted to put my 7900 rings on the Quard to see how that works but haven't gotten around to it.

The only two minor issues I've had are: chain rub when doing 39x12, which worked fine with 7900 chain rings; the unit gave me a bit of grief while trying to replace the battery...for some reason it was acting like the battery was dead but fiddling with the battery cap fixed it (minor but admittedly odd/worrisome.)

My calibrations before riding typically float within 5-30pts (e.g. -48 yesterday, -70 today...hotter/more humid.) in the dead of winter, it rarely fluctuated more that 5pts @ -15c. I admittedly haven't checked for drift in the rain but the unit has been drenched and it operated without issue.

I'll probably go with a SRM when I upgrade to DA9070 as I do think Shimano crank arms are stiffer and prefer their chain rings.

Edit: interesting point about side loading the bearings...that did bother me a bit having to torque the crank arm bolt so much; Shimano's pinch-bolt system seems more elegant and potentially easier on the BB shell.

shovelhd

There should be no chain rub with 7970. Something is a bit off.

The offset on my Quarq has been slowly drifting up. Now it's approaching -400. This is how the last one died, a slow crawl to -2000. But it has been unusually hot here lately, so the test will be if it comes back down to around -300 which is where it settled a while ago.

Alaska Mike

I have 2 Quarqs- an S975 and a RIKEN. Other than a single battery contact issue on the S975 (which was quickly resolved by bending the tabs), I haven't had any issues with them. The zero offset has been pretty solid, allowing for temperature variances, and I have no issues with my S975 on my Madone 5.2 with stock Trek bottom bracket seals/bearings.

Would I prefer an SRM? Maybe. I have no issue soldering, and the SRM is the gold standard for accuracy/reliability. That said, no professional teams have been knocking on my door, and the Quarqs have performed well up to this point. I ride a lot in the rain and other conditions that aren't electronics-friendly, and am satified with my purchases. YMMV.

I considered the Stages powermeters as a backup before I bought the RIKEN, but I have a noticeable difference in power between my right and left leg (working on it) that would make swapping between the different standards questionable. Again, YMMV.

I have no idea what direction I would go if I had to do it all over again, and it really doesn't matter. What I have works for me, and I'm not seeing a reason to change.

Digitalfiend

The rubbing was with the SRAM rings on...I haven't tried my 7900 rings with the Quarq yet, but since I don't cross chain much, it's not a pressing concern.

shovelhd

I have SRAM rings on mine. No rub.

Digitalfiend

Weird. What bike was your Quarq installed on? The rub is very faint and only happens on 39x12 (or 11 if I'm running my 11-25.) Chain seems to graze the inside of the big ring. Other than that front shifting is perfect...maybe slightly slower/less smooth than when I had my 7900 crank upfront but otherwise perfectly acceptable.

mike868y

cdr posted a link to a story about this a few weeks back (not specific to the quarq). I believe it's a factor of which chainring sizes you have on the front and the length of your chain stays. if you think about it the chain on all bikes has to move the same distance between the biggest cog in the rear and the smallest. but on a smaller frame with shorter chain stays the chain has to make a more sever angle to cover this distance. so whereas cross chaining might not result in this rub on a 60cm frame, on a 48cm frame it might.

shovelhd

Good point. I was just saying that one of the benefits of Di2 is that it adjusts yaw automatically so that all gear combinations are usable.

I ride a 54cm Felt FC with a S975 GXP with Wheels Mfg. BB30 adapters.

Digitalfiend

Good point. That could very well be the issue, as I believe the DA7900 rings are spaced a bit wider than the SRAM rings, which would explain why there is a bit of rubbing.



I'm not referring Di2's auto-trim; the chain isn't rubbing on the cage, it is rubbing on the inside of the big chain ring itself. The chain doesn't touch the cage at all, even when it is rubbing the ring itself.

gsteinb

track chain?

shovelhd

That's just not right.