SRAM Red crank to replace SRAM Force crank?

I've been looking for a good way to add a power meter to my Gravel bike for training. I've been looking at different options that are out there but it seems as though Quarq is generally considered to be one of the best. I ran across a used SRAM red crank the other day with a Quarq power meter and was wondering if I could replace my SRAM Force with the SRAM Red? Here is what I'm thinking I need to find out (unless somebody else knows):

1. Spindle diameter - appears to be the same - 30mm
2. Spindle length - don't have this info yet, but couldn't I replace the spindle on the SRAM red with the spindle from my SRAM Force?
3. BCD of the quarq spider - The spider on the Red crank is a 2x and I'd like to replace it with a 1x ring - preferrably with the one I currently have.

What am I missing?

Seth

It would require a BB change, but switching to Shimano cranks with a Stages arm will still likely be the least expensive option. PM accuracy is way less important than consistency, and the 1 sided ones are fine for that. Pro-tip: any Hollowtech road crankarm are compatible with one another. I've used both DA 9000 and Ultegra 8000 left arms with the GRX 600 cranks on my gravel bike.

I'm less familiar with SRAM, but I'd suspect the Force and Red to be cross compatible. Gravel bikes have road spec BBs, so any road cranks should work. I would probably only pay a $200 premium for a spider based PM, though, all else being equal. But the Red crank will also be quite a bit lighter so that adds value. I also bet that the 2x spider on the Quarq won't be easy to make 1x, but 2x is better anyway.

/Ramble

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Originally Posted by climberevan

I would probably only pay a $200 premium for a spider based PM, though, all else being equal.

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Talk me through this statement. My current understanding is that in the world of Power Meters you have roughly: Pedal<Crank Arm<Spider (Pedals being least accurate/precise). I have no idea where the Spindle-based PMs lie and I don't' really have much of an interest in the hub-based PMs.

I had been leaning heavily toward the 4iii/Stages route due to cost ($300) until a road racer friend in Seattle stated that Quarq is superior to these crank arm-based PMs. I don't think my crank is compatible due to the mounting mechanism, so I had written off the Quarqs as I don't have budget for a new crank. At this point cost is King for me so I would be more likely to go with something cheaper. I don't think I'm going to be held back by any specific type of The Red cranks are about $400 w/ PM. A new 4iii arm PM is $300, but I lose my crank for a couple of weeks. :-/

In terms of what I want, I would really like to have a pedal-based PM because then I could move it from bike to bike as needed. I could train with it on my gravel/road bike but when I'm doing that mtb race I could put the pedals on there. But the $600 price tag for the Garmin Rally pedals is a little hard to swallow at this point.

I'm open to other suggestions as well and appreciate your insght.

Seth

Which versions of Force and Red? E.g. 10, 11, or 12 speed?

BCD isn't an issue if you go direct mount (which I think you can do with 11 speed but not 10). If you're using a spider and want to keep the same chainring you'll need to make sure they match (both cranksets come in either 110 or 130). You'll also need spacers or shorter chainring bolts if using a spider and converting from 2x to 1x (not a big deal).

Also 12-speed AXS has a different direct mount interface than the 11 speed stuff (or DUB).

Other thing to check is crank length.

The main disadvantage of a single sided PM is just that. Accuracy so close to the spider ones (apart from SRM, which is more accurate but $2500) that it really doesn't matter.

Yes, you're only measuring one leg and doubling that. Most people are within a couple of percent of balanced, and your can't do much to change that anyway, so measuring just one side is fine. The main objective of using a PM is to gauge your own efforts against yourself, so as long as it's consistent, it's a useful tool.

The nerd in me would love some power pedals to geek out with, but I know that money is much better spent elsewhere. The roads pedals seem good now, especially Assioma. The MTB pedals might be ok when new, bit as hard and often as I hit mine on rocks i can't imagine they would stay good for long.

I just bought another Stages arm for my MTB for $200 from Stages direct. They still had a bunch on sale. I had one on my road bike that I would sometimes swap to the gravel bike, but I stole my GF's Ultegra arm for that so no more regular swaps. With Shimano cranks it's a super short job though.

All of that said, for $300 vs $400 I'd just get the Red crank and save a little weight too. Do be sure it's a really recent Quarq, though, because I believe they had some reliability issues for a while.

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Originally Posted by climberevan

Do be sure it's a really recent Quarq, though, because I believe they had some reliability issues for a while.

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How recent?

The more I consider the SRAM red crank and spider the less I'm certain that it will work. However, I ran across another spider for sale which appears to be the one pictured. My *hope* is that this spider would interface properly with my Force 1 crank that runs a BB386EVO bottom bracket, just like the SRAM Red crank that is referenced in the image. The cost for the spider I found is less than $300, the BB version is the same (386EVO). I suppose I might just need to buy the sucker and see if it bolts up properly. . .

If anybody knows for sure, though, I'd appreciate the insight.

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Just closing the loop on this one. Ended up with a SRAM Red crank and a new Quarq DZero PM spider. The interesting thing for me was recognizing that the difference in weight between the Red crank and Force 1 crank was very minor. The Crank arm/spindle combo was only 14g lighter on the Red crank than the Force 1. The Quarq spider + Red crank arm vs Force 1 + aluminum spider was 54g heavier, so all told, there was a small weight penalty (40g) to moving to the Red crank with quarq PM. I was expecting the Red crank to be a bit lighter than the Force 1 crank - the big advantage that I see is that they have the 8 bolt interface for the spider allowing for this (and other) Power Meters.

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