wouldn't it be easier to swap out the BB on the new bike?

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Eric Reid AeroFit | Instagram Portfolio
Aerodynamic Retul Bike Fitting

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Yes, with a few caveats. You probably mean Force GXP for the new crankset, not Red. Non-powermeter Red does not have a separable spider. You'll notice that Quarq "Red" power meters look like Force cranks.

Second, Quarq has been moving from a 3-bolt hole pattern (between crank and spider) on their older PMs to a newer 8-bolt pattern (DZero). Make sure that your new crank has the same pattern as your existing PM. If your existing PM happens to be 8-bolt, then your only option is to call Quarq and purchase the 8-bolt version from them (which they're pretty good about, from my experience.)

The last thing is it's helpful to have a really long Torx wrench to get at those bolts. Because they're so close to the crank axle, it's hard to get a wrench in there perpendicular. I used a Torx socket attached to a standard ratchet wrench with a long extender.

Just pulled mine apart. It's the 3 bolt. But since it BB30 and the spindle is 30mm, won't it be too big for the GXP which is only 24mm?

Ah yes, that's possible. In fact you're probably right.

No. I think your Quarq spider will work fine with any SRAM removable spider crankset. The spindle diameter is independent from the spider interface. And having the older 3 bolt spider interface will make it much easier to find a set of GXP cranks to swap for your BB30 cranks.

Just talked to Quarq. If you have the 3 bolt spider you can switch the spider to the Force crank. Just need to send the spider and drive side crankarm back to them for re-calibration.

Or, can send them the spider and they will put it on a new Red crank. Although the Red was $395 from them. Can get a Force around $200.

Don't need to send it to them...just calibrate it yourself using the Qalvin app.

Anyway...I agree with Eric above...why not just put in a BB in the new bike that can take the 30mm spindle? Seems to be the easiest choice...

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http://bikeblather.blogspot.com/

The BB86 standard uses a 41mm shell ID and is intended to use reducing cups pressed into the shell to fit 24mm cartridge bearings. To run 30mm spindled cranks requires some means of fitting standard cartridge bearings into the shell or the use of proprietary bearing assemblies made just for this use. Some have fitted smaller 37mm OD/30mm ID bearings with spacers to allow insertion into the 41mm shell, but these are typically 4mm wide and much less durable. So sometimes these bearings are then doubled up to provide more durability. Wheels Mfr makes a conversion with proprietary double row bearings that press in directly. This option costs nearly as much swapping to the Force GXP crankset. And when it is time to replace the bearings it will be much more costly than with standard off the shelf cartridge bearings.

Some of these smaller bearing options may work fine, but I can see where just using a standard BB86 BB and a 24mm spindle crankset would be preferable.

Yeah, what he said.

Thanks for reminding me why the custom frame I had made uses a BSA threaded BB ;-)

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http://bikeblather.blogspot.com/