Swapping wheels and cassettes with Shimano GRX 600/800

Question

I am in the market for a gravel bike. I plan on getting a second set of wheels for road rides. This bike will most likely have Shimano GRX 600 or 800 2x and an 11-34 cassette. Assuming the rear derailleur is set up properly for that cassette, I'm curious if there any issues having an 11-28 cassette on the road wheels to get closer ratios:

• Would any derailleur adjustment be needed when swapping?
• Would a chain sized for the larger cassette work with the smaller one?
• What is the maximum difference that would likely operate satisfactorily?

Most of the trails out here are quite rough and steep, so there isn't an ideal tire or gearing for both road and dirt rides.

Answer 1

My experience with swapping wheels is disappointing.

I had to adjust the derailleur (limit screws, cable tension) and rim brakes (due to slight difference in rim width and dish) every time I swapped wheels. Maybe if you have exactly the same hub and rims on both wheels it will work better. I think my derailleur adjustments were necessary because the cassette position was ever so slightly different between the two hubs.

The longer chain should work fine on the 11–28 cassette. After all the small-small combination is the same, so your rear derailleur should be able to tension it enough.

Answer 2

The min large sprocket size that Shimano specifies for the RD-RX810 is 30 teeth. A 28 might work ok but I’d personally stick with 30.

As others have mentioned swapping wheels is not plug and play. The disc rotor and cassette end up in slightly different lateral positions which requires derailleur and caliper adjustments. Using identical model hubs should mitigate this, and I heard the cassette and rotor can be shimmed.

Answer 3

There isn't really a coherent RX600 groupset.

Basically GRX is a glossy re-marketing exercise for a bunch of different parts from different sources

The RX400 rd is a repurposed Deore T6000 and designed for 32-36t cassettes. It would shift both 10 and 11 speed road perfectly but it's not a good choice when you hope to fit narrower cassettes, it's much more towards the MTB/granny gearing range.

Rd-Rx812 is based on the Deore t8000 and it works with large cassettes in the 11-40 or 11-42 range

Rd-rx810 is officially rated 11-30 to 11-34. It has the 13t jockey wheels Shimano has come out with for their latest stuff to drive sales with the cult of the new. It's not quite the same as the rd-rx800 ultegra Rx rd, which is arguably higher quality being all aluminium instead of using plastics. Rx800 uses the same derailleur cage as r8000, and both rx800 and r8000 are rated 11-28 to 11-34.

It's likely rx810 is ok for 11-28 too for this reason

In terms of wheels, nominally all road disc hubs are 5mm wider than rim hubs used to be. Shimano didn't bother updating the road chainsets though I think SRAM do. So it was a selling point that the grx chainrings are moved out to where they should have been in the first place....

Anyway this means that chainline is actually quite flexible in that you can increase hub width without moving out chainrings in most cases except on very compact framesets, so nothing too much to worry about there. I wouldn't trust different freehub models to have the same dimensions, not even necessarily two by the same company. So ideally you'd measure this yourself when purchasing the wheel.

I don't think the different cassettes will itself cause an issue - it would be the different freehub measurements.

Answer 4

My experiences here differ from some others.

I have 2 sets of wheels from the same brand (hunt) 1 700c aero 25mm and 1 650b fat 38mm gravel. Both disc but the gravel wheels with a 11-34 and the aero wheels with a 11-30.

Moth mechs were med-cage (GS). Originally 1 was Tiagra now its 105 5800. The other 105 5800. Absolutely no disk rub or shifting issues.