How much would this setup charge overall diameter thus revolutions per mile compared to what it is designed for?

 

Diameter is 0.22 inches more for 235/50 and revs per mile is 5.5 less.

255/45-R19 vs 235/50-R19 Tire Comparison - Tire Size Calculator | Tacoma World

235/50-R19 tires are 0.22 inches (5.5 mm) larger in diameter than 255/45-R19 tires and the speedometer difference is 0.7%

www.tacomaworld.com

 

I'm pretty sure Volvo put the wider tyres (and wheels) on the rear for a reason. Probably something to do with vehicle handling at the limits (rear tyres wider so they will have better traction, so you would be less likely to get oversteer). Given you can't rotate the tyres front/rear anyway due to the wider rear wheels, the only benefit I can see is saving a few $$ on a more readily-available tyre size, right? Would I do it? No, not unless I had to. In reality, you'd probably be fine, so if it's worth saving the $$, it's a decision you might be prepared to make. Also, if you're putting narrower tyres on the rear wider wheels, there may be a bit more stretch in the tyre, so it could look a bit odd...probably not that significant though.

 

Yes, the square tire configuration is acceptable for our Volvo's.
For my winter 19" wheels I use Michelin Pilot Alpin 5 235/50R19 XL 103H.

 

Are you using stock wheels, wider rear or 4 the same size?

Thanks

 

I used a square 235/55/18 set for winter last year with no issues so far.

 

Yes, bought a 2nd set so that I can swap them myself.