V60 wheels/tyres for rough roads
 

Just bought a V60 2019 inscription pro. It has 20 inch wheels and the roads where I live (rural England) are full of pot holes. I feel every bump and I'm worried about blowing a tyre - this happened to me in my old V70 and I replaced its 18 inch wheels with 17 inch - nice high profile tyres, comfy ride etc. But V60 is a computer with wheels and I'm not sure what to replace my 20 inch wheels with as I think it has to be re-calibrated at Volvo dealer. The day I bought it I also test drove a V60 which had 225/?/17 tyres (wish I'd recorded the size). Dealer says smallest I can fit are 18 inch - recommended wheels at the (non volvo) place I bought my V70 replacements are 235/40/18 - and they look very flat to me. A bit fed up with driving the V60 very slowly to avoid the potholes! I can afford the change over as I got a good trade in on the V70.

A good wheel/tire shop should be able to provide you with a chart of wheel size/tire dimensions that will allow you to compare the rolling radius of your current fitment with alternatives.

Any significant difference in this measurement will affect your speedometer/odometer accuracy. I do not know if there is a compensation adjustment available.

There are at least three other functions tied to wheel rotation speed: ABS, ASR and, at least in US versions, TPMS (tire pressure monitoring system) Logic would suggest that these function by detecting differences in rate of rotation among the wheels. Some other speed sensitive functions - emergency warnings and possibly damper function and steering response (if the latter two are available/fitted) could be impacted but, since there are size variations for the same spec tire among manufacturers, It would be surprising if a small difference mattered

wheel-size.com is a good online resource for finding any OEM rim/tire (tyre?) combination. In addition to going to a shorter rim with higher profiles, you can also maintain higher tire pressure than what the door sticker recommends. Not many people will recall but there was a class action law suit years ago against Volvo as the 850s were prone to blowouts (we had a few) - which stopped happening when I added about 5 PSI to what the factory spec called for. On my 2012 with 235/45-17s I typically keep 36-39 PSI so you should consider a similar plan. Note on the sidewall there's a stated maximum PSI for reference - typically its in the upper 40s or lower 50s.

Thank you
 

Hi,
I've found a helpful man at the company I bought the V70 wheels and tyres from. He's specified 245/45/18 ZR PIRELLI P ZERO and the Volvo dealer has confirmed that the TPMS is an indirect system so it is monitored via the brakes rather than needing a sensor in the wheels. I gain only from 86mm between rim and road to 110mm but I think that's the max I can do without sacrificing warranties and getting into trouble with insurance provider for modifications.
Thank you so much for your advice. You have given me more confidence to proceed.
Sarah

BTW, the TPMS system looks for differences in wheel speeds then calculates a threshold to determine if one is going flat. So, as long as all four tires are the same size, the TPMS will be happy. 45 profile tires are still pretty short so I'd recommend keeping the pressure on the high side.