In the process of changing our car. The old one had 185-65-15 tyres and the new one will have 215-55-16 tyres. We have a set of winter tyres for the old car. I want winter tyres for the new car but the new size seems to come at a massive price premium so I thought I could possibly get a set of steel wheels for the old winter tyres and swap wheels/tyres round as and when required. There will be a size difference (which obviously will affect speedo/odometer) but how big a change is considered acceptable (if any). By my calcs this will mean the winter tyre/wheel combo will be 3.4% smaller in circumference leading to a speed difference of -2.3mph at 70mph? Any guidance?

What speed/load rating are they, and the current ones? Can you get steel wheels that will both fit those tyres and fit the car?

Maybe better to just sell them on and do a deal with the new car to get winter tyres/wheels too?

976.1mm Vs 1009.7mm circumference by my calcs.

Its only slightly more than the difference in circumference you would get from brand new to worn tyres. I can’t see it being an issue to be honest so long as the load sand speed ratings are okay. And when you put the bigger wheels back on in spring the roads will come alive

You can get that much variance between 2 tyres from different brands that are officially the same size tbh. Personally I’d be checking in with my insurers though just to avoid any future hassles

You might wish to cross check those numbers….
Should be around 3.5% as op suggested

Actually this is quite a large difference & in my experience too big.

Google for tire size comparison or calculator and using them you can double check your calcs and the difference it will make to your speedo.

Steveh – my calcs above came from an online calculator – I need to know whether they are within acceptable parameters?

Check the tyre label quite often there is a narrower option for winter tyres (m+s)