All things being equal, an increase in sidewall of 10mm isn't going to turn it into a plush riding car though - that was my point really.monkeyhanger wrote: Wed Dec 19, 2018 3:38 pm Assuming the 17s are 215/45 R17 (the Brescias are 215/40 R18) Brescia has 86mm sidewall and Parker has 96.75mm, a 12.5% difference.
It may not be as simple as comparing sidewalls - tyre choice comes onto it too with flex and sidewall stiffness.
A stiff 17" tyre can be noisier and less comfortable than a supple 18" tyre. I'd guess that the 17" Michelin Primacy tyre is a little more flexible than my 18" Bridgestone Turanza. When I swapped out my R's Bridgestone Potenza with Michelin PSS of the same size, the difference was like night and day. These Turanzas are ok vs the woeful Potenzas.
The 17s will probably be slightly conifer (I emphasise "slightly") whether the difference is enough to want to swap is another matter. You need a Parkers test drive to be sure.
In fact, I reckon any improvement in ride felt could be down to the placebo effect.
In other words, the driver 'convinces himself' the smaller wheels/higher tyres are giving him a better ride.
