Does the ride quality suffer noticeably when upgrading from 15's to 16's or 17's? In this instance, presume using tyres giving the same or very similar rolling radius in order to keep speedo accuracy. I'm not looking to go mega-wide so will settle for 195's on, say 6 or 6.5" width rims.

Vehicle ref: 2011 Mini One, standard suspension.

Also, what is the standard wheel offset?

Given tires with the same rolling radius and same width, those on smaller wheels will have a better ride because they will have more sidewall.

195/60 on 15" wheels
195/55 on 16" wheels
205/45 on 17" wheels

15" OEM wheels are ET45 and 16" and 17" OEM wheels are ET48.

Does the ride quality suffer noticeably when upgrading from 15's to 16's or 17's? In this instance, presume using tyres giving the same or very similar rolling radius in order to keep speedo accuracy. I'm not looking to go mega-wide so will settle for 195's on, say 6 or 6.5" width rims.

Vehicle ref: 2011 Mini One, standard suspension.

Also, what is the standard wheel offset?

I can't comment on 16" rims but, if you change from 15 to 17" rims the ride quality will deteriorate significantly. Assuming that you are moving up from the standard width tyre for a 15" rim, you will also notice it being slower on the motorway, it will tramline and it will be thirstier. In addition, if the wheels are heavier (which is almost inevitable), you may find the wheel weight overcomes the damping capability of the standard shock absorbers.

I started on 15" wheels (with standard 175/65 tyres) and changed to 16" wheels (with standard 195/55 tyres). The 16s are a little rougher but I found they seemed to 'thump' where the 15s 'crashed' - like they were more damped, if that makes sense - so I wouldn't say there was a significant reduction in ride quality. Swapping between my winter 15s and summer 16s is not a night-and-day difference in ride.

I've never driven for long on 17s so can't compare those.

On Tigger's points - the 16s do dull the acceleration of my justaCooper a little and I lose about 1mpg (after correcting for the different mileometer reading) but there's not a dramatic increase in tramlining. But there is a dramatic increase in cornering grip, which makes it a worthwhile change for me.

I have 16" on sports suspension plus, very bumpy ride. Tram lining is very frequent and you wonder what the hell is going on! But I like the bumpy ride and being low-ish, its fine on the motorway and its got good handling. I imagine 17" is even worse, but Id put up with that as the wheels look a lot better, does mean some slow travelling over speed bumps annoying impatient drivers/******s up your arse.