Will fitting smaller wheels to my car improve ride quality?

I have a Mercedes-Benz ML-Class, with Airmatic suspension. The car is on 21-inch wheels at the moment. Would it make a big difference to the ride if I fitted 19-inch wheels?

I do 12,000 miles per year with occasional long trips - should I get a petrol or diesel car?

I'm considering a nearly new, top spec Nissan Qashqai and I'm unsure whether to opt for a petrol or diesel model. The car will be mostly used for commuting. My journey is 20 miles from home to office,...

Will changing the wheel size make the ride more comfortable?

I have a 2009 Ford Focus with 17-inch alloy wheels. What is the standard size and, if I changed to the standard size, would the ride be more comfortable?