Thanks Hurdy that's really useful information!
What differences could be felt when going from 17" upto 18 or even 19", is it noticeable?
The difference between a lightweight 17" wheel with grippy tyres and a 19" bling wheel is amazing.
You will be able to get an alloy at 17" weighing 7kg (OZ Alleggerita for example)
a typical aftermarket 19" bling alloy can weigh 14kg (Helios)
The tyres weigh about 0.5kg extra in the 17" size, so you have 6.5kg extra at each wheel = 26kg on the unsprung rotational weight.
To get the equivalent effect of this as deadweight in the car you need to multiply by 5, so......
26kg x 5 = 130kg
This affects accelleration, decelleration, fuel consumption, handling and ride quality.
Extra weight on the unsprung part of the car cripples the ability of the suspension to react as fast as it should and so a choppy, harsh ride is the result...compared to a lighter set-up.
I'm currently on 18" Team Dynamics Pro race 1.2 alloys that weigh 9kg a corner and I can easily tell the difference from the 13kg 19" BBS CH's I had on before. The CH's were a lovely wheel and one of the best 19" wheels for a Golf, but they didn't do much for the outright performance, so I sold them on to someone who would appreciate them more.