Thanks Calbriggo

[Araf]

That is correct. Lip of the wheelarch to the centre of the wheel. It makes no difference what size the wheels are, as the centre will always be in the same place.

Anyway, even though I have 15s on, they have 50 profile tyres, which makes them just about the same height as the standard wheels.

 

[MovingShadow]

I took pictures as proof when I measured them. I can show you them when I get back home.

 

[Araf]

I'm sure it's correct, so don't worry. It's surprising how different the stance is, with just a 20mm drop - but when you think about it rationally, the distance between the top of the tyre and the lip of the wheel arch can only have changed by about that amount.