How is your L/100 km with 17" wheels? (205/40/17 tyres)

I'm thinking of getting that size, but was worried that it would affect the economy too much.

I drive a 1.9 TDI Combi

Got 16's on mine & it has made about 3 or 4 mpg difference, same engine in mine as yours

dunno about litre/km but I have 17's on mine and my average overall is 46mpg, my normal driving usually see's about 40mog around town.

Get average of 48 with around 44 in town on 16's

I put 17s on mine when it was still standard (long time ago now ) and the economy dropped by about 10% - This was probably in part due to the larger rolling radius compared to the 14" steels (so not a "real" drop) and also the new rubber was 205 wide, and the old tyres were 185 wide - so had more contact with the ground. This helped with grip though.

Larger rolling radius? So your speedo is out?

The rolling radius should remain the same, just with more alloy and less rubber.

The unsprung weight will increase however and it's this that's the killer.

Also, as you say, extra width increases grip but also rolling resistance.

True, the 16's I put on mine are way heavier than the standard steel 14's that came off.Had mine into dearlership for a couple of days last week & they leant me the same model as mine as a courtesy car, it felt a little more lively not sure whether this was down to having standard 14's on it or the fact it only had 8k miles on the clock, my car has 70k?