Originally Posted by tex
too big - they will be heavy - try 14 or 15 max. 13 is good but limited tyres. the heavier they are it affects unsprung weight
LOL I can tell you haven't built a roadster then! You need 15" wheels to clear the rear suspension arms. 13" and 14" wheels are a no go. If everyone was fanatic about unsprung weight you'd have aluminium brake calipers and magnesium wheels. Its not really an issue for a car that weighs around 600 kgs.
Also as Mr Henderson correctly pointed out, 17" wheels just mean you'll have some stupidly expensive low profile tyres on, to correct the rolling circumference of the wheel. To highlight the point, my 15" Toyo tyres were £28 each. 17" tyres to give the same profile are £70 each.