Gear ratios

[wanda]

Might be a silly question but bare with me, if you up size your alloy rims from say 17" to 18" or 19" does that indirectly affect your ratio? I was thinking if you are increasing the circumference of the wheel meaning one hole revolution would take you slightly further would that mean the revs of your car would go down at a steady speed?

[Stranger]

I would've thought so

[morganjake1544]

That's why tyre choice is important.
Larger diameter wheel needs a lower profile tyre to compensate (and look the part).
It's the overall diameter (wheel and tyre) that matters.

[wanda]

Could it ever affect it in a positive way? If currently cruising at 70 mph the revs are at 2200 - 2400, would bigger tyres and alloys lower this?

[morganjake1544]

Theoretically yes.
However, this would affect the car in all gears not just top/cruising gear. ie harder to pull away and less acceleration in the lower gears.
Greater minds than ours have spent thousands of hours and millions of pounds (well, Euros) to come up with the exact wheel,tyre and gear ratios that are currently in our Meganes. On this occasion I'm prepared to give Renault the benefit of the doubt.