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The wider tyre is going to improve cornering and braking quite noticably but will result in more resistance as you have a larger contact patch on the road. ie. economy, acceleration and speed will suffer a bit.
The lower the profile the harsher the ride as you have less rubber on the sidewall of the tyre to absorb bumps but the trade off is less flex in the sidewall and hence better grip particularly when cornering. I also used to find with bad roads it was very easy to damage the rims with ultra low profile tyres (Sparco Racing wheels weren't made for Sydney roads).
The wheels rim size and offset is also going to impact how wide you can go as the rim has to safely support the tyre width and the tyre shouldn't protrude beyond the wheel arches.
Alot of people are happy with the tradeoffs of going even to 16" (or even larger) with really wide tyres but personally I intentionally chose only 14" Honda (Enki) alloy wheels to maximise performance. I'm considering going the next size wider in tyres when these wear out but not up in wheels or any wider than just an extra 10 wider in tyres.
Guys with 17"s report very noticably worse fuel economy and sluggish takeoff. The car isn't really designed for them but some people are only concerned about looks at all costs.
Tyre compounds will also effect performance. As wonderful as Silica is for grip particularly in the wet it means more resistance. Its interesting to look at the tyres chosen for the hybrid cars as these really maximise a cars economy due to absolute minimum resistance.
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