Wheel question
 

I asked my friend about my decision to put 18 inch wheels on my car. He said that I should get 7s because if I put 18s, I will loose torque.

Any truth to this? Feedback would be greatly appreciated.

OmarTT
180fwd

18"s are heavier than identical 17"s. More metal.

And more unsprung weight translates into performance detriment.

Lighter 18"s would be better than heavier 17"s tho, less weight by rim *and* tire, smaller sidewall.

If wheel + tire heavier, acceleration suffers...
 

Really it's about 'moment of inertia', but practically it's about weight. Think of the wheel and tire combination as a 45 lb (or so) flywheel on each corner of the car that must be spun up from 0 to 750 rpm (about 60 mph), in 7 seconds or so.

Now increase each wheel/tire weight 5 lbs. near it's outer edge. Now you're spinning up 4 50 lb. flywheels. This takes more power, so there is less left to accelerate the vehicle. You could probably measure the diffrence. The extra 20 lbs. of weight also makes a tiny difference in acceleration. (a little over 3 gallons of gas worth of weight)

Second point is 'unsprung weight'. 5 lbs extra can probably be felt by someone who is very sensitive to ride/handling motions, but most of us won't notice, nor be able to measure, the difference.

Heavier tire/wheel combinations probably hurt vehicle performance more than they help handling, (assuming you are starting with 225/45-17 Portenza 040's). If you are concerned, look for a tire/wheel combination the same weight or even lighter than stock. That weight data isn't easy to find from manufacturers. Ask people here to weigh their aftermarket tire/wheel combinations.

In the end, changing tires/wheels on a TT is often about looks, not performance. If it fits well, and you like the look, go for it, as long as you know the +'s and -'s.