[tirod]

There is an assumption that the 17-18" rims and tires have better grip, etc. It's measurable, and can't be disputed.

But it's not all that it seems to be - there's a lot of marketing being repeated in the comment. What you are also getting is a low profile tire, which in and of itself is the cause of much of the performance increase.

Short sidewalls and wider rubber does that, not the diameter. What is supposed to be happening is a rim diameter increase because the brake rotors are oversized.

Well, that's incremental - you can increase braking power quite nicely with more pistons, and having balance - it's getting to be known the rear brakes on these cars need to be four piston, too, and do more work than the (inadequate) Lincoln or Mustang setups deliver.

On the track, cars raced with tire rules move to low profile rubber and get much of the same improvement. And when rim size goes up, there are offsets of a negative character - mounted wheel weight goes up, there's more rotational inertia, and handling in other areas actually suffers. It's not all sunshine and roses. And, it's measurable.

Since street tire 17" tech isn't nearly in the 15" race tire league, the major component of this current fad - there, I'm saying it - is entirely based on looks. The performance is there in an incremental degree, but it is not that substantial.

Which brings up, How much does it cost for the difference? Are you getting your money's worth? Again, if you spent that difference on better brakes, would the overall increase in performance be superior?

Here's the comparison to think about - will fitting 17's on a factory donor equipped power brake set up be better than a dual master fitted four piston setup with 15" race tires?

Dollar for dollar, all parts bought new, I hazard they cost the same . . .

Rim size is just one small part of the overall tire/brake package that meets the road, and the focus on plus oversizing seems myopic. It's not all about rim size in the big picture, it's about what delivers the best performance with the available assortments. We're jumping forward to choosing the rim size when in fact it should be a natural result of the size brakes and overall performance goals.

If 15's look like they might be fading away, I put it as simply that part of the overall marketing cycle, and as soon as the consumers become more educated, then rim sizes based on overall factors will be the choice - not what is a current fashion.