Steering brace is a very simple add-on. About 15 min.

I went from 17" Cups to 18" Solid Twists. Very happy with the change overall. There are a number of variable's to consider when switching diameters. Aside from weight, I think your choice of tires will have the most great impact on the change. Every tire selection has a unique set of handling characteristics. Although 18's have a shorter sidewall, some tires will have a softer sidewall and some stiffer. Bottom line....very happy with the change to 18's (simply looks way better). If it looks better, it must handle better. ;-)

 

My comments are relevant for track use only and if you're looking to maximize the rubber in your wheel holes. I started my long quest for tire/wheel selection by searching Rennlist and then started doing my own research. I ended up with MY02s (8ET50 front, 10ET65 rear) with 235/285 respectively Michelin Pilot Sport Cup tires. I know Bull and others commented on easily and continually running 295s in the rear at the track but I felt more comfortable with 285s since the general consensus was there was never a problem with that size.

I added the Technical Service Bulletin (TSB) brace mentioned above.

The part I wanted to comment on is the myth that staying in 17" offers more of a variety. I found variety is not greater, but price is what I call reasonably more expensive when trying to find rubber in 235/285 sizes. The only 17" options close to 235/285 were Hoosier A6 and Kumho V710 and even then, I had to go to 225 front and either 275 or 295 rear, not to mention you won't get that many heat cycles out of these tires so replacement is frequent and expensive. Yokohama Advan AO48 only went to a 255 rear, Pirelli PZero Corsa wasn't an option, and Michelin PSC only had 225/275 as an option. As soon as I started looking at 18", there were many more sizes available in 10mm increments including the 235/285 combination I was trying to achieve. The interesting thing is that when comparing the 17" to 18" in price, the 18s were only about $30-$40 more per tire on average, but you were getting more rubber front and rear for the extra money.

For example, the 225/275/17 MPSCs are $250/$288 at Tirerack. By way of comparison, the 235/285/18 MPSCs are $283/$328. Another example is Yokohama Advan AO48s where 235/255/17s are $271/$266 while 235/285/18s are $289/$314.

As Bill mentioned, the tires run cooler but since the contact patch is bigger, you are spreading all the forces of the car onto a larger patch and thus, wear rate is also better. An 18" tire of the same size and compound as a 17" tire will have better longevity because of this.

This is what I determined anyway and even if anyone disagrees, please let me live in my imaginary world with these comforts.

 

The contact patch area will always have the same area within a small range due to sidewall and pressure deltas.

the shape of the patch is what changes, the lower profile tire of the same width will have a wider but shorter patch, this is good for grip as grip is developed more at the leading edge of the contact patch than at the trailing edge and temp due to lower slip angles distorting the rubber less for the same grip. It's bad for feedback as there is less warning at the edge of grip. As w/ brakes the cooler the greater the lifespan

 

Beauty is in the eye of the beholder! I did the exact opposite swap that 99_993 did and other than the order in the first sentence, I could make the same exact post as he did.