Many of us have read or experienced that listed tire specs are not totally accurate.
For the last 8 years my car has run: Yokohama Advan AD08Rs, 255/35-18 front on 9X18 rims and 285/30-18 on 9.5x18 rims.
The fit was perfect as well as clearance.

Since I do not participate in any competition, I decided to go to Michelin Pilot Sport 4S with better wet control for street driving.
Their 255/35-18 specs match almost identically with the Advans and actually when mounted look about the same in size.
The problem comes with the rears, 285/30-18.
The Michelin web site lists section width for the 285s and the 295s as 11". Advans are listed as 11.2"
Tire Rack lists the 285s as 11.4" but I measured 11.75",
Visually they are about .25" wider than the Advans per wheel side.
The Advans 285s looked like perfect fit while the MIchelins look a little too bid for the rims due to bulging.

I read years ago that sometimes tire makers use the same carcass size for different tires sizes with only the tread width being different.
Wonder if this is the case with these American made Michelins. They my actually be 295s with 284 tread width.

Inside tire clearance is fine, but outside looks very close. I will have to test with small radius fast cornering.

ANY EXPERIENCE OR THOUGHTS.

 

Today with the rear sway bar disconnected, one rear wheel was lifted all the way up until the car started lifting.
Due to the increasing negative camber of the suspension, the clearance was good between the tire and fender.

 

sure, a few years ago when we were running the NASA PT/TT series the Hoosier R6 was the fast tire. the 205/50/15 Hoosier was about the same width as a 225/50/15 Toyo/Kumho...
in the current class they make us build a little jig to measure the tires width, so we can't have tires that say 205 but actually are 225's....

interestingly the 205 Hoosiers ran wide, but i think the 195's and 225's were more true to size