Tire guys-
I used to sell alot of tires and I have a number of observations to make:
1) I like to match the stock diameter of the tire to maintain speedo accuracy.
2)
The wider the tire the wider the tire contact patch or the greater the
amount of tread on the road is not always the case! If you put a
relatively wide tire on a relatively narrow rim the narrow rim will
pinch in on the beads of the tire and curl up the inside and outside
edge of the tire diminishing the contact surface. Also, the pinched in
sidewall of the tire will be floppy and reduce the transient response
of the tire (The car will be slow to respond to steering inputs) This
is not what you want in a sportscar. In fact, a wider rim will
cause the sidewalll of the tire to become stiffer resulting in crisper
response and more grip all else remaining the same. If you look at a
picture of a Formula one car you will notice that the rim is usually
wider than the tread of the tire! Those guys know how to make a car
handle. The rim pinching effect does not take a wide discrepancy in
tire to rim size to occur.
Case in point: My Mustang (I know,
this is a British Car site but tires and wheels are tires and
wheels) has15x8 rims front and rear. The front tires are225/50ZR15, Any
bigger rub on the upper ball joint. The rear are245/50ZR15.
Here's
the punch line...Even though the rear tires are 20 mm wider they have
the same tire contact patch as the front tires due to the phenomenon I
described above! How do I know this? My driveway is dusty and you
can clearly see the contact patch the tire makes in the dust on the
tire. One day I actually measured it.
So what does this mean? The
225/50-15s have a tread width that is about ten percent bigger than the
rim width.It seems like any wider tread would give no benefit and may
actually hinder the car's handling. It could even be that a narrower
tire would still have the same contact patch! Anyway, it seems if you
are going to run 205s on your car the rim should be, at minimum 90
percent of that width= 7.25 inches wide or you will just be adding
weight, expense and lost responsiveness to your car.
If you don't
believe me there is a book titled "How to Make Your Car Handle" by Fred
Puhn which will explain the point in depth. It's an awesome book with
stuff that can be applied to any car.
Allright guys, I said it- Now let me have it!
LCJUTILA (Not the law, just my opinion)
P.S.- I'm going to get the rear rims widened an inch on the Mustang to fix the problem.