I need new tires fast

the OEM tires are 225/40ZR18 front and 265/40ZR18 rear

The fronts have a rolling diameter of (18*25.4)+(225*0.40*2) = 457.2+180 = 637.2
The rears have a rolling diameter of (18*25.4)+(265*0.40*2) = 457.2+212 = 669.2

The OP fronts would have a RD = (18*25.4)+(245*0.40*2) = 457.2+196 = 653.2
The OP rears would have a RD = (18*25.4)+(295*0.35*2) = 457.2+206.5 = 663.7

So, the fronts are WAY TOO BIG while the rears are perfect.

The proper front would be (225/265*295) = 250.47
And would have an aspect ratio of 0.36

So, lets look at 245/35ZR18 instead

This new front would have a RD = (18*25.4)+(245*0.35*2) = 457.2+171.5 = 628.7

Which fits the bil quite nicely. Loose 8.5 at the front and 5.5 at the rear, probably pick up a touch of understeer (well within the range where air pressure adjustments can set up oversteer/understeer relationship.)

 

This link has all of the tire size info on the PS2. I agree with the above comments. Try to have the relative change in tire diameter the same front to rear. A larger front tire diameter will change the attitude of the car, creating more front lift (and less control) at high speed.

http://www.tirerack.com/tires/tires.jsp?tireMake=Michelin&tireModel=Pilot%20Sport%20PS2&tab=Specs&partnum=635YR9SPORTPS2N1&fromCompare1=yes&vehicleSearch=false

 

http://www.miata.net/garage/tirecalc.html

 

I would suggest that the best size is the size that Ferrari specified.

 

Call Tirerack and get ahold of one of their tech/pre-sales people. They are all very knowledgeable and should not steer you wrong (no pun intended).

Of course, you can always just use their online tool to find the matching OEM spec tire or "all sets" that will fit and then go from there.

I have Michelin PS2s and couldn't be happier.

 

If you stay with what Ferrari designed for this car you can not go wrong. 225/40ZR18 front and 265/40ZR18 rear

When you change the size you will sacrifice something.

 

255/35/18 in front on original rims would probably start looking really awkward. I have 235 in front and even that starts to look a little too big... I would stay on original size if I were you.

 

Rick, I'm planning to put PS2's on my car. What size do you have in the back? The reason I as is that I don't think they make a PS2 in 265/40ZR18 (they're 35's right?)

 

Those are the exact size tires I have on my car, although I have CH wheels, which are slightly wider...

 

The front wheels are 8.5" wide or 215.9mm
The rear tires are 10" wide or 254mm

The tires are designed so that their side walls are approimately verticle when properly mounted.

So we have a 12" tire at the rear being mounted on a 10" wheel with a 4.2" sidewall height. At the front we have a 10" tire being mounted on a 8.5" wheel with a 3.5" sidewall. Might work, biut the tires will stick out a full 1" wider (rear 0.75" front) on the wheel than the OEM tires. This might cause some fender interference issues.

 

I recently put a set of Goodyear F-1's on my car sold in the factory sizes from Tire Rack. (98 355 GTS). It is absolutely amazing the improvement in handling, ride and sound in the car.

My wife who hated riding in the car with the Pirellis is now enjoying the car and the improvement in the handling is fantastic. I also beleive these will probably wear a lot better.

Bobert

 

I would like to seem some pic's with those on. Keeps us updated on these


Cheers!

 

So Mitch, will there be any handling issues with going three sizes wider in the rear? I would suspect more understeer from this set up. When I bought tires three years ago, I did go up one size in the rear to a 275/40/18, but mainly because there were pretty limited selection on 265's if I recall correctly at the time...

 

I run 255/35/18 on the front and 295 on the rear on HRE wheels. The fronts are 9 inch rims. I had to bend in the fender lip since the car is lowered. Ride is great and braking is better than with the 225 fronts.

 

I actually run 275/40/18 because of the availability, and had the rear ride height lowered to rebalance the roll couple distribution with these taller tires.

As I aluded to before, the tires are designed so that the sidewalls are supposed to be roughtly vertical. When the wheel is wider than the tire, the outside edge will roll under under cornering. This is perfect for strut cars that loose camber while cornering. When the wheel is not wide enough, the outside edge will effectively add camber while cornering. Something well setup Ferraris don't particularly need.

So, if you are currently using factory camber you can probably get away with the wider tire on the standard wheel. Even here, however, it is probably best to dial some camber out (0.10-to-0.25 degrees) to make up for the wheel width issue. The wheels will also alow the car to move laterally by some 0.25 inches or so, and a sensitive driver WILL notice this uncertanty in longitudinal position while driving (on standard width wheels).

You shold also dial out some toe because the amount of toe one wants is found in the centering force. The wider tires will have more centering force. Go from 2.0mm toe to about 1.75mm toe (in).