Mitch or other Tire Experts - need Help - 355 Spider

First question: what tires are on the front? what pressures?
Second Question: how did the car feel before you put these tires on?

Lets just assume that you have a set of tires and want to find the right air pressure for the setup you car currently has.

First lets get the pressures in the right ball park:

Get up one morning and overinflate the tires to 38 PSI, and drive to a streach of road with gentle turns, swales, and changes in tarmac. Drive the road, forth and back. Drive for feel and consistency, not speed. Then take 2 PSI out of all 4 tires. Drive the road, forth and back. Repeat until you feel the grip level come up. Write down this pressure. Now move in 1 PSI increments. We started with enough pressure to reduce the contact patch and the car should be squirly, as we let pressure out we will find a point where the girp level comes up and if we continue it will go back down.

After we get the pressures in the right ball park, reset all 4 tires to the maximum pressure at which grip became good. Drive the road to refresh your memory. Choose one end of the car. Take out 2 PSI on 2 wheels. Drive the road. If you liked the direction the chassis balance was moving take another 2 PSI out, if not then change ends and take 2 PSI out of that end. Now work down in 1 PSI increments. Drive the road. When you feel the chassis balance that inspires confidence. Measure the tire pressures and determine the difference from F/R. Over a wide range of pressures, your car will feel balanced with this difference F/R. As you get better at setting pressure and reading the car you can converge on 0.5 PSI differences to optimize the handling and balance.

In the end, the overall inflation should be between a maximum and minimum pressure (say a 4 PSI window) and the F/R difference should be constant.

I happen to like my tires on the harder side of best grip as it enhances the response of the car, others can enjoy theirs on the softer side and enjoy easier to read feedback. Either way, its the balance that delivers confidence to throw the car around.

General rules of thumb: Pressures stay above 30 PSI and below 38 PSI and you are seeking a difference of less than 2 PSI. If you car wants pressures outside of this range, you can change the rear ride height to minimize the f/r pressure difference.

 

With a car as responsive as a Ferrari, you have exactly two choices when it comes to new tires. You can replce the rears with exactly the same tires (brand,, name, compound, tread, of proper size for the rear) as are on the fronts, or you change all 4 tires.

I suggest you replace the fronts with what you just put on the rear as the easiest way back to a stable car.

classic symptom of the absolute level of grip at the back on new tires not being as good as the grip level of the partially worn fronts. Therefore oversteer. You can learn a lot with a car this unstable, tune your reflexes, learn to steer with the throttle; its real fun, but its is not fast, nor particularly safe.