355C Hoosier Tire Pressures?

Mark
In the absence of anyone chiming in with 355 numbers, I can tell you that I use 30 front, 33 rear, cold on my 308. I never bother with hot pressures, except to use + or - depending on what the pyro says.
Those numbers were established with a Pyro and settings of 2 deg neg camber front and 1 neg rear.
Good luck with your testing - I hope this is some sort of help.
John

 

You might want to contact Hoosier directly, or a Hoosier dealer with Ferrari experience like Bob Woodman Tires. they could probably provide the best information regarding ideal pressures and temperature ranges. They will let you know not only what is ideal, but also the danger zones (both too high and too low) for pressures. I know that Hoosier tires in general like hot pressures in the 38-42psi range, which does seem high, but consider that their tires are street tire based, and lack the firmer sidewall of a slick like the Pirelli typically used on a 355C. Even the 'slick' Hoosier's used in Grand-Am are still pretty much street tire based, and still require that high hot pressure. They need that extra pressure to not only work well, but also prevent tire failure which could occur by running them at incorrect pressures (ie using pressure baselines from a genuine slick [Pirelli, Yokohama, Dunlop, etc] instead of the CORRECT numbers). Hope this helps.

Jeff

 

You know it is partly track dependant I.E. too many right turns gets the left side hotter, and alignment set-up dependant too and ambient temp too. So you need to have the alignment baseline in your logbook too. Run a reasonable starting cold pressure say 30psi cold and expect a 7-10 degree rise using air. Check with a pyrometer for even temps then adjust in 3 lb increments up or down to suit even tire temps will get you close today.

 

The biggest factor in determining your pressure fluctuation is the quality of the air you put in it.

Specifically, it's moisture content.

if you use regular compressor air, it will have high moisture, bottled air from a gas supllier will be better, but nitrogen is the best to use for minimising fluctuation in pressure. or at least use a water trap on your compressor...an in line one.

It's still quite normal to see 20-40% rise, but if you can keep it to 20%, it's a more consistant lap time than a 40% fluctuation.

Nitrogen also has larger molecules, so leakage is reduced over extended periods.

 

FF is correct. IMO the real problem is not the air quality but the tire mounting quality. The tire monkeys always use water based soap to apply the tire. The water gets in the tire in higher volume than the water content in the air. It is difficult if not impossible to get the water out and it stays their just like if you spit/blow into a ballon and tie it off. So IMO if you really want to get the good stable pressure you have to use nitrogen and install tires with waterless soap and you can get maybe 3lb hot/cold differences instead of 7-10lb hot cold differences with compressor air/ water mix.

 

Direct from the Hoosier site:

________________________________
Tire Pressure Recommendations
Hoosier tires typically require higher pressures than other brands. Autocross applications require higher ranges of pressure; road racing tends toward the lower end of the recommended pressures.

Reference the following chart for suggested pressures:

Vehicle size
Recommended Hot Pressure
Cold Pressure

1800-2200 lbs.
Hot 39-42
Cold 30-36

2200-2600 lbs.
Hot 40-43
Cold 31-37

2600-3000 lbs.
Hot 42-46
Cold 32-37

over 3000 lbs.
Hot 43-48
Cold 32-38


Higher pressures will improve the performance capability but will require a more sensitive feel to take advantage of the increase.

One characteristic of the Hoosier P-Metric radial tires is the tendency to "skate" initially (when inflation pressures are correct). It is important to resist lowering the pressure to attempt to eliminate this feeling. Dropping the pressure may improve the "feel" of the tire however it will also lower the performance and increase the wear on the tire, particularly on the outside tread edge.

The above chart is a general recommendation which is intended for a standard configuration vehicle (i.e. front engine, rear wheel drive). Factors which can radically affect your pressure set up would include front wheel drive, independent rear suspension, rear engine, McPherson vs. control arm front suspension.

Independent rear suspension
With IRS and proper geometry up front, tire pressures can be reduced from the recommendations listed above. When there is adequate camber gain and good roll control, the Hoosier radial tire will perform very well at the reduced air pressure. This results in a bigger "sweet spot" and easier control at the limit.

When tuning at reduced pressures use the following formula to determine the minimum safe pressure: Divide the total vehicle weight, including fuel and driver, by 100 to arrive at the minimum safe pressure. Example: Your car weighs 2750 lbs. as raced. The minimum safe (cold) pressure is 27.5 psi.

Extreme care should be taken when tuning at reduced pressure. Tire damage can occur that is not visible to external inspection.

______________

Personally, I think it is best to work off of hot temperatures. Obviously, if it is 30 degrees outside in winter or 110 degrees in summer there will be a differential in the increase in pressure from cold to hot, as the hot temperature in any case will be relatively consistent. Besides, the car is driven at hot temperatures, so that is how I believe the critical pressure should be measured.

I don't know any specific front to rear pressures for rear engined cars like the 355C, but my race Viper's weight distribution is 47%F/53%R (3000 lbs with driver and 5 gallons of gas) and I found hot pressures of 42 psi front and 40 psi rear work real well for me.

Hope this helps.

Best regards,