TIRE PRESSURE QUESTION FOR NON RUN FLAT TIRES

[Racer Robbie]

I am about ready to install a new set of OEM size Michelin NON RUN FLATS on my 2003 SRT-10 Viper. They are going on a new set of Copperhead ( Sidewinder ) wheels from Parts Rack. I have decided to run my old pressure sensors, though I hear it is not necessary to do so. These Sidewinder wheels are 34 lbs lighter than the stock OEM wheel and the tires are 10 lbs lighter than the OEM Run Flats. This is a total weight savings of 44 lbs of unsprung weight. Using a stock suspension, with this 44 lbs of saved weight, what would you set the pressures at front and rear cold? Also what pressure are you looking for once the tires have come up to temperature?

 

[Viper X]

I run this combination on my 04 SRT-10 for some events and also got my Sidewinders from Parts Rack. A cold tire pressure of 30 front and rear seems to work well.

At the track, you will want to start at 32 psi cold and adjust as needed. Hot tire pressure at the track tends to be about 37 - 38 psi, depending on the air temp that day.

 

[Racer Robbie]

Thanks Viper X.
Are you running Michelin NON Run Flats? Luke at the Tire Rack had told me to *** 34 front and 30 rear so as to increase the oversteer in the cat. That seemed a little radical to me.

 

[rcl4668]

Take my input for what it is worth because I have not yet tracked my Viper; however, various car magazines have noted at least a slight tendency towards understeer or push in the SRT-10s (both coupe and roadster). Given this, I am not surprised by Luke's recommendation to bump the front pressures relative to the rears. I run my car 29 psi rear and 33 psi front for the street to dial out the understeer and achieve more neutral handling. I will also start with these pressures as a baseline when doing my first track day.

This is of course with the OEM runflat tires, but I would call both Luke at TireRack, JonB at PartsRack and perhaps even Michelin to ask them about the need to change pressures based on going to the nonrunflats which do not have the sidewall stiffness of the OEM tire.

Hope that helps.



/Rich

 

[Vipera Russelli]

I use 25 rear and 26 fronts when cold in Sport Cups, which brings them both to the same 34 or 35 on the track when hot.

 

[Viper X]

Atro,

Yes, NON run flats, 30 front and rear to start.

The run flats are a different tire and I've tracked them too. They seem to like 34 or so cold both front and rear. They have much stiffer sidewalls.

Cups seem to like 32 or so cold front and rear to start.

All of this depends somewhat upon the weather, how hard you push the car and the track layout itself.

Both my GTS and my SRT-10 tend to push a bit in the turns - understeer - with stock tires. At times I have gone to larger front tires and find 295s, 305s or in some cases 315s to work better than the stock sizes up front. This kinda depends on what you like.

I wouldn't recommend varying the tire pressure too much front to rear or you may have some interesting handling challenges.

Jon B / Parts Rack is a good source of information. This is where I started getting this type information a couple of years ago.

Good luck,

Dan

 

[Racer Robbie]

Thanks Viper X and to all you others. I ran 34 all around on the Run Flats and that seemed perfect on the street, 36 on the track and never felt any understeer. Luke at The Tire Rack has told me 2 different pressure settings and I do not know why. First off he said to run 36F, 32R and then another time said 33F, 29R. Both of these will increase oversteer and dial out the push. I think Viper X is right on with 30 PSI all around for NON RUN FLATS on the street and 32PSI all around for the track. Again, thans Viper X.