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Tomcat0815 2/26/19 03:38 PM

Boss 302 owners manual tire pressure recommendations for track
Hello y'all,

I have a question concerning Boss 302 track use.

I own my 2012 Boss 302 for about 8 months now and have been to about 6 track events so far here in Germany.
During the last event, I had to use my normal road tires since I could not find anyone to haul 2 of my semi slicks (they did not fit into the Boss - they DID fit easily in my former E46 M3 though).

Because I was unsure how my Good Year Eagle F1 tires would perform, I checked the car's owners manual.
And the manual recommends 283 kPa (hot) as tire pressure. That sounded like an awfull lot to me.

Does that make any sense? Do you race your Bosses and GTs with that much tire pressure? Why does Ford recommend such a high pressure?
Instructors recommended a far lower pressure to me. I used 2.2 bar (220 kPa) front and 2.4 bar (240 kPa) rear, I did not get around to just try these 283 kPa.

In this video, you can see that the car understeers like hell with these pressures:

(sorry for the broken sound of my iphone)

And I'd expect it to get much worse with 283 kPa hot.

Do you have any ideas or recommendations on this?

Suspension is stock so far and dampers on 5. Changing front dampers to 4 only made it worse.

Thank you very much for your input.


Oliver aka Tomcat0815

5.M0NSTER 2/27/19 12:26 AM

283 kPa is roughly 41 PSI, and that is WAAAY high. I can't believe that's the recommendation. On street tires I would not recommend going over 35psi or 241 kPa. I would typically run my max perf summer or extreme perf summer tires at 28psi (193 kPa) cold at the track so they warm up to 34-35 PSI warm. But over that they start to get greasy fast.

Tomcat0815 2/27/19 01:11 AM

Originally Posted by 5.M0NSTER (Post 7039207)
I can't believe that's the recommendation.

It's in the original Ford Manual that I downloaded as .pdf:

"Track use preparation", Page 37:

"For track sessions, it is recommended to run 41 psi (283 kPa) hot for
the OEM tires, front and rear.
  • Depending on track temperature, ambient temperature and driving style, you may need to reduce the starting tire pressure by as much as 4 psi (27 kPa).
  • The starting pressure may be lower in the rear tires relative to the front tires to achieve 41 psi (283 kPa) hot.
  • Reset tire pressures to placard recommended pressures before leaving the track."
On the other hand, I am not using Prielli P Zeros but Good Year Eagle F1, as I said. But I cannot believe that makes such a big difference.

Maybe it's safety concerns to prevent too much oversteer?
Or to protect the tire's sides/flanks from damage?

Bert 2/27/19 07:25 AM

I am also surprised to see the manual recommending such high pressures; I guess they are being overcautious for some reason, not sure why.

It does vary by tire, but my experience is similar to 5.Monster's -- around 34-35 psi hot seems to be about right for the street tires I have used.

You are probably familiar with the "roll-over" test -- most tires have marks on the sidewall to show how much the tires should roll over on hard cornering. You can use chalk on the sidewall to make it easier to see; but basically you take a few laps and then check to see how far the tires are rolling over. The "best" is usually right in the middle of the mark. If the tires are rolling over beyond the mark, increase the air pressure; if not reaching the mark, reduce the pressure.

Tomcat0815 2/27/19 08:28 AM

Hi Bert,

that roll over test sounds like quite a neat method, I am gonna try that on my next track day.

I just hope I do not forget to bring chalk.

5.M0NSTER 2/27/19 02:00 PM

Meppen! I recognize the cooling tower. I wasn't doubting you, it's just a surprisingly high pressure to recommend when the door sticker calls for 35psi. :-)

Nice driving, you handled the understeer quite well! I did the following to help with understeer: Lowering springs, Panhard bar to center the rear axle after lowering, Steeda Competition front sway bar and Steeda Camber Plates. Then I set the front camber to -2.1 degrees. No more understeer unless I overdrive the car or overheat the tires. I had the front bar set to middle setting, but in all honestly I could have had it on the softest setting and It would have been fine for body roll, and even less understeer.

TymeSlayer 2/27/19 02:07 PM

I start out around 29 PSI on 300 TW tires, a bit lower on 200 TW tires and they'll heat up to about 35-36 typically.

Tomcat0815 2/28/19 12:42 AM

5.M0NSTER I already ordered H&R camber allignment bolts. I was hoping to be able to get -1.5 camber from them but maybe I will try going to -2.0 as you did.
also got the whiteline adjustable swaybar kit, BMR UCA and LCAs and an adjustable panhard bar with panhard bar brace. All of this is going to be installed over the next weekends until the next track session on March 16th on the same track.
It is possible to order the origninal Boss 302 lowering springs from Eibach USA via UK and I might do that.
I would prefer the ST XTA coilovers though because they come with adjustable strut mounts. I first need to source another 1000 for that, though :-(

I tried to counter the oversteer by steering in more softly and also tried to drive all radius a little larger than the racing line.
Like I said, I have semi slicks but had no one to bring them and 4 tires do not fit into a mustang.
Next session will be on semis, they help a lot with the oversteer, maybe because it is a square set up.
I use 18" 265 on al four corners because I get them for free.

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