PCA SDR

Alright, so I've got these funny looking tires that have as much tread on them as I have hair on my head.

Now I have to figure out what tire pressures to run with these "new-fangled tars" as they call 'em in the South.

Here are the relative stat's:

225x45x16r Hoosiers A6 all around.

Car weight with me in it: 2820 with me in it.

250+RWHP with no limited slip diff.

Tire pressure =?

Or,

8.5x23x15r Front and 9.5x23x15 Rear radial Dunlop slicks

Same vehicle weight.

250+RWHP with no limited slip diff.

Tire pressures = ?

Any help, guidance, suggestions, or ideas would be greatly appreciated (other than I should Go "Stuff" Myself ).

Okay techies, whadaya got?

Dan: I have a good deal of experience with the Hoosier A-6. I settled on 38 psi hot, front and rear for Snickers, and 36-37 for Butch.
Important info on my cars; Snickers is 2750 lbs with me, no LSD, Butch is 2500 with me, has LSD. Both have -2.5° to -3.0° camber F/R.

The A-6 does like negative camber, and are sensitive to rim width. Note the lower psi for the lighter car.
I don't think they make a 225/45-16. There's a 225/45-15 (wants a 8.5" rim), and 245/45-16 (9" rim ideally). ± ½ inch on the rim widths is okay.

The A-6 works best in the first couple of laps (ideal for Autocross or Timed Runs), then gets slower. They work best with "Tidy" (smooth) driving.

pdy wrote:Dan: I have a good deal of experience with the Hoosier A-6. I settled on 38 psi hot, front and rear for Snickers, and 36-37 for Butch.
Important info on my cars; Snickers is 2750 lbs with me, no LSD, Butch is 2500 with me, has LSD. Both have -2.5° to -3.0° camber F/R.

The A-6 does like negative camber, and are sensitive to rim width. Note the lower psi for the lighter car.
I don't think they make a 225/45-16. There's a 225/45-15 (wants a 8.5" rim), and 245/45-16 (9" rim ideally). ± ½ inch on the rim widths is okay.

The A-6 works best in the first couple of laps (ideal for Autocross or Timed Runs), then gets slower. They work best with "Tidy" (smooth) driving.

Thanks, Paul. I'm not sure the side-wall-percent number (I'll have to look), but I'm going to have to "use what I got" for wheels. The tires were used for 2 heat cycles, so they're a bit "broken in."

I'll play with the tire pressures using your recommendations as bench-marks. I'll also monitor heat at the end of the sessions if you think that will help.

They work best with "Tidy" (smooth) driving.

Well, then I'm hosed!

Dan Chambers wrote:
Thanks, Paul. I'm not sure the side-wall-percent number (I'll have to look), but I'm going to have to "use what I got" for wheels. The tires were used for 2 heat cycles, so they're a bit "broken in."

I'll play with the tire pressures using your recommendations as bench-marks. I'll also monitor heat at the end of the sessions if you think that will help.:

Unlike the R-6, Hoosier A-6 tires are "broken in" after about 50 feet.

The pressures I listed are what I adjust to right AFTER a session.
For autocross, each lap adds a couple of psi, so ideally you would drop them down to the target psi immediately after each run (that's what your pit/grid crew is for!).

[/quote]

Unlike the R-6, Hoosier A-6 tires are "broken in" after about 50 feet.

The pressures I listed are what I adjust to right AFTER a session.
For autocross, each lap adds a couple of psi, so ideally you would drop them down to the target psi immediately after each run (that's what your pit/grid crew is for!).[/quote]

And he does mean RIGHT after...I wondered what he was doing zipping out of the car and checking pressures with his helmet still on Now I find myself doing the same thing.

pdy wrote:
Unlike the R-6, Hoosier A-6 tires are "broken in" after about 50 feet.

The pressures I listed are what I adjust to right AFTER a session.
For autocross, each lap adds a couple of psi, so ideally you would drop them down to the target psi immediately after each run (that's what your pit/grid crew is for!).

Aha, more sage advice. I wonder if I can get a certain white German Shepard to work my tire gauge while I'm in pre-grid.

What about "de-pressurizing" a couple of psi prior to runs/heat/practice sessions? Have you ever experimented with that?

On another front: have you ever run radial slicks? I've heard you runs slicks a bit lower than DOT/R tires. Any thoughts on that?

Okay techies, whadaya got?

No sweat, braddah--don't let the hoosiers go over 40 PSI and you'll be good to go.
Less on the slicks.

Word.
TT

Dan,

For the slicks: 19-20 cold. Maybe 21 with that wt. No wait I think maybe 40-45 cool.

John

Dan
My car also weighs 2820 with me in it and I get 252hp to the rear wheel. Don't know anything about Dunlops but I have run Hoosier slicks for about a year: Front 250/645/18, rear 285/645/18. I have also tried 265 front and 305 rear.
I run them hot 28 front 30 rear.Depending on the track they will go up 6-8 pounds in a session. Willow and Fontana 1-2 pounds less on the out side tires.
I have tried camber -3 to -3.2 rear,-3.0 to 3.8 front and like -3.8 front, -3.2 rear best. Don't run the rears below -3, they will cord within 4-5 sessions. I lost two sets of rear tires in one weekend.Have fun and keep that credit card handy

John Straub wrote:Dan,

For the slicks: 19-20 cold. Maybe 21 with that wt. No wait I think maybe 40-45 cool.

John

John
That is the 914- set up. For a 911 like Dan's car I think it's more like 45 on the RF and LR and 21 in the other two tires.
Unless he runs with a spare tire and then he must run aother 5 psi in the left front tire.

Dan, All season tires will heat up the quickest in an AX; you light want to try Brigdestone Blizztaks snow tires.
Always glad to help....

Steve Grosekemper wrote: For a 911 like Dan's car I think it's more like 45 on the RF and LR and 21 in the other two tires.
Unless he runs with a spare tire and then he must run aother 5 psi in the left front tire.

Dan, All season tires will heat up the quickest in an AX; you light want to try Brigdestone Blizztaks snow tires.
Always glad to help....

Dan-
Ain't it wonderful the way folks in this club will just give, and give, and give, until there ain't nuthin' left?
I'm sure you're feelin' all the luv by now...

TT

Mr Tweed...and the Grosemastergeneral

Actually I would think that 250+ HP to the wheels should be help enough...

I can help you Dan...I'll just need to drive your car a lap or 2...

Thanks, Gunter. Sounds about what I thought. The max air rating on the Hoosiers tires is 44-psi. So 36 to 38 hot would seem reasonable.

John, I know slicks require a little less air than Hoosiers or RA-1's, etc., but 21 to 24-psi???? I was thinking somewhere near the 30-psi range give or take 4-psi.

...Dan, All season tires will heat up the quickest in an AX; you light want to try Brigdestone Blizztaks snow tires.
Always glad to help....

Gosh Steve .... THANKS! Good to know the guys I compete against are so .... Uhm .... giving! I was thinking about those Blizztaks, too! But, I can only use 3-mm spikes in those tires. I figured I'd go with something more aggressive with 5-mm spikes for the Q parking lot. Since the temps are so low I'm gonna run 55 to 60 psi and let the cooling affect of old asphalt compensate for the pressures.

Dan-
Ain't it wonderful the way folks in this club will just give, and give, and give, until there ain't nuthin' left?
I'm sure you're feelin' all the luv by now...

TT

Yeah, I'm feeling a whole lotta love in this 'hood. Those I-I competitors ... they're all about the lovin'!

I can help you Dan...I'll just need to drive your car a lap or 2...

Why sure! Tell ya what Mr. Generous: I'll give you the keys to the Black Pearl for one run session and you give me the keys to the GULF stream-machine. Let's see who has more cord showing at the end of the day. Oh yeah, I almost forgot: Got Rev Limiter?

You guys are killin' me!

Any way we can help!

John

On the A6 in the 2900lb Boxster I run 31 rear 34 front hot. And sometimes drop to 29 rear, it tends to allow a more subtle break loose point and thus more catchable. Makes it feel a bit more like a v710..