Tire pressures for 84 Carrera

[450knotOffice]

Sorry if you guys have seen this before but I can't seem to find a straight answer without wading through way too much chaff.

I've got an '84 Carrera with 205/55 16's mounted on 7's up front and 225/50 16's mounted on 8's at the back. The car originally came with those size tires and the sticker in the engine compartment advises 29 psi front and 36 psi rear.

I know that the factory was looking for a good amount of understeer to protect the poor driver from oversteer hell. However, I'd like more neutral handling.

What would the experts out there recommend for tire pressures that would give me a little less understeer? I've read from a few sources on this board that I should go with a more even split, for example 32 front and 34 rear.

The car weighs 2575 empty, has about a 40% to 60% front to rear weight bias, sits at about Euro height, has been corner balanced perfectly (to within 3 pounds front and 0 pounds rear), and has these alignment numbers: camber front - Neg 1.4 degrees, camber rear - Neg 1.25 degrees, Toe front - +15', Toe rear - +20', Caster - all the way back, I believe.

Do you have any recommendations?

[Bill Verburg]

To decrease understear, you want the following

• reduce weight at the front
• more neg front camber
• more pos rear camber
• larger front tires
• smaller rear tires
• higher tire pressure in front
• lower tire pressure inback
• wider front track
• larger front spoiler
• smaller rear spoiler
• wider wheel in front
• narrower wheel in back
• lower front spring rate
• raise rear spring rate
• smaller front swat rate
• larger rear sway rate
• softer front shocks
• harder rear shocks

Some of these require $, others are freebies

[drsimonwong]

Stay with 36 at the back and up experiment with the fronts. Try 32 for a start. I've found a 7psi difference to favour understeer.

Simon

[Rot 911]

I run 32 front/36 rear

[PatrickB]

Hey Scott~
You've seen how low my ride is...
I go just the opposite, and my car rarely swings it's arse out...
32 front, 29 rear!

[450knotOffice]

Thanks for the numbers guys.

I checked my tire pressures just before I stepped out and found all of them way off.

LF - 27
RF - 26
LR - 29
RR - 31


When it stops raining I'll straighten that right out.

[slodave]

I have an '84 Carrera, I try to keep the fronts at about 32-33, rears at 36. That's cold air pressure of course. I like the way it drives...

[bigchillcar]

boy, i must have totally missed 'p-car tires 101'...i thought we just all went by what the tires say! mine say 35 max pressure cold, so that's what i've been doing all along. do i need to be running something different then on my totally street car? i run 215/60/15's on 6 inch wheels.
ryan

[PatrickB]

It's all about what you are comfortable with!
Most daily drivers really aren't able to discern between 1-2 lbs.difference. However, 5lbs, yes! F1 drivers will ***** about being a 1/4 lb change!

Just experiment on your favorite corner, or better yet, highway onramp at the same speed, but different combos!! I'm sure someone will chime in and say that's what auto-x is for, but not all of us are interested in that!

[Tim Stevens]

.

[Tim Stevens]

On the track I run 32F 36R HOT on Kuhmo VR - 30F 35R Hot on Pirelli Corsa. For street I would run close to the same 30-32F 34-36 R. I measure hot because it will change greatly when they warm up. But as stated above do what is comfortable to you

[slodave]

Another thought. My '88 VW Scirocco 16v was setup for canyons - and did a fine job too. I added a tire monitoring system. Was a good device, gave temps, pressures, alarms for various conditions... You will find that each tire will report a different temp. after running around for a while. Engines are not completely symmetrical and air temps are different around each tire. I'm pretty sure that my 911's right front tire would be hotter than the left - due to the oil cooler in the fender well. Tire pressure also affects mileage. We all are paying very high prices for that premium gas.

Dave

[450knotOffice]

It didn't stop raining until late so I'll add some air tomorrow.

What brought all this to light was our run on Sunday in the canyons around Mulholland. On the super sharp second gear corners, my car would understeer so badly that I ended up completely in the opposite lane a couple of times with the wheel hard over. The only way to get it to tuck in would be to chop the throttle.

I'm guessing I might have gotten a little bit of tire roll due to the low pressures up front.

[masraum]

Originally posted by bigchillcar
boy, i must have totally missed 'p-car tires 101'...i thought we just all went by what the tires say! mine say 35 max pressure cold, so that's what i've been doing all along. do i need to be running something different then on my totally street car? i run 215/60/15's on 6 inch wheels.
ryan

Ryan, you definitely don't want to run what the tires say. You may end up running that, but that's a max inflation, not a recommended. You'd be much better off running what the car manufacturer says.

Most people run something in the range of 32-34 cold in the front and 34-36 cold in the rear. I used to run about 2-3 lbs higher in the rear and that served me quite well.

[masraum]

Originally posted by 450knotOffice
.


The car weighs 2575 empty, has about a 40% to 60% front to rear weight bias, sits at about Euro height, has been corner balanced perfectly (to within 3 pounds front and 0 pounds rear), and has these alignment numbers:

camber front - Neg 1.4 degrees
camber rear - Neg 1.25 degrees
Toe front - +15', Toe rear - +20', Caster - all the way back, I believe.

Do you have any recommendations?

Can you double check those alignment numbers for the camber? If those really are your numbers then you may be in for a surprise. The most common alignment specs call for .25-.5* more camber in the rear than in the front. I've seen one or two people recommend/use the same camber front and rear, but I don't think I've ever heard anyone using more in the front (unless the car has huge rear tires maybe, and even then).

A common street/track number would be -1* frt and -1.5* rear. Some go much farther if they can.

No expert, just thought it seemed unusual.

[Carl83911]

Originally posted by bigchillcar
boy, i must have totally missed 'p-car tires 101'...i thought we just all went by what the tires say! mine say 35 max pressure cold, so that's what i've been doing all along. do i need to be running something different then on my totally street car? i run 215/60/15's on 6 inch wheels.
ryan

If that is the case, then i'd have to inflate mine to 50psi