proper tire pressures

Hi,

You could start out at 36 or so HOT AFTER PROPER WARM UP and go from there. Please remember that tire pressure increases approximately 1 psi per 10 degrees F increase. It also depends on the suspension, road temps, road condition, tire compound, etc. There are variables and there is no substitute for driving the car near limits to tune the pressure front and rear accordingly. If you are looking for a "set and forget", then perhaps 33 psi at ambient temps of 72 F when the tires are cold.

Of course this is just my opinion. Usually tune the air pressure by "feel" and take readings accordingly. ALSO, get a GOOD pressure gauge and NEVER use air filling at gas stations as they usually have water in their system (bad).

Hope this helps.

 

Best place to get a good compressor then?

 

Rust is a possibility, but the real point is that water expands/compressed more than air as temperature changes. If you want to go "trick," use nitrogen

As for air compressor... i have one of the $50 battery powered jump starter/light/air thingies. It has no "real" reservoir so the water content in the air is basically the same as the outside humidity factor. Also, the $50 jobbie fills the tire VERY slowly for a touch more "precision," but i ALWAYS check the tire pressure (to within 0.5 lbs) using a digital pressure gauge.

 

That all depends on what you want to call proper pressure. IMHO the proper pressure for the front and the rear is achieved through driving the car and having the PSI set to achieve the handing desired for the application at hand.

Hope that does not sound like mumbo-jumbo, yet different driving conditions dictate different tire pressures to achieve maximum handling. How many times have you watched an F1 race and heard how they made some last minute tire pressure changes? Hope this helps make the point.

 

Husky brand, $99 at Home Depot. Electric, great for small things, but not running air tools. Perfect for inflating tires.

 

I will echo Steve's posts. IMO the best place to start is at the recommened pressure settings, and see from there. In general, more air in the front, the more 'floaty' the front will be (if high pressure) or more understeer (too little pressure)

More pressure in the rear relative to the front and more understeer you get, and vice versa...

Thanks Mule for the tip!

 

I forgot to add, less air in the front the heavier the steering will be too...something notable when you lack PS.

 

I second Steve and Mule. Cheapo 12V air compressors will do. You can probably get one for less than $25 out of Wal-Mart or Target. They hardly break, unless you drop them or drive over them. Used to sell tons of them out of China. I use them all the time, in conjunction, with a digital tire gauge. I always keep a 12V compressor and digital tire gauge in the trunk. They will definitely pay themselves many, many times over, in terms of saved frustration and possibly towing fees.

A while back, I had a slow air leak (took many hours for the tire to become flat) due to an embedded nail. So, I simply pumped up the leaking tire and drove very slowly for a couple of miles to my neighborhood tire shop to patch up the hole for less than $5. If I didn't have a compressor with me, I would either have to get a tow truck or use the spare (which won't be good, as the aftermarket wheels are a bigger size.) Either way, it would have costed either lots of $$$ or time.

A quick question for our resident experts. For rainy season, should I set the tire pressures slightly lower than during dry season? It's been raining cats and dogs here lately. My reasononing is that lower pressure = more contact with road = better wet traction. Correct? Thanks!!

 

Yes, you could lower it a bit but REMEMBER rain also means lower street and operating temps too (usually). So odds are the tire temps are naturally lower in the rain than the same "cold" to "warm" operating psi when being driven in clear weather.

CAVEAT: It also depends on the tire formulation/tread pattern. This is why i am opting for new Mich Pilot Sport PS2 so it will do well for both dry and wet track/spirited drives.

 

I run 36 in the front and 34 in the rear. Both as cold readings and based on tire temps and handling from a track day that I was goofing off at. We were actually testing a Trans Am car, but I couldn't resist blasting around in my 308 during lunch. Took Dad and the girlfreind for a thrill ride. All that crap.
Anyway, if you're driving a 3x8 36lbs. front and 34lbs. rear cold is a good place to start to achieve a neutral balance.
The pressure to handling equation is relatively simple. Increase air pressure to sharpen the handling on a particular axel. Got a car sluggish (understeering) in the front on corner entry or mid corner, increase the pressure in front. Got a car that turns in sharply followed by an unstable twichy rear, increase the rear pressures. Exit symptoms can sometimes be tricky as lessening pressure in the rear can cause a car to go from sloppy in to understeering out because of the forces caused by application of power and it's corresponding effect on the chassis, i.e weight transfer planting the rears ala drag cars launching off the line.

One more note. Contrary to popular belief, increase air pressure for wet conditions. Seems ass backwards, but it's the truth. Increasing pressure actually puts a better and firmer footprint on the road surface and allows the tread pattern to effectively channel water away from the tires. Think of it this way: lowering pressure will cause the tire to squat and become wider at the contact patch. That in mind, stick your hand in water and move it briskly with your palm facing front. Now turn your hand 90 degrees and try it again. A knife goes through butter easier than a spoon. This is the reason snow tires are skinny and plastic pig Corvettes with their fat rear tires go nowhere in the rain. No offense to Vette fans out there.

Credentials: I've raced for 14 years and logged thousands of miles testing anything from Toyota Atlantics to IMSA GTP cars. Spent lots of time in GTU and Trans Am cars as well. I'm certainly not the definitive authority on chassis set up, but I do know what's going on concerning tires, shocks, springs, and sway bars.

New to the site and lovin' it,
John

 

I use 30psi front 35psi rear on QV 16" rims on a gt4

 

EXCELLENT ADVICE!!!!

Of course you are correct, i was backwards. Was a long day yesterday... and today looks to be equally bad

 

I was running Yokohama Intermidiate , z-rated tires, on the stock wheels my 308 QV at a consistent 35 psi. Given the very soft compound of these tires I was ablle to observe tread wear in a fairly short period of time. With this tire pressure , virtually all of the wear occurred in the center of the tire, indicating a clear over-inflation. Needless to say, I'm now rumming 30-32 psi in my new tires.

 

Thanks, John, for clearing up my misconception. That's most helpful.