LANJET

What should the hot pressure be?

Thanks

TommyBoy72

My car seemed to like 36-38psi hot. Stock weight 01Z with 18x10.5 all around running 305/35/18s. I have a pretty aggressive alignment.

jpobrien

I run 37-38 psi hot in my C4. Not too agressive alignment on it.

LG Motorsports

World Challenge tires 275x18 front on 10.5" wide rims and 335x18 rear on 12" wide rims we ran 32psi
HOT. (31psi on street courses and 33psi on high speed tracks with high speed corners.)

Thanks
LG

bobmoore2

Lou, I'm sure those pressures work best with your race car, which has a very aggressive alignment and suspension. With our near stock HPDE cars, I've found that somewhere between 36 to 39 psi works better, because it helps prevent the RA-1's from rolling over onto the sidewall so much with our nearly stock alignment and suspension.

Rob's 73

I was always told to keep the RA1s under 40 psi hot. I usually air down to 39 hot and call it a day.

rikhek

I remember reading a tech article on RA1's stating the TOYO RA-1 tire performs best with a "hot pressure" of between 38-42 lbs.

Lots of experimenting by myself over the last couple years. With a somewhat aggressive alignment I run at 42 hot. Yeah, lots will say that's high but it gives me the longest life out of them and I don't notice a significant performance trade off.

Start at 35 cold. I'm running 305's on 18 x 10.5 on all 4 corners.

LG Motorsports

I am sure that it has a lot to do with the wheel width.

We have 12" wide rear wheels, and 10.5 fronts. and we are running 325 rears and 275 fronts.

It all matters.

If you have that wide of wheels, then the pressures should be close to ours.

If you do not have the proper camber or wheel width, then you are playing with the side walls of the tires which would explain some handling quirks.

We tested every pressure and found our best lap times over the entire race at these pressures.

At any rate, you have to know that to achieve the hot pressures where we ran them, we had to start so low that most would be "spooked" by the squirmy feel until they get hot.

The funny thing about racing is that when someone asks a question at the track, and I tell them the exact right answer, they don't believe it and they do everything but.

That is why we beat the new guys.

A tire is a tire. And a 305 on a 10.5 rim is a good combo. You can go up or down a couple of psi but you will get the best performance in terms of lap times and tire wear at the pressure I suggested.

With all due respect, if you don't have the correct camber or toe, then why worry about the pressures?

Just my .02

LG

bobmoore2

I'm running 305/35-18s on 10.5s at the rear and 275/35-18s on 9.5s at the front. I've found that starting with 35 psi cold results in 39 to 41 psi hot. For camber, I've got -1 1/4* rear and -2* front. And even so, the outside of the tire cords while the center still has the grooves. Obviously the tire is rolling onto its edge in the corners.

I think the big difference in the way we wear our tires is the huge difference in our suspensions. Yours is totaly race prepped, while mine is totally stock Z51 except for the alignment. Your suspension controls the tire's contact patch MUCH better than mine does.

I'm not telling you anything you don't already know. I'm just reminding you that you can't apply one or two details/specifications from a race car onto a street car. Every detail has to be tailored to work with every other part of the car.

We also have different priorities. Your first priority is the fastest lap times for 30 to 45 minutes, then you throw away that set of tires. I have to watch the tires budget, and try to get several hours out of a set of tires, while still setting a few respectable lap times.

I may be completely wrong when I question the opinions of a seasoned professional race driver. However, from my point of view, it looks like we're both correct for our differing situations (all out racing vs. occasional HPDE's).

What do you think, Lou?

LG Motorsports

I think that looking for fast lap times is not mutually exclusive to proper tire dynamics. The level of a car's suspension does not control WHAT the tire contact patch will be. You must set whatever suspension you have to achieve the best the elusive tire contact patch.

On the other hand, just having a good suspension does not guarantee optimum tire contact patch, it just means that you adjust your cambers and caster to match what your car needs.

Yes, Lap times are important. But what makes the best lap time with regard to the tire? the answer is that a good lap time requires using the most rubber available in whatever tire you are running.

That means that you must "Read" the tires. And by reading the tires means that you ultimately check your tire wear and adjust your suspension to take advantage of the available rubber.

For example; Too Low pressure wears the outsides of the tire, and too high pressure wears the center. But if you have the wrong alignment then you might see a combination of bad wear from both the pressure and alignment.

Not enough negative camber will wear out the outside of the tire. Then combine that with too high pressure and you might think you are using 75% of the tire in terms of wear because the high pressure wears the center and the lack of camber wears the outside.

In reality, you are only using a small portion of the available tire contact patch during cornering.

So if you want to maximize your tire life, then maximize your alignment and set up first and you will use more of your rubber during the on track sessions.

The biggest compromises come when the car is set up for Both Street and Track which results in not having enough neg camber.

Stock suspension is not a bad thing. All you have to do is set your suspension up to use more of the tire contact patch during cornering. then you will get the most tire life and the best performance at the same time.

Every car is the same, but no track is the same. Take your tire temps and look for a 15 degree hotter on the inside. Also keep in mind that the last set of corners will skew your temps. The best way to dial in your cambers would be to stop on track after the corners and take the temps. OR better yet, log your temps with sensors taking real time temps on track and look at the data.

But I digress. Not very many teams have that kind of data so the ultimate test of camber and pressure set up is tire wear on the track you run at. (Lime Rock is all right handers but one corner, so you give up the right hander to maximize your tire patch for the right hand turns.)

Also keep in mind that I ran plenty of Showroom Stock series in my early years. And the theory has always been the same. Find the pressure that gives the maximum tire contact patch and set your cambers to achieve this during cornering.

Also keep in mind that in the early SS classes we were running a 165/70x14 tire sometime needed pressure to keep those early tires from flopping over but that is not the case with corvette size tires.

sorry for all the confussion. Just enjoy your cars on track and you will be on the top of the world and ahead of most who will never experience the thrill of being on track.

Thanks
Lou G

2K3Z06

I run 31 front and 30 rear, cold psi. The pressure usually goes up 3 or 4 LBS. Good to know, i was pretty close.

I tried the 36 and 35 cold pressures. Which went up to about 40 psi hot. The thing would slide around a lot. I always see people posting about 40 psi pressures and wondered what i was doing wrong.

I guess some people like their tires as hard as hockey pucks........

C6400hp

With the alignment I use on my C6 -1.3 camber and .06 toe out front and -1.0 camber with .04 toe in rear. using 275/35 on 10X18 Front wheels and 305/35 on 11X18 rear wheels with RA-1's anything over 38 hot will make the tires feel greasy and anything under 36 will wear the edges off. With my setup I shoot for 37-38 hot.

bobmoore2

Lou Gigliotti said,
"For example; Too Low pressure wears the outsides of the tire, and too high pressure wears the center. But if you have the wrong alignment then you might see a combination of bad wear from both the pressure and alignment.

Not enough negative camber will wear out the outside of the tire. Then combine that with too high pressure and you might think you are using 75% of the tire in terms of wear because the high pressure wears the center and the lack of camber wears the outside.

In reality, you are only using a small portion of the available tire contact patch during cornering. "



Wow, I never thought of that - With high pressures I might be seeing relatively even tire wear, but still be using only a small portion of the tire most of the time. I thought the higher pressures were stiffening the sidewalls, preventing the tire from rolling onto its outer edge so much. I now understand that with higher pressures the tire still rolls onto its outer edge in the curves, but it is mainly just on the center of the tire in the straights.

This explains a couple of other things I had seen.
1. My tires didn't wear much near the inner edge, because there was never any serious weight on the inner edge, only on the center in the straights and the outer edge in the curves.
2. I once flat-spotted my front tires by locking the brakes and skidding in a straight line for several yards. (I don't know why the ABS didn't kick in, but that's another subject for another time.) The flat-spot was mainly in the center, nowhere near the edges, because the high pressures were causing a narrower contact patch.

I'll try running lower pressures and see how it feels. I now expect that I should get much better grip with the lower pressures. I'll try about 34lbs hot. I might ask the alignment shop for a little more negative camber, too.

Sorry for the aggravation you must have felt, having to explain something that seems so obvious to you. Thanks for your patience.

Bob

LG Motorsports

NO aggravition. these race cars humble me on a regular basis until we learn.

None of us are right all the time, including and mostly me. The engineers always have the right answer and they don't hesitate to tell me.

Even after 30 years of racing, I learn something new at every race.

for 2008, we will have a full time Tire Engineer from the tire company that we are using. the Slicks require 27-29 psi and they grip so good, I was hurting in my ribs.

So every tire is different. And every car has needs based upon the alignment and geometry. Again, if you could test tire temps 100% of the time, You could map exactly what the tire needs and biase it to help the car more of the time.

Testing, testing and more testing is the answer. and if you are standing still, you are falling behind!

LG

Sidney004

Lou:
Can you tell us what tires you will be using yet?

C6400hp

$100 says they're Michelin

LG Motorsports

Send me the $100

they are not michelin.

LG