SSober

Just got V700s in 275/40/17 so I don't "drift" my way through autocross courses. Can anybody recommend a starting point for tire inflation? I was told 40 PSI and when running them on the street one day, I noticed that the whole tread was not meeting the road. The outer 1 inch didn't seem to be dirty like the rest of the tire...or is it to be that way until I rip around the track? Any input would be appreciated.

jhelms

iTrader: (2)

You could use a tire temp gauge to check out and make sure the entire tread area is heating up to the same temp.

Here are a few links that might help:

http://www.tirerack.com/tires/tires....ictoRacer+V700

http://www.tirerack.com/tires/tirete..._v700_care.jsp

Inflation Pressures

The V700 will work well on most cars with inflation pressures between 35 and 40 psi ("cold" inflation pressures for autocross use and "hot" inflation pressures for racing use). Cars that are light, well balanced and relatively easy on tires will find slightly lower pressures may work for them, while heavy, high horsepower cars that are generally harder on tires may find that they need slightly higher inflation pressures.

Generally adding air pressure in small increments (2 psi) to the tires on the end of the car that looses traction first works best. For example, if a car is understeering, add pressure to the front tires. If the car is oversteering, add pressure to the rear tires.

Tire Temperatures

Tire temperatures are taken with a tire pyrometer which can measure how hard your tires are working and how evenly the work was distributed between them during the most recent corners. While the V700 tread compound operates well over a broad temperature range, it is most effective in the 160° to 200° F range.

When preparing to take tire temperatures, the driver should enter the pits using moderate braking. The temperature's of the car's outside tires on the last corner should be taken first, followed by the inside tires. Depending on the distance from the last corner to the pits, tire temperatures may not be even across the tread face. Your first goal is to achieve an even temperature spread between the tire's outside shoulder, center, and inside shoulder.

SSober

Thanks for the info - but I read most of that information before...I was hoping someone could have told me the following information as it relates to the way my car is set up currently (trans, HP and gearing).

In case anyone wants a good recommended starting point, 38 pounds for the rear and 36 for the front is where I ended up. Stagger seemed necessary and any less had me running below the indicator-arrows on the sidewalls. These were the best runs and the time savings over 40 pounds all the way around was about 1.5 seconds on a 54-55 second course

jhelms

iTrader: (2)

Is there any way for you to borrow a pyrometer? That would probably be the most (maybe only) way to get an accurate answer for you.

There are usually a few around the road course on open track days (same for autocross days as well).

rushman

For autocross I run 38 front /30 rear. If it is a slick lot or is cold out I end up at around 37 front 28 rear

Sam Strano

iTrader: (41)

For 275's you should be about 36-38 front, around 30 rear like Rushman said. The rear in an f-body should never be higher than the front. All the weight is up front, the front takes the majority of the loading, and you don't want the rear any stiffer than you need it......

SSober

Great - thanks for the information. I was thinking the stagger like you mentioned, but didn't know the poundage.

SLIDER

Hey Ssober, I wish I could say the same...

You mention the OUTER 1" is not making contact w/roadsurface. (We assume normal straight highway driving.) FRONT OR REAR TIRES? Here are my thoughts:

IF FRONT:

1. Negative Camber. Probably a good thing, as you start ripping around the track, that outside 1" WILL show wear for certain.

2. Air Pressure. Crawl under your car, and be absolutely sure the INSIDE edge is making contact. If BOTH edges are not making contact, lower your air pressure a good 5 PSI.

IF REAR:

1. Air Pressure, same as above -- your inside edges probably aren't contacting either due to overinflation. It's impossible (well, very difficult) for your rear to have much negative camber, so if your rear tires are not making contact on Outside edges of Left and Right side, you have problems....
Usually air-borne excursions are the culprit for negative camber in the rear....the more air, the harder the impact, the more negative camber you will create in rear.. It's a lot of fun, usually, but you might break something too, so I don't recommend this approach, unless you have big pockets.

Good luck, and YES, buy a pyrometer for more accurate tire feedback!

SSober

Thanks for all of the information. I am getting the hang of this stuff now.
The last race was my best finish - 2nd and with a little playing with the tire pressure, I ended up with 36 front and 28 rear. The 28 was an 8 pound guess at what would provide the traction I wanted when coming out of a turn.

I am doing the whole race in second gear and learning to not "over drive". Easing into the power coming out of the turns versus smashing it to the floor has helped too...V700 don't eliminate spinning altogether.

rushman

.... notice how they don't squeel? Wait till they do :-)

Cal

iTrader: (1)

Ditto.