track results and problems

[drtbiker]

I had my car to the track today and i am pretty happy with it other than the last two runs, my first run was almost my best w/ 14.270 @ 98.56mph after about 7 runs letting the cool down, then i went through some more runs, i was filling up my tank with gas at the pumps and i told the guy i was empty and told him i dont have enough weight in the back to hook now on street tires he asked me how much air i had in my tires i replyed 30 he said OOO wow u running that much pressure

[90'5.0 Conv]

Try 15 lbs in the rear and see if that helps. If not you may need some slicks.

Good Luck, James

[Green9550]

Dude, good job with the times. I don't think it would be wise of you to take air out of your street tires man. I saw a brand new T/A put his street tires at 20psi and then loss it in second gear and hit the wall. When you take air out of a street tire they don't touch the pavement as well as when they were full. It is your call, but I would hate to hear you messing up your car at the track. Good luck man. Take it easy.

-Billy

[Mr 5 0]

drtbiker:

Do Not lower the air pressure in the rear tires.

It will not help traction and it can affect handling and braking negatively. Bad idea.

Increase the front tire pressure to the max but leave the rears alone.

In my experience, taking racing advice from some guy pumping gas doesn't usually work out too well. ;)

[90'5.0 Conv]

I guess I look like an ***** here but I've never heard of such a thing. I go to a street legal car race at the tradk every Friday night and have never seen such an event. As a matter of fact, everyone I know does it and it DOES help traction. I had 35 lbs in the rear tires when I first started and as good as the track was and as slow as my car was, I couldn't hook up. I lower them to 15 lbs when I race and fill them back up when I'm done. I'm not trying to tell you thats what you should do. I'm just saying that it worked for me and many others safely. By the way, i'm not flaming anyone, just my opinion from my experiences. No disrespect intended to anyone.


James

[Green9550]

Hey man, no problem. I am happy it worked for you safely. I just wanted to say what I had seen happen. I don't want anything to happen from something as small as that. If you try it be VARY careful. Good luck.

-Billy

[red82gt]

Try putting your tire pressure down to about 25lbs, it'll soften the impact but you won't decrease your contact patch, this dropped my 60' times by 1/10 (They're still not very impressive but pretty good for 17's and suspension meant for cornering). I'm running on 17's and I only use about 29lbs of pressure normally or else the ride is pretty harsh.
By all means, definitely pump up your fronts to the highest reccommended pressure to reduce rolling resistance.

[gtsr515]

NO! NO! NO! NO! NO! lowering pressure on a street tire has ZERO benefits, the bottom line is "contact patch" and that is when the tire is inflated to its maximum stated on the sidewall, especially prudent when drag racing.

[red82gt]

I don't buy that contact patch argument, last night I went from 2 back to back bad 60' times (2.671 and 2.405)with 33lbs in the rears to consistent 2.20's with 25psi. The difference in contact patch between 25# and 35# is a couple of mm, big deal. The difference in friction is quite a bit different. It is not unsafe to run 25lbs of air pressure.

[red82gt]

Oh, another thing, say you've got the max air pressure in your rear tires, you then do a burnout to clean them off, guess what? your tire pressure just increased by approximately 3lbs from the heat, you're now running over the maximum reccommended pressure and that's not prudent either. So when mine are set to 25lbs they are likely at about 28lbs for the run which is only 1 lb less than reccommended for normal driving.

[Standard Missile Mustang]

I hate to break this to you guys, but dropping the pressure in a tire INCREASES the tire contact patch. It has to from the laws of physics. Here is an example to prove my point:.

Let's make the following assumptions, to make the analysis easy:

1) Your Mustang is standing still
2) Weight = 3300 lb
3) Weight Distribution = 50/50 (F/R) ... yeah that would be nice
4) You have 35 psi in all four tires

Tire Contact Patch = 3300 lb / 35 psi / 4 = 23.57 in^2

Let's say we change assumption (4) by dropping the pressure in ALL FOUR tires to 20 psi (I know, you wouldn't do that, but I'm just making a point):

New Tire Contact Patch = 3300 lb / 20 psi / 4 = 41.25 in^2

Now, what happens when you launch and the tire deforms is another story. Your transient tire contact patch will depend on many factors, including sidewall stiffness, temperature, compound, rim etc.

I have found that 16" drag radials seem to hook well and still handle well at the strip at 18-20 psi. I haven't had any safety issues so far, and most people at the track drop their tire pressure and then put it back up when they leave. I've pulled 1.86 sec 60 ft's in my 290 rwhp road race suspensioned car with this technique, and I average a 1.9x sec most of the time.

As for "true" street tires (I have had my Nittos for 2 years now, so I will argue that they are my "true" street tires), I use to just run them at 35 psi and do a quick clean off. The Nittos hook much better with a 4-5 sec 2nd gear burnout.

Anyway, back to work.

[mysweetlx]

I somewhat agree w/ SMM on the contact patch argument. I'm sure lowering or increasing tire pressure will vary in it's results from car to car and driver to driver. Lowering to 20-22ps has helped me drop .2 in my 60' times on street tires. Drtbikr, try it out, raise it, lower it, see what works for you.

[drtbiker]

yeah c i droped my tire presure down in my rear tires and then i had troubles with the last to runs that i ran with lower pressure it seemed that the car did not want to shift in to 2nd. But that may have been my faulty bbk clutch cable that i have heard bad things about, i hav heard that they stretch like crazy witch i think may be true but maybe i am just going crazy also

thanks
rl

[Dark Knight]

dont drop them to low... they cup in the middle... thats why an underiflated tire wears on the outside and not the middle.....25-30 is usually good, depending on the tire.. I run mine at 28.. but I have a tall sidewall.... drag radials can be run alot lower though...