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Standard Missile Mustang · 05-29-2002, 02:08 PM

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.

05-29-2002, 02:08 PM	#11
Standard Missile Mustang Registered Member Join Date: Oct 1998 Location: McLean, VA Posts: 2	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.