The truth about tire psi?

[02TafWhtSi]

Can anyone explain to me how lower or higher tire pressures affect a car? For instance, how is gas mileage affected? Handling? Safety (blowouts)? Ride quality? Steering feel?

I've gotten alot of different information on this subject over the years so I'm a little confused. Any info would be great!
:)

[xlr8]

im not an expert, but what i do know is that lower pressure will decrease your gas milage because lower pressure will give you a better contact patch. thats better for a launch, but i dont know about handling

[chunky]

good question.

tire pressures affect a lot about your car, gas mileage, traction, ridequality, handling balance.

in general, here are the rules that apply:

1) lower tire psi increases contact patch for better traction. the tradeoff is reduced grip & predictability during cornering due to increased sidewall roll over.

2) Lower tire pressures cause more internal heat in the tire. Underinflation is BAD anytime you will be driving at highway speeds for an extended period of time.

3) Higher tire pressures reduce contact patch. the overall rolling tire daimeter increases slightly, so you get better gas mileage.

4) higher tire pressures help increase grip during cornering by preventing sidewall roll over. More pressure means that the sidewalls have more support, and are less likely to roll over.

5) higher tire pressures help reduce internal heat buildup in a tire during high speed driving (note in the 2002 si's owner's manual, a higher tire psi is specified for high speed driving).

6) higher tire pressures reduce contact patch resulting in less grip in most cases (in some cases, higher psi increases grip, see #4)

7) generally, you want higher psi up front than in the rear on a FWD car. this helps the car rotate and helps reduce the amount of inherent understeer that most fwd cars have.

[JDM Whore]

Yup, that about sums it up. YOu might also want to look into a lower profile tire. That will reduce sidewall flex or roll over. The trade off however, is you feel every bump in the road, and the possibllities of a bent rim.

Hope that helps

[02TafWhtSi]

WOW, thanks alot guys - this really helps! One last question - If I over-inflate by about 3 or 4 psi (36 psi total) for all four tires will the steering feel any differently compared to leaving the pressure at 32 psi (reccomended)? By different I mean "over-boosted" or artificial like the car is not gripping the road.

[SLOlife]

Originally posted by 02TafWhtSi
WOW, thanks alot guys - this really helps! One last question - If I over-inflate by about 3 or 4 psi (36 psi total) for all four tires will the steering feel any differently compared to leaving the pressure at 32 psi (reccomended)? By different I mean "over-boosted" or artificial like the car is not gripping the road.

Hmmm that is strange in the owners manual it states that the pressure should be 33/29 psi, but on the driver side door jamb it states 33/30. I wonder why:confused: , then you say 32 psi why all the different numbers?

[JDM Whore]

I think it's always been 32 recommended

[SLOlife]

Originally posted by JDM Whore
I think it's always been 32 recommended

What does your manual and door jamb say?

[2sloSi]

Hey, chunky nice post, great info! :)

[SLOlife]

Hmmm that is strange in the owners manual it states that the pressure should be 33/29 psi, but on the driver side door jamb it states 33/30. I wonder why , then you say 32 psi why all the different numbers?

Am I the only one with the differences in pressure:confused:

[chunky]

look on page 194 in the owners manual (yes, i've read it cover to cover =P )

33/29 for "most normal driving conditions & speeds"

and 36/35 "for speeds over 100mph"

gotta love that honda put in a reccomendation for high speed driving :D

[SLOlife]

What does your driver side door jamb say? I am not sure if I should use the manual or the door values, but I want to know if I am reading the door(although it is on the body side) wrong.

[chunky]

Originally posted by SLOlife
What does your driver side door jamb say? I am not sure if I should use the manual or the door values, but I want to know if I am reading the door(although it is on the body side) wrong.

1psi isn't going to affect the tires much.

I actually run 45front/40 rear b/c it suits my driving style the best.