tire pressure & weight distribution

[88accordSF]

i'm running Kumho 205/40R-17XL 84H BSW Ecsta AST tires

The tire data shows Max Load 1102 Lbs and Max Pressure 50 PSI.

1102 Lbs divided by 50 PSI would give a contact patch of 22.04 square inches.

....in calculating the optimal tire contact patch for the accord, i used an approximate weight of 2500 lbs, with a 60% front, 40% rear weight distribution (i approximated the percentages... anybody have exact data on this?)

which would result me about:

...front wheels: 1500 lbs
...rear wheels total: 1000lbs

...each front wheel rate is 750 Lbs
...each rear wheel rate is 500 Lbs.

Rearranging the numbers to find a pressure for that contact patch area at the front, divide 750(Load) by 22.04(desired contact patch)= 34.02 PSI

The rear, 500 divided by 22.04 = 22.68 PSI.

i'm running 34 front, 28 rear right now.... dunno if i want to go as low as 22 on the rear, mainly for gas mileage reasons

what kind of pressure(s) are people running? what kind of tires?

[frantik]

i usually set mine to a lil under 30 on the front a lil over 30 in the back.. i thnk thats what it recommends in the passenger side doorjamb

[89T]

:huh:
how are you figuring weight divided by tire pressure = contact patch???

does that actually calc out?

i may have to go outside and see if it is phisically right. nah i am too lazy right now.

[88accordSF]

:huh:
how are you figuring weight divided by tire pressure = contact patch???

does that actually calc out?

i may have to go outside and see if it is phisically right. nah i am too lazy right now.

its an oldschool method to a get a baseline estimate of contact patch. however, there are a lot of other factors that should be in that equation, like sidewall deflection, polymer composition, things that could make it a lot more mathmatically accurate than just a 3 variable equation... its definitely not exact, just a way to get some approximate numbers going: i don't think i'd be running 22psi rear at any time, thus the thread discussion

was going to try the talcum power method so see if that works

where's stephen hawking when u need him?

[2ndGenGuy]

22.04 square inches is the contact patch as maximum load. Just curious why you are trying to achieve this size of contact patch? Is there some reason that under max load the contact patch is optimal? Or is that just the maximum contact patch you can get?

I think what you'll have to do is find a compromise for handling. Dropping pressure to attain the largest possible contact patch for the tire will likely result in poor handling. That would be due to the pressure being so low that the sidewalls will flex and your tires will track all over the place on the road.

What I see people do quite often, is mark thier tires. What they do is right before a run on the track, they dab some shoe polish or chalk on the tire on the corner near the top of the side wall. As they corner, the mark erodes away, and they can see how much the sidewall is flexing and coming in contact with the road.

A good, high-performance tire should have a little arrow on it at the top of the sidewall. This usually indicates where the optimal sidewall wear is occuring. If you see wear down past the arrows, not enough air, if you're not getting close, too much air in the tires.

Remember also, as you drive you will warm up your tires, and spirited driving will warm them up even more. I've seen people gain as much as 5psi just in a 60 second run on an autocross track.

Of course, if you're looking for straight-line performance, you want to go with the lower pressure. 22PSI may actually be optimal. Maybe even lower. But kiss your cornering goodbye.

[shepherd79]

28psi in the rear is way too low for that tire.
i think you will be happer if you made all 4 corners ay 36 psi.

general rule is to take Max PSI on the tire - 10% - 15% and that should be your optimal tire pressure.
read this and it will tell you everything you need to know about tires http://www.carbibles.com/tyre_bible_pg2.html
page 2 explains about tire pressure.

[evil88accordLX]

where's stephen hawking when u need him?

rolling around in a wheelchair talking through a speak and spell somewhere. but if he were here, id be willing to bet he would include tire volume surface area divided by max PSI to get the amount of force expelled on each square inch of the tire and wheel. then he would probably figure PSI at the sidewall vs. the tread vs. the wheel. after that he would have to calculate the amount of downward force the vehicle itself applies to each wheel, the shift in pressure inside the tire because of the downward force of the car, tire flex due to pressure shifts, man this is getting way to complex and im a huge math geek. i like the old school way!

[2ndGenGuy]

rolling around in a wheelchair talking through a speak and spell somewhere. but if he were here, id be willing to bet he would include tire volume surface area divided by max PSI to get the amount of force expelled on each square inch of the tire and wheel. then he would probably figure PSI at the sidewall vs. the tread vs. the wheel. after that he would have to calculate the amount of downward force the vehicle itself applies to each wheel, the shift in pressure inside the tire because of the downward force of the car, tire flex due to pressure shifts, man this is getting way to complex and im a huge math geek. i like the old school way!

LOL! Speak and spell.... :D

The PSI is going to be the same at every surface inside the tire. The air distributes evenly across all the surfaces. There may be uneven pressure on the outside (from the weight of the car pushing against the ground) of the tire, but inside, it's the same. I know it seems complex, but I'm pretty sure the old-school method is actually accurate.

[evil88accordLX]

LOL! Speak and spell.... :D

The PSI is going to be the same at every surface inside the tire. The air distributes evenly across all the surfaces. There may be uneven pressure on the outside (from the weight of the car pushing against the ground) of the tire, but inside, it's the same. I know it seems complex, but I'm pretty sure the old-school method is actually accurate.

if the volume shifts (like squeezing a balloon), i believe the surface pressures adjust accordingly. i could be wrong though, its been a long time since i was in school. either way, thats too much thinking!

[2ndGenGuy]

if the volume shifts (like squeezing a balloon), i believe the surface pressures adjust accordingly. i could be wrong though, its been a long time since i was in school. either way, thats too much thinking!

True, the exterior surface pressure will change. The contact patch on the outside of the tire will be pretty much the only place with pressure above atmospheric. The pressure inside would remain the same I would think... But yeah too much to think about on only one cup of coffee. :lol:

[Hauntd ca3]

A tire of that size, you should be good at 30/32 psi front and rear.
To much pressure and the tread surface will go convex and you wear out the middle of the tire. to little and the tread goes concave and you wear out the outside edges of the tire. If yoyu have any doubts talk to a tire speciallist and
they should be able to set you right.