How much air pressure?

ratrod13 · June 3, 2008

I jus bought new General Grabber UHP 255/55 R18 tires what tire pressure should i use?

sjr033 · June 3, 2008

The side wall of your tire should tell you the max pressure. I would not run max, but that should give you some idea.

Anime · June 4, 2008

Start with the max psi rating, then go down until you find the highest pressure that still gives you a decent ride. If the max psi is 44, you'd probably want to run somewhere between 35-40. With a max psi of 35, probably something like 30-32.

Tbars4 · June 4, 2008

...A good rule of thumb is 10% less than the max. tire pressure..This gives you the best footprint on the road with good tire wear, nice ride, and minimal drag...

...Example:...35psi max -10% (3.5 psi) = 31.5...I round it up to 32 psi myself...

...Hypermiler's use max. suggested psi to get the best milage, but they never tell you about their tire wear...(center of tire wears out)...

ratrod13 · June 4, 2008

Today i put 2.7 bar (35psi) in them , runs smoot.

Thanks for the answers

Tbars4 · June 4, 2008

...Just curious...What does your tire say it's max. psi is ????

CBII · June 4, 2008

tbars4 said:
...A good rule of thumb is 10% less than the max. tire pressure..This gives you the best footprint on the road with good tire wear, nice ride, and minimal drag...

...Example:...35psi max -10% (3.5 psi) = 31.5...I round it up to 32 psi myself...

...Hypermiler's use max. suggested psi to get the best milage, but they never tell you about their tire wear...(center of tire wears out)...

So if the tires on my wifes car say Max 51 psi I should be running them at 46 psi?:scratch:

Right now I have them at 38 psi...ride seems good but I also want to get nice even tire wear as well.

Tbars4 · June 4, 2008

...What kind of car, and what tires???

...Run them at 45 psi for a tank or two of fuel, then let us know what you think...You should get more responsive handling, better gas milage, and less wear to your front end...

...Tire wear starts with good tires and keeping up on maintenance and alignments...Most big tire shops offer lifetime alignments for $10-$50 more than the normal alignment...So, as long as you have the vehicle, for a one time fee of about $80-$100 you are set...

CBII · June 4, 2008

tbars4 said:
...What kind of car, and what tires???

...Run them at 45 psi for a tank or two of fuel, then let us know what you think...You should get more responsive handling, better gas milage, and less wear to your front end...

...Tire wear starts with good tires and keeping up on maintenance and alignments...Most big tire shops offer lifetime alignments for $10-$50 more than the normal alignment...So, as long as you have the vehicle, for a one time fee of about $80-$100 you are set...

The guys a Kal-Tire have always treated me very well and fix a lot of stuff for me for free.

The car is a 91 Cavalier with Falken 215/50/R16 on it, they are only 1week old. I'll bump the pressure up today and see. I just got back from a road trip with them at 38 psi and it was much better then before.

Tbars4 · June 4, 2008

...I have had several tire shops mount tires with 32 psi, even on 80 psi tires..

...I can't wait to here your report back as Falken's will respond...

CBII · June 4, 2008

tbars4 said:
...I have had several tire shops mount tires with 32 psi, even on 80 psi tires..

...I can't wait to here your report back as Falken's will respond...

Do they ever...They are way better in the rain, less road noise and from the small amount of driving I have done on them they are more responsive then the BFG traction TA's that I had.

So I took a quick look at my gas receipts and it looks like I averaged out at 10.68 KM/L. That was at the 38psi, mainly highway with 1 day of city averaged in as well.

If my math is correct that should work out to around 25.12 MPG. (It should be noted that the car was fairly loaded with tools and parts, plus it has the 3.1 multi-port V6)....over all not to bad.

Flandry · June 4, 2008

Since they're new, you should use the Chalk Test:

GJarrett said:
Finding the Perfect Tire Pressure - the Chalk Test

There is a trick you can do to determine precisely how much pressure to keep in your tires for your particular vehicle. It will give you the best tradeoff possible between mileage, tire life, and comfort. Make sure you use an accurate tire guage so that once you learn this pressure you know it is correct.

With a cold vehicle and cold tires, air them up over pressure - 40 psi or so. Take a chalk and mark a chalk line sideways across the tread of a front and rear tire. Drive your vehicle several yards in a straight line (30-40 or so should do it). Now look at the chalk marks.

You should see the inside of the chalk marks worn off but the outsides should still be showing. In other words, the bowed out overinflated tire was wearing the middle of the tread and not touching the outside of the tread.

Release a couple of pounds of pressure from the tires and repeat the experiment. Continue until the complete chalk marks wear evenly. (Once there, you might want to then release another pound of pressure to make sure the entire tire is bearing down across the tread with weight). You have now determined the tire pressure at which you are keeping the entire tread on the road.

Under this pressure you are wasting available fuel economy, generating excess heat, and prematurely wearing the tread. Over this pressure you will get better fuel mileage but it will come at the cost of comfort from the rougher ride and decreased tread life from wearing the middle of the tread out prematurely. Keeping at this pressure will wear the tire evenly and thus extend its life to its greatest extent and offer the best compromise possible between gas mileage, comfort, and safety (you'll have your whole tread on the road). The pressures may be a couple of pounds different between front and back for your particular vehicle application.

A caveat: this needs to be done on NEW tires as soon as you buy them. If you have already logged 25,000 miles on overinflated tires all you will be doing is verifying the excessive pressure you have already been using (in other words, the chalk line will wear evenly even though the middle of the tread may be quite a lot shallower than the outside tread).

ktnj · June 4, 2008

Flandry said:
Since they're new, you should use the Chalk Test:

Question: If the I "calibrate" my tires to the perfect pressure so I pass the chalk test with cold tires, what happens when the tires get hot? My intuition says that they would then appear overinflated. But then again, my intuition is not that reliable

.

Tbars4 · June 4, 2008

...You can do the 10%, then try the chalk test...

...Actually, I kind of excited to see CBII's result's...As long as he can keep off the gas pedal once he feels the response difference... :burnout:

Tbars4 · June 4, 2008

...Btw, I just added this to the "How To" thread.. :thumbsup:

http://www.explorerforum.com/forums/showthread.php?t=216933

CBII · June 5, 2008

tbars4 said:
...You can do the 10%, then try the chalk test...

...Actually, I kind of excited to see CBII's result's...As long as he can keep off the gas pedal once he feels the response difference...

LOL...ya no. What a difference, I was into the gas pretty good trying them out today. I didn't think 8lbs extra would make that much of a difference.

Here's what I noticed right away.

-Less body/tire roll going to a corner.
-steering while moving slowly or stationary was easier.
-the car was less sluggish off the line.
-the ride was over all nicer and I felt more connected to the road...if that's possible. Remember I just did a 5+ hour road trip the other day so to notice these improvements today is saying something.
-MPG...well that will take some time to figure out as I was playing around quite a bit.

-only negative was that I felt every bump in the road. That being said the ride over all was better. These tires seem not to be a harsh as the BFG TA where when running higher PSI's. Then again the foot print between the 2 tires is very noticeable.

Over all I'm impressed and kind of feel like an idiot for not knowing this earlier.
Just thought 35 psi was good enough and went with it.

SuRrEaLNJ · June 5, 2008

as a general rule of thumb i run 35psi cold in my tires. for most things ive owned thats a couple of psi over manufacturers spec, but id rather err on the high side and let it bleed down to spec then run em low

Tbars4 · June 5, 2008

...Congratulations on a free mod with multiple benefits... :chug:

...Besides fully tuning up a vehicle when I get it, doing the 10% to the tires is one of the first things I do...Next is alignment and then I start finding shocks...Tires do ride differently and trying to find shocks to perform the way you want is kind of a personal thing, and a little tricky, depending on how they are set up too..

...Most people don't realize tires are as important to the ride as shocks and the suspension..

SuRrEaLNJ · June 5, 2008

id say more important, because not only can a tire and its pressure make or break a vehicles ride and handleing, but tire pressure is the easiest and most neglected thing to check and change when it comes to a vehicles ride

Flandry · June 5, 2008

ktnj said:
Question: If the I "calibrate" my tires to the perfect pressure so I pass the chalk test with cold tires, what happens when the tires get hot? My intuition says that they would then appear overinflated. But then again, my intuition is not that reliable .

Actually, most tire heating occurs because the tire is under-inflated and is the result of the sidewalls flexing as the tire rolls under load. Proper inflation pressure mean less flexing of the sidewall and therefore less heat. After you've done the chalk test, you can drive for about 15 minutes at highway speed, then measure the pressure again. If the hot tire pressure is more than about 3 psi, then the tire may be under-inflated.

I run 30 psi on my Michelin LTX M/S tires (max rating is 35 psi). This is my second set. I got 101,000 problem-free miles out of my first set.

How much air pressure?

ratrod13

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sjr033

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Anime

EF YEAH!!

Tbars4

ratrod13

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Tbars4

CBII

Well-Known Member

Tbars4

CBII

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Tbars4

CBII

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Flandry

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ktnj

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Tbars4

Tbars4

CBII

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SuRrEaLNJ

hail to the king, baby!

Tbars4

SuRrEaLNJ

hail to the king, baby!

Flandry

Well-Known Member

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