Tire pressure for hwy driving

Door panel sticker says cold pressure on tires is approx 30psi. But that seems low on the OEM Wrangler tires. Mostly I’m on highways and paved streets so what’s an optimal tire pressure? 40psi?

 

Start with the door panel.

Do simple chalk tests.

Adjust pressure (if needed) till test is perfected.

Assuming you are interested in optimal tire wear, not hyper-miles

 

I run 35psi and haven't had abnormal wear. I wish these stock tires would hurry up and go bald. I've got enough patches in them to justify new ones at this point though, lol.

 

this is my fourth Toyota 4wd pickup. I always run 35 front, 29 rear and rotate every 5 to 6 k miles. They always wear evenly for me at these pressures.

 

My dealer inflates my OEM wranglers to 40 psi

 

40

 

There is no right answer. The vehicle manufacturer sets the maximum low pressure and the tire manufacturer set the maximum high pressure for the tire. I would never go below the vehicle pressure unless going slow off road. I would never go above the tire pressure. Anywhere in between is all about your comfort and feel. The higher the pressure the better the gas mileage and the better the road feel. Lower pressure will give you a softer more comfortable ride. Always remember that the air pressure is when it is cold. Driving as little as a mile can increase your pressure 3-4 psi.

Please don't waste your time with chalk. There is nothing scientific about a chalk test. It is one of those internet legend stories. It is really pointless when you are talking about highway air pressure. (Sorry Bill. I respect your opinion, but this test is just a gimmick).

 

The manufacturer sets the max load of the tire and tells the minimum pressure required to use that max load. Max pressure is well above 150 psi with passenger tires. No reason to go anywhere near that of course.

And the chalk test is a great tool to find out what pressure is best with the load you are running... math is better though.

 

I have wondered about the chalk test, and have not done it yet.

Do you do it when tires are cold?

Do you do it when tires are at 'operating temps'?

 

Chalk test tells you nothing. Absolutely nothing.

The max tire pressure isn't the most that a tire can hold before it blows up. It is the maximum amount of air that you can safely drive while inflated. While it probably is lower due to liability concerns, but if you want to try driving around with 150psi, let me know how well that works out the first pot hole you hit.

 

I keep mine at 33 psi. At highway speeds and 100 degrees, they reach 37-38 psi.

 

General rule of thumb....

Tires should heat/cool about 1 PSI for every 10 degree variance in temp.
Driving on the highway should not heat your tires up more than ~10% over the temp variance from cold (plus / minus any temp variations from "cold" of course). If they are heating up too much, you're gonna cause uneven wear on the outsides b/c its too low and creating more friction with the additional contact.

My garage is normally around 70 this time of year, highs in the 90s, so having mine at 32 realistically means I see 36-37 on the highway when the day heats up.

following these simple rules and adjusting as necessary, as well as understanding that temperature swings AND time (losing about 1 PSI / month generally) will require topping off or letting air out when it gets cold has always worked for me.

personally I generally want to minimize the hard hits from potholes and uneven city streets during the week, then I may add another 2 psi or so if I'm going to be primarily highway miles. on my stock wranglers, I preferred running them at 30-32 cold b/c much more made for a less comfy ride. On my Cooper AT3 4Ss, I run them at 32-34 cold for about the same ride and even wear.

 

I run 34psi.

 

My firestones stayed about 30 psi for over 40k and had tread left. Went up a size and the dealer set them at 38 cold. Did the chalk test several times and chalk was gone whether it was 200 ft or 1,000. Going to leave them for a few hundred miles and buy a jumbo piece of chalk. They ride smooth and the mileage only dropped 2/10ths or so.

 

Care to expand on specifically why the chalk test is "a waste of time"??

Cheers,

db

 

There are a number of reasons. The greatest reason for someone that really doesn't want to put any thought into it is you don't see it done in any form of motor sports. If this were something that could provide any form of valuable feed back is you would surely see Nascar, NHRA, etc. doing this. They don't.

As for the reasoning here are a few -

• Tires don't maintain their shape when you drive
• Radial tires have a contact patch that doesn't change over a wide range of air pressure
• It is impossible to maintain a straight drive on a perfectly flat road
• Air pressure changes as you drive an heat builds into your tires

I can get more into detail over what happens, but it is easier to see for yourself. Watch any drag race and notice how the tire changes shape as it increase. Now obviously we don't drive dragsters, but distortion occurs in passenger tires just not as extreme.

The only real way to get scientific about your air pressure is to use a temperature gauge. That is what is done in motor sports. You can get a lot of information by measuring the temperature across the face of the tire. The challenge is knowing what it means.

 

"highways and paved streets"
35-40 psi, 40 wen doing hwy is optimal imo on the wranglers
35-38 seems to be good on surface streets. Always take into account weather n tread remaining adjust accordingly imo.

 

Ahh--now I see why you made the comments.

NASCAR and NHRA use treadless high adhesion compound tires. They have little interest in tire longevity and gas mileage is not a high priority. They simply want the absolute best traction for the duration of the race. In this regard, unlike street tires, heat is their friend in that it makes the high adhesion compound even stickier and creates even better traction--hence the preoccupation with tire temperatures . Notice the burn outs used in NHRA and the weaving of NASCAR units prior to the green flag--all to bring temps and traction up.

However, in the case of street and all terrain tires such as those we use on our Tacomas, most are looking for a good balance between longevity (total tread life), traction, and gas mileage. One way of approaching this is to find a pressure point for your particular vehicles tires that engages the maximum tread contact patch under your most typical weight and driving conditions.

So how do you do this--one way is to start with the chalk test to find a pressure that distributes the vehicle weight over the max tread contact and then check tread wear across the tire at each 5k mile tire rotation. The chalk test gives you a starting point and the measurements allow you to fine tune. BTW, keeping the truck in a straight line to do a chalk test is not difficult and you only need to move the truck a short distance in order to provide enough "chalk wear" to determine if you are over or under inflated. I have used this technique with good result on five Tacomas and numerous other vehicles.

Your technique for optimizing tire pressure depends on your objective!

Cheers,

db

 

Negative. I knew I would have to get deeper. You are completely missing why chalk doesn't work. You do not drive at the 10 to 15 miles an hour that you would with your chalk test. You drive much faster and the tire changes shape as it spins. This is simple physics. It is called distortion. As your tire spins faster, the center of your tire lifts. Watch any dragster to see this. Your chalk test simply cannot account for this action therefore it will provide you absolutely zero in terms of meaningful data. Let's add to the fact that you are running steel belted radial tires. Steel is much more resistant to distortion. If there were some way to possibly chalk your tires at speed, the steel belting makes this effort even more difficult because your tires will remain flat at much higher variation of speed.

It doesn't matter the type of tire. You are claiming that putting chalk across your tire tells you your contact patch. It simply doesn't. Heat tells you where your tire is working and where it isn't. That is why in racing they look at temperatures to adjust their air pressure along with alignment adjustments to get even temps across the face of the tire. That is how you know you have the best contact patch. If the chalk test worked, they could just chalk their tires and save a lot of time. It just isn't the case. There is nothing scientific about chalk. Neat gimmick and you can wow your friends by doing something that seems cool and doesn't hurt, but in reality, it does nothing. It is one of those internet legend things. Much like Amsoil, JB Weld, Sea Foam, etc. Because it doesn't hurt anything, no one really cares that it does nothing. Not a lot different than the "door close" button in an elevator. It is there. We push it. It does nothing, but we feel like we are doing something. Such is life....

 

I fill the tires until I like the way it drives. Always lower than my brain says I should and the seam to wear well. Guess I’m old school, but I let the drive feel govern this.

I’m not on stock, but the manufacturer states I should run at 50 cold, I run at 34.