Tires: 35's, 37's and beyond . PSI TP

[Ole Cowboy]

Making the move to bigger meats begs the question: What air pressure do I run them at?

The door jam tells us what each vehicle as equipped is to be inflated to. Beyond that you are on your own.

2 key things about tires:
1) Co-Efficient of Friction. CoEF

2) Contact Patch "CP"

Number 2 has to be right or you are not optimizing the tire for the application. My jeep with 37's and BFG KM2's runs 3 lbs psi and 16 lbs psi, Moab and street/Hwy.

The question is: How did I arrive at 16 lbs psi for street and Hwy? The answer is simple, "contact patch". Tires are designed to have a full lateral contact patch (according to my buddy was a Tire Engineer at Cooper Tires). Overinflation reduces the CP and the result is your ride and wear out the center part of the tread. Underinflation puts the sidewalls in contact with the pavement and you wear out the edges.

Knowing that how do I determine what PSI to run on the street to obtain a proper CP? No so difficult, drive your car upon a glass table top, adjust tire pressure until you get the full CP for that the weight of the car.

Since I don't have a glass table top I use the same method I learned from my father that goes back to the very early days of autos.

Dust & Water: Find a parking lot with some rain puddles left over and the rest is dry*. Drive your car thru with a slight steer to the L or R to leave 4 sets of tracks on the dry pavement. Do same on a dusty parking lot looking now at the tread of the tire to see where the dust is. adjust your tire pressure in 2 lb increments till you get a full contact patch. The dust method is my preferred approach, it is easier to see the results.

Things to consider: Goodyear MTRs and BFG KM2's were at different psi's on my Jeep which was due to sidewall flex, IIRC the MTR's were a bit stiffer and came in at a different psi.

I have been doing this all my driving life and it has really paid off in longevity of tire wear. I get a lot of miles out tires.

* note, try to find shallow rain puddles so the water does not come up over and onto the side wall.

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[Tire Guy]

Good ideas but I believe a little on the low side at 16lbs for street. Remember to take into account the centrifugal force at speed. Low pressure is going to allow a lot more flex and sway in the sidewall which is good for ride but normally bad for longevity and cornering. At that low of pressure many tires will show underinflation wear in the shoulders, specially with the more highway miles. It will also create higher levels of heat in the tire which is very bad for the tire. I'm glad it has worked for you. I but I would be very careful running tires at that low pressure on the street. Ask your tire engineer about that low pressure. I would be interested in his response. I am guessing he would be against it. I'm no engineer but I do have 33 years in the tire industry. Off road it doesn't matter because of the low speeds but on the street I would run close to the door placard psi.

Would you run your corvette at half its stated psi?

 

[Ole Cowboy]

Good ideas but I believe a little on the low side at 16lbs for street. Remember to take into account the centrifugal force at speed. Low pressure is going to allow a lot more flex and sway in the sidewall which is good for ride but normally bad for longevity and cornering. At that low of pressure many tires will show underinflation wear in the shoulders, specially with the more highway miles. It will also create higher levels of heat in the tire which is very bad for the tire. I'm glad it has worked for you. I but I would be very careful running tires at that low pressure on the street. Ask your tire engineer about that low pressure. I would be interested in his response. I am guessing he would be against it. I'm no engineer but I do have 33 years in the tire industry. Off road it doesn't matter because of the low speeds but on the street I would run close to the door placard psi.

Would you run your corvette at half its stated psi?

Certainly not. Today's Corvette in stock form is optimized for the tire size: psi: HP. Just as my F 350 is and I run door jam size and psi. In the early days of Corvette whether you had a 350/350 small block or a 427 L88 monster you got the same size of tire...narrow and small and if you are spending your weekends only driving 1320 feet at a time you better get that contact patch right or you burn off a set of tires the first time you come off the clutch at nearly 7000 rpm.

Just wondering if you remember or head of the 'poor man's' race tires: Atlas Bucron's or Casler Cheater Slicks?

But when you are making the jump from 33 to 35/37/40 etc we are talking a whole 'nother ball game. You going way outside the box in height and manufacturing and you have to account for it...to much psi and the center tread wears out fast, to low and you are driving on the sidewalls and wallowing everywhere you go. I know I am singing to the choir here.

Contact patch and tire pressure are critical to performance and safety on anything you drive and I watch it like a hawk...I look out the window of this old ranch house and I got 36 tires in play, I better get it right or its gonna cost me a hellva lot.

I have been doing dust on the tires since the 60's in my racing days and the only tire failures I have ever had was from a set of OEM Firestones. Failed with less than 5000 mi on them and Firestone would not warranty them...days before class action lawsuits were common. IIRC it something to do with cord separating from the rubber. Firestone did take a real hit on it as a result.

Bottom line is non-oem size and grade then you need to ascertain how much psi to support the weight, then look at the contact patch that is the tale of the tape as they say in the boxing game.


Here is the tire at 3-5 lbs, note the sidewalls.

Pic 2 is the tires at 16-18 psi. I would add 2 lbs (18 psi) on trips from Dallas to California, Moab etc.

As for tires: I got far better longevity and performance out of my BFG KM2's than I did my Gy MTR's.

 

[Tire Guy]

I guess my cautionary is for those not running the larger sizes. Too many times good information like yours gets twisted and you get guys running unsafe tire pressures.

I lived through Firestone recall on the Wilderness ATs. Which was caused by too low air pressure in All Terrain tires dictated by Ford. My office processed and gave away millions upon millions in claims. I was with Firestone for 20 years. I joined Firestone at the tail-end of the 500 recalI.

I love my 2014 Stingray. It is my pride and joy to own. I'm hoping that get as much enjoyment out of the JT when I take delivery.

 

[Ole Cowboy]

I guess my cautionary is for those not running the larger sizes. Too many times good information like yours gets twisted and you get guys running unsafe tire pressures.

I lived through Firestone recall on the Wilderness ATs. Which was caused by too low air pressure in All Terrain tires dictated by Ford. My office processed and gave away millions upon millions in claims. I was with Firestone for 20 years. I joined Firestone at the tail-end of the 500 recalI.

I love my 2014 Stingray. It is my pride and joy to own. I'm hoping that get as much enjoyment out of the JT when I take delivery.

GOSH, I just saw where you work...this morning I ordered a new wheel for my wife's Cad Escalade ESV Platinum, got some curb rash on those Chrome Platinum wheels.

Yes exp with Firestone was in the mid 70's. Not good, had to buy brand new tires on a brand new car, never bought, never will. Firestone again.

I am fanatical about tires, I constantly inspect for damage, check for psi and ensure all tires are +/- .5 psi and I rotate at 1st/2nd oil changes.

 

[Tire Guy]

GM is having a lot of problems with the finish on those wheels. We are the official wheel repair company for GM but nothing can be done with those chrome buggers. What part of Texas you in? I grew up in Grand Prairie.

 

[Ole Cowboy]

GM is having a lot of problems with the finish on those wheels. We are the official wheel repair company for GM but nothing can be done with those chrome buggers. What part of Texas you in? I grew up in Grand Prairie.

I am in Boerne now but lived in Dallas, went to school at UTA and SMU. I retired (first time) to Colleyville. I always like GP, in fact I ordered my Z06 Corvette from the Chevy dealer there and did the Factory/Museum pick up out in Bowling Green. You GOT to do that if you buy another one!

 

[Tire Guy]

I am in Boerne now but lived in Dallas, went to school at UTA and SMU. I retired (first time) to Colleyville. I always like GP, in fact I ordered my Z06 Corvette from the Chevy dealer there and did the Factory/Museum pick up out in Bowling Green. You GOT to do that if you buy another one!

The museum delivery is on my bucket list. But unless the C8 is something I can't live without I doubt I will buy another Vette. I am very happy with the C7. I do like going to the museum. When I work in Nashville I always try to get up there for a look around and buy more Vette stuff.

 

[Ole Cowboy]

The museum delivery is on my bucket list. But unless the C8 is something I can't live without I doubt I will buy another Vette. I am very happy with the C7. I do like going to the museum. When I work in Nashville I always try to get up there for a look around and buy more Vette stuff.

I am torn on the C8. Bought my '64 in Dec of '64 and have had a LOT of them since. As bad as I want a C 8 it would need to be the much talked abut "Zora" model which is not due for 3+ years the rumors say. I go full bore on my vetts, gimme all the HP I can buy. But at my age the chances are it would be nothing but a barn queen. I recently turned down a COPO 2019 Camaro, just for that reason. They only made 69 of the Camaros and I thought on it hard, but in the end, I called up Chev and told them to pass it on to someone who won't put it in the barn...never owned a Camaro, why start now!

Love my F 350 King Ranch and getting ready to order an F 450 KR.

 

[Tire Guy]

When I had the C6 I modified the hell out it. But the C7 is bone stock. It doesn't need a thing. One of the most perfect cars I've owned. Not many cars put a smile on your face like a Corvette. That F450 is one damn big truck!

 

[Ole Cowboy]

I need that 450 or I would not buy it!

 

[steffen707]

Making the move to bigger meats begs the question: What air pressure do I run them at?

The door jam tells us what each vehicle as equipped is to be inflated to. Beyond that you are on your own.

2 key things about tires:
1) Co-Efficient of Friction. CoEF

2) Contact Patch "CP"

Number 2 has to be right or you are not optimizing the tire for the application. My jeep with 37's and BFG KM2's runs 3 lbs psi and 16 lbs psi, Moab and street/Hwy.

The question is: How did I arrive at 16 lbs psi for street and Hwy? The answer is simple, "contact patch". Tires are designed to have a full lateral contact patch (according to my buddy was a Tire Engineer at Cooper Tires). Overinflation reduces the CP and the result is your ride and wear out the center part of the tread. Underinflation puts the sidewalls in contact with the pavement and you wear out the edges.

Knowing that how do I determine what PSI to run on the street to obtain a proper CP? No so difficult, drive your car upon a glass table top, adjust tire pressure until you get the full CP for that the weight of the car.

Since I don't have a glass table top I use the same method I learned from my father that goes back to the very early days of autos.

Dust & Water: Find a parking lot with some rain puddles left over and the rest is dry*. Drive your car thru with a slight steer to the L or R to leave 4 sets of tracks on the dry pavement. Do same on a dusty parking lot looking now at the tread of the tire to see where the dust is. adjust your tire pressure in 2 lb increments till you get a full contact patch. The dust method is my preferred approach, it is easier to see the results.

Things to consider: Goodyear MTRs and BFG KM2's were at different psi's on my Jeep which was due to sidewall flex, IIRC the MTR's were a bit stiffer and came in at a different psi.

I have been doing this all my driving life and it has really paid off in longevity of tire wear. I get a lot of miles out tires.

* note, try to find shallow rain puddles so the water does not come up over and onto the side wall.

Neat, i'll have to give this a try. What about just spraying some water on your driveway and driving just the fronts or rears through it? Is the key the water, or does it need to have dirt on it to properly see the results on the pavement?

 

[homerun]

Neat, i'll have to give this a try. What about just spraying some water on your driveway and driving just the fronts or rears through it? Is the key the water, or does it need to have dirt on it to properly see the results on the pavement?

Just draw a chalk line on the tires and look to see where it wears off, hopefully evenly. Borrow your kids sidewalk chalk.

 

[Ole Cowboy]

Just draw a chalk line on the tires and look to see where it wears off, hopefully evenly. Borrow your kids sidewalk chalk.

Another good approach!!!

 

[Ole Cowboy]

Neat, i'll have to give this a try. What about just spraying some water on your driveway and driving just the fronts or rears through it? Is the key the water, or does it need to have dirt on it to properly see the results on the pavement?

Anything that shows across the tread so you can get a reading. Adjust in 2 lb increments. Minus 2 if your sidewall is getting wet, + 2 if its not going to the edge...

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