What's the consensus of opinion for tire pressure in Firestone 7.50x16s? My 28 highboy tudor rides hard with anything over about 20 lbs max, so I'm curious to see if that's considered normal? I think they're 6 ply so I expect them to be a bit harder.
Bias plys have pretty rigid sidewalls. On a light car I'm sure they will feel rigid and they will get flat spots when they sit for a while. Running too low a pressure can increase the risk of the tire rolling off the rim, especially in a curve. You need to keep them at the recommended pressure.
I'm not saying this is right, but I have to keep mine at just under 20 as well. It's a light model T roadster with a 8ba Posted using the Full Custom H.A.M.B. App!
A friend of mine has 820's on the rear and runs them at 25 max. He just made the trip from here to LAR show and back with no issues.
I have the same tires and I run all my hot rods at about 20-25 (with tubes). I'm no expert but my feeling is on a car that is as lights as our hot rods dont need more than that.
I keep the bias ply tires on my 31A at 25psi. I recently put on new tires and noticed a significantly softer ride at the same pressure. My previous tires were pretty old. I guess they harden with age????
Hi Marty, the other side of the coin with tire pressure is how much tread contact do you have. On my T rpu the rear is so light that at 15lbs I on have 2/3 of the tread contacting the ground and if I lower if I could run the risk of spinning the rim in the tire. Adding weight may be an option and try lubricating the spring leaves as that can make a big difference to the ride. JW
And what exactly is the recommended pressure for a '28 Highboy tudor? There is a formula that design engineers use to determine tire size and pressures for a given vehicle, I don't happen to have it at my finger tips. Maybe someone does. 6ply tires are going to ride rough, I would not back them off to less than 18 psi and would probably would want to keep them as hard as possible for less rolling resistance and a good patch. IE not wearing the centers or the sidewalls (take a chalk and draw a line across the tread then drive it, if the chalk is not wearing off evenly adjust to suite). Then adjust your spring rate to gain the ride quality that you want. Using your tires to adjust ride quality is a recipe for disaster.
FWIW, I've run the 525-16 and 750-16 Firestones on my roadster @ 26 lbs for several years and thousands of miles with good even wear and normal tire temperature. I initially used a water test pattern to arrive at reasonable pressures, and kept a close eye on wear, but recently decided to reevaluate. The car weighs just under 2600 lbs with 3/4 fuel, top, hood, tools, etc. Add about 400 lbs for two people and a few gallons of fuel brings that worst case weight up to near 3000 lbs. (approx. 1550#frt./1450#r). Calculating pressure based on tire ratings (1070# @ 32psi for the 4 ply fronts and 1660# @ 40 psi for the 8 ply rears), plus adding a 1.25% safety margin recommended by some tire companies, results in about 26.5 psi for the fronts and 23 psi for the 750s. It looks like I was close, but will drop the rears to 23 and leave the fronts at 26 in hopes of a slight ride improvement.
I run 26-28 in my firestone 750-16's with tubes, 15,000 miles so far so good. My 450-16's wore out at 15k but wore evenly with 28 psi. They are on my 32sedan that weighed in at 2735 pounds. Posted using the Full Custom H.A.M.B. App!
7.50X16 is a big tire meant for a heavy car like a Buick, Packard or Cadillac. On a light car 20PSI should be fine. Back in the sixties when bias ply tires were all we had, 26PSI in the front and 28PSI in the back was standard factory recommended pressure for most cars. Corvair recommended 16PSI front 26PSI rear.
My hiboy Model A has Coker wide white bias plys. I run them at 22 pounds. My deuce has big n little radials. 22 seems to be the best riding comfort on that car and they're not showing any wear. I tried 26 psi but it rode horrible, would knock your eyeballs loose.
My 41 buick has Coker firestones - factory air pressure says 24 psi front and 28 psi rear . Any more air and it does ride like a rock . Posted using the Full Custom H.A.M.B. App!
I kept my bias plys at 22 lbs for "ride". They were squirrely as hell especially on hot so. Texas black tops. Blew them up to 28 lbs, much improved!
Used to run 32lbs. Seen this post last week , now I’m running 23 in front and 20 in back. Big difference in ride.
You’ll find the sweet spot. Had a set that for a while I couldn’t figure out a “suspension” Issue at speed. Dropped the front tires 3 pounds and it’s 100 times better. You’ll figure it out. If it works then it works but in these light rigid cars they are absolutely part of the ride/ suspension and playing with psi will yield noticeable changes. that being said I’ve got 750:16 on my A sedan and with 6 pounds they look the exact same as with 35 pounds in them. Just harder to push suppose I should go check them now lol
Still a good question worth answering. I’d rather do a search and find good info all In one thread than have to start a new thread and wait for a consensus.
I believe this is how to determine the correct pressure for the tires (not necessarily the ride): Read max tire pressure and load rating from sidewall data, weigh the car - at least front and rear, each corner would be better - then do this: (weight on the axle / (load rating listed on tire x 2 assuming 2 tires on that axle)) x max pressure listed on tire. From my front axle with Excelsior Stahl Sport Radial 5.00 x 16: load rating per tire 992 lbs at 35 psi Weight on front axle: 1450 lbs 1450/(992*2) = 1450/1984 = 0.73 0.73 * 35 psi = 25.55 psi. Giddyup. John
The best way i have found is to put a stripe of masking tape across the tread a and drive down a straight road and see how the tape wears. JW
I adjust the air pressure by looking at the tire. If the outside edges aren't touching the pavement I lower the pressure. I look for an even contact patch across the tire.
Several years ago I read an article that expressed Michelins thoughts on tire pressure. It said that after driving your vehicle enough to warm the tires they should gain 4 lbs of pressure. If they gain more they were underinflated, if they gain less they were overinflated. Now I have no proof that what I read was indeed from Michelin but my butt tells me that it is a good way to establish pressures for each vehicles tires. I tried having different pressures in each tire on my 40 then drove it down the highway. When checking them warm this procedure seemed to be accurate and is what I use on all three of mine with no unusual tire wear patterns.
Hello, As far back as 1958-59, the tire pressures were listed on tires and were told to us from the tire dealers. They knew their customers, so it was a thing they did to keep all of us coming back. There were two tire and wheel alignment places for us teenagers. They were near our bixby knolls cruising grounds. Our normal tires from the factory were set usually at 30-32 lbs. We drove for miles and then when we got gas, checked the tires for leakage and air. If it was low, then of course, added some with the gas station hose. As the years rolled on and tire technology got better, the 30-32 lbs of air seemed standard for the tires we got mounted on our steel rims and mag wheels, when we were 20 somethings. But, recently, in the last 5 years, the tire shops had a new technology of inflating any well built radial tires for passenger vehicles a little over the normal amount. We were surprised when they told us it was 34-36 lbs. so, they knew what they were doing as far as a warranty was concerned. Jnaki It still surprised us that in 2021, I had to get a set of 4 tires and the air pressure was set at 36-38 lbs. I asked why and the technology has improved and the more air allows the tire to grab the ground well without wearing the underinflated edges on most cars. The tire guys had over 40 years of local So Cal tire experience from the popular Tucker Tire Service in Laguna Niguel to the San Juan Capistrano dealers to now, their own shops. Experience and new technology surprised all of us at this new thing. The station wagon rides perfectly and it is a hands off experience with a good alignment included. YRMV
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