My new deuce highboy sedan has Coker built 285-70-R15 BFG radials on the back. Can't seem to get a straight answer from Coker on what tire pressure to run. Car has a horrible vibration between 65 and 75 mph with 30 lbs of air. Today I was coming back from the shop 80 miles away and stopped about half way home and lowered the pressure to 25. Shazam no more shake. Doesn't seem like enough air to run in the rear tires on a sedan. I'm sure some of you will have an opinion?
I find the lighter the car, the less air pressure required in the tires. I only run about 20 in back and a bit less up front. To much air pressure and a lightweight car = bouncy. You want the sidewalls to do their job and be "cushiony"
A word of caution. Low inflation can cause tires to overheat such as the Ford Explorer fiasco. Any radial should handle 36 lbs. without any problems. I would be tempted to take an infared temp gun and check tire temps after driving it for several miles. I would put the tires and wheels on another car and see if you get the same results.
Not on a sedan but I run the same tire on the rear of my Deuce roadster and my Deuce five window, both hiboys. I run 28 psi in them both and have had no issues.
Tire PSI on hot rods,is by how it rides,not spec. you read off a chart. Nearly no hotrod is the same lbs.. All ways look at the tire side wall,down near the road > your looking for load on tire=If it shows about a 1/2 in swell, that close to good{ adjust up or down just a little by how it drives. If tire had more,add air,if no swell > take out air
I run Firestone 14x31x15 double diamond repops from Coker on the back of my roadster. They work very well at 25PSI. they practicality rattled my teeth out at 30. Many many miles with 25 and good ride.
I run 25 in the rear tires, otherwise the center of the tread wears noticably faster than the edges. I run 32-35 in the front skinnies. I had a wheel bead bend when I ran the fronts below 30.
I like the "Roll through water" method to determine pressure on a big tire hot rod-look at the tracks, are they even across the tread? That ensures the tread is laying flat/evenly loaded on the road.
I usually run a 235/85/16 on my hiboys on a 7 " rim (32 " tall) and run 25lbs nice ride full footprint
I've ran those 235/85/16's on a couple highboys and they worked good. It's been a while but I think they might have been either 8 or 10 ply. I did 25lbs with no problems. Always got mine at Sam's, they were Michelin's. Seemed to have the best price? I wanted a different look with this car. This is the 3rd highboy sedan I've done with this style. They've all had the same look. All used the same rear tires and wheels.
Tires are part of the overall suspension system. Pressures molded into the sidewall correspond to the load rating/capacity molded there as well..... so, logic tells us that a tire rated for 4,500 lbs. at 35 psi is going to be hard as a rock and provide a ride (and handling) to match. I always start around 30 psi and drop it from there. Hot rod rearends are usually very light, and most front ends are lighter than modern cars, so you can't really go by the sidewall recommendations. The water-patch method listed above is a good guideline.
Sidewall load rates and pressures are maximums, not starting points. The more plys, the rougher the ride especially on light vehicles. LT (light truck) tires are pretty stiff.
The Jalopy Journal
