I have a 1930 Model A coupe Hot Rod. I have no idea what it weighs, but I'm sure it's pretty light. It's the typical setup, small block Chevy (for now), 700R4, Ford 8.8"rear. The front tires are BFGoodrich Silvertown radials in size 165R15. The rear tires are also BFGoodrich Silvertown radials in size P255/70R 15. I have been running the pressure in both front and rear at 30PSI for all. Does this sound correct to you guys? Would you suggest a different pressure setting? I bought the car already built, and that's what the old owner set the tires at, so I figured I would just continue that. However, I just thought today as I was checking the tires that I really don't know if that's the correct setting at all. Lastly, I'm having a 354 Hemi built for it. I know that engine will be significantly heavier than the ZZ4 small block Chevy that's in there now. Any changes to recommended pressure after that engine is in due to the additional weight?
How do the tyres look? Do they have nice even wear across the treads? If so, you’re at a good pressure. If they’re not worn evenly, you’ll need to adjust up or down.
Like David said. I always start with the pressure rating of the tire at its load rating, printed on the sidewall. Then adjust as he said, based on wear patterns. Of course if the alignment is off, that can make it difficult to get a true wear pattern due to pressure.
This question comes up often enough, so you might try a search. In the mean time, I have found around 28 in front and 20/22 in the rear works. Depending on the car and tire in question you may even go lower than those figures. And monitor the wear pattern.
Over time i've found to forget the pressures "recommended". Key is how does it drive and feel-sluggish steering, tracking, overly sensitive, etc. Use what feels best driving-that's the "recommended".
Mine are at 26 front and 20 rear. I watch the wear across the tread. Make sure it wears all the way across .
I keep my front tires aired up ( 205/75-15 ) to 40psi, it makes it steer easier, the rears ( 235/75-15 ) I run about 28psi, my truck is 3300lbs with 50/50 split and two people in it.
This is yet another use for those cheap infrared temp guns. Provided you aren't running super skinnys, check temps across the treads. you want even temps all the way across.
I’m a high pressure guy…..rolling resistance is important to me. Max on the tire is where I put it. Soccer moms and Ford Explorer dealers reluctance to inform customers they bought a vehicle built on a light TRUCK CHASSIS screwed the works…..
Read a while back about how you can measure the car's weight by checking the 'footprint' size of the tires. Kind of makes sense, but the thing is, if you can slip a sheet of paper under the edge of the tire, it's probably over inflated. EDIT: https://www.studocu.com/en-us/docum...e-a-pressure-gauge-to-measure-weight/22779205 Really points out how the same tire on different weight cars requires different pressures to provide a full contact patch. Then there is ride quality (cough, Explorer) and proper alignment to have the tire flat on the road.
On my old touring it liked about 24# front and 28# rear. The rears were Hurst cheaters, caps. So they were so stiff I could not get em to flex much anyway
Sprinkle some talcum powder on the concrete and push the car so the tires go through it. The tread pattern left should be the full width and even across the whole tire print. You can also wet the tire with water and roll the car so the tire turns a couple of revolutions to get a readable print. Tire pressures are matched to a particular vehicles mass. 30psi could be too high for a light hot rod. Check out the pic below, and pay particular attention to the inner and outer edges of the rear tires. Over inflated.
As the others said, the “footprint” is the key to the best tread wear. You’re looking for one as close as possible to a rectangle shape. If it is football shaped, the tread edges will be lifting sooner than the center, and the resultant squirm will accelerate the edge wear. Turning will make it worse. Lower the inflation, (or increase the load). Acceptable tire wear may not coincide with an acceptable ride. A compromise may be needed. As you are running radials, the belt package will help stabilize the tread pattern, but lower inflation will let the radial body plies flex more, generating more heat. On my old roadster, I ran 28 psi front, but only 20 on the bigger rears. Less weight on a bigger tire didn’t need the extra pressure. Just do what these guys do, weigh it and adjust accordingly.
I have very similar tires on my Deuce highboy. After putting a lot of miles on it, I've settled on 30 front, 25 rear. For me this seems the best for long tread ware, best ride and enough to prevent bending a rim hitting unexpected freeway pot holes.
My 32 sedan with similar tires sizes; I experimented with pressures for a couple of months, doing a reasonable distance on each setting, changing a couple of psi each time. Kept notes. Currently running 32 psi all round. Experiment and note taking worked for me. Each car / driver combo is different.
<<<2000 lb car. 15's on the front w/18 lbs of air. 17's on the rear w/19lbs of air...........The ride and handeling is good. Like everyone said U have to experiment..........................
A trick I learned many years ago, it to get 4 sheets of white typing paper 8 1/2 by 11. Position all four sheets lengthwise in front of the tires. Roll the car forward across the sheets of paper and inspect each. An even imprint will indicate that the tire has full road contact. Heavy center imprint indicates over inflation and heavy outer imprint indicates under inflation. Adjust tire pressure and repeat procedure with fresh sheet of paper adjusting pressure 2 pounds until an even imprint is on each sheet. Write each down and use that as your reference when servicing the tires in the future.
Radial tires don't like low inflation pressures. 28 PSI is the lower limit I use. That was found to be the main cause of the tire failures in the Ford Explorer/Firestone radial tire debacle, too low of a recommended pressure. Adjusting pressure was/is standard practice for ride/wear purposes with bias ply, but doesn't work nearly as well with radials while creating problems.
I have 165-80R15 on the front. The car weighs in at just over 1800 lb and have been running with 20 psi for 3 years now. Handles quite well.
Hello, When we bought our 327 SBC 1940 Ford Sedan Delivery project hot rod, it had bias ply tires all around. Thank goodness it had the same size wheels and tires, in case of a leak or blow out. At least, the style of the sedan delivery allowed the same size tire in the openings and when adjusted correctly, fill the openings to a “just right” look. But, to get to that stage, we fiddled around with an ill handling front end and the ride quality was terrible. At the time we took a ride around the neighborhood where it was for sale, the happiness of a real hot rod overshadowed anything else. It was a fun car, power, A/C and it did not smell from the previous owners. (After a terrible almost purchase of a modified 50 Ford coupe and its aroma) I drove it home and again, the happiness of having a hot rod project was the main thing. By the time we got home, my hands were shaking and felt like I had caught a ton of baseballs from the whole New York Yankee’s pitching roster from a catcher’s position. The ride was ok, but a little on the awful side. It bottomed out on small bumps and dips at slow speed, shook when getting up to speed and the brakes were almost to the floor to fully stop. It was not the good road trip hot rod in the current stage. Jnaki We spent our off hours working on the suspension, the brakes, the shocks and whatever else was necessary to get it to drive and stop right. In talking with the local alignment folks, they said a new set of tires and alignment would take care of most of it. Most of it? Luckily, I got wind that our favorite front end alignment guy/suspension expert we had been going to for all of our cars since 1959, moved from West Los Angeles to the big OC, a few miles from our house. So, after spending a ton of hours trying to repair, replace items and getting the sedan delivery to drive right, we resorted to having our friend look at the problem. He kept the sedan delivery for a week and made changes in almost every aspect of a front suspension. The tires were the first to go and good radials were shaved round and mounted/balanced individually. Then he went to work on the whole replace worn front suspension parts and get everything in correct working order. The old shocks were replaced with new shocks and almost the whole front suspension was reworked or replaced. Bushings and all. By the time we got it back for a test drive on surface streets and the freeway system in the big OC, it was the best handling, stopping and straight driving hot rod we had ever known or experienced. It was a "no hands on the steering wheel drive anytime on any road surface and it stopped on a dime. I had a hard time keeping my wife from calling “first dibs” when it came time to run an errand or visit friends. She loved driving the 327 powered sedan delivery. It drove like a factory build El Camino we had spent so much time traveling up and down the Westcoast road trips since 1966. Actually, with the upholstered rear cave, it was a quiet road worthy hot rod. So, check the suspension and replacing most or all of the parts may be necessary to get the handling under control. Radial brands have their PSI printed on the side walls. But, most tire alignment shops and warehouse tire sales places are adjusting those PSI pressures to give a good ride while still keeping the alignment in place. Assuming we don’t run over a road hazard and get the alignment out of whack, again. The fronts for both of our current cars is a lower pressure of 30-32 in front with a higher 36-38 in the rear. (in the late 50s and 60s, the bias ply tires from the factories and shops all had the same pressure.) The higher rear pressure is to compensate for more weight being put in the back with supplies or normal activities with a loaded rear storage place. No one can just look at any tire and say what is what, other than seeing uneven wear due to out of balance, alignment or worn parts. Then a local expert is necessary to correct the problem. Higher pressure makes a crown of the tread, so that is not the best. Lower pressure develops outside wear faster as one turns corners or changes lanes. We needed air in our tires and the local installer said that all tires/wheels leak due to various situations. So, we just keep checking the air pressure in the garage at the same time every couple of weeks. We old folks don’t like to get stuck anywhere or have to call the AAA for tow service. Note: In recent days, we had to have air put into our station wagon. It was a little on the sluggish side when turning and parking. They looked ok, but visual checks are usually for flat tires or nails. The mechanic at the tire shop where we got the tires a long time ago said they were all on the low side. So, he read the recommended tag inside of the car and proceeded to fill all of the tires up. 33-34 in front and 36 in the rear to compensate for any heavier loads. YRMV
Radial tire inflation tables NEVER go lower than 26 psi regardless of tire size or vehicle weight. That said, in theory you can calculate the correct pressure if the vehicle weight is known. Simply divide the corner weight on the tire by the sidewall rated weight and multiply by 36 psi. My '30 Tudor has a front corner weight of about 700 lbs. The calculated 165/75R15 pressure for that weight is 23 psi. Sounds pretty reasonable because that is an appropriate tire size for the weight. The rear corner weight is 775 lbs. and for the 225/65R17 tires the calculated pressure is only 16 psi. So, while that pressure is appropriate for the weight and would give a nice even contact patch, at that pressure the sidewall is unstable and feels like it is ready to roll the tire off the wheel. Increase the pressure to 22-24 psi and it handles the way it should. Use great caution when using pressures in the low 20's and below.
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