how much air in a model t tire?
21" 32#, 30X3.5" 65#
I have always run 55# in the 30X31/2
35# in 21X4.45-4.55
My experience is in my 30" I run 55#....In my 26" I run 45#. I've blown out tube valve stem cores by caring too much pressure. The problem seems that the tubes we have available now are of such questionable quality that the valve stem cores will leak around the rubber stem if stressed. I put small hose clamps around each stem as a preventive. Know it doesn't look T'ish but it seems to work..
All the early treatises say 20 pounds per inch of tire for clinchers. So that is 60 pounds for a 30X3 and 70 for 30X3-1/2.
35 in a model A but 27 is enough in 21" T tires since a T has no shock absorbers (dampers).
With 35 lbs. and no shocks the tires tend to bounce with 35 lbs..
In my touring I run 27 in the front and rear unless it is loaded, then I go to 30 in the rear. That is more than Ford recommended I think.
One current mfg recommended pressure. 65psi.
As for Ford specs, remember the clincher tires back when the specs were printed, were true 30" x 3 1/2".
Today, our 30" x 3 1/2" are really 31" x 3 3/4" as they are Oversize, so you need 65psi.
Oversize tire for T's
And comparison of today's new Firestone 30" x 3 1/2" Oversize tire to old Sampson 30" x 3/2" tire.
Why you need more psi in today's clincher tires
Guess I'm a bit slow, but why would the oversize tire need more pressure ? Wouldn't the oversize tire need LESS pressure for the same load carrying capacity ?
I have been going with 55 on my 30 X 3.5's. No problems so far with a good amount of driving that they have been getting. At 55 I think you are getting a bit more road contact with the tires. With stop and go traffic and wet pavement I'll take all the contact between the tire and road I can get.
I go with 55 in my 30 X 3 1/2 clinchers. Higher just scares the @##$% out of me
You have to remember that the tire pressure is what keeps the bead in the rim and is all that keeps the tire from spinning inside the rim and ripping the valve stem off. Those tires were designed to run at those high pressures. I agree that the quality of the tires we are getting from God knows where is an issue but I have been running at those pressures for years and am currently running at 70 pounds on a new set of tires I put on last year.
I've tried 55 to 65 but I agree with Mark and Mike and.run my 30x3 1/2s at 55. I don't want higher pressures with today's hard pavement ruts.
In an Overland owner's manual I saw it said to use 85 lbs. in 30 X 3 1/2 clinchers.
Most folks I know use 55 but the recommended pressure was 65 for the T ford.
I run my 30x3 1/2 clinchers at 55PSI on my '25 coupe. I once got caught in some post frost mud in the spring here on a country road in the hills a few years ago and had a h--- of a time getting out. Had to get a run at a hill, then back up a bit and hit it again at full throttle and would get about 3 or 4 feet at a time. Did that about 8 or 9 times and finally got to the top, left ruts 6 inches deep plus. I didn't have any problems with the tires slipping on the rims, but I do have old Wards Riverside tires on it. Oh, and by the way, I am using Kevlar bands and had no problems with them. I did let things cool a bit before I charged at it again each time though. No trouble with the drums or with overheating with an old era correct(late 20's early 30's flat tube radiator) either. Rest assured, that poor old T got abused that day, and made me a believer on how tuff they are. Dave
I think the weight of the Model T should be considered. Lower pressure in a roadster 55 psi would be enough but higher in a heavier vehicle.
Peter, I could agree about the weight issue but first, you need to know the true weight of your car. The common knowledge is that a T weighs 1200 lbs. I believe that is the spec for a 1909 Touring and the1200 legend carried on. My little Runabout weighs 1600 empty on a scale but, it is a 1919. It has a starter and generator, doors (or door rather), a bigger rad, heavier wheels and so on. You can imagine even more weight for a same year Touring, closed car or truck. Of course these weights have been discussed before. You really need to put it on a scale.
If you don't have scales handy, check Bruce's encyclopedia. Shipping weights are listed for each year's various body styles.
I'll go along with the 55-60# crowd. I inflate them to 60#. They leak down to 55# soon enough!
Mine is a Huckster.
There are two reasons for running the clinchers at a high pressure. One is the way they fasten to the rim causes them to slip if the pressure is too low resulting in tearing off the valve stem. The other reason is that too low pressure can cause the tire to flex right at the edge of the bead which will result in wearing out the tire at that location and a blowout. Use at least 60 or 65 psi. It will drop in about a month and need to be pumped up again, so check it every time you drive the car or if a daily driver about once a month.
Tire pressures indicated are intended for max load. If you use 1500 lbs for a T divided by 4 = 375 lbs per tire, with that weight 65 lbs would be excessive. If the vehicle was regularly loaded to capacity then 65 lbs would be appropriate. Boat trailer tires have a max 50-55lbs at max load wheelbarrow tires have indicated 55 lbs if you are carrying cement on a regular basis. For general purpose use, most tires can have substantially lower pressures.
A typical 1923 T touring is about 1700 lbs empty. Add a couple people, a Ruckstell, cooler full of frosty beverages, set of gas oil water cans on the running board and it is going to be near 2400 lbs.
A 30x3.5 tire is really 30x4 so that would be 80 pounds.
A 30x3.5 tire is really 30x4 so that would be 80 pounds.
30x3.5 is a 23 inch rim. 30x4 is a 22 inch rim size.