MTFCA Forum

60 front & rear. Where do you get your pressures from?

Damfino.

I agree with John.

70 # will make for a more spectacular event with a tube failure.

Here is what Ford stated.


55 psi for clinchers, 30 x 3 1/2". Normally put in 60 and don't let it fall past 55 for safety.

Thanks Dan.
This is from Floyd Clymer's reprint of a Tire and Rim Book. (1915 to 1927) While the new tires are better in many ways than those made in the teens and twenties it serves as a guideline. Note that it says "minimum" inflation. I have been running 40 in the front and 45 in the rear with good luck. I can see more may be better.
Rich

For whatever it is worth?
When I switched my firsts speedster to clinchers from the 21 inch balloons it started out with, I learned quickly that pressures needed to be somewhat above 55 psi. So I ran the then advised 60 psi for quite a few years. At some point, I heard that a bit more was better, so raised that to about 63psi.
I never did figure out a real reason for it. However, maybe because I was running some older tires? I had one car with a full 65 psi in all tires manage to slide the rear tires enough to shear the valve stems, twice! So for a couple years I ran 70 psi in the rears and 65 psi in the fronts.
It has been a few years since I was able to drive any of my antiques more than a couple miles. If I can get back to being able to get out and tour again? I will probably try to continue running 70 in the rears.

Seeing Dan's illustration, I recalled that Bruce's encyclopedia comes with owners' manuals for all years. This is from the 1915 book.

I have a circa 1910 treatise for chauffeurs and it says the safe tire pressure for clinchers is 20 pounds for each inch of tire. That's 60 fronts and 70 rears. That is what I run and I have never had a stem cut. While 55 pounds might have been ok on dirt roads I expect that a hard stop on asphalt pavement puts a lot more stress on those clinchers than they can take at 55 pounds of pressure.

In the first couple years of motoring, you would want to purchase this tin litho encased beauty. You would then need to do some serious ‘ciphering’ before heading out.

By the time of model Ts birth, things got a bit easier, at least to US Gauge standards. 60psi for 30”, 70psi for 30x3 1/2 . The invincible was patented in 1906 , so just perfect for the early T.
Less is almost always more.

At 55-60 I have never sheared a valve stem with 30 X 3-1/2's.

Mark Gregush wrote: ↑

Tue Jun 14, 2022 10:32 pm

At 55-60 I have never sheared a valve stem with 30 X 3-1/2's.

The tire rotating & shearing the valve stem is most common with powder coated rims.
That slick surface must be scuffed for more bite on the tire.

I would assume that using a metal valve stem, bridge washer and retaining washers @ the rim would protect against tube rotation and that most of the shear issues are coming from using rubber valve stems. Is this a good assumption? I've been running mine at 55-60# with no issues as of yet.

Retro54 wrote: ↑

Wed Jun 15, 2022 8:48 am

I would assume that using a metal valve stem, bridge washer and retaining washers @ the rim would protect against tube rotation and that most of the shear issues are coming from using rubber valve stems. Is this a good assumption? I've been running mine at 55-60# with no issues as of yet.

Fair assumption. The metal stem locked in will stop the shear.
You want to have some talc in the tire case. If the tire does move a bit, no harm.

Just for the heck of it...thought I'd mention it...an old way of measuring the weight on each tire was to take four 3x5 cards and 'box' where the tread meets the road tight against the rubber. Mark them, remove them and figure out the square inches of rubber on the road.

Tire pressure gauge and take pressure reading...

Multiply the PSI seen by the square inches...and...walla, walla.... magic!

speedytinc wrote: ↑

Wed Jun 15, 2022 8:20 am

Mark Gregush wrote: ↑

Tue Jun 14, 2022 10:32 pm

At 55-60 I have never sheared a valve stem with 30 X 3-1/2's.

The tire rotating & shearing the valve stem is most common with powder coated rims.
That slick surface must be scuffed for more bite on the tire.

RE powder coated, I am thinking that could be a factor. Panted might but plated would have different grip factors. I have yet to have any metal stems, mine are all rubber with cold galvanized spray-painted rims.

I am going with the Ford instructions as 55 front and 65 rear - plus another extra 5 on each as I am used to do it also with modern cars.
I prefer that to the danger of getting too low pressure and from all the reading over the past 40 years I took the rule that too low is worse for a tire.

How are we coming to the conclusion that the skinnier 30 x 3 tires, (fronts), need less air pressure than the 30 x 3-1/2 tires, (rears)? That runs counter to everything I've ever heard about tire inflation. By this thinking, the 21" balloon tires should have what, 100 psi? (of course not)

If we assume even weight distribution and we look at one of the charts above, we'll see that for a 450 lb. load, a 3" tire should be inflated to 55 psi and for that same load, a 3-1/2" tire requires only 40 psi. That's based on tire data from the Model T era of course. I would inflate the 3-1/2" tires to at least 50, (but wouuld scared to do 70!!).

This chart doesnt mention clincher or non clincher. The higher pressure keeps the tire in the clincher rim. Remember also, back then clincher beads even overlapped in the middle. Todays tires do not. There is a high risk of the tire coming out of the clinch. Along comes balloon tires. Air pressure was determined by load, not a standard 32psi. Charts show much lower pressures.
Clinchers ride hard. Thats got to be why they went to balloon tires. You can get a safe soft ride. You that have both on different T's can attest.
On my 27 R/P I run 26/28# unless I am hauling a load. then 32/34#

Case in point: Late 20's Harley tires were semi balloon tires in clincher rims @ 26#. That might have worked in the day, but, again not with todays incorrect tires. I know of several guys that learned the hard way rolling a tire off an early Harley @ speed. For this reason AMCA does not deduct points for later , drop center wheels on earlier bikes. Its a safety issue.
Later 16" drop center Harley tires(Knuckle & panhead) run 12# pressure. Thats how we get a softer ride on a ridged frame. There is a price to pay. These tires are real mushy in the turns.

Hi John K,
In 60 plus years of Model T driving I have never heard your statement that "back then clincher beads even overlapped in the middle" being expressed.
That seems to be a puzzle to me, how would one ever be able to put the valve stem into place if there was overlap?
Years ago we had tires which some cut the area around where the valve stem was so it enabled easier placement of it when replacing the tire and tube but if the edges of the beads actually overlapped the tube with 60 psi it would fail pretty quick I would think.( my opinion)
In the 1970's we had BE tires which came with a feather edge at the end of the beads which required trimming to prevent the thin rubber cutting into the tube on the Rolls Royce's I was involved with ( at that stage flaps were no available ) Here are two illustrations which show period cross section drawings of beaded edged tires which clearly show a space between the two beads when in place on the BE rims. Looking forward to you to show us that there were tires which overlapped.

The beads NEEDED to be notched for the valve stem. If you tear down older clincher tires you will see the difference. War vintage & earlier. I dont know when the current tire mfg's decided to change a venerable design.

Even with the wide foot on the Olympic BE Tyres we used to be able to buy, there was room for the valve stem, metal or rubber, to fit between the beads on 3.5" rims. The notch cut in the bead is a reflection of the tyre fitting method used. If you fit one bead first, when you go to put the tube in, the fitted bead is drawn across the valve stem hole, when you pull on the tyre to get at the valve stem. So you then cut a notch in the bead to be able to get the valve stem down the hole.
If you fit the tube in the tyre and then fit BOTH beads into the rim at the stem hole, and lever both sides on at once, they is never any need to notch the beads.
I know many tyres were notched. That does not mean that notching was essential. It is even less necessary on today's skinny beads.

Allan from down under

Today's tire construction and material is quite different than those made in the past. So using 100 old pressure charts arn't likely to be applicable. Current DOT laws https://www.govinfo.gov/content/pkg/CFR ... 71-109.pdf --
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Example --
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Load Chart https://www.tiresplus.com/tires/tire-bu ... dex-chart/ --
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So what's it say on your tires - values vary by brand so its not one value fits all

How many Model T guys does it take to inflate a tire?

How many Model T guys does it take to inflate a tire?


Six.
One to pump, one to hold the tire pump base, one to hold the nozzle to the stem, one to hold the tire steady, one to stand there barking directions, and one more to take a nap in the car while the others are working.

Much easier to pump up a football than a clincher tire. What is enough for a balloon tire is only about half way for a clincher, and the second half is much harder. I hope you have a good pump.
Norm

I put 60 to 65 in all of mine.

A double cylinder pump with a large and small bore makes pumping up high pressure tires easier, especially if you don't weigh 250 lbs.

John K, Thanks for the reply, as you can see from Allan's great answer what you were seeing was the result of incorrect installation of the tire and tube.
Some tires were so small in diameter if one side was stretched onto the rim first it was so tight on the base of the rim it was impossible to move it to under the rim bead, so it covered the valve stem hole, until both sides are in the rim and air is pumped in to force the beads of the tire out to the side the valve hole was blocked off, hence the cutting away of the bead for the valve stem.
While I'm here I should mention also that the rubber stem valves now on tubes are "not fit for purpose" another cost cutting problem the suppliers have inflicted on us. The rubber valve stems can't take the high pressure as they are only vulcanized at the very end of stem and the air pressure forces it's way up to the end. If you are lucky you may get a slow leak whilst parked but if you are driving and it starts to leak the tire will lose its ability to grip the rim and driving or braking will allow the tire to move around with the valve stem being ripping it off and sometimes a few seconds of no control until you come to a stop ( or worse)
Here is a photo taken of such a valve stem cut open, note the chalk powder along the metal tube and the right hand end of the stem where the thread begins, the white mark is the small vulcanized seal of the rubber to the metal stem. That happened on the Pincher Creek tour in 2011, The immediate fix was to put small clamps around the valve stem on the other tubes below the threaded end. I still have one on a wheel 11 years later holding air. The best answer is obviously to replace the rubber stems with metal ones which everyone has intimated before.