Tire Force On Rim

Wouldn't the tire pressure be the same force that is pushing against the rim?

...times the total contact area, I think. (F = P x A)

...or maybe a bit more complicated.

http://hal.inria.fr/docs/00/50/65/75/PDF/dl_cep_09_17_11_p.pdf

I think you're a factor about 2 high, as at least 1/2 the force will be taken as tensile load across the tyre on the tread part. Maybe more than 2, as the circumference there is greater than at the rim.

Well I did just get out of bed and I am far from being fully mentally functioning at that time of day.

And I think this whole exercise is moot, since the inflation force is nothing compared to the real forces acting on a wheel in a hard left turn, at 150 MPH, when it's 120°F outside.

But interesting to think about.

The next time I'm in a car doing a hard left turn at 150 mph when the air temp outside is 120 F, I can assure you that I'll be mentally calculating the pressure that the air inside the tire is exerting on the rim.

Well that or "Oh my god! What the #^$#*@&*^&**# am I doing! I'm gonna diiiieeee!"

I've never done a hard left turn at 150 mph when the air temp outside is 120 °F either, but I have done a hard left turn at 100 mph when the track temp. was 120 °F.

It resulted in flat sheet metal, where curves had been before, on the right side of the car. And a flat tire. And some suspension damage.

Just another day.

tcmtech has a factor of .5 in the calculation; half thru the tread and half at the rim as a first approximation.

Ah yes, you're right, I missed that

It's almost frightening what people may find in my posts if they actually took the time to read and understand them.

Now if they also found the Easter eggs I occasionally hide in them at times as well that would really be something..!..

Your numbers look good, but rims do get damaged. The load they can handle is then considerably less. A tire shop working on large truck tires inflates them inside a cage so no one will be injured (or killed) if the wheel explodes.

Still, good answer.

As promised I did a bit of ciphering, and basically confirmed your result even though I went at it a different way. I used your sizes and pressure, but assumed a sidewall strip 1" wide and 8" long from rim to tread. I ignored the width taper and the curve of the sidewall; thus it acts a bit like a beam with half of the force at each end. Thus:

1" x 8" x 100 psi = 800 lb / 2 = 400 lb per inch at the rim. Since the circumference is 62.83", this is a total of 25000 lb. Close enough to your figures for the approximations we are using. The load at the outer end (the tread) is balanced thru the tread by the other sidewall.

But tcmtech's factor of safety of 32:1 will not be true, because we also have to consider bending of the lip on the rim in addition to the tensile loading. Plus we recognize that operational (dynamic) loads may control the design--but that is not what was asked.

Don't know. But I know that a locking rim, if incorrectly fitted to a truck tire, can (and some have) fly off and kill people at less than 100 PSI tire pressure.

That's exactly why I'm feeling for an answer. Several of my antique trucks have multi-piece rims, and many others in the hobby also have them. I'm thinking that they don't really know the force, and therefore don't appreciate what can happen.

Guess I'll have to do some ciphering and see what comes out. Yes, rim designers have to consider many other forces--weight, turning, bumps, etc.

I have use chains wrapped around the tire and rim, and a clip-on inflating chuck, then do gradual inflation with plenty of careful inspection since I'm a hobby operation and don't have access to the proper safety cage.

I do believe that all split rims with separate outer rings have been outlawed for quite some time. there are several companies that make replacement rims in all of the commercial sizes including fire apparatus/fire truck. A friend of mine lost two fingers and broke two trusses in his shop working on his old dump truck. The roof was 30Ft. in the air he was lucky and landed on a pile of the old tires he was changing. I believe he might not be here today if not for the pile of old tires. Yes it was him who broke the rafters not the tire or the rim he left the ground in a long high arch through the shop. That was his come to Jesus moment he no longer tries to do split rims without a cage nor does he purchase any old wheels to get the tires since it is almost impossible to locate the 1/2 size tires like the 16.5 or the 22.5 last time I talked to him he was in the process of purchasing new bud aluminum rims for all of his old trucks. They are lighter and safer, plus they look better Duke