Tire Inflation Info

[29plycoop]

!!!! LOW TIRE PRESSURE CAUSES PROBLEMS ON CLINCHERS  -  COME ON SPRING !!!!*
Here is some surprising info found on the Model T Forum I thought was interesting. The question was why his Model T valve stems were failing. The answer is:
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ANSWER: Usually a valve stem failure is caused by one of two things - the tire slipping on the rim, carrying the tube with it, or the tube it self "sloshing" in the tire. Both of these are usually caused by insufficient pressure - clinchers take 20 p.s.i. per inch of width, so on 30 x 3 1/2 tires you need 70 PSI. (3.5 X 20 = 70 PSI)   If you go with a standard oversize, which is 31 x 4, that puts it up to 80 PSI. (4 X 20 = 80 PSI)
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Dont underinflate clinchers.... a lot of people seem to think 40-50 PSI is OK and wonder why they have tire problems.  Clinchers are high pressure tires and designed to run in that way.
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There may be another, tho... If your rims have been powder coated, the slickness of the finish *can* cause the tire to move even at 70 PSI.  You may need to "de-coat" insides to get rid of that glass smooth finish in the rim where the tire sits.
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One reservation I have is if your tires have a lot of age on them the sidewalls won't hold to this theory. 

[29 doUg]

Wow, those seem to be some ridiculously high pressures. I'll stick with Chrysler's recommended psi of 40 in the front and 35 in the back! Or was it the other way around? My manual is in the garage and it's 25 below right now, I don't need to know for sure right now, LOL!

I have, what appear to be, orginal Goodyear Marathons on my U and there is a fair amount checking in the sidewalls; even 40 psi makes me a little nervous.

I know a couple guys that powder coat everything and I just don't get it. To me, it's a waste of time and resources and it seems to cause more problems than it solves!

Interesting info, thanks for the post.