A Note on Tyre Pressure

[SVOboy]

When we look for small tires holes at the shop we sometimes put 75-80 pounds of air in a tyre, plenty safe. In fact, 120 has been put in one.

Besides, I have a feeling that the max pressure is based on an "and" relationship with the max load. Por ejemplo, 44 psi would be my absolute max only when I've got 4000 pounds loaded into my 2000 pound CRX. I dunno about this second part though.

[krousdb]

Originally Posted by SVOboy

When we look for small tires holes at the shop we sometimes put 75-80 pounds of air in a tyre, plenty safe. In fact, 120 has been put in one.

Another anecdote... A short time ago when a friend and I picked up a certain hybrid for a drive to NY from Chicago for a certain event, we checked the tire pressure to make sure that is was at the max sidewall pressure of 44PSI to ensure that we were playing by the rules of the event. Much to our surprise, the tires were at 80 PSI. As painful as it was, we reduced the pressure to 44.

Just checked my tires yesterday and they were still at 60 where I left them. The traction has improved such that I have better cornering that I had previously with the 15" tires. Also smoother and quieter.

[SVOboy]

As it turns out I have oem traction bars on my crx, I've never heard of it, mehbe everyone has it, mehbe it's very rare, I'll figure it out I guess. Time to Cross some shizzle off the lizzilt.

[krousdb]

I haven't any use for a traction bar. Do you? Why not sell it to some ricer, make a few$ and lose a few pounds?

[JanGeo]

My brother was working on a ATV tire that a customer tried to mount himself, in the process of seating the bead the tire got up to about 40psi (they run at about 6-15psi off road) and as customary he stands away from the mounting machine with a hand on the tire feeling for the pop when the bead seats. Well what happend next was a bit of a surprise - turns out the customer had broken the wire in the bead so the tire blew out bast the bead on the rim ! First thing my brother did was to look down to see if any of his arms or legs were scattered on the floor. Nope just a wicked concussion and ringing in his ears. Made quite a noise. Imaging higher pressure! If you guys ever get a blow out - it will sound like a bomb going off and it will probably shread the tire.

[SVOboy]

Eh, I'll keep the traction bars just because. Having a nice suspension setup that won't really impact weight all that much is nice, nice.

[krousdb]

Yes, defective tires often end up blowing out and shredding. I guess inflating it to 3X the normal pressure didn't help things either. I don't plan on going 3X.

[JanGeo]

Just do some math . . . if you had 80 Pound Per Square Inch a 24 inch tire on a 15 inch rim has about 275 square inches of surface being pressed upon by the air pressure so multiply 40x275 = 11,000 pounds pulling the tire apart.

[krousdb]

Originally Posted by JanGeo

Just do some math . . . if you had 80 Pound Per Square Inch a 24 inch tire on a 15 inch rim has about 275 square inches of surface being pressed upon by the air pressure so multiply 40x275 = 11,000 pounds pulling the tire apart.

And your point is?

When engineers design things they build in a factor of safety. The rule of thumb for non critical areas of design is 2-3. When designing something as critical as tires, I would expect the FS to be much higher.

Although I have not found anything published on the net about auto tires, I have read that truck tires, which tend to have 60-80PSI sidewall ratings, have to pass a burst test of 400 psi.

I have had discussions with one person in particular about auto tires which makes me very comfortable with my current selection of tire pressure.

And I have yet to see one report of a tire failing due to high pressure. But there are a myriad of reports of tires failing due to low pressure.

[JanGeo]

NO I'm more concerned with the rims blowing apart!

But also that tires age so a new tire may meet the spec but we already know that the glue used has a life of about 5 years from when the tire was made - not put into service.