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The Anti Yam!
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Discussion Starter #1 (Edited)
I had my tires trued and balanced Friday. The gentleman who did the work asked me what PSI I ran in them.
(38x15.5-15 TSL Radials= 35 psi Max air pressure rating)

I told him I ran 32psi in them and occasionally tow with it. He said that was a little high and suggested I run 20psi in them, for everyday street driving, then air up the rear for towing. Said I would get a much better ride, and that this large of a tire did not need that much air pressure.

Is this accurate?

I had him air them down to 20psi and then true them. The tires look fine at this PSI and it drives great. Just a little bit of normal bow in the sidewall like any tire should have (Before it had none)

So, is 20 psi OK?


Also, the tire truing process is fascinating to watch, and these tires where definitely out of round. It rides MUCH better now. :thumbup
 

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He is correct. I run 40psi in my 315/75/16 (max 80psi) in my F350. The best way to find ideal air pressure is the chalk method. Find the ideal pressure where it will wear evenly. Where it wears evenly (so long as you have an approved rim width) it'll ride just fine too. The tire is suppose to have a little bow to them. Grab the chalk and see what it looks like. You may need to play around with it a bit to find the perfect air pressure for YOU. Just because a pressure works for them doesnt mean it'll work for you. You'll probably need to come up 2 or 3 psi.
 

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With a tire that size 20 would be good. I run my 36x14.50 usually 18 on the front and 22 on the rear. If I'm going to be hauling a lot of weight I might fill the rears to 30 or 35
 

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i would guess 20psi at the most but i have never ran that large a radial just bias.
so how does the truing process work? never seen it done.
 

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MARBLE GARGLER!
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I loloked it up on youtube, there is a buncha videos. It showed a guy getting the flatspots out of a diesel truck tire by basically chucking it in a lathe and spinning it, it shaves the tread to get flat spots out of them if you skidded real bad and i guess it makes them round-er than the factory made them.
 

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AKA: Butthead
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Cool thread. :)

x2 on the lower pressure but I go by the "foot print" the tire makes. :)
Way back in the 60's, Popular Science had an article on tire pressures.
Hadn't seen that information since! :(

It was great, was all about the tire's "foot print" and had lots of pictures.

Going by the "foot print", covers everything, semi-truck to hybrid car.

A little shorter foot print for highway speeds over city streets, and dirt
roads and sand dunes is pretty obvious what to do in those situations
too, even. All by simply getting down low and looking at the tire from
the side. Look across to the far side while you're that low too. ;)

Make the two sides the same tire pressures and you're done. :)

---------------------

Tire truing kicks butt! :)

Not needed so much anymore tho, the tires are rounder now than ever
and the aluminum wheels are about as true as anything I've ever seen.

I've seen guys bring their 4wd rigs in to have the tires balanced and the
tires were big-open-treaded-suckers and were cupped to hell and back!

As a fellow customer I'd just mention to them about truing their tires and
forget the stinkin' balancing and they'd look at me like I was friggin crazy...

"take expensive tire tread off on purpose? :/"
{Yes. :) ...either that or throw those f#$ed-up tires away} -I thought

Alvin in AZ
 

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The Anti Yam!
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Discussion Starter #8
i would guess 20psi at the most but i have never ran that large a radial just bias.
so how does the truing process work? never seen it done.
With the bronco on a lift just a few inches off the ground, and the tires on it. They placed a "Lathe/tire truer" under a tire and it's motor spins the tire. Then the operator slowly turns a hand wheel that moves a spinning cutting wheel towards the tire until it touches, then slowly turns another hand wheel to move the cutting wheel sideways across the surface of the tire.

Only the high spots on the tread are removed, just enough to make the tire round, no more. It's fascinating to watch, and looks like it takes a great amount of skill. Almost an art-form.

Here is an article I found using the exact same machine.
http://www.fourwheeler.com/techarti...ruck_tire_truing_balancing_shaving/index.html

Two of my tires where egg's, the other two where pretty round.
 

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besure not to run to low on highway. If the pressures are to low the rubber will heat to much and seperate.. ask firestone about the ford explorers.. i run mine at 26 psi..
 

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i was just going to say that too low pressure will blow out your tires it wasnt firestones fault. ford had too low a pressure on the door plackard...... ford exploder haha what a waste
 
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