Fixing Out of round Tires

[Jason O]

Here's a few pics of the tire shaving process. Keep in mind this could make the weight balance worse if an uneven amount of material was removed. I had already added Counteract balance beads.

As for tire pressure, the AT2A's are rated for 9900lbs at 100psi. Our trucks empty don't weigh very much (maybe 3-4000 per tire?) I couldn't find a load chart from Goodyear, but when I go over 60psi, I begin to lose contact area with the ground.

 

[dawico]

I want to learn more about the A2 variant so I went and did some sleuthing.
I have a lot to say, not a mean spirit within...

Does the TM say 55PSI is OK for normal, on road use, at speed?
I didn't think so.

The -10 TM says;
HWY MODE
The highway tire pressure selector is the normal operating mode of CTIS. The HWY mode (Figure 1, Item
is 90 psi (621 kPa) (80 psi (552 kPa) for M936A2 wrecker). If a lower tire pressure mode had been selected the last time the vehicle was operated, CTIS will automatically begin to inflate to the highway setting.

and

Hwy Mode. CTIS highway selection is automatically programmed HWY (Figure 1, Item 4) when you start the engine.

and

Highway (HWY)
(M939A2 Series Vehicles)
Tire pressure selector is the normal operating modes of CTIS.
The highway mode is automatically set each time the engine is started.

So the truck was designed to run at 90 PSI normally, and you are at 55 so problem #1.
This needs to be addressed immediately.

55 PSI? ...and what is the "factory recommended" normal tire pressure called
out at as written right on the tire? It is ONE HUNDRED PSI COLD, right? But
the TM is clear, 90 PSI so it overrules the Mfg in my book so 90 it is.

You are WAY under pressure running at ONLY 45%? of what the TM says
they want the tire pumped up to at speed? Why??? Because the CTIS
has it there? I don't care what the CTIS is doing read the TM, and
you said you were driving at 55MPH, I assume this is not off road
and you are on-road in normal conditions, 90 PSI is where every
tire needs to be at, not a penny less.

Fix the CTIS but,

First thing I would do is disable the CTIS 100% and fill all tires manually to 90PSI.
Go back in 1 hour and recheck pressures, looking for leakers.
MAX air all of them up to NINETY PSI COLD, not a penny less
just like the TM engineers designed the truck to run at
and let it sit for a couple of days, but move the truck so the tires spin
only 90* twice a day to try to ensure your not sitting on a flat spot.
If you can see where a flat spot is after full pressure throw the tire away!

Side Note;
I have personally witnessed big deep cracks in these tires and flat
on the ground. I filled it w/ air to 100 and the crack disappeared!!! Scary!
Freaking CRAZY but I saw it w/ my own eyes. (Not on my truck,
on 7 like trucks I towed once off base.)
End Side Note:

After a couple of days don your driving gloves, make sure spare is aired
up and chain-fall and irons and jack are onboard (or carry phone
number to the local mobile tire repair guy!) BIG $$$, and
filler-up and take it for a spin for a couple of hours @ 55 MPH,
down the freeway, w/ a couple ton onboard, non stop and report back
to us.
(Check pressure in EVERY TIRE twice a day, if a small leak
is proven AIR IT UP to 90 psi. Not an RCH less.) I bet you
see a difference.

If your worried about anything blowing and you not being
able to handle it, sell it, or go buy new steer axle tires, but that is
no assurance you will not have a blow out leaving road
alligators in your wake and the truck dropping 10"-12" in a split
second, at speed, and that rim hitting the bead w/ a flopped
over tire and the steering wheel being tired to be yanked & pried
out of your control, pray not in an opposite turn as in a right,
front flat, in a left turn. No granma's mittens, no slippery material gloves,
only good worn in slightly dirty leather gloves or non slip gloves.
NO SLIPPERY GLOVES / HANDS EVER driving these beasts!

Hands at 9- O:Clock and 3- O:Clock holding VERY firm, like
you could have a blow out at any minute, because you could,
even w/ new tires. Certainly the chances are slim to none
w/ new tires but the possibility is there.

These are tactical military vehicles, comfort was never an option.
Wearing helmets was mandatory too!

If you still have a problem shave away, but I don't think I would
shave an old steer axle set of tires, just get anew. I myself
am saving for a brand new set of steer axles tires. PUNT!

This is a screen shot from TM 9-2320-272-10 with last changes dated 30 September 2004. If there is something newer that I need to track down please let me know. Mine is a 923a2 so it appears the CTIS will run them to 70psi front and rear in highway mode.

I haven't checked them manually but will do.

I also thought I read that the rims are only rated for 80psi. I will have to do some more research on that.

This is 1-25 but the actual page of my download is 43.

 

[Artisan]

I actually think you are looking at the 2012 -10 issue that supercedes the 2004 issue.
Re-read that part at the beginning and look at he bottom of that page.

Having said that, the table you list is clear, FOR EXTENDED HWY USE 70PSI,
for Normal USE use CTIS pressures.

From PDF pg #71;

" For M939A2 vehicles, highway inflation levels pertain to extended highway use. Normal

CTIS pressure can be used for other than extended highway use. Refer to PMCS Table 2-3

CTIS Tire Pressures Chart. "

So in my mind, I am still at 90 PSI.

I guess if a guy never runs a load it would be OK to lower pressures.
At this second I have about 3Ton in mine.

 

[Artisan]

But the jest right now is to try to get the flat spots out right?
It is worth a try to MAX AIR them IMO, even to 100 PSI
and let them sit, and then run it w/ weight ON, a coule
of hours and work them GOOD and
see what happens. Right? I mean it's your call but I
would try something easy before spending $ and shaving
very expensive tires.

 

[Motorcar]

My M923A2 was a May 2011 overhaul, stenciled eveywhere is TP 70 PSI. It's bouncy at lower speeds and drives nice at 55 mph, I don't see a problem. Has run-flat inserts inside the tires, found that when I went to change a leaky o-ring. That may have a bit to do with a feeling of unbalance, especially at too low air pressure.

 

[Floridianson]

I might look into getting some new 155mph tires from GL.
Also flipped your pic.

 

[m16ty]

I was once at a local truck line-up shop and a truck driver there was getting his tires shaved. It appeared that they were taking off 1/4 of the tread (I'm sure it wasn't that much but it did seem like they were removing a lot of rubber). After talking to the owner of the truck, he said they were brand new tires and by having them shaved he could increase the mileage by 1/3. That sounds good but I'd have a hard time buying a brand new tire and then shaving some of the tread off.

Shaving is a fairly common practice in the big truck world and the people that have it done swear by it.

 

[Jason O]

I attempted riding around with lots of weight (8k or so in the bed),varying tire pressure for many miles and the tires never improved. The trucks do ride better with weight added though. Wearing the tire down with road use will also not improve any distortion or run-out.

If you try it, you guys will find the 1400 R20's have something in common with certain parts of your GF's / wives.
You prefer both to be shaved.

 

[tennmogger]

Here are some shots of truing a tire and re-grooving it. All done by hand, a slow process, but got another 10k km out of the tires. Truing and regrooving was followed by putting 16 oz of balancing beads in each tire. They ran like new ones. The tires were only regrooved by 1/4 inch at a time but little of my driving is in mud so deep threads are not needed.

Please don't laugh too much at the primitive truing setup. It works. The hydraulic jack sets cutting depth by lowering the axle. The Hi-lift jack holds down the board with the grinder attached. The grinder is held down by 90 deg brackets mounted to the two handle holes.

If there's any interest I can show how to add beads without breaking the tire off the rim (go through stem hole).

 

[dawico]

Here are some shots of truing a tire and re-grooving it. All done by hand, a slow process, but got another 10k km out of the tires. Truing and regrooving was followed by putting 16 oz of balancing beads in each tire. They ran like new ones. The tires were only regrooved by 1/4 inch at a time but little of my driving is in mud so deep threads are not needed.

Please don't laugh too much at the primitive truing setup. It works. The hydraulic jack sets cutting depth by lowering the axle. The Hi-lift jack holds down the board with the grinder attached. The grinder is held down by 90 deg brackets mounted to the two handle holes.

If there's any interest I can show how to add beads without breaking the tire off the rim (go through stem hole).


View attachment 533286View attachment 533287View attachment 533288View attachment 533289

Thank you sir. I was thinking of a similiar setup with a belt sander. Looking at it though the grinder may work better.

 

[gimpyrobb]

What grit disk is that?

 

[tbar123]

I run the Michellin XZL in size 14.00 R20. Stamped on the wheel itself it reads MAX 85lb TIRE PRESSURE. So I filled them to 70 and the truck rides pretty nice. I've only put about 40 miles on it though.

 

[tennmogger]

What grit disk is that?

The disk has chunks of carbide maybe 1/16" height. Search for "tire cutting" disks.

Btw each of the 14.5 x20 Michelin XLs has 3500 lbs load on them and I run 35 psi. Lots of
miles on highway, over 10k km a year, usually at 55 to 60 mph but up to 70 if needed.

 

[Csm Davis]

But the jest right now is to try to get the flat spots out right?
It is worth a try to MAX AIR them IMO, even to 100 PSI
and let them sit, and then run it w/ weight ON, a coule
of hours and work them GOOD and
see what happens. Right? I mean it's your call but I
would try something easy before spending $ and shaving
very expensive tires.

No, no, no, please don't put 100 psi in 939 A1 or A2s the wheels are not made to handle that much and may catastrophically burst and if not the o-ring may fail. I know because I screwed up and did it and got lucky only my o-ring failed. Look up large tire cage on you - tube and you won't over pressure your big wheels ever again.

 

[todds112]

If there's any interest I can show how to add beads without breaking the tire off the rim (go through stem hole).


View attachment 533286View attachment 533287View attachment 533288View attachment 533289

I would be interested in this. Can you use the beads with CTIS still hooked up?

 

[Artisan]

No, no, no, please don't put 100 psi in 939 A1 or A2s the wheels are not made to handle that much and may catastrophically burst and if not the o-ring may fail. I know because I screwed up and did it and got lucky only my o-ring failed. Look up large tire cage on you - tube and you won't over pressure your big wheels ever again.

Why does the tire wall say 100PSI Cold then?

 

[Jason O]

The pressue limit is for the 2 piece rim, not the tire. They're stamped 85 psi max.

 

[Artisan]

...but the TM says CTIS HWY Mode is 90PSI right? Right.

Certainly any tire can be dangerous at any PSI, personally
I do what the TM says usually which is a valve 10' away
or I connect w/ a clip on and set the pressure at the tank
regulator.

 

[Castle Bravo]

I don't have any in front of me, but don't the A1 wheels (5/8" studs) have a lower allowable tire pressure than the A2 wheels. (3/4" studs) I can assume (but we know what that does) that the FMTV 20 stud wheels have a yet higher allowable tire pressure.

 

[Andyrv6av8r]

...but the TM says CTIS HWY Mode is 90PSI right? Right.

Certainly any tire can be dangerous at any PSI, personally
I do what the TM says usually which is a valve 10' away
or I connect w/ a clip on and set the pressure at the tank
regulator.

Not trying to change the subject, but can CTIS output pressures be adjusted; like in HWY mode it inflates to 60 instead of 70 or 90?