Charlie Aarons, please read

[landcruiserbob]

762 x 39, I agree to your above statment . I realize I was traveling 5mph over the recommended speed of the tires & they were in used condition. I also know that most tractor trailers running down the road have tires that are rated for 55mph to 65mph loaded. Most e rated tires for 1 ton trucks have max speed of 65mph. We have lots of time bombs rolling around out there. I just looked at the leased Kenworth out front with the bull dog trailer & the tires are rated for 62mph on the tractor & 55mph for the trailer. I live in a state where the speed limit is 75mph for all vehicles. I will always travel down the interstate between 50mph & 62mph. I will go up 70 if I get trapped in the tractor cruise control war that we all hate.rg

 

[Jeep]

Hi Robert, sorry about you mishap. You mentioned that you were taking your Mog for one last trip and was about to be sold, well a friend of mine Tim D from Calgary was supposed to be buying a Mog but it was in a roll over on it's last ride. Is this the same rig? It sure looked good in the pictures!

Regards,
Mark

 

[landcruiserbob]

That would be me Mark. I'm glad the blowout happened to me & not your friend. We all came out okay & the truck handled the accident well. Just needs a new cab & of course some 70mph 395 xzl's.thanks/robertg

 

[Jeep]

It's a small world isn't it. You might want to give Tim a call if your unit is going to be repaired as he is still actively searching for a Mog, even if the camper is not on it I'm sure he would still be interested.

Regards,
Mark

 

[landcruiserbob]

Mark, have your friend email me at landcruiserbob@hotmail.com I can send him photo's before & after the accident. The camper is in great shape & is attached to the truck. The cab sustained substaintial damage to the passenger side. As a result the cab has several structural tears in the A pillar. Yanni (unimog N.A.) wants me to put a new cab on it. A bare cab is 13k. The passenger side is the only part of the truck that made contact with tera firma. I wouldn't say it was a slow ride down but we didn't move more than 2ft once contact was made in the deep sand. The drive line checked out & so did the engine. There is a small crack in the manifold which is a common issue & probably didn't occur in the accident. I'm heading out friday to possibly throw a plexi glass wind shield on it & drive it 400 miles home. Low Low boy trailers get expensive. cheers/robertg

 

[wolf359]

Robert,

I am pleased to hear your mog mostly survived. I would be very interested in pictures and more details. Email wolf359@shaw.ca. Thanks in advance.

Tim

 

[charlieaarons]

I've been away from a computer for a while.
Robert, I'm very sorry if my posting caused you distress. I'm also very sorry about any injuries, and damage to your vehicle.
However, a couple of points:
1) The speed rating of 15.5/80R20 XLs is 50 mph, not 55. The thermal stress on a tire goes up as the square of the speed. At 61 mph the thermal stress is ~48.8%> than at 50 mph.
2) My stock U500 tops out on a level road at 70mph indicated (speedometer), but only 68 on the GPS. 16.00R20 XZLs are exactly 12.5% larger in rolling circumference (397 rev/mile vs. 447) compared to 395/85R20 XZLs. One can calculate that with 16.00s a U500 could go 76.5 mph; not 86. How does your U500 go 9.5 mph faster? You must have also been reading off a GPS, the speedometer only goes up to 75.
3) When was the last time you weighed the vehicle? Expedition trucks are like people, they gain weight as they age. My rear axle load gained 1100 kg over 2 years.
4) It's not at all clear from your comments how you knew that the tire only had 30 psi in it when it read 65 psi, since it and its' axle-mate were probably quite flat after the accident

Thank you for your warning about the beadlocks. I am aware of that possibility. I tried mounting one at a truck tire shop in Tucson and when they finally got it installed they couldn't fill it presumably due to inlet hole obstruction. When I got home I drilled 1" holes over the inlet fitting. But my local truck tire shop couldn't even get them installed. With that in mind (the impossibility of working on a tire in the field with beadlocks) I decided to go "bare" and not go below 22 psi in front and ~35 in the rear.
Lastly, I have derived a formula for calculating tire temperature from pressure change (assuming the indicated pressure is correct!):
Thot = Tcold X (Phot + 1 bar)/(Pcold + 1 bar). Temperatures are on absolute scale. 1 bar is added because a "flat" tire has 1 bar in it. This is of course only valid near sea level. That this means is that on a 80 deg morning in the desert, a 95 psi cold tire reaches 114 psi at 180 F.

Again, my apologies for any distress I caused you.

Charlie

 

[lowenbrau]

Robert,

I am pleased to hear your mog mostly survived. I would be very interested in pictures and more details. Email wolf359@shaw.ca. Thanks in advance.

Tim

Welcome, Tim

I suspected the quading would get old eventually. :roost:

 

[Bajaroad]

I have derived a formula for calculating tire temperature from pressure change (assuming the indicated pressure is correct!):
Thot = Tcold X (Phot + 1 bar)/(Pcold + 1 bar). Temperatures are on absolute scale. 1 bar is added because a "flat" tire has 1 bar in it. This is of course only valid near sea level. That this means is that on a 80 deg morning in the desert, a 95 psi cold tire reaches 114 psi at 180 F.

Charlie

Umm, I think that's called the ideal gas law. (PV=nRT)

The formula assumes no volume change as the pressure increases, so maybe the pressure change won't be quite that much when starting with a low pressure tire.
The infrared thermometer is a great idea since the black tire surface should give a very accurate indication of the air temperature inside. Gonna have to test it.

 

[charlieaarons]

Umm, I think that's called the ideal gas law. (PV=nRT)

The formula assumes no volume change as the pressure increases, so maybe the pressure change won't be quite that much when starting with a low pressure tire.

Of course it is the gas law.But the sneaky part is adding the ambient pressure to the indicated pressure, otherwise inaccuracies are introduced by just reading the pressures off a gauge and taking the ratio.
I've read that tires increase in volume 2% up to 30kph then don't expand any further with velocity. I'm not sure what the volume-pressure coefficient is.

Charlie

 

[landcruiserbob]

Charlie, I was fortunate to get the 365's not the 395's. I do remember that on my gps running the 365's I would be about 73mph when the govenor kicked on. Thus the 86mph run in the salt flats. The 15.5 were 55mph rated not 50mph; I took a long look at them this weekend in Utah. My truck ran a straight exhaust that's where the extra ponies came from.

Unimog never turned my truck down on the recall since I had already replaced the tires. No new tires = speedo being set for 365's @ 70mph.

I weighed my truck 2 weeks before the accident & it weighed 21,592 lbs full of water & gear. Unlike most my truck lost weight over the years.I removed roll cage(dumb).

The 30psi was just an assumption. The 30psi was a reading in a previous incident when I noticed the tire being low & the axle showing 70 psi. I put air into the rear axle & it went up to 80psi but the tire in question sat at 30psi. Hence a possible blockage. Pulled tire & found the blockage. 10 minutes after the accident we were inspecting the tires when we noticed we had lost pressure in both rears.You would think there would be a check valve somewhere.

We drove the truck this weekend & it ran great w/o the windshield. New owner picked up the u500 today & I finally get my new crew cab mog I've been looking for. Have fun on this web site I must start building my new camper.rg

 

[Chas Stricker]

Robert when do you get your DoKa? Do you have any pictures? Is it in country yet?
Chas