Charlie Aarons, please read

[landcruiserbob]

Charlie, when you speak about an accident you should have your facts right.
-I was driving my u500 camper 21,000lbs @ 61mph on 15.5 20 michelins XL tires when I had a blowout. There are several reasons for the blowout & one of those reasons should concern you if you have CTIS.
-The 15.5's XL's were new & never mounted but spent a few years sitting around at 10,000ft.
-The CTIS system showed both rear tires having a pressure of 65 psi but it was incorrect. The inner bead lock had covered the CTIS inlet & was giving me a false tire reading. The tire that blew out probably had about 30 psi when it failed. It was 20 degrees when it failed & maybe 30 minutes from our previous nights camping spot.
-Tires were rated for 55mph & we were going 61mph. Since we were at half the rated load & it was cold this shouldn't be a problem unless the tire was under inflated.
-You are incorrect stating that the govenor had been removed; I never drive over 65 except for the time I tested the 16r 20 & hit 86 for a couple of miles. I used the 16r 20's for an extra ovedrive not to go faster. Get the facts correct before you post. I got 35k miles out of the XZl's without a problem.
-I have had four blow outs in Unimogs. Three have been at speeds under 20mph. Three have been Michelin's & one a MPT. I was four wheeling when I lost the MPT on a u1200.Two other blowouts were at 30mph & I had an implement on the u1200. All of the Michelin blowouts were on XL tires.
-I do not think Michelin has a problem with the XL tire but they do have a hop that is due to the tread pattern that could generate uneven heat.
-All of my unimogs are still running Michelins & I would never use anything else. Robert g

[Christian P.]

I must have missed something...

[landcruiserbob]

It was an old thread from maybe January & a buddy of mine at Mercedes forwarded it to me tonight. A member of this forum was speaking without any facts on an accident caused by a blow out. I was just clearing up the facts.Robert

[Joaquin Suave]

Robert, Are you sure that Charlie was talking about you?

I've heard of several BAD Unimog / tire experiences! From sources that are truely "in the know" & could be "jobless" if some if what he shared with me got out.

Hopefully your Mog didn't damaged too badly.

Didn't you notice one tire was lower than the others before you started driving? The XL's (395/85's) on Libelula change profile drasticly between the different pre-programmed steps of the CTIS.

[landcruiserbob]

Hi Joaquin, I'm sure Charlie was speaking of me since we conversed during his buildup & I told him about testing the 1600-20's at 86 mph out on the saltflats of Utah. I built the first u500 in North America back in 2003 & my truck was oringinally outfitted with the 365-85 xzl's. They were recalled after a Unimog North America driver was involved in a blow out. I choose the 16r 20's to get better mileage. When my speedo showed 45mph I was running down the road between 58 & 60 @ about 1300rpm's. Perfect, & milage was great.

These are huge trucks & I know more people who have had blowouts on their mogs than people who haven't. It's inherent with large trucks. I work my mogs pulling loaders, plowing, blowing snow or whatever comes up. Large truck loose their tires all of the time.We are running super singles & the blowouts can end ugly. I remind my employees everytime they jump into one that it can get ugly.

To answer your question I did notice the tire looking a little low but I was sitting in deep sand. We four wheeled the day before & I could have damaged the tire; I will never know. The tire completely delaminated & took out the exhaust & rear bumper(1/2 steel plate). I had control for about 50yds & then I felt like I lost the other rear since there isn't a back flow preventer on the CTIS. I found the complete carcass 200yds away & the inner tire was still on the truck; maybe I traveled another 50yds before the final blow out? My son was driving behind us & thought both tires blew. The deep sand & the road being elevated 6ft put the truck on it's side. The camper saved us. It took the brunt of the accident & looked the best afterward. The cab (carbon fiber) was ripped up pretty good.

The truck needs new paint & a new cab. Insurance was great & accepted the appraised value. The truck was about to be sold & we were taking our last trip in it. I'm glad it happened to me & not the new buyer. I'm done with the U500 & I'm about to buy a 1300L crew Cab(Doka). I was never happy with the u500's size & off road abilities(really rough if not fully laden & no torque tube). Our SBU's out work the 500's & are much more capable.

*****One more quick point; THE Accuride RIMS Are Rated For only 90psi of air pressure & I know many Unimog u500 owners that run their air up to 100 plus psi.*****

In no way is Mercedes Benz or Michelin responsible for the incident above, they didn't twist my arm to go out & buy it & then convert it to a camper.Have a good day.robert g

[Chas Stricker]

Howdy Robert,
From your experience do you believe that most blow-outs are caused by heat and flex? I check my temps(by touch) after each fill up. Even driving at 60-65mph here in the desert I've never noticed them being hot to the touch. I run MPT81s. Any other advice you might give seeing your time behind the wheel? I have some trips this summer and always think about tires. Thanks, Chas

[oonimog]

Chas,
I've had two blow outs on my U1300L37, one in front and the other at the back. They were separate incidents but both were well used Michelin XS's and both occurred at ~60mph on the highway. The rear was no big deal, just bang, and I gradually slowed to an easy stop. The front was a lot more dramatic, bang and a sudden right turn, Clyde. It was all I could do to keep the truck from shooting off into the ditch. The rim slammed down onto the road so hard that it was bent and what remained of the tire bent up the fender. I think I was lucky in that I was going down a staight road, had I been in a left curve, it could have been disasterous.

I believe that heat, as a result of low tire pressure, likely contributed to the front tire failure. I have found that occasionally, mud or pebbles get lodged between the rim and tire (from off road driving at lower tire pressures), causing a slow leak. It's important to check the tire pressures often to ensure they haven't changed, especially after four wheeling.

I'm certain that low pressure was not the case for the rear as the inflation was correct and the truck was lightly loaded. Also, I do not believe speed was the killer, rather age. Tires have a shelf life, whether worn out or not. This is why the military sells off all those "new" surplus tires and why they sell tire covers for parked RVs. In my case, the tires were the ones that came on the truck from new and althought they looked to be ok, close inspection showed that there were small cracks all over them, a result of age (ozone, the sun, etc.)

Cheers,
Pete

[landcruiserbob]

Chas, Pete is correct regarding heat & pressure. Low tire pressure = heat. I have never seen a tire blowout if it was inflated correctly. All of my blow outs were operator error. Most have been surplus tires. If you buy surplus tires take a good look after about 1000 miles to see if you have any cracking especially after you have aired up & down. No cracks = a good carcas.

Pete, what rims are you running?rg

[762X39]

-The 15.5's XL's were new & never mounted but spent a few years sitting around at 10,000ft.
-Tires were rated for 55mph & we were going 61mph. Since we were at half the rated load & it was cold this shouldn't be a problem unless the tire was under inflated.
I never drive over 65 except for the time I tested the 16r 20 & hit 86 for a couple of miles. I used the 16r 20's for an extra ovedrive not to go faster.

No disrespect to anyone but...for starters, tires are not new if they have been sitting around for a couple of years. In fact they may as well have been mounted and in use because they have aged and hardened a bit by then.
My 2nd point is why does anyone ever drive a mog at speeds over 90 kh (55mph)?
If tires are rated for 55mph then that is their speed rating, not higher regardless of load and air pressure.

[Chas Stricker]

Howdy 762X39,
I also do pay attention to speed ratings on tires, especially for this truck. The MPT-81s are rated for a top speed of 120kph and load rated at percentage of 110kph. I stay below that for cruising. It seems to use a gob(technical term) more fuel above 100kph also.
Chas