M923A2 Doing 80 MPH!!

[tobyS]

Front tire not even close to it's rated load capacity, aired down for the logging road, and doing under 50km per hour. Tires are old but with very low miles on them.

The side wall completely blew out, fist size hole. Driver noticed a couple minutes before it blew that something didn't feel right. He most likely had those minutes due to the low air pressure in the tire.

Had an older tire on my welder trailer, a radial, do that. Not at highway speed. It was obviously getting checked but not near as bad as some bias tires that held for years around the farm on the 4x4 boomtruck (recently replaced with newer NDCC m105 trailer 9.00's).

I think most tires give an operator warning if they are paying attention.

 

[red]

Sorry to hi-jack, but what are the long swooping metal poles that start from the left side of the grill. Some kind of antenna? Looks like every accessory and light possible is bolted on those things! AWESOME.

That's a "power line pusher". In Iraq they hang the power and phone lines low. Without the pusher they tend to get caught on the turret and rip down the lines.

The front and middle mounts on my truck(right truck in the pic)broke free and started swinging into oncoming traffic during the drive from Baghdad to Taji. Oops haha

 

[quickfarms]

80 MPH speed limits are here.

Nevada just became the 15th state to authorize there highway department to set the speed limit at or above 80 MPH.

You can be ticketed for traveling more than 15 mph below the posted speed limit unless you have a Placarded or permitted load or for weather conditions.

Trucks are capable of triple digits but most current highway truck tires are only rated for 85 MPH.

So if you want a truck that can run 80 MPH just get a highway truck. These trucks are geared for off-road, have to high of a center of gravity, too flexible of a frame and the wedge brakes are an obsolete design.

Wedge brakes have a serious issue trying to get them to apply at the same time, the ABS masks this issue to a point. This issue can cause some real problems at 60 MPH.

 

[Csm Davis]

I dont think what the driver was doing was Smart, Prudent, or Safe.

I understand the point about the wheels, and you are correct. I only pointed out the example because i know of 1600R20's in industrial/ AG use on different wheels in the exact situation I described.

Tires that come apart via seperation or centerfusial force to not "Blow out". The tread comes off the casing and the casing still holds air... Until you wear out the steel belt from braking or driving. One example of misuse of a tire rating is this. I had relaced one tire on my trailer for a trip. it was the same make/size design ect as the others but was a load range C instead of D. (on accident) Since i was loaded to capacity, and doing 60mph for about an hour the LR C tire seperated and the tread came off. The tire still held air and i was able to change it out with my spare.(letting the air out of the tire before doing so).

Part of the additional reason why centrifugal force may NOT have been an issue has to do with how much tread is on the tire. I belive the tires come with 35ish 32nds if the tread depth is much less than that the force would not be so great.

That's what I was gonna say. They blow due to heat buildup due to sidewall flex. Lots of air, no load, no flex, minimal heat. Course the front is always heavy, so the fronts will always have some flex.

I'd go 80 in a 900 series, not in traffic and whatnot though. It's one thing to endanger yourself and another everyone else.

Because I'm a smart ass here, I'm just going to add this:

It's not centrifugal, it's centripetal. Centripetal force is a force. Centrifugal "force" is not a force, but a feeling that results from centripetal force.

The tires speed rating is figured with the tires at maximum pressure and load.

Okay which of you fellows have actually talked to a Goodyear or Michelin tire engineer about these large tires? I have and it is not rated at 55 for load and heat, it is speed restricted to 55 to keep them from ripping apart due to the forces of what ever Alexsha wants to call it. If load and air pressure were the only hold up I could run 16.00 x 20's on a land speed racer and have no worries, not! If you don't think it will come apart at speed because of the weight, pull up some YouTube video of cd-roms coming apart at speed and remember a 14.00 x 20 weighs 300 lbs give or take.

I am not one to bash idiots for taking their life in their own hands and chunking it into a toilet as long as you don't endanger somebody else. That's where I draw the line and by continuing to spout this stuff that is true about small tires as true for these over sized tires is going to get someone killed. There are a few of the bigger tires that are not speed restricted to 55 because the engineers are trying to help our soldiers to be able to get out of harms way safely and quickly but the 14.00 has been left behind as it is no longer being used. If you are running 16.00's fast I hope you are no where near me.

I'm curious about the Army (or BMY actually) putting 63 mph on the dash as max on my M936A2 if the 1400x20's have a 55 mph speed rating!!??

Same reason they have 90 psi on a 936A2 with 85psi wheels, they make mistakes.

 

[red]

Care to post the email from them explaining the details?

In this idiots statement I did not say that air pressure and load were the ONLY factors in the speed rating. None of us stated that it won't come apart at speed, but an increase of 5-10mph should not be a problem.

I run 395's.

 

[marchplumber]

Care to post the email from them explaining the details?

In this idiots statement I did not say that air pressure and load were the ONLY factors in the speed rating. None of us stated that it won't come apart at speed, but an increase of 5-10mph should not be a problem.

I run 395's.

I would think the force would multiply. There are MANY on this site FAR wiser than me. The more I learn, the more I realize, how little I actually know. How much would five or ten mph gain me? If I'm in a hurry I don't take a MV. Now if I gotta go cross country? You betcha....They weren't designed/built for higher speeds. It would sort of be like trying to make a ship fly......can it be done? Yup.....would I wanna be on it? Nope. Just me two cents.......I tend to error on the side of caution for myself and others....especially when I can.

 

[Special T]

For offroad tires goodyear /mich produce air/speed/load tables. I dont know of a manufacturer that produces those tables for dot rated tires.

 

[Csm Davis]

Care to post the email from them explaining the details?

In this idiots statement I did not say that air pressure and load were the ONLY factors in the speed rating. None of us stated that it won't come apart at speed, but an increase of 5-10mph should not be a problem.

I run 395's.

It was not an email, sorry I wish it were so I could post it. Also they are limited to this speed by folks that have way more knowledge on this subject than anyone here, including myself. I probably have one of the newest sets of 14.00's on here and they are 2012's and I understand your comments but you and the others who are saying it's okay to go faster are leading other guys to do stupid speeds, like the one the OP posted 80! I even saw one of you post a scale of weight and pressure vs speed! And I would bet that a unloaded 923 at 80 will fit that scale. So a pair of major tire companies with more tire engineers than you have ever even seen make the same call to speed limit these tires to 55 mph and you and the other guys posting this junk engineering think you know better? So I tell you what do the math on the exact weight of just the tread going around a 14.00 at 60, 70, and 80 mph and tell us what the g force is at each and what speed it will tear apart, OH WAIT YOU CAN'T you are not a tire engineer and even if you were you don't know the exact weight or composition of the rubber. Yes I would expect the tires to hold up to some amount of abuse above 55 mph, but where is that upper limit? How are you going to feel if someone gets on here and takes your advice to go over 55 and someone dies? I have been lucky I have been over 55 many times and my wake up came from a blowout at around 60-65 on a tire that had just been topped off with air 60 psi on the rear of a 932 I had gone 10 miles and it came apart I cannot tell you the age of the tire because there was nothing left. One of the things we do on here is give sound advice but we can all make mistakes I have made many.

 

[Triple C]

You all do what you want, here is my experience with exceeding the rated speed. I didn't have my glasses on when I picked this truck up. I should have paid more attention to the rated speed because after 3 hrs doing about 62, the front left steer tire exploded in rush hour traffic while I was in the center lane. The tire had very little wear on it and a little low when I picked the truck up. I aired the tires up and left. I was very fortunate no one was hurt. The second issue was the speedometer was off and I didn't realize it. That is one reason I was driving over the rated speed limit as well. As I said, do what you want but I can tell you from experience, when the steer tire lets go, it gets interesting in a hurry.

 

[98G]

The thing about limits is you don't know exactly where they are until you exceed them. We can say the absolute limit is "somewhere above 55mph" but that could be 62mph or 81mph. Until you exceed that limit you can't accurately define it.

Unfortunately, exceeding that limit results in catastrophic failure.

The question we end up debating here always comes down to "who owns the safety cushion? " clearly the limit isn't 55.000001mph, but is higher than that. So there's a no man's land between the rated 55mph and the actual failure point. Entering that no man's land is a risk to yourself (your call. on your head be it) and a risk to everyone around you (unacceptable)...

 

[Amer-team]

Thank you for the engineering and tech tips in this thread. I have an 84 M923 with Goodyear 11x20's that are 10 years old with 6,000 miles. I like to run at 50 to 53 for fuel purposes, but the truck will creep to sixty if I am not watching it. The truck proof tested a deer at 50 on the way to a Memorial Day event. No damage to the truck. This could have easily been a Honda or Lexus that decided to pull out in front.

We used to show a video years ago on proper operation of a truck in a paving operation and the advice then was to drive 2 to 5 MPH lower than the speed limit to maintain your safety space. Then maintain your cool when someone has to take up all that space that you are leaving for a safety cushion.
Thanks again for the insight into tire limitations.

 

[98G]

Thank you for the engineering and tech tips in this thread. I have an 84 M923 with Goodyear 11x20's that are 10 years old with 6,000 miles. I like to run at 50 to 53 for fuel purposes, but the truck will creep to sixty if I am not watching it. The truck proof tested a deer at 50 on the way to a Memorial Day event. No damage to the truck. This could have easily been a Honda or Lexus that decided to pull out in front.

We used to show a video years ago on proper operation of a truck in a paving operation and the advice then was to drive 2 to 5 MPH lower than the speed limit to maintain your safety space. Then maintain your cool when someone has to take up all that space that you are leaving for a safety cushion.
Thanks again for the insight into tire limitations.

I splattered a coyote at highway speed otw back from Carnac's a few months ago. Never hit the brakes. In fact I didn't even have time to let off the accelerator. I had my 1ton Ram on towbars behind the M923A2.

In response to your comment on driving speed: on a motorcycle I've always been of the opinion that you're safer driving 5 -10 mph faster than traffic. That way you're more in control of the interaction with traffic and less reliant on other drivers to watch out for you. Braking distance from a motorcycle at 75mph is still way less than braking distance from even a high end exotic car at 60mph. Your advice for the trucks makes sense - since braking distances with heavy trucks are further than a car it makes sense to enhance that reaction time by having a uilt in speed differential as well as the following distance. Personally I get in the right lane, set a 4 second interval and pace whoever is in front of me in the right lane...

 

[Special T]

For offroad tires goodyear /mich produce air/speed/load tables. I dont know of a manufacturer that produces those tables for dot rated tires.

The main reason being liabilit

 

[Swamp Donkey]

The main reason being liabilit

Liability is the main reason for this thread. Without it, this thread probably wouldn't exist and the world would be a lot different. Some folks try to mitigate it, and some folks try to create it. We do this by making decisions based on our knowledge and experiences, and following restrictions and limits based on the same things.

Exceed the tire rating...liability
Exceed the speed limit...liability
Exceed the limits of the vehicle itself...liability, and on and on.

The manufacturers have already done the homework for us by using their knowledge and experiences, and as you've pointed out the manufaturers have already protected themselves by passing that information on to us. Would it not be prudent for us to use that information to do the same? Just some food for thought...

 

[trukhead]

I got my M35A3 up to 75 Mph with the tires it had on it. Oh wait, truck was on a drop deck trailer being pulled by a big old Ford tractor on the interstate when we did the recovery. Now I drive it about 45 MPH every where. I only go on back country roads. Speed is commensurate with terrain.

 

[peteybabes]

i can run 67-70 in my 923a2 with 80psi up front and 55psi in the rear...

 

[infidel got me]

i can run 67-70 in my 923a2 with 80psi up front and 55psi in the rear...

You blow a tire at that speed and you are in for a wild ride, hope you don't kill anyone

 

[Suprman]

Just because you can does not mean it's a great idea to do it. I think your fronts and rears should be within 10 psi of each other.

 

[gottaluvit]

i can run 67-70 in my 923a2 with 80psi up front and 55psi in the rear...

If its an A2, how do you control the air pressure? My CTIS puts it where I figure it should be. Thinking its 45 psi. Agree with lower speed than it's capable. I get nervous when mine hits 50 mph. If any failure it's game over for me or anyone in her path!

 

[peteybabes]

Just because you can does not mean it's a great idea to do it. I think your fronts and rears should be within 10 psi of each other.

I'm just going off of the spec for "HWY" mode on the CTIS system... I believe it is 80 up front and 60 in the rear?

I don't do a whole lot of highway at all, but am considering moving up to the 16.00x20.00 Michelin that is 53" tall. If I buy new "virgin" tires do you think that they can handle 70?