Tire Sizes

[MSeriesRebuild]

Have driven many thousands of miles on pavement with NDT's. All kinds of weather conditions, never encountered the 1st problem as pertaining to vehicle handling. The only real issue I personally have with NDT's & pavement is that the tread wears out quickly. I'm certainly not saying better tires don't exist these days, technology has taken everything a long way. I'm just saying I have never experienced all the issues that many express after running NDT's. They are a very good tire when used as intended in my opinion.

[peter e mark]

Thank you for that clarification. And I am looking forward to successfully finding these tires...Hey KNATTRASS, once I get them, lets have a race !

[k8icu]

Charles,

I think NDT are more squirly in wet or ice road conditions with 1/4 tons vrs. larger trucks like 3/4 and larger. I know it was never an issue with my M211 or my M35A2...but my M151 well that was a different story. I know from personnal experience that I was on a road once in the wet and had to make a quick stop for a traffic light that changed from green to red with only a hint of yellow and slid on the wet pavement right through the intersection. Again not as much as a problem though in the bigger trucks.

[Lifer]

I think you guys misunderstood my comment about the skid hazard. I was not talking about military NDT tires, although they can present a small problem in that respect. I was referring to the bar-tread tractor tires that he proposed using on his truck. I think that if they were overinflated (over 15 PSI) or driven too fast (over 25 MPH), they would be a funeral waiting to happen. Misunderstanding or not, however, a good discussion of tires and their safety limitations is always in order. Thanks for bringing up the "fine points" again.

[pfrederi]

I to have heard about non-directional being used so the enemy couldn't track you. I think it may also have to do with the fact that non-directional work equally well (or poorly) going forward or backward.

Trust me having two tractors, Ag treads are absolutely damn near worthless backing up!!

[MSeriesRebuild]

I'm a little unsure of where this thread has headed also. Ag type treads can be had that are suitable for the weight application, but to my knowledge none are designed to handle on highway speeds of more than 20mph. These aren't suitable at all for on road applications on any truck for many reasons, I wouldn't even attempt it. There is a huge danger the tire would simply disinergrate at even low highway speeds.

[refit1701]

Hmm...this topic may change my mind about NDT's. I was afraid that driving around town with NDT's might be hazardous in wet weather and the hilly terrain around Birmingham.

But now I wonder if that is an urban legend and with proper driving techniques the NDT's wouldn't be just as safe at speeds that are safe for the 37. I won't be driving the truck everyday, just out to play or to meets or parades.

Perhaps proper air pressure will help give a better footprint for the tire on pavement?

Maybe I will get NDT's after all.

[knattrass]

From my perspective, the question is "what are your plans?" If you are looking to restore the vehicle back to somewhat correctness, then the 9/16 spec NDTs are the only choice. As already stated, the NDTs are going to handle 90% of your needs for around town driving. Unless your vehicle is perfectly aligned/tracking correct, tread scrub is going to take its toll on any tread/tire construction. The curved profile of the NDT lends itself to a minimum tire patch versus a flatter bias/belted tire. The experience with NDTs discussed by the experts above should be enough explanation. Doing 45mph on wets roads is similar to looking down in an airplane reading "floatation device is under your seat." No amount of rubber is going to get you outta what lies ahead....

[Lifer]

Good analogy! I like it!

[Paul in Kempner, TX]

This thread introduces several topics.

First; as mentioned by several, the Army went to non-directional tires for one reason and only one - they were non-directional. For you city kids who never had a tractor, directional tires may have only 40% as much traction backing up. On a motor vehicle, this meant that a directional tire that was not rotating in the right direction might have significantly less traction for pulling or for stopping. If the tread on one tire on an axle was not facing the same as its mate, steering and other handling issues were present. At the factory, all the tires were installed for maximum traction when going forward. In the field, the tires were mounted so the rear axle had maximum traction going forward. The tires on the front axle were mounted for maximum traction when reversing. The thought was that this would let a vehicle back out of the mud with the front tires "pushing" the vehicle out of its predicament. It was also thought that this front axle set up would have maximum traction for braking since the front brakes did most of the braking. All this was MOOT since there was a 50-50 chance that the spare would end up facing the wrong direction.

Next, the original non-directional tread (NDT) used on the WC & M37 3/4 tons had square shoulders ("JEEPs" too) Heavier vehicles, particularly those with dual wheels used "Non-Directional Cross Country" (NDCC) tread which had rounded shoulders. Notice that we are looking at different weight classes of vehicles.

NDT's and NDCC's have different road manners. Those manners were considered by the engineers who designed the suspensions to be used with specific tires. The Army officers and other bean counters who procured the replacement tires were not automotive engineers and the replacement tires came in many different footprints in the same tire size. Look for yourself - how many tread lugs in the circumference? - how deep are the lugs? - do the lugs intersect the center rib in a "V" or are they rounded?

For many years, our Allies in NATO copied our NDT tires but put in grooves that made their tires work better on the wet roads.

Another factor that affects the road manners of the NDT/NDCC tires is their age. I have some of these tires that are very old. They are okay on a trailer, but are best suited for storing and moving the vehicles that are not running. The rubber in old tires becomes hard. Old tires do not flex and grip the road surface.

Charles does not use old tires - and he does not have problems with them. How many of you who are not happy with your NDT/NDCC tires are running new tires? Are you running them AT THE PROPER INFLATION? These tires are designed to carry a load. Most of us do not usually carry much weight. They will appear to be properly inflated at half the specified inflation. How many have lowered the inflation to get a smoother ride - or just don’t check the air.

Bottom line! My “parade” trucks run recently manufactured original design tires at the correct inflation. I drive the trucks some miles to parades and shows and they work fine. My “play” truck is an M37 with 11.00 x 16 Michelin XL tires. There is no load aboard and I run the air pressure at around 30 p.s.i. This is primarily “off road” and they work fine.

[MSeriesRebuild]

Good points Paul, all things should be used within design guidelines or the outcome will most likely be a disappointment, this is especially true with tires.

[HWooldridge]

I have owned two trucks that ran a directional tread made by Cordovan Tire, which is a chevron pattern and very similar to a tractor tire. However, it is a true high speed truck tire and not an ATV or other completely offroad design.

As Paul states, the problem with directional tires like these is that they load up when going the "wrong" way. Several years ago, I had to pull a couple of modern trucks out of some gumbo mud. The winch would not reach so I drove within cable range, hooked up to both trucks with a chain between the two and pulled them to me, then released the winch and tried to back out. That took some doing as the lugs loaded up almost immediately but I was able to get on hard road and winch them the rest of the way.

That is the parallel with a conventional tractor tire - they pull great in one direction (which is usually forward) but will load and slip going in reverse. I've seen more than one big tractor buried to the axles in wet weather because someone was trying do something they shouldn't have tried.

[CREEPING DEATH]

http://www.garbee.net/~cabell/photos5.htm has good pictures and descriptions.
http://miami.craigslist.org/pbc/pts/891231262.html is a pretty good deal!
I had used Israeli-made 10-ply ND-NATO tires from Gensco on my M37.

CD