Max tire load is being mis-calculated according to Tx. DOT

[rickhans]

Every posting I have read here has referenced the maximum tire load to be the max. weight posted on the side wall of the tire. According to the Texas Highway Patrol Weights and measurements Division that is incorrect. They said that Texas law completely ignores that number as a meaningless number and has its own formula: Tire tread width X 650 = pounds per square inch x number of tires on axle = max weight, unless the axle rating is less.

I purchased a 16k trailer this week, has 2 8k axles with 7. 5x16" tires, 10 ply bias, load rating D, max weight according to tire is 2024 lbs. That would mean the max I could carry the way I have been understanding the postings here would be 8096 pounds.

Texas says the tires capacity is 7. 5 X 650 =4875 pounds max per tire, = 9750 per axle for singles, and for my trailer, 19,500 max load.

Why all the talk about the ratings on the tires. I assume that Texas rules are the same as the US DOT. Who else knows about this?




------------------
98. 5 24V QC 4x4 SB 3:54 5sp

 

[mbrolin]

Well,Id sure do more research on this. I would think that a tire manufacturer would know more about what the load capacity of their tire is. Tread width is just one part of the load carrying factor. There is also the sidewall design and the rubber compound used.

 

[rickhans]

I have spent the last month researching trailers and weight requirements to be sure I bought a trailer that would be within the legal guidelines. Every trailer manufacturer I talked to in Texas that makes a trailer similar to this, had a trailer weight limit that exceeded the stated tire weight limits execept when the trailer had 10k axles with dual wheels. I asked each one about tires and weight ratings and they ignore what's on the tire.

The manufacturer I bought mine from insisted that 4 of these tires exceeded the 16k limit of the trailer, and had a similar formula that he used to determine the correct tire for the trailer. That was when I called the Texas DPS and talked to an officer in the enforcement office who told me the dealer was correct and quoted the state law, then gave me the formula they use when inspecting trailers to determine if it meets the weight requirements.

I just want to know if other states do it differently. If you check different brands of tires, with different ply ratings, you will find large tires and small tires alike with the same rating, such as D or E. All E's I have looked at from the smallest to the largest have the same 3K (3204 I believe) rating. Obviously an 8 ply 16" tire will be stronger than a 4 ply 14" tire under a 16k trailer. I really don't understand why and how the rating can be the same for different size tires, therefore don't understand why the rating is even on the tires.


------------------
98. 5 24V QC 4x4 SB 3:54 5sp

 

[klenger]

It sounds to me like the Texas Highway Patrol is more concerned with damage to the roads (pounds per sq. inch of tire) than they are about the safety of the vehicle.

------------------
Ken Lenger
On Order - 2001. 5 2500 QC 4X4 SWB SLT, ETC/DDX 5 Speed, 3. 55 (no antispin), camper group, trailer folding mirrors, RBR CD/Radio, LT265/75R16E AT OWL tires, trailer tow group, Patroit Blue / Agate,
Replaces 98 Jeep Grand Cherokee V8 which is for sale.
Trailite 21' Travel Trailer, ~4000 lbs loaded.

 

[Alan Reagan]

I think Klenger is correct. The calculations they are making have to do with what they call the Bridge Law in Georgia. They are doing weight calculations based on how much weight will be evenly distributed on the pavement and in what span that weight will fall. For example, under the bridge law, you can legally have an 80,000 lbs GCVW under Georgia's law but you have to be 65 feet long to do it (legally) and have 5 axles and the correct width tires, etc. Any shorter and the gross weight decreases per a set formula. That puts 12,500 on the steering axle with the rest distibuted evenly on the other four axles giving a max axle weight of 16,875 on the drive and trailer axles. They are worried about distribution, not tires (or safety or so it would seem).

 

[Champane Flight]

Alan,in Colo they have almost the same bridge law. An outfit in the valley got around it by putting a boat trailer behind there short 38' end dumps. They did this for 3 years,before the state could rewrite the law. It was funny to see a little boat trailer behind a rig. But legally it was a extra axle!

------------------
95 Dodge 2500 Luverne grill guard,headache rack,running boards and Amzoiled. Soon to be mildly bombed. 84 Dodge d-150, 318 Hooker headers,Edelbrok intake,mallory ignition,Carter Afb,Accel coil,and Custom dual exhaust. Boat,fifthwheel,motorcycles,and shop. 72000 as of 3/1/01,not even broke in yet. Old Dodge 126000 miles and running better than new.

 

[Bill Stockard]

Klenger & Alan Regan,
You are right. The TX DOT figures are for figuring max loads on axles and are not for specific tire load ratings. These figures are for "Bridge Law" and for registration(tax) requirements.

Bill

 

[Steve St.Laurent]

Rick, different size tires do have different weight limits within a rating. For example my stock tires were 235's (75/16's I believe) E rated @ 3042 lbs/tire. My BFG's are 285/75R16 and D rated @ 3305 lbs/tire. There is a sliding scale. Onto your first question there is no way I'd EVER overload a tire. They are quoting you what's legal - what's legal and what's safe aren't always the same. Remember all the firestone tire stuff going on?

-Steve

 

[rickhans]

What brand of tires are made in a 7. 5x16 that have a rating of 4,000 pounds or greater and where do you buy them. Every trailer company I talked to said that they don't exist. They all also told me that they have not had any problems with the tires they put on this size of trailer.

I do not believe that the Firstone tires are failing because of weight capacity. I have been towing light weight trailers (under 10,000 pounds) for over 30 years, and driving pickups and utility vehicles the same length. I have had problems with two other brands of tires separating and blowing out for no reason. I went through 7 tires of the same brand on my 4wd Suburban, and several of another brand on two or 3 compact cars. Neither brands were Firestone, but all were steel belted radials of the size specified for the vehicle they were on. The problem is poor quality tires and has nothing to do with the load capacity, as none of the vehicles exceeded the rated capacity of the tires.

------------------
98. 5 24V QC 4x4 SB 3:54 5sp

 

[rob10858]

rick, something else that goes into the equation is the weight of the trailor itself. despite the fact that the weight is being transferred to the axle of the truck, the trailor itself can cause tire overload. lets see, your tires can handle 9500 lbs gw, when you consider the weight of the trailor then your load capacity can be reduced by at least that much. i hope this makes sense, the longer the trailor the heavier the frame and they can be surprisingly heavy. take your trailor empty to a cat scale and get the readings on your front, rear, and trailor axles this will give you a good idea of how the weight is distributed. ive run across problemns with our 28 ftrs with two six thousand pound axles. thats 12000 lbs gvwr. i was pulling an implement that weighed about 9000 lbs, so i figured i was safe, after about three blown tires i finally went to a scale, and the third [trailor plus load] weight showed me at 12560, grossing at 24500. deduct about 7000 for the truck [one ton] tools, etc and the remaining 5000lbs or so relate directly to the trailor weight. sometimes we assume that the fifth wheel takes most of the weight, and thats where we it helps to check to see where the weight really is.

------------------

 

[rickhans]

I understand all of that. As I said my trailer is rated at 16,000 pounds with a load. This excludes tongue weight. With 2 8K axles, the load and trailer weight should not exceed 16k pounds, although legally, you can exceed that up to 2000 pounds, depending on what type of scales are weighing you. Portable wheel scales have a tolerance of +/- 2000 pounds I believe.

My point is, if you can not purchase tires with a 4k rating (=16k pounds for 4 wheels), yet most of the trailer manufactures are building and selling single wheel trailers with 14 to 16k GVW with D and E rated tires, then based on the postings here, all of these thousands of trailers on the road like this should be having blow outs and be dangerous.

If this is the case, then what tires,(brand, size, and weight rating) are being purchased to replace the tires that are sold with these trailers. I obviously do not want to have tires blowing out, and the state says they are safe. But if they are not, what else is available? If someone can tell me, I can go back to the traile company and get these tires replaced. I orginally asked for tires with 4k ratings but they could not find any and said that this is the standard tire used for the 16kGVW trailers.


------------------
98. 5 24V QC 4x4 SB 3:54 5sp

 

[mbrolin]

I understand your predicament. Is this a utility trailer or a 5er? Most 5ers that are in the 16kGVW use triple axles and E rated radial tires. Even with a tire rated at 3042 your max load is 12186k with 2 axles and 18252 with 3 axles. This is on the axles. Theoretically 1/3 of the weight should be on the tongue. Im assuming you have talked to some tire dealers as well.

 

[rickhans]

This is a gooseneck 20' with 5' dove tail flat bed trailer, with 2 8k axles, 4 tires total.

 

[QRTRHRS]

Rick,

Did you crawl under the trailer by chance to see if the axles have the 8k rating on them? My Dexter axles have a sticker stating they are 7k rated. Some crooks will misrepresent ratings.

My gooseneck is rated for 14k gross. It runs 5400 empty so that does not leave much. I forget the tire spec/maker. Have to check that out.

 

[Steve St.Laurent]

IMO for a trailer of that capacity with tires that small you'll need 3 axles or dual tires on double axles. I have a friend that got a great deal on a high deck trailer because the trailer was pretty heavy and it only had double axles with 15" wheels and tires - therefore it doesn't have much carrying capacity.

The firestone tire thing is in a way a capacity issue, the primary cause has been pointed out as underinflated/overloaded tires. The manufacturers have a weight rating on the tires for a reason, JMHO.

-Steve

 

[rickhans]

Doesn't anyone know what tires do have a rating of greater than 4,000 pounds in a 16" size?

------------------
98. 5 24V QC 4x4 SB 3:54 5sp

 

[Bill Stockard]

Rick,

Go to a Michelin tire dealer and ask them look in their Tire Data Book for the ratings in tires of the size you want. Unless you go to a truck tire dealer, you'll probably get the "deer in the headlights" look when you ask. I have found, in past experience, that Michelin is your best bet for high capacity special tires. The next problem is that if you find a tire like you want, besides affording them, is getting them.

Good luck.

Bill

 

[rob10858]

thats basically what i was trying to say with longer heavier load axle four wheel trailors, the tire ratings are just on the fringe of being overloaded. we have twelve 28 ft fifth wheels, mnf by four diff makers. we lost almost all of our tires in the summer months. it didnt take long to realize why. a third axle isnt too hard to install, and can pay for itself in no time. just make sure that your brake controller is designed to handle that extra axle. ive went to an eight wheel trailor and no longer worry about the tires or axle springs failing, but the stiffer ride is about to beat me to death.

 

[Frank J. Lloyd]

Originally posted by Rick Hansen:
Doesn't anyone know what tires do have a rating of greater than 4,000 pounds in a 16" size?

Michelin and Goodyear and most of the other manufacturers have them. Look for tires with a load rating of F or higher. They are not uncommon to find here in GA. I found several online at the Toyo site and a few others. Try there, maybe somone else can chime in on where to find F or G tires in your area.



------------------
2001 3500 4x4 H. O. 6 speed 4. 10, SLT, Cab and Chassis, 163" wheelbase western hauler stake bed, silencer ring AWOL, boost & pyro gauge, K&N, Geno's one touch oil valve, Cobra 29 bombed, Halogen backup lights, cargo bed loading area flood lights, 6" driving lights, underbed boxes, pacbrake, 5" stack and exhaust, straight!
ready to bomb
Big Red is ready to roll!

 

[dmurdock]

I do tech support for the division of Txdot that deals with this. The 650psi (the number of times that figure has been entered in our programming code is painful to think about!) deals with pavement pressure. . ie: max allowed in Tx is 650psi for inch of treadwidth (on the ground). For example, legal weight for a single axle is 20000lbs... however, if you have standard tires as found on an 18wheeler, your treadwidth is probably 10 htinches. . so... your max weight allowed on this axle (given 2 tires per axle) would be 13000 lbs (2x650x10), because the 650psi would be the limiting factor. Now say you had tires that were 20 inches wide... your max weight according to the psi calculation would be 26000lbs (2x650x20). . but you could would only be allowed 20000 (max allowed by law). Basically, there are many factors which are used to determing your max weight, and in all cases, the lowest figure is you legal weight.

Concerning tire ratings, as far as i can remember this is addressed by federal statute and Tx just uses the federal standard.

If you want to know for sure (or want something you can carry in your truck to feel safe), send an e-mail to mcd-respond@dot. state. tx. us and ask your question. It will be researched and they will send you a response. You can also check out the website at www.dot. state. tx. us then go to the bottom right and click on "trucking and vehicle storage facilities".

hope this helps!

ps. . now the legal stuff: this post was made by me as a private citizen, not a TxDOT representative or spokesperson. . these views are mine and mine alone and do not necessarily represent the views of TxDOT or any other entity of the Great State of Texas!!

------------------
'01 Eth 3500 4x4, Amsoil air filter, AutoMeter boost & egt on pillar mount. See My Truck and also be sure to read What tools & methods to use for an easy 1st oil change!!!
"Be happy you don't get all the government you pay for. " -W. C. Fields