mitigating risk of 65MPH trailer tires

[jeffw]

Our car hauling trailer is tri-axle (8,000 pound axles) with 6 215/75R17.5 tires.

 

It looks like most of the tires on the trailer are 65MPH rated. We tend to cruise at 65-72, give or take. The truck is governed at 75mph, so we don't ever go past that :-)

 

Looking at ratings for a couple of the tires, I see they're good for 4330# @ 110psi, 4805# @ 125psi

Right now they're set at 110PSI.

 

Our axle load with a single car in is 15,380. I don't have a weight with 2 cars in (i'll be able to get that next week), but assuming all the additional weight stays over the axles (and doesn't transfer to the pin), let's say 18,000 pounds on the axles.

That puts me at roughly 3,000 pounds per tire, which seems well under the 4330# @ 110 psi.

 

Am I at enough of a margin that I don't need to worry much about 65MPH vs 75MPH ratings?

 

We're in the northeast, so we'll never be driving thru the Arizona desert at high noon :-)

 

I've got the TST pressure/temp monitor on all the tires, and the highest temp I've seen on a 90 degree day for a hour tow was around 115F.

 

Thanks!

 

-jeff

[NoDirectionHome]

If accurate at 115 degrees, my opinion is yes you have a ton of margin.

 

The tire bible of information: http://www.hhrvresource.com/sites/default/files/dfiles/Michelin_34501-truck-tire-ser.pdf

[HERO Maker]

"

Our car hauling trailer is tri-axle (8,000 pound axles) with 6 215/75R17.5 tires.

 

It looks like most of the tires on the trailer are 65MPH rated. We tend to cruise at 65-72, give or take. The truck is governed at 75mph, so we don't ever go past that :-)

 

Looking at ratings for a couple of the tires, I see they're good for 4330# @ 110psi, 4805# @ 125psi

Right now they're set at 110PSI."

 

Jeff, are you saying that not all of your tires are Goodyear G114 tires? Where are you getting the 65MPH rating from?

 

Take a look here http://www.goodyearrvtires.com/pdfs/rv_inflation.pdf

[jeffw]

Right now they're set at 110PSI."

 

Jeff, are you saying that not all of your tires are Goodyear G114 tires? Where are you getting the 65MPH rating from?

 

Take a look here http://www.goodyearrvtires.com/pdfs/rv_inflation.pdf

 

I don't have any G114s.

i have 2 Bridgestone R184, 1 Hankook TH10, 1 Firestone FS560, 1 Geostar G650 and 1 Linglong LLF86.

I think I found the Firestone for $215 each. I'm thinking of having the Geostar and Linglong taken off and replaced by a pair of Firestones and keeping the 2 chinese tires as spares.

Thoughts?

[HERO Maker]

So you're saying those tires are only rated at 65MPH. In that case, like we always say about suspension limits, you need to stay at the lowest limits listed.

[jeffw]

Yes the ones I've found details on are 65MPH.

[Big5er]

Passing another vehicle and exceeeding the tire speed rating for a minute or two isn't gonna kill the tires. Driving 4,5 or 6 hrs at a speed greater than the rating is gonna cause excess heat build and heat is what kills your tires. I'm with Rocky. My tires say 65. An extra 5 mph is not worth the blow out.

If you can get past the mumbo jumbo on any tire manufacturers web site "we don't recommend traveling over 60 mph while towing" you will also find little hints like:

Speed

• All "ST" tires have a maximum speed rating of 65 mph.
• As heat builds up, the tire's structure starts to disintegrate and weaken.
• The load carrying capacity gradually decreases as the heat and stresses generated by higher speed increases.

There is a reason they put that number on the tire.

 

Cute little tire video too

[Raquel]

We are conservative regarding our trailer tires. Sometimes, when going down a grade, we get up to 65, or even 68 for a few moments. However, we stick the cruise control on 58 mph and stay there. Where are we going that we are going to try to cut a few minutes off the travel time?

[grumpydoc]

I worry there might be a potential legal liability of knowingly operating a vehicle in excess of any stated limit for any of it's equipment including the speed rating for tires. We often debate the risk of exceeding the various weight limits of our equipment. Shouldn't there be some element of concern about knowingly exceeding tire limits? Best Wishes, Jay

[the sailor]

We cruise at 62/63 mph for both tires and better fuel mileage, what is the hurry?

[Broncohauler]

Most of Arizona is going to be around 117 120° outside this weekend don't think I'd want to change one tire let a lone two which usually happens.

62 mph on cruise with a cold Dr Pepper sounds a lot better.

[jkennell]

Actually, I'll play devils advocate here. Remember, most of you are running your 5r tires at near max load. As noted, its heat that causes the problem. The higher the load, the more sidewall flex and more heat generated. The higher the speed, the more heat generated. SO how do the tire mfg. rate them? Logically, (ignoring outdoor temps) it should be max speed at max load, right? I would think that as long as you made sure the temp stayed down, you should be at no risk of a blowout.

 

I've paid special attention to this issue in the past, as a farmer. An example from farm tires clarifies my point, as they carry the speed/load thing to an extreme. Most farm implement tires are designed to flex a LOT--to spread out the footprint. They also have a very low Max speed rating...25MPH. I have a water trailer I often tow down the road for miles. Empty, you can drive 65 (over twice rated speed) for miles, the tires stay cool, and no problems at all. Fully loaded, at 25mph the tires are too hot to hold your hand on after 2-3 miles. I don't want to even think of what driving 65 would do!

 

Now, this is extreme compared to what road tires do, but the point remains...its the load/speed combination creating heat that ruins the tire (OK..OK, there is an increase in outward forces the faster you go, but we aren't racing at Bonneville here). So know your tire load, know the ratings, watch the temps.

 

Its still safest to stay at or below rated speed though (even if the tire MFG won't believe you after the blowout ). The 62 and cold Beverage sound a HECK of a lot better than work...even if you are heading for that old swimmin hole and want to get there sooner!

[jeffw]

Looking at the above-mentioned Michelin document, they talk about de-rating the tire (and increasing pressure) at 70 and 75mph.

 

Considering that I'm 30% under the load rating at 110 psi (3000 pounds actual pounds vs 4330 rated pounds), I'm going to assume I've got a good margin of safety at 70mph....

 

 

[Big5er]

That chart says "inflation must comply with the following limitations unless a speed restriction is placed on the tire". Isn't the speed rating a "restriction"??

 

Where is Trey when we need him?

[jeffw]

That chart says "inflation must comply with the following limitations unless a speed restriction is placed on the tire". Isn't the speed rating a "restriction"??

 

Where is Trey when we need him?

None of my tires have a speed limit on the sidewall.

[Mark and Dale Bruss]

Few due, it is the tire specifications you find on the web site.

[spindrift]

And is it always better to pressurize for load as opposed to the maximum pressure rating of the tire?

[Star Dreamer]

And is it always better to pressurize for load as opposed to the maximum pressure rating of the tire?

Not always, after having individual tire weights determined, you would then take the largest loaded tire, figure the pressure required for that load, add some reserve and set all tires at that pressure. Most likely you will never load exactly the same way each time and since you will not get new weights every time you load you have to have some reserve. In our case we run at max pressure because two of our 6 tires on the trailer are close to max load.

Dave

[Star Dreamer]

 

I don't have any G114s.

 

i have 2 Bridgestone R184, 1 Hankook TH10, 1 Firestone FS560, 1 Geostar G650 and 1 Linglong LLF86.

I think I found the Firestone for $215 each. I'm thinking of having the Geostar and Linglong taken off and replaced by a pair of Firestones and keeping the 2 chinese tires as spares.

Thoughts?

Since you have a mix of tires on the trailer, that tells me they have had multiple tire issues. I would put at least 2 new tires on that have the speed and load rating you want and take two of the old tires that are still good and mount them as spares, you may (will) need them. Get a TPMS. Then experiment and see how many you blow out running at 70 miles plus an hour.

 

We have replaced a lot of tires (15+) on our triple axle trailer, we are now getting about 30k miles out of them (ST rated) but I am running at 63-65 mph and watching out for tight turns. We just had a blowout on one of 2 tires that had 30k on them so they both were replaced. It was also a warm day (80 degrees) and we had been running for over 4 hours. We think the heat and time plays a big part but it is hard to work around that when on a schedule. I also now stick with only one brand of tire Hercules) but we are limited in choices as we only have 15" rims, we have used many brands and only this one brand has given us the best mileage.

 

Dave

[steiny93]

I personally dont believe speed is the major problem contributing to tire issues on trailers. I believe the vast majority of issues are from heat which is amp'd due to misalignment, incorrect inflation, over load, etc.

 

Keep those elements in order and you can pull at whatever speed you want. (my philosophy)

[jeffw]

Since you have a mix of tires on the trailer, that tells me they have had multiple tire issues. I would put at least 2 new tires on that have the speed and load rating you want and take two of the old tires that are still good and mount them as spares, you may (will) need them. Get a TPMS. Then experiment and see how many you blow out running at 70 miles plus an hour.

 

We heard from the broker that we purchased the trailer from that the previous owner lost 2 tires on the road. I suspect they were limited by whatever they could get roadside.

 

We do have a TPMS on the trailer (and it tells us tire temps). I'll be keeping an eye on it.

 

Does anyone make a 75mph-rated 215/75R17.5 tire? I've not seen one in my searching. I think the Hankook are rated at 68 MPH, but I suspect that is a result of converting from 110KMH.

 

I've found a good deal on the Firestone FS560 locally, so I'm planning on picking up 2 of them and taking off the Chinese tires. The Chinese tires will become spares.

 

We had the FS560 on our previous truck and they were good for the 7 years I had them.

[HERO Maker]

Goodyear. Look at this chart.

[TreyandSusan]

The short answer... to "Am I at enough of a margin that I don't need to worry much about 65MPH vs 75MPH ratings?"

Contact the manufacturer of the tire and ask if the speed/load inflation adjustment is allowed for the specific tire.

AND get measured loads on the tires.

 

Some extended information...

Some manufacturers MAY allow the adjustment for these trailer specific tires some do not. (the intended design purpose of trailer tire is primarily for low boy trailer heavy equipment hauling - usually not highway speeds). Michelin does NOT allow adjustment for the 62 mph speed rated XTA (G114 capacity equivalent).

 

Newer design model tires have a letter code for speed rating, which is found in the service description on the sidewall of the tire or in the tire manufacturers specifications.

The service description is a 1 or 2 3-digit load index code followed by a speed rating (letter) code. e.g. 135/133J

Some pertinent Speed Rating Code Examples: J = 62 mph, K = 68 mph, L = 75 mph, M = 81 mph, N = 87 mph (Notice there is no code for 65 mph)

Speed rating on Truck/Bus tires has evolved as speed limit laws have changed. The standard speed rating for Truck and Bus Highway tires was 65 mph which was sufficient for quite some time due to the speed limit laws. On the page above the previously posted clipped chart there is some red text that refers to this concept by saying - "exceeding the speed limit is neither recommended or endorsed". If you do not to comply with this statement then you will be more likely get a very special invitation, possibly delivered personally by Big5er, to visit the local dignitaries. So, now, for Truck/Bus tires, if there is no service description or speed rating identified in the manufacturers specifications, the speed rating is considered to be the 65 mph. Most of the tires in Jeff's tire collection do fit this qualification.

So, If allowed by the tire manufacturer, the adjustment would probably only be allowed on a 65 mph speed rated tire and unlikely to be allowed on any newer model tires with speed rating codes.

 

Also, the greater than 65 mph part of the speed load adjustment chart posted above is no longer even included in the more recent TRA Tire data books. The Michelin Tire service document above is an older outdated document.

As stated above exceeding a tire's speed rating for extended periods will significantly reduce the life span of the tire.

 

Personal Opinions ...

To lesson the risk it would be best to either comply with the speed rating of the tire OR buy tires with a speed rating for the speed which one desires to travel (and does not beg Big5er to have a friendly conversation with you on the side of the road). Personal preferences vary.

In this instance it appears that traveling near highway speeds (75 mph) is important, therefore, when purchasing replacement tires the speed rating would seem to be an important specification in the selection of new tires.

 

If cost is a compelling issue, there are some lower cost 215/75R17.5 tires (same load capacity - 4805 lbs) that have 75 mph ratings. (e.g. Continental HTL2 Eco Plus, Yokohama RY023, Cooper Roadmaster RM170, Sailun S637)

Or there are some All position 215/75R17.5 tires with lower carrying capacity (3750 lbs) that are also speed rated at 75 mph.e.g. Michelin XZE2, Hankook AH11, which are also less expensive than the G114.

These lower capacity options could be good options but ONLY IF the loads allow.

Again personal opinions vary and there may be others tires that are not listed above.

 

The Goodyear G114 Rocky mentions is probably the most popular choice for larger fifth wheel RV owners and is speed rated at 75 mph.

 

A little about weight...

On a two car hauler, it is possible (not sure how likely) that there could be front to back loading differences (different loads on each axle). It may even be possible to have significant side to side differences depending on the loading of other things in the trailer. (tools, toys, stuff).

For fifth wheel RVs (all RVs) it is not good to assume equal weight distribution across the axle or front to back differences.

For all trailers it is not good to assume or GUESS at loads. The only way to know tire loading is to put the vehicle on scales and measure.

For living/recreation type vehicles it is best to get wheel position loads to confirm any differences so that tires are not overloaded either by fitment or improper inflation pressure.

Even though the tires in a multi-axle system are relatively close together, they may or may not be carrying similar loads. For greater understanding of each one's own vehicle and how it is loaded, it is a good practice to get wheel position weights.

 

Also, FYI

Times change. Special Trailer (ST) tires are no longer ALL rated at 65 mph. Recent rulings for imported tires also address speed ratings for ST tires. So, some ST tire manufacturers (yes, all ST tires are manufactured overseas) have begun to include service descriptions or speed ratings in their specifications. So, the same is true for Special Trailer tires - the speed rating is 65 mph unless otherwise identified in the service description or in the manufacturers specifications.

Currently there are only a handful of ST tires speed rated greater than 65 mph, but that will likely continue to increase. Some smaller ST tires are rated at less than 65 mph.

A few ST tire manufacturers allow similar type of inflation/speed adjustment, and in the case of ST tires the manufacturer should verify the allowable adjustment before it is done by the consumer/operator. e.g. Goodyear Marathon does allow this type of adjustment. (PSB #2014-01)

[CDR]

I am with StarDreamer, I stick to only one brand also. Gladiator, and only one model (slips my mind now) it's the one with the large block pattern. These have to be the coolest running tires I have ever seen. And I have seen plenty! I don't know how the carcass construction is made up, I just know that block tread pattern is cool running with fabulous wear characteristics.

 

My 2 cents.

 

Curt

[jeffw]

Thanks for the leads on the 75mph rated tires. I will take a look at those.