What effect does speed have on tire failure?

Question:
"What effect does speed have on tire failure?

I have an 8000 lb trailer with 4 Goodyear Marathons. The truck is a Dodge 2500 diesel so I can cruise at 75 mph subject to wind and hills.

How much if any does speed factor into tire failure? I replace tires every 4-6 years regardless of what the look like, and keep them inflated at the PSI marked on the tires."

Basically, increased speed means increased temperature in the critical areas of a tire. Here is a graphic showing the relative temperature in different areas of a tire.

with Red being the hottest and dark blue being the coolest.

When you increase the temperature of rubber you are effectively increasing the rate the rubber is aging. I believe we all understand that old rubber is not as flexible as new rubber. If it isn't as flexible you end up with cracks or cracks that grow every time the rubber is flexed. More cracks and larger cracks are what result in tire failure.

For the above reasons plus others, the major tire companies suggest that in RV operation tires never be driven any faster than 75 and you can see this max speed stated in their literature for many of their RV tires.

But wait, you say your tires have a "Speed Symbol" that relates to 87 or 99 or maybe even 130. HERE is some information on speed ratings. Just because you have a tire with a fast symbol doesn't mean it can be driven at those speeds for 20 or 40,000 miles. About the only thing you can count on is that tires with a "higher" symbol will provide better steering response than a tire with a lower rating.

Now back to the question of how fast can you drive or tow your RV. I previously mentioned 75 as the upper limit but for some tires, there are other things to consider. With ST type tires as found on many trailers, we need to remember that the load capacity is based on a formula that originally specified a max speed of 65 mph. In the past, there were Technical Bulletins that advised that inflation needed to be increased (but not above the sidewall max) by 10 psi to go 70 mph. In addition, load needed to be decreased by 10% if you want to go 75. Still, there was that 75 max.

Many trailer owners know that they need to replace their tires before they wear out. If they don't they are probably going to have some type of failure. But those same people will not replace the tires on their pick-up till they are significantly worn. Why?

The answer can be seen if you simply compare the load and speed ratings of an LT tire and an identical size ST type tire.

LT235/75R15 101Q LRC1985# 50 psi 99mph

ST235/75R15 110R LRC2340# 50 psi 106mph

So exactly what type of magical engineering has tire company X used to achieve both increased load capacity plus increased speed capacity when it is the air pressure that supports the load? If they have the ability to make that ST tire really perform at those speed and load conditions what is wrong with their LT type tires?

IMO what we are looking at is a marketing plan taking over the engineering reality.

Bottom line

You may be able to pull the trailer at speeds above 65 or drive the Class-A diesel pusher faster than 75 but you will be consuming the finite life of the tire and can expect a failure before you wear it out no matter how you maintain your tires.

##RVT817

Will confusion on how much inflation be resolved?

Hi Roger. Do you think the tire pressure issue will ever be resolved to people accepting the values recommended by the tire manufacturers based on actual loading, or will some always be confused between the tables, the placard and quotes of Federal FMVSS Regulations from some on the forum? It seems so simple and logical, but some just don't get it. I still think a sticky written by you could settle the issue, but the moderators disagree. I suspect a concern for liability for the forum to advise something that contradicts the MH placard. I have a question for you about my RV. I carry 5 psi above the minimum for the load on my steer tires on a 60* morning @ 1100' altitude. When traveling, I had a morning @ 5000' and temp in the upper 30's. This produced a pressure of 1-2 psi below the minimum. I was going to be traveling into a warmer climate (95*), so did not adjust pressures. This type of condition can happen when we are traveling. I don't want to chase the pressures, so if traveling into warmer weather, I just go and watch the TPMS. I don't feel this is a problem but wanted your thoughts. Thanks for your thoughts and time.

Not sure if there ever will be a resolution to the Inflate to the placard vs Inflate to the actual tire load. I would liken this to the change oil every 3,000 miles vs change when the car's computer advises.

DOT has a goal of trying to make things simple and keep people safe. DOT also knows about the data that indicates that over half of the RVs on the road today have one or more tire overloaded (either too much load or too little air for the actual load) I really can't fault their approach as IMO many RV owners aren't willing to make the effort needed to learn the proper inflation and to then maintain it.

We have had tire inflation stickers in cars for many decades and there have been massive vehicle recalls because their tires were underinflated, I have read that many as much as 30% low. We don't hear anyone making a case that the accidents and fatalities were the driver's fault. That would be blaming the victim which isn't acceptable, even if true.

OK to your question. I am guessing your CIP is in the 90 - 110 psi range so IMO +5psi isn't enough to avoid the pressure fluctuation that results in your overload. This is why I suggest a +10% value for inflation margin over the table minimum number..
In my Class-C RV, with LT225/75R16 LR-E tires, I am lucky as my RV is rather light. I really only need 60 psi F & R based on my "4 corner scale readings. My certification sticker says 65 / 80 and my dealer delivered it at 64 psi all around. 

For my application +10% would indicate 66 psi and a  +15% margin > 69 psi. I run 70-75 
Even though I can be a bit "anal" about inflation I also wrote THIS post and I really do not mess around with my tire inflation.

My TPMS is set to warn before I would be in overload and I run across a scale once a year just to confirm I am not too far from my original "4 corner weights".

In 2014 I drove Ohio > OR > Calgary > Yellowstone >OH over a seven-week period with temperatures ranging from 90's to snow and elevation of 20' to 8,000' and never had to adjust inflation.