Tire inflation ideas

[Tireman9]

Many good comments.

Simple answer is ALWAYS set the inflation when tires are cool (not in the sun or driven on for two hours)
Know the actual corner loads. HERE is a worksheet for the calculations
Once you know the actual load use the Load Inflation table from the tire MFG to learn the MINIMUM inflation needed based on the loads on the heavier end of the axle.
Your cold "set" pressure should be at least 10% above the minimum calculated.
All tires on any one axle should be the same as needed for the heavier load.
If you don't do the worksheet assume the weight balance is not 50/50 but 45/55% of the actual scale weight
If you don't want to confirm the actual weight follow the placard and cross your fingers.

You can read more on proper tire inflation HERE if interested.

[Gordon Dewald]

I wonder often if we are overthinking the tire pressures. Tireman make good points and I doubt anyone will have an issue by following his advice. I have learned several things from reading his information that will make my running of tires better.

I wonder about the tire inflation charts. Having worked with engineers for most of my career I have observed that they are a very cautious bunch. Safety factors are built in during every step of their design process.

Thinking about the charts I suspect they have built in a 10 or 20% cushion as part of the process. They are creating these charts for tires that have been tested thoroughly during the design and build process. They would have considered high heat, speed, whole of life, materials, rolling resistance, traction, ride, etc. At least I would hope that they were doing that??!!

After considering all of that they probably added another little bit for factors they were unaware of (possibly poor or lackadaisical tire maintenance).

As an example if an engineer told you to use 2 x 8 on 16 inch centers to build a deck would you as a matter of course substitute 2 x 10's or build on 12" centers? Obviously been watching too many deck shows!

Are tires similar? By inflating them to a higher pressure are we any safer? The surface condition of highways nowadays is almost criminal with transverse cracks, potholes and poor patches giving a very harsh ride. Does the higher tire pressure translate into more vibration that incrementally shakes and damages the coach?

Everyone is able to do what they wish based on personal experience or beliefs. I believe the tire charts are correct and use them as the guideline for the weight I am carrying and not second guess highly paid engineers who developed them.

[donandmax]

Originally Posted by ImagineIF

Never run tire pressure at less than that required for the carrying the most weight, on a per axle basis. Don't run at a pressure less than the lowest pressure on the chart. There is a minimum to keep tires on the wheels. Most manufactures set the low limit to about 80psi. When in doubt, over inflate as long as you don't exceed the tire's maximum rated pressure.

This may be true on a diesel coach but if you try this on a gasser it will shake it to pieces and you'll end up having the dashboard in your lap. And thats a fact , I usually run 10 lbs under and thats even to high but don't want to go any lower for obvious reasons !! A change of tires really worked for me a little better. I use Hankooks and they got rid of most of the hard ride...

[Robin_M]

Originally Posted by Gordon Dewald

I wonder often if we are overthinking the tire pressures. Tireman make good points and I doubt anyone will have an issue by following his advice. I have learned several things from reading his information that will make my running of tires better.

I wonder about the tire inflation charts. Having worked with engineers for most of my career I have observed that they are a very cautious bunch. Safety factors are built in during every step of their design process.

Thinking about the charts I suspect they have built in a 10 or 20% cushion as part of the process. They are creating these charts for tires that have been tested thoroughly during the design and build process. They would have considered high heat, speed, whole of life, materials, rolling resistance, traction, ride, etc. At least I would hope that they were doing that??!!

After considering all of that they probably added another little bit for factors they were unaware of (possibly poor or lackadaisical tire maintenance).

As an example if an engineer told you to use 2 x 8 on 16 inch centers to build a deck would you as a matter of course substitute 2 x 10's or build on 12" centers? Obviously been watching too many deck shows!

Are tires similar? By inflating them to a higher pressure are we any safer? The surface condition of highways nowadays is almost criminal with transverse cracks, potholes and poor patches giving a very harsh ride. Does the higher tire pressure translate into more vibration that incrementally shakes and damages the coach?

Everyone is able to do what they wish based on personal experience or beliefs. I believe the tire charts are correct and use them as the guideline for the weight I am carrying and not second guess highly paid engineers who developed them.

Gordon,

I don't know if Roger Marble (Tireman9) was "highly paid", but according to his blog (which he links to in his signature) he was a tire design engineer with over 40 years experience before he retired. So I'd guess he knows about tire load ratings as well as anyone. As you know from the other thread you mentioned earlier here, Roger recommends inflating to a rate that will yield a 20% under-load in order to run the tire cool enough to obtain maximum sidewall life.

I've looked at this, and 20% represents a relatively large pressure difference of about anywhere from 15-20 psi above what the chart says. Again, keep in mind that this increase in psi is NOT intended to insure safety, but to run the tire cooler to achieve maximum sidewall life. Roger defines the chart inflation rate as being "what is needed to meet or exceed the load".

All that being said, I realize that this does not necessarily address the point you raise. Your point about engineers building in some degree of safety reserve is a good point. Like you, I'm sure they must do that. In trying to resolve this issue in my mind, I have studied the truck data tire manuals for both Michelin and Goodyear. Neither address where the chart figures come from, but BOTH suggest, as you do, that the chart represents the recommended inflation rate to safely carry the specified load.

So, are these arguments at odds to each other? I don't think so, and that's perhaps where we might tend to disagree. I have suggested earlier in this thread that I believe that, just like tread design itself, inflation rate is a also a matter of compromise. Manufacturer placards usually recommend close to maximum inflation rates to take the "reserve load" into account, as Roger explained here in the other thread. But as you pointed out, if we know our corner weights and inflate accordingly, we don't necessarily have to be concerned with adding extra pressure to account for reserve loads.

On the other hand, what is wrong with a little over inflation to make the tire run cooler and thus prolong sidewall life? As you say, everyone is free to do what he believes makes the most sense. After reading all these threads (and others over the years) and after studying the tire manufacturer's literature, I've come to the conclusion that, for me, the best compromise between safety, performance, comfort, and sidewall life, would be to exceed the load charts by about 10 psi on each axle. So that's what I'm gonna do from now on. And it is just that - a compromise.

Maybe "Tireman" will chime in here with some thoughts of his on on this point. Sorry to be so verbose here, but this is a really interesting and thought provoking thread.

[Gordon Dewald]

Yes Robin - I am enjoying the thread very much. Much of my career training has been to question things that do not make sense on the surface. If it looks, smells like then it must be. I worked with engineers, reviewed their work and had my work reviewed by them. The charts were not done in isolation and were subject to review.

It was the 20% that started me on the questions. It is valid for small loads on big tires but when the load gets to about 85% of the maximum tire capacity you are at 100% inflation and I suppose you no longer add air. I have read that over inflation has several side effects of uneven wear, reduced traction on wet surfaces and rougher ride.

Tires should run cooler at a higher tire pressure as the sidewalls will flex less. A cooler tire should last longer but as it has been suggested in another thread that tires will time out on most MH long before the tread does. Does the incremental increase in vibration and pounding warrant the extra pressure?

Roger being in the industry for 40 years must have taken part in preparing the inflation charts for numerous tires. He would then know intimately the factors going into the charts and perhaps would share some of the details.

I like you will stay closer to the industry recommended tire inflation.

I apologize if I have offended anyone. That was not my intention. I simply want the facts devoid of personal bias so I can understand and make quality decisions.

[Bobs911]

Responding to Vanwills statement....... " But there are always those who will cite all kinds of reasons for not running max pressure, even though ALL the trucking companies do."

Here's their reason for max inflation on truck tires:
Sometimes the truck is loaded, sometimes it's empty. An empty 18 wheel tractor trailer weighs about 35,000lbs, loaded at 80,000lbs. It is not practical to adjust inflation for every load.

[Robin_M]

Yep, that's exactly the reason. Plus that will enhance fuel economy. Having managed a small trucking company, I can affirm that safety and economy, when under load, will always trump everything else. Drivers hate running empty, as they get shaken up sitting in the cab. In a motor home, we have the luxury of adjusting our inflation pressure for a much more "constant load".

[Tireman9]

My 20% is more than I expect most people are willing or can do. I was asked what I would do to get the max tire life so I was responding with that question in mind.
I have a small Class-C. The OE tires were LR-D and specified 65psi (max for the tires).

I got my corner weights and after consulting the load inflation tables learned I only needed 50 psi. Setting my cold infl to 65 would give me a 21% Reeserve Load (Safety Factor)

Right now my LT tires are 6 years 36 weeks old and they have no sidewall cracking or any external signs of damage or overload. The tires are always covered with white covers unless I am driving or just stopped for one night.

I expect/hopw to get 9 to 10 years out of my tires. I will probably state changing tires, two at a time when I get to 8 years and do the fronts one year then two more the next year moving the one year old tires back to a dual position and the new tires on the front and the next year the final two new again placed on the front with older tires moved to dual rear.

An advantage of having a 21% "under load" is I get between 10 and 11 mpg TOTAL fuel economey with my 6L gas engine.

When I suggest a 20% margin it is based on the assumption / hope that you can increase load capacity with larger tire or higher Load Range. I know this is not always possible and for that I blame the RV manufacturer for doing a poor job in design and component selection.
I am confident that if/when I buy a new RV one of the "musts" will be the ability to have large or strong enough (Load Range) tires to again have at least a 20% margin.

RE Load/Inflation tables.
Tables have been around since before I became a tire engineer but new sizes and new types get added all the time. There are published "Industry Yearbooks" in the US, Europe and Japan. Basically with only a very few exceptions all tire companies follow one of these published guides. When a nes size is introduced there is a lengthy process of review and approval as well aas calculations and testing to establish Load & Inflation information for the new type/size tire.

Yes I have done the calculations for a few new sizes but I didn't invent the formula.

Let me know if you have specific questions. You might find I have already posted an answer on my blog RVTireSafety.