Tire Advice

JBarca wrote:


Hi Stircrazy,

I agree with much of your post; the lack of extra reserve capacity in the tire in a tandem or triple axle trailer setup is an issue direct from some of the RV manufacturers.

And I agree to upgrade a load range to gain more capacity, but not airing up the tire to the max sidewall cold pressure does not give you the full benefit of the upgrade. If you are going to upgrade, you need the extra pressure to gain the benefit to help ward off interply shear.

I may learn something new in this next area, so please explain your thinking. I "thought" I understood you are saying the LT tires with a more aggressive outer tread do not allow the LT tire to slip as much as an ST tire in a turn. Did I paraphrase that correctly? If so, help me understand how you came to that conclusion. Here are my thoughts on why I cannot connect the dots on the tread pattern to hard surface road slip in a dry setting.

I believe we both agree on the friction of the tire tread determines tire slip on the pavement between the tire and the road.

Friction is the main part of the slip equation, and there are only a few ways to change friction on a hard surface road to the tire. Again, I am talking hard surface road, not loose gravel, snow or dirt, mud, etc.

Here is my take based on the friction formulas. To change the friction between the hard surface road and the tire tread contacting the road, these two main variables must change.

1. The weight of the camper pressing down on the road
2. The coefficient of friction between the road surface and the tire tread

There is no variable for tread pattern or contact patch area of the tire in the friction force formulas.

Please help me see your point where the tread pattern changes friction between the tire and the road surface.

I agree with wet, slimy roads, tire rubber compounds, temperature, and the makeup of the road surface. etc. are factors in changing the friction coefficient. Just not sure how the tread pattern on a clean and dry road surface changes the fiction.

On your quest to sort out ST to LT on your camper, yes, sizing is an issue in some cases in finding LT tires rated in the right capacity. I went through the same issue when I had my first set of ST tire failures. I was on 15" ST225/75R15's load range D on a 10,000# loaded camper. After I sorted out what made the ST tires fail, I had 2 choices, upsize to Load range E in ST or jump to 16" and go LT load range E. I ended up going 16" LT load range E. I had to deal with vertical clearance between the top of the tire and the bottom of the camper clearance. I had to modify the suspension setup to get this extra clearance, I could do the work myself, and I'm glad I did. In my case, tire width was not the issue, but vertical clearance. If you want more on this, I did posts over the years on RV.net of each issue and how to overcome it; let me know, and I'll dig them up. And, I went with a highway tread pattern, not AT or other. I did not see any need other than the highway tread pattern in an "on-road" trailer setting.

John

so, the all-important third thing you missed is the actual rubber compound itself. so, ST tires " reportedly" use a different rubber compound which is stronger and stiffer (less grippy) which is why they can carry more weight for the same tire size. so this will reduce the coefficient of friction and when the tire is under shear it will slide on the surface easier. granted we are probably not talking a great deal of difference but enough that it also gets you better gas milage as that rolling resistance (friction) is also reduced.

what I was getting at with the tire pattern is that if you try to slide a tire with an aggressive side lug sideway that lug will actually try to dig in and fold over rather than sliding (a little bit of exaggeration, as it won't really fold, but you get the point) this helps prevent your truck from sliding sideways when off roading. This action acts as a friction modifier and increases the shear. now again small amounts and really, I have never seen a real trailer tire that had agressive side walls, until reading the forum the only people I knew that put LT tires on the rv's were serious off roaders who wanted that extra traction.

I would be interested in seeing what you did to increase the height as I would like to increase mine a couple inches just for a little more box rail clearance.