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Wednesday, June 24, 2020

Valve stems and TPM Sensors

I read the ongoing discussion on what valve stem to use with an external TPMS sensor.

A standard 65 psi max, rubber valve stem is very flexible as seen here.

 Some people think the 80 psi max, "High Pressure"

 HP 600 rubber valve stem is Ok to use with external TPMS sensors but you can see the HP-600 is still flexible.

 Here is proof that an HP rubber stem can fail when a TPM sensor is installed.

IMO staying with any "snap-in" type stem is false economy given the metal bolt-in stems only cost $3 to $4 each. Not all tire stores will have the metal valve stems so check first. if they don't you can get stems at AutoZone, O'Riley's, Advance Auto Parts or NAPA or most any auto parts store or even on Amazon.
They are easy to install too. Don't let the service center tell you installing metal stems is a lot of work.  Watch and you will see.


Friday, June 19, 2020

Another post & question of "Trailer tires vs Truck tires"

Original post and question on a 5th wheel RV forum I follow.
"Searched this forum (no, didn't search travel trailer forum) for any info on using LT (truck) tires instead of "trailer" tires on a 5th wheel.
Nope, didn't find anything - So,
Any problems with using a 6 or 10 ply LT tires on my '99' trailer instead of the replacement tires for trailers?"

He gave the dry weight and stated GVWR but no actual scale readings. He also did not provide information on his current size or type or Load Range of his tires. He did provide info heard around various campfires. In the forum, there were a number of replies. A few OK and sadly a number just plain incorrect.

In the'60's RV trailers were mostly smaller single axle and towed behind a car or 1/2 ton P/U. RV companies wanted less expensive tires. Speed limits and actual travel speeds were lower so Goodyear came up with "Special Trailer" tires with a 65 mph max speed as part of the load formula specification. This speed reduction and decreased tread depth theoretically offset the increased load capacity when compared to the same dimension LT type tires.

In 2002 after the Ford Explorer fiasco, new tougher standards for tires were implemented by DOT. RV companies fought to keep the old test requirements for ST type, the same as they were in 1968, while P-type and LT-type had to meet new, tougher standards for the 21st Century.

In 2017 China was accused of "dumping" cheap tires of all types into the US market. Trade restrictions by FTC (not tire safety standards) identified speed-rated tires as not having to pay the import duty. Almost overnight almost all ST type tires became speed rated. The SAE test for speed rating is stated as a "passenger car tire test" but was applied to ST type. It only requires tires to run for 30 minutes at the stated speed and to not come apart.

Back to the OP. "Dry weight" and GVWR are of no value when selecting tires. GAWR is almost useless as it is well documented that a majority of RVs have tires and /or axle in overload when actual loading is measured on scales.. The only weight number that really means anything is the actual scale reading for each tire, as RV weight is almost never exactly split 50/50 axle to axle or side to side. Some big RVs have been found to be 1,000# or more out of balance.

Reserve load is the extra load capacity above the actual load. Cars and P/U have reserve load in the 20% to 40% range while RVs have 0% to maybe 10%. That is a MAJOR reason for the difference in durability. There is also the shear forces seen in trailers that can be 24% higher than an identically loaded tire on a motor vehicle. This is a function of suspension dynamics. Tire Interply Shear was a complete unknown back in the 60's and not as well known or understood even in the 80's. You see the large tread distortion due to lateral loading when backing into a parking spot when the tire bends sideways. You never see this bending on a motor vehicle. The shear is always there in every curve or turns not just when backing into a parking spot. Even the normal sway observed when a trailer is towed down the highway is generating high Interply Shear. You can lower, but not eliminate the Interply Shear by increasing your Reserve Load.

So how do you improve your Reserve Load? An increase in load capacity would be a good approach. For most trailers, there are a number of options. Increased Load Range is one as long as you confirm wheel limits on load & inflation. Changing to larger tires. Even changing to larger diameter wheels might increase load capacity. I have seen some that increase all three specs, with reports of eliminating all tire failures other than road hazard or valve-related issues that can occur on any size, brand, or type tire.

If or when you replace tires the new tires should ALWAYS at a minimum have equa load capacity.

I have covered the above in numerous posts on my blog if you care to learn the facts from an actual tire design engineer.

Or you can listen to the guy in the camping space next door or the salesman at "Billy Jo Bob's Cheap Tire and Bait Emporium".


Sunday, June 14, 2020

New updated post with videos on how tires are made.

The original was posted July 2019 but there are new and better videos available so I updated all the links.

Friday, June 12, 2020

Tire "Flat Spotting" when parked

Another post from an RV forum
"I'm no tire engineer but I always thought of a "flat spot" as an area ground off from a long skid. The old bias ply tires of years ago would "deform" or become "out of round" (especially in cold weather) but a few miles of rotation would flex it back into shape. But that's all just semantics."

Well I am a Tire Engineer and the correct terms are "Flat Spot" for an out of round condition. and "Brake Flat Spot" for having an area of the tread worn off due to locking up the brakes so the tire is dragged along the road and does not rotate. When I was racing I would sometimes lock-up the brakes to avoid a spinning car. This would give a strong vibration and we would have to change the tire at the next pit stop.

You can develop "Flat Spot" from long term parking. The degree or level or amount of this type of flat spotting depends on time, temperature load, inflation pressure, rubber chemistry and tire construction.
You can decrease this flat spotting with:
Lower Load  or Higher inflation or not parking when the tire is still hot or keeping the tire out of direct sunlight
The owner has no control over the rubber chemistry or tire construction.

FYI In general tires with Nylon cap ply (seen in tires with higher speed rating) tend to develop and hold the flat spot longer, but I would not reject tire purchase because of the Nylon cap ply as that might give you more life of the tire.

You can see and probably measure the amount of flat spotting from either brake lock or long term parking if you check with a "Free Spin" inspection as seen in the video in THIS blog post. 


Friday, June 5, 2020

Tire Advertising claims ???

Read this on an RV forum.

"I am using Carlisle Radial Trail HD Trailer Tire, not at all but I think it is a good tire for my trailer. these tires have an added protection against the heat with built-in weathering and ozone protection. And with the summer months getting into their absolute hottest parts, this feature could be a nice addition to have in my trailer tires. Additionally, these tires have interconnected tread blocks that I find encouraging. See, this interconnected tread blocks ensure the tread will last for a longer time and that’s something I find it very intriguing."

I have nothing against Carlisle.  I do find the ability of Copywriters to make features common to almost all tires sound unique and special. I do question the ability of anti-ozone waxes and oils to provide any "protection against heat" and I consider that claim a serious stretch. I would love to see any test data that supported that claim.

Be a smart shopper and don't fall for slick promotional claims. Ask to see the data and results from direct comparison tests. You will many times just get the sound of crickets.