Tires and failure

danemayer

Well-known member
The comments are from Roger Marble (Tireman9) who often comments on tire issues on this forum.

I read through quickly, but one thing I didn't see mentioned is the uneven weight distribution in RVs. One of the years when I got individual wheel weights, there was a 500 lb difference between left and right on one axle. That ate up just about the entire margin on the heavy side.

To increase the safety margin, I moved from 16" Goodyear G614 tires rated for 3,750 lbs., to Goodyear G114 tires on 17.5" rims, rated up to 4,805 lbs. I inflate them to 110 lbs. which provides about 4,100 lbs. of carrying capacity.
 

RickL

Well-known member
This link is a good example of not believing everything you read on the internet. For one thing there is built in “safety zone” when it comes to ST tires. No engineer is going to tell you as most people load them them to the max as it is. Publishing or letting people know what that margin is would only further encourage people to overload the tires even more.

Additionally, I’m not sure where he is getting his speed test procedure, however it may have changed since I was taught by Goodyear, but speed ratings are a none tire failure at the speed rating run for 8 hrs. In the newer FMVSS the test are a 2 hour conditioning test, followed by consecutive 30 minute intervals at various speeds.

The author of article states he would go with LT tires over ST tires. While LT may work, due to the increased tread depth the tires will be more susceptible to irregular wear issues then a shallower tread depth of a ST. To provide better longevity the tread compound of a ST is going to a “stiffer” compound over a LT tire.

Again the point is to research various sources for the information so you can make an informed decision.
 

danemayer

Well-known member
This link is a good example of not believing everything you read on the internet.

From the author's Bio:


Before retiring, Roger Marble spent 40 years in the tire industry, working for a major manufacturer developing tires for applications in North, Central and South America. During his career he worked on many kinds of tires -- heavy truck, passenger, light truck and Indy-car types.
 

Bogie

Well-known member
This link is a good example of not believing everything you read on the internet. For one thing there is built in “safety zone” when it comes to ST tires. No engineer is going to tell you as most people load them them to the max as it is. Publishing or letting people know what that margin is would only further encourage people to overload the tires even more.

Additionally, I’m not sure where he is getting his speed test procedure, however it may have changed since I was taught by Goodyear, but speed ratings are a none tire failure at the speed rating run for 8 hrs. In the newer FMVSS the test are a 2 hour conditioning test, followed by consecutive 30 minute intervals at various speeds.

The author of article states he would go with LT tires over ST tires. While LT may work, due to the increased tread depth the tires will be more susceptible to irregular wear issues then a shallower tread depth of a ST. To provide better longevity the tread compound of a ST is going to a “stiffer” compound over a LT tire.

Again the point is to research various sources for the information so you can make an informed decision.

Rick,

While you are correct that most (If not all) good engineers design above published specifications, no insurance company is going to pay if the can wiggle out of it. Deciding that someone exceeded specifications (overloading) just invites them to do so.

As far as the author, i have read a great deal of Roger Marble,s writings and have personally had an email exchange with him. As an engineer myself, I believe he is extremely well qualified and knows what he is talking about.
 

RickL

Well-known member
Rick,

While you are correct that most (If not all) good engineers design above published specifications, no insurance company is going to pay if the can wiggle out of it. Deciding that someone exceeded specifications (overloading) just invites them to do so.

As far as the author, i have read a great deal of Roger Marble,s writings and have personally had an email exchange with him. As an engineer myself, I believe he is extremely well qualified and knows what he is talking about.

One I’m not an engineer, but having real world experience, in my case 38 years, goes a long way. I have dealt with passenger, light truck, trailer, industrial, agricultural, medium commercial, off road/mining. And while I have seen a lot I still don’t believe I have seen “everything”. Never professed being an expert, but rather a person with a large “hands on” experience. Over my career with the big 3, Goodyear, Michelin, and Bridgestone I have worked with engineers. Most are steeped in theory with little field experience. The ones that worked warranty claims in the field in my opinion have a much better grasp of tire issues.

I’m not not discounting what Mr Marbles says, I’m just pointing out that one must do their research from multiple sources to make an informed decision.
 

SNOKING

Well-known member
For one thing there is built in “safety zone” when it comes to ST tires.


Safety zone on ST tires? Any margin with a ST tire is used up by their higher ratings for a given size compared to passenger carrying tires, which was justified with the 65 MPH speed restriction. Now with most upping the speed rating to make the bass boat guys happen, we are right back there with not much margin left.
 

JWalker

Northeast Region Director-Retired
To increase the safety margin, I moved from 16" Goodyear G614 tires rated for 3,750 lbs., to Goodyear G114 tires on 17.5" rims, rated up to 4,805 lbs. I inflate them to 110 lbs. which provides about 4,100 lbs. of carrying capacity.

Dan,
Recently had an opportunity to pick up a set of 17.5” wheels at a great price and just ordered tires to match. I was thinking of going to the 125 psi for the full weight rating. But according to what you’re saying. At 110 psi and the 4100 pounds of capacity, it would still be a significant upgrade from my 16” Goodyear G614s.
 

danemayer

Well-known member
Dan,
Recently had an opportunity to pick up a set of 17.5” wheels at a great price and just ordered tires to match. I was thinking of going to the 125 psi for the full weight rating. But according to what you’re saying. At 110 psi and the 4100 pounds of capacity, it would still be a significant upgrade from my 16” Goodyear G614s.

Exactly Jamie. With weight fairly equally distributed, each of my tires is carrying about 3200 lbs. Inflating for 4100 lbs gives me a 28% margin (4100-3200 = 900 lbs margin, or 900/3200 = 28%). If ever unequally distributed, as with my first weigh-in, one tire could be carrying 3450 lbs, which would still leave a margin of 19%.

At my first weigh-in, the tire carrying 3450 was 300 lbs under the max capacity of the G614, leaving only 8% margin at full inflation.

If I inflated to 125 psi, for capacity of 4805 lbs, with actual weight of 3250 lbs, I think I might end up with uneven tread wear.

My opinion, speaking as a consumer, not as a tire expert, is that the minimum 20% margin that's required on passenger car and LT tire ratings, has a lot to do with why we don't have a lot of blowouts on those vehicles.
 
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