LT tires on TT

JJBIRISH wrote:

CapriRacer wrote:
...... At first, I was going to challenge the statement about the differences in failure rates.....

........It would seem by your opening comment that you have some different and more current data…
Would you be willing to share…

First, I was taking issue with the term "blowout". In tire engineering circles, this term is rarely used - especially by those folks diagnosing tire failures. As I pointed out, laymen use the term to cover a wide variety of failures, some of which are road hazard related and shouldn't be used to justify rulemaking. That was why I called the data suspect.

OTOH, it was one of the few bits of data available to them and as such they needed to use what they had - even as suspect as it is. I can understand why they used the data. I am just cautioning folks to understand what they are reading.

And to answer JJ's question.

I used to work in the warranty department of a major tire manufacturer and I used to calculate failure rates - so, yes, I did have information that would have been useful for that report. I worked there from the mid 1990's up until last year (when I retired), so obviously I had access to more up to date data.

Obviously this data would be quite proprietary - and it would be specific to one particular tire manufacturer. But I honestly only remember generalities about the data, and only some limited impressions about what the overall industry picture would have looked like.

Yes, P type tires failed less often than LT tires - and by failure, I mean a failure not related to external causes, such as a road hazard. Part of the analysis done at the time of the Ford/Firestone situation revealed that most of the failures of P type tires came off SUV's and pickup trucks. There are 2 things that are different about tires on pickups and SUV's as opposed to cars.

1) Those vehicles use larger tires
2) Those vehicles, do have any reserves (unused capacity) when tires are specified.

It was speculated that #1 was the result of a shortcoming in the formulae used to calculate load carrying capacity - and that might have been true, but it could not be undone once the load tables were published. The tire manufacturers were going to have to live with the problem until a different sizing system was introduced.

And #2 was in essence what Firestone was pointing to when they talked about inflation pressure. - and they had a point. Passenger car tires were typically oversized by 2 steps - but failures were not the reasons that occurred. SUV's and pickup's were not oversized.

Since that time, though, all the vehicle manufacturers have specified more load carrying capacity. Looking at the data, it is hard to sort out if the reason P type tire failures decreased was because of the improvements made to the tires, or the changes made to the vehicle specs. I'm sure someone did that, but it wasn't me and it wasn't obvious from the data I saw.

Changes in LT tires lagged behind P type tires. Not only were P type tire a much larger proportion of the marketshare, they also were not the focus of NHTSA's investigation. I'm estimating that at this point in time, 2 iterations of changes have taken place in P type tires, where only one iteration for LT tires.

So, JJ, does that answer your question? Do you have more?