I've often wondered why mudders bother with E-rated tires. If you don't inflate past 50psi, there's no difference between C, D, and E load ratings in terms of load carrying capabilities. The higher load rating just means the tire (in particular the sidewall) can handle a higher PSI. If you run at 45 psi, then a C, D, or E rated tire will all carry the same maximum load at that pressure. Load C tires can go to 50 psi, load D to 65 psi, and load E to 80 psi. Is it just the hope that a thicker sidewall will hold up a little better to punctures?
The "...hope that a thicker sidewall will hold up a little better to punctures" is a big part of it. As this chart from Tirerack.com shows, it is not unreasonable to assume that a 10 ply rated tire would be more resistant to punctures/abrasion than one rated with fewer plies (even though the actual number of plies used may be the same - and far fewer):
There is a gentleman who posts regularly as "CapriRacer" in a different forum who offers the following credentials:
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Credentials:
I am currently employed as an engineer by a major manufacturer of tires. Some powers that be within the company don't think it is a good idea for people to be posting on the internet. This creates an odd situation for me. On the one side, I have access to a lot of interesting information. On the other side, there is some information that is considered quite proprietary. So I will not identify the company and disguise anything that might help you figure it out. I hope you will understand.
Besides, the information posted here will be generic in nature - It will apply to any tire, regardless of who manufactures it.I have been in the tire industry - well...... - let's just say it is over 30 years. I've worked in manufacturing, design, testing, and my current assignment is quite diverse.
I serve as the technical consultant to the 800 number. I have served on committees for various tire related organizations: Society of Automtove Engineers (SAE), The Rubber Manufacturers Association (RMA), The Tire Industry Association (TIA), the Tire and Rim Association (TRA), etc.
I am a member of SAE, Tire Society, and the Sports Car Club of America (I used to hold a competition license, but it has expired).I have a BME from the University of Dayton and have attended graduate school, but did not complete it - something I regret.It will not be too long before I retire. If you feel you need my services, please contact me.
Barry@BarrysTireTech.com
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One of his recent posts covered (in part) your questions:
CapriRacer said:
A couple of thoughts:
1) There is a quirk in the LT load tables. It was felt that there ought to be a point where people ought to move out of the LT type tire and into medium truck tires. The way those LT tires were going was much too open ended.
So the powers that be decided that NEW entries to the LT load table would stop at 3195# (1450KG). Why that value? That was about the point where trucks crossed over to 10,000# GVW and pretty much everyone in the vehicle business and the government say that puts the truck into a different category and the rules are different for those kinds of vehicles.
When did this happen? I don't know, but it has been a while.
And here is where the quirk really stands out: If the table already had entries that exceeded 3195# (1450KG), then they left them. (The general principle is that you can't undo something that's already been done.)
But that doesn't prevent people from "inventing" entries on the table - and a Load Range E LT285/70R17 is just that. Many tire manufacturers "invented" parts of the table, but they (as a general rule) comply with the 3195# (1450kg) limitation.
2) The load curve is indeed a curve. There is a formula, but please don't make me look it up and try to write it. It involves a odd power figure and those require some fancy formatting to get it to come out right. Plus, it's hard to find and I may have lost access to the formula.
But for a curve, the load curve is pretty linear and you can interpolate between data points. I would urge caution when using the last point as the above explanation should inform you that that point might not be part of the curve, but an arbitrary value.
I would also urge caution extrapolating - for the very same reason.
Also, while the curve is fairly linear, it doesn't look like it intersects the zero,zero point. (That is zero pressure = zero load). What the curve looks like is that it will intersect zero pressure at some positive load value - which makes sense in that even a completely deflated tire should be able to carry SOME load.
One of the points made is that even though the Pressure/Load Limit tables may not show it, E-Rated tires may not "officially" have a higher Load Limit at higher pressures, but in fact they do - it was simply agreed by convention not to recommend/publish it beyond 3195#.
If you, or anyone, wants to learn A LOT MORE about tire technology, I encourage you to visit Barry's site and settle in for a good read.
HTH
