G614 Tires

[LonnieB]

quote:By PSFORD99

I would like to hear Lonnie weigh in on this subject of E rated LT tires rated at 3042 on 7K axles, and fifth wheels with the GVWR of 15-16K

Ok, here is my weigh in.

I cannot, and will not, recommend to anyone that they install tires on any type of vehicle that aren't capable of safely carrying the loads that they will be subjected to. Does this mean I won't recommend an LT tire with a lower load rating than an ST tire? No, it doesn't. The reason is, LT and ST tires do not undergo the same testing procedures, and the ST tires aren't held to the same safety standards as the LT tires in order to come up with the load ratings. LT tires are rated to carry the load for which they are rated at speeds ranging from 99 mph up to 112 mph. St tires are rated at 65 mph maximum speed. LT tires have a large reserve capacity, ST tires have NO reserve capacity. LT tires have to be able to safely carry passengers at the speeds for which they are rated, ST tires cannot legally carry passengers at any speed. IMHO, if LT tires ONLY had to meet the standards the ST has to meet, the LT would far surpass the ST testing standards.

I have sold and installed the LT235/85R16 load range E on numerous Montana 3400's and many other brands of comparable size and weight, and I have not had one single failure due to the tire being overloaded.

In the end, it all boils down to what you feel comfortable with. If you feel safer with an ST rated tire, or a higher load/ply rated tire, then that is what you should go with. I have attached the following from DQDick to help you have a little better understanding of the difference between LT and ST tires. It's a little long, but I feel it's worth the time it takes to read before you make your final tire decision.

quote:By DQDick

Ok, here it is again, by popular demand:


I have asked many times for someone to explain how a ST tire can be rated to carry more weight than a LT tire in a similar size, without a good answer.

The answer lies in what is called reserve capacity. To quote from Trailer Parts Superstore and this same statement exist on just about every tire site:

HEAVY DUTY 'LT' TRUCK / TRAILER TIRES
'LT' signifies the tire is a "Light Truck/Trailer" series that can be used on trailers that are capable of carrying heavy cargo such as equipment trailers.

If a tire size begins with 'LT' it signifies the tire is a "Light Truck-metric" size that was designed to be used on trailers that are capable of carrying heavy cargo or tow vehicles. Tires branded with the "LT" designation are designed to provide substantial reserve capacity to accept the additional stresses of carrying heavy cargo.

So what is reserve capacity? It is capacity beyond the rating of the tire, capacity that is held in reserve. This reserve capacity comes from the heavy-duty sidewall of the LT type tires. LT's rank at the top of the list when we look at P, ST and LT tires.

Now I finally have an answer to how a ST tire can be rated to carry more weight than a LT tire of similar size.

The ratings of ST tires infringe into the reserve capacity of the tire. This is double bad, because the design of the ST gives us a tire with less reserve capacity to start with as it has a lighter sidewall to start with as most ST tires are much lighter than their LT counterparts.

To quote one tire site:
"Put a different way, the load carrying capacity of an ST tire is 20% greater than an LT tire. Since durability is strictly a long term issue - and the results of a tire failure on a trailer are much less life threatening than on a truck - the folks that set up these load / inflation pressure relationships allow a greater......ah......let's call it load intensity."

There it is in print to be read. They make a calculated decision to give the ST tire a higher load rating because a failure is less life threatening.

I have on a number of occasions pointed out the weight difference between the different tires and have been told that does not matter. Well it does matter. The rubber in the average tire only makes up around 40 some percent of its weight, the rest is in the steel belts, gum strips, steel beads, and the carcass plies. The remaining 60 or so percent of the stuff in a tire is what builds in the reserve capacity.

So to review again, here are some weights:
1. Michelin XPS RIB LT235/85R16 LRE (rated to 3042lbs) Weight 55.41
2. Goodyear G614 LT235/85R16 LRG (rated to 3750lbs) Weight 57.5
3. Bridgestone Duravis R250 LT235/85R16 LRE(rated to 3042lbs) Weight 60
4. BFG Commercial TA LT235/85R16 LRE(rated to 3042lbs) Weight 44.44
5. Uniroyal Laredo HD/H LT235/85R16 LRE(rated to 3042lbs) Weight 44.44
6. GY Marathon ST235/80R16 LRE(rated to 3420lbs) Weight 35.4

So which tires on the list have the most reserve capacity? Well that is not a completely simple answer, as one of the tires is a G rate 110 lb tire and the rest are LRE at 80lb inflation. So if we disregard the G614, then the Michelin XPS RIB and the Bridgestone Duravis R250 due to their all-steel ply construction will have the most reserve capacity inherent in their construction. The twin Commercial TA and Laredo will be next and the Marathon would have little or no reserve capacity available because it was used up in its higher load rating, AND because of it's much lighter construction it had much less inherent reserve capacity to start with.

So what have we learn from this?

I think that the first thing that we learned was that a LT tire can be used at or near it max rated loading without having issues, as they built with "substantial reserve capacity to accept the additional stresses of carrying heavy cargo".

The second thing we may have learned is why ST tires are failing on mid to larger 5th wheels, in that they do not have inherent reserve capacity beyond that rated max loading. Again this is because they have less reserve capacity to start with and their greater "load intensity" used up any reserve capacity that might have been available.

Now, here is an interesting bit of information. I just called Maxxis Tech Line and asked the weights for two tires.

ST235/80R16 LRD 3000 lb rating at 65 lbs of air weights 38.58
ST235/80R16 LRE 3420 lb rating at 80 lbs of air weights 43.43

What??? The Maxxis load range E tire weights almost the same as the Commercial TA?? This is a ST tire that has heavier construction than the GY Marathon at 35.4 lbs. So it has more inherent reserve capacity due to its heavier construction.

Those that claimed its virtues maybe did not know why it was a better ST tire than some of the others, but there it is! It is a heavier built tire with more reserve capacity.

So as one chooses a replacement tire or is asking for an upgrade on a new trailer please get educated on where the reserve capacity exist. Is it inherent in the tire you choose or do you have to factor it into the weight rating of the tire you choose.

Those with heavy trailers that are switching to 17.5 rims and tires rated to 4805 lbs and getting a double injection of reserve capacity, in that they are using a tire with lots of inherent reserve capacity and the tire has much more capacity than the application. It is all starting to make sense.