I am running Goodyear Duratrac's and they are E rated. It is my daily driver and I spend most of my day in my vehicle driving between clients.

little bumpier but not a big deal.

 

The 37" Toyos you speak of are huge load tires, not only E rated but capable of supporting 4300lbs. If your JK doesn't weigh in at 6500lbs, you can't let enough air out of them to keep minimum on road inflation rates, or at minimum suffer from some over inflated tires which negates much of the tires spring rate given the actual load weight placed on them.

That should not be a wholesale indictment of an antiquated system of rating tires, much as what Teej suggested. Same line of tires, with the same E Rating (in 33s to 37s) carry as low as a 2910lb maximum load rating. So it's not an E rating that makes some of these tires undesirable, it's flotation, recommended inflation rates and weight supported.

In the dozen or more 33-37" Toyo MT E rated tires in 16-18" wheel sizes, there are about 3 tires that wouldn't work for my JK. This is simply because they have too much load capacity for my vehicle. If I look at C rated MT tires from BFG, Goodyear or for that matter Toyo in the same sizes, there are plenty that wouldn't meet my weight and load requirements.

To be dismissive of E rated tires in their entirety is short sighted, just the same as wholesale praise of C rated tires. If that's your primary criteria for selecting a tire then there is a good chance you will be disappointed. If I was moving to a 37" Toyo MT, I'd either be going down to a 15" wheel or up to an 18" wheel to get a tire that works for me. The 37x13.5x17 Toyo MT however just doesn't fit the bill for me, but it also doesn't make the case for the condemnation of all E rated tires either.

 

I'll be the first to admit I am no expert on tires. However when getting ready to buy 37's I looked pretty hard on this site for feedback. There was little or no negative feedback on the Toyo 37x13.5R17's. Actually there were many positive comments (long wearing, quiet, easy to balance etc.), including a moderator that seemed to be pretty happy with these tires, so I bought them.

I was not expecting a car ride, but then also I was not expecting a 6-ton truck ride either. I think you are right I could not let enough air out of them to smooth out the ride, without causing flat spots in the morning.

I'm not against all e rated tires, I just think (for my JK atleast) there are better choices for 37" tires than the Toyo's.

 

There are also C and D rated 37s available from Toyo, so "different choices" might be a better choice of words.

 

I think the ride with my 37" toyos is fine

 

Would you base your tire decision on the weight carrying specification of the tires?

I am trying to choose between a D and an E tire (2 different sizes of the same model). The E rating has a load capacity of 3195 lbs. This seems a bit high for a 2 door JK but the model I am purchasing is not listed (D range) however, the line of tires have ratings in the same vicinity except for the C rated tires.

I am getting the impression from the posts that the only way to judge a tire is to put it on and try it but that is a very expensive method.

Is there a particular specification to look for (or combination of specs) and if so what would the range be for a 2 door (or 4 door if you have it)?

 

It doesn't take a whole lot for a JK to wind up weighing in at over 5k without passengers or a payload. Bumpers, rails, tire carrier, winch, recovery gear and added weight from bigger suspension components and tires. Doesn't much matter if it's a 2 door or unlimited and there are quite a few people here who's rigs are in the 3 ton club.

Stock tires at their stock inflation rate have roughly a 2,000lb load rating. These are set up for a stock vehicle that weighs in right around 4,000lbs and a 1,000lb payload (including passengers). That's 8,000lbs of load rating for 5,000lbs of vehicle/payload, or 60% above the vehicle weight. If we increase the vehicle and payload weight by 20%, adding 1,000lbs, we should also raise the load rating of the tires by the same 20%.

Additionally ETRTO and ISO guidelines call for increasing the load by a factor of 1.10 for plus size tires. Using the example above, our 2,000lb tires needed to become 2,400lb tires and then a plus size factor of 1.10, indicating a 2640lb load capacity tire.

Now lets look at a couple popular load range C, D and E tires.

GOODYEAR WRANGLER MT/R WITH KEVLAR
35X12.50R17LT/C
Max Load 2405@35psi
This tire would be on the thin side of having enough load rating for a 5,000lb JK with a ETRTO/ISO load rating of 111

BFGOODRICH Mud-Terrain T/AŽ KM2
35x12.50R17/D
Max Load 3000@50psi
BFG uses the ETRTO/ISO Load Rating and this tire has a load rating of 119. What the ETRTO/ISO table shows is this tire will have an appropriate load capacity inflated to 31psi for a 5,000lb JK.

Toyo Open Country M/T
35X12.50R17LT/E
Max Load 3640@65psi
Toyo uses the ETRTO/ISO Load Rating and this tire has a load rating of 125. What the ETRTO/ISO table shows is this tire will have an appropriate load capacity inflated to 25psi for a 5,000lb JK.

In conclusion, we have 3 of the same tire sizes that require 3 different inflation rates to support the same vehicle. Throw the dated C/D/E rating stuff out as it's about as useful as counting plys.

 

Again...

When the tire says it supports some max weight...that's at the MAX PSI that goes with it.

E rated tires are essentially 80 psi max weight rated, so if it says it supports 3,195 lb, it means at 80 psi.

The rule of thumb for minimum psi calculations is based upon the weight of the rig.

The practice of taking 35% of the rig's GVWR, and assuming ONE tire should support that, typically works out to what the car makers spec for the psi.

So if your rig's GVWR is 5,400 lb, each tire should be able to support ~ 1,890 lb.

If the tire supports 3,195 at 80 psi, it will support ~ 1,890 lb/3195 lb = 0.59 of that at ~ 0.59 x 80 psi

Or

~ 47 psi.

The above is ball park, as the psi/load capacity is not perfectly linear, but, it tends to work out fairly close for estimation purposes.

Now, for the above scenario, some tires will ride harshly, and some will ride softly.

Some tires are thicker walled, tougher tires, and tend to ride more harshly than street tires anyway.....as it takes more force to deform the rubber.

...so I find that those switching from one thick meat to another are OK, but those going from a more mild tire to a thicker beast can assume the harshness is due to the load rating, etc.

The fact is that the harshness is largely a function of the ease which the tire is deformed.

When a tire is on your rig, its flat on the bottom, and round on the rest...but, as you roll, the part that is flat changes on a, um, rolling basis.



This means that as the tire rolls, it has to change shape...which requires force.

The more force it takes to deform the tire, the more road force is transmitted to the suspension/frame...

....as the softer tire just dents in, without pushing the rig up...

...but the harder tire is partly dented in, but transmits the rest of the force (Harshness).

I have D rated AT ko's that ride smoother than the C rated swampers for example, as the swampers have roughly inch thick rubber, and the ko's have the moral equivalent of a thin film of rubber.

The ko's deform easily compared to the swampers, and have lower rolling resistance/better mpg and a smoother ride...but remind me not to slice them open on the rocks...

...the swampers have a higher rolling resistance, worse mpg, and a harsh ride...but can crush rocks.

 

Now that makes sense!!!! I would assume you have some design knowledge of tires - or one he** of a bs'er!!! - JK

I would suspect there is a range of tire pressure that would produce the minimum wear. Doesn't this pressure range need to be known to further evaluate the tire. Another words I could reduce the pressure based on your explanation above but at some point on both ends of the spectrum the pressure adjustment becomes detrimental I would suspect.

I'm guessing higher pressure would cause the center to bulge and wear quickly (but I would also guess would increase mpg). Lower pressure would cause excessive wear with the most wear occurring on the outer portions where there is the most tread support (I assume mpg would also go down with lower pressure). This excludes issues due to alignment, balance, suspension, etc. These seem to be fairly straight forward.

Based on all this it sounds like one would need a good set of tire specs to evaluate a tire for there particular use. I am more than willing to study the details but I don't typically see the information available. Things such as load vs pressure, rubber hardness, flexural modulus, etc would sound very useful.

Probably a dumb question but is this information available?
I also suspect if it is available the manufacturers bias it to make their brand look better unless there is a regulated standard to oversee the testing and reporting.