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Cooper STT pro 37" D vs E rated

YJLOPES

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45acp

37x12.50r17 D rated

vs

37x13.50r17 E rated

I'm looking at a set of these for my beater.

Why would I want one vs. the other for my stretched YJ?

Load rating obviously isn't a concern. I've heard the E rated 37x13.50R17 is a tougher sidewall for resisting damage/cuts, any truth to this?

The E is 7# heavier at 84# vs 77# for the D, according to this. I like lightness.

The E is $30 cheaper, so not a deal breaker either way, but worth mentioning.

I got turned off of E rated tires on a Jeep years ago, but maybe my bias is bullshit.
 
I had e rated tires on my tacoma that I daily drove for a long ass time. I never noticed a ride quality difference between them and non e rated, air them down from the 65psi the tire jockeys put in them when they mount them and go drive. These were bfg km2s and I never took out a sidewall if that has anything to do with the e rating.
 
As you mentioned, one is 12.5 wide and the other is 13.5 wide. So your backspace will come into question as to which one will fit without rubbing.
Personally I'm not a fan of E rated on a Jeep, I prefer C or at least D for the better grip.

FWIW we currently run 2 sets of the STT Pro, one in 37/12.5/17 (D rated) and one in 40/13.5/17 (C rated). The 37s currently have over 60k on them, my wife's daily with mild trail use. In comparison I got about 75k out of my last set of 37/13.5 Toyo OC MT, these Cooper's look to be on track for the same mileage.
 
45acp

37x12.50r17 D rated

vs

37x13.50r17 E rated

I'm looking at a set of these for my beater.

Why would I want one vs. the other for my stretched YJ?

Load rating obviously isn't a concern. I've heard the E rated 37x13.50R17 is a tougher sidewall for resisting damage/cuts, any truth to this?

The E is 7# heavier at 84# vs 77# for the D, according to this. I like lightness.

The E is $30 cheaper, so not a deal breaker either way, but worth mentioning.

I got turned off of E rated tires on a Jeep years ago, but maybe my bias is bullshit.

The only difference besides the extra width is tougher sidewall. If its a trail rig, I'd definitely run the E's (and do). If it sees some street time, just run 25-28psi to get some of the ride quality back. While E's might ride like a tank on lighter vehicles, you don't have to run recommended pressure on the street. If 22psi makes it comfortable and there's no noticeable bulge... run 22psi.
 
Weight of your rig comes into play too, if it's really light the E rated might be just too stiff to flex much when aired down. Some of my Toyota friends have to get into single digits for regular trail use just to get their E rated tires to conform to rocks.

As for the sizing, the 37x13.50 is still a good size if you have the right backspacing/offset and it clears your suspension. I have 37x13.50r18 on my Taco but it's D rated because 18" (not my choice on the wheel size, they came with the rig so I kept them). I try to stick with C or D tires the closer the rig is to 4k lb.
 
The only difference besides the extra width is tougher sidewall. If its a trail rig, I'd definitely run the E's (and do). If it sees some street time, just run 25-28psi to get some of the ride quality back. While E's might ride like a tank on lighter vehicles, you don't have to run recommended pressure on the street. If 22psi makes it comfortable and there's no noticeable bulge... run 22psi.

My rig is around 4400# before the family and I get in, so add another 500# for the 4 of us and a tool bag.

I run my old school MTR's at 20 PSI on the street, and 8-10 on the trail.
 
Weight of your rig comes into play too, if it's really light the E rated might be just too stiff to flex much when aired down. Some of my Toyota friends have to get into single digits for regular trail use just to get their E rated tires to conform to rocks.

As for the sizing, the 37x13.50 is still a good size if you have the right backspacing/offset and it clears your suspension. I have 37x13.50r18 on my Taco but it's D rated because 18" (not my choice on the wheel size, they came with the rig so I kept them). I try to stick with C or D tires the closer the rig is to 4k lb.

I have the room for 13.50s, so that's not an issue.

I'm probably around 4900# ready to roll on the trail.
 
My rig is around 4400# before the family and I get in, so add another 500# for the 4 of us and a tool bag.

I run my old school MTR's at 20 PSI on the street, and 8-10 on the trail.

Get the E's. Run whatever feels good on the street. Low psi on a road trip isn't gonna hurt anything as long as there isn't any excessive sidewall bulge.
 
Personally not a fan of E sidewalls, but I do a lot of snow wheelin where the more sidewall flex, the better.

If you are the type that is hard on side walls, get the E. If you want a more flexible, lighter tire, get the D.
 
Personally not a fan of E sidewalls, but I do a lot of snow wheelin where the more sidewall flex, the better.

If you are the type that is hard on side walls, get the E. If you want a more flexible, lighter tire, get the D.

If you want more sidewall flex, = less air. If it takes 1psi to get the squishy right... then run 1psi. :confused:
 
If you want more sidewall flex, = less air. If it takes 1psi to get the squishy right... then run 1psi. :confused:

Sometimes 1 psi in an e rated tire is still not flexy enough. C sidewall is really where it's at for snow.

I'm talking deep snow crawling type stuff, I realize that's not a common thing and get why people like E sidewalls for durability though.
 
Yea I have zero snow wheeling experience, I assumed everyone ran 15" load C iroks or Eskimo scalps or some kind of baby seal tread with self tapping screws. :flipoff2:
 
Yea I have zero snow wheeling experience, I assumed everyone ran 15" load C iroks or Eskimo scalps or some kind of baby seal tread with self tapping screws. :flipoff2:

Well yes, if that's all you do, baby seal carcass at 1 psi is the ticket. :laughing:

Most of us don't like having 2 set of tires for winter and summer though. Instead, we try to find something that works good at both. Most c rated radials fit that bill pretty well, and some D rated aren't bad either.
 
I always thought E rated was tougher, so I ran them and never noticed how crappy they road. Someone brought to my attention how much better C rated tires ride on choppy roads and nuisance rocks, both comfort and performance by conforming to the ground. After switching back to C rated I don't think I will go back to E unless its required for hauling or towing.
Yes you can lower the pressure to make an E ride better but it will still ride hard and not hold the road like a C will.
When I got a Tundra TRD, it came with P rated tires and I thought what kind of idiot puts a passenger tire on a truck that also has a tow package. It road smooth, quiet, and tracked great. I switched to KO2's in a heavy D rated tire and instantly it was louder, road harder, didn't track as well. Next tire change I dropped down to a C rated KO2 and it was a noticeable difference.
For the buggy which is lighter I was looking at tires and many are available in E rated, but I made sure to get a C rated tire.
 
Sometimes 1 psi in an e rated tire is still not flexy enough. C sidewall is really where it's at for snow.

I'm talking deep snow crawling type stuff, I realize that's not a common thing and get why people like E sidewalls for durability though.

So "fill" you tires with a vacuum pump instead of an air compressor :flipoff2:
 
i run ~6 to 8 psi in my XJ's 36x13.5R15 IROK BIAS on the street, and do 70 mph (downhill with tailwind and at WOT:laughing:). I still need to try drop it to 4 or 5 psi to improve shoulder contact to road, as they still looks like they're inflated at maximum psi, zero bulge, whatsoever.
 
I have the room for 13.50s, so that's not an issue.

I'm probably around 4900# ready to roll on the trail.

Get the D rated tires for sure. E rated will give you no benefits, except for stiffer tires and a weight penalty.
 
i run ~6 to 8 psi in my XJ's 36x13.5R15 IROK BIAS on the street, and do 70 mph (downhill with tailwind and at WOT:laughing:). I still need to try drop it to 4 or 5 psi to improve shoulder contact to road, as they still looks like they're inflated at maximum psi, zero bulge, whatsoever.

Bias are completely different. They don't really sidewall bulge like a Radial, but once you rocks or whatever, they will wrap around stuff.

Bias is kinda more like an inner tube where the whole thing will flex(or not :laughing:​​​​​​) the same. Where a Radial is kinda like a stiff band with more flexible sidewalls. I'm sure there is someone who can explain it better, but I think I'm not too far off. :laughing:
 
I run the 40" STT Pros in load rage E on my wifes JKUR. They get 24psi for street driving and have gone on two 3000 mile round trips so far with zero issue. On the trails 8-10psi is the range they work best for me.
 
i run ~6 to 8 psi in my XJ's 36x13.5R15 IROK BIAS on the street, and do 70 mph (downhill with tailwind and at WOT:laughing:). I still need to try drop it to 4 or 5 psi to improve shoulder contact to road, as they still looks like they're inflated at maximum psi, zero bulge, whatsoever.

Have you broken them in? You need to run them at or near zero until the tire warms up. Then you fill them back up and they will perform better.
 
Get the D rated tires for sure. E rated will give you no benefits, except for stiffer tires and a weight penalty.

I dunno, tougher carcass and more durable sidewall is definitely something I'd consider a benefit in a trail rig.

BUT, the D's aren't junk... its not like 1 has bias SX sidewall and the other has Ching Sho 1 plys from a stock 94 Civic. In a hardcore trail rig that sees highway... im happy with the E's. Either one will be fine.


From a weight standpoint- even though unsprung is critical- you're not gonna notice 6lbs a tire.
 
Bias are completely different. They don't really sidewall bulge like a Radial, but once you rocks or whatever, they will wrap around stuff.

Bias is kinda more like an inner tube where the whole thing will flex(or not :laughing:​​​​​​) the same. Where a Radial is kinda like a stiff band with more flexible sidewalls. I'm sure there is someone who can explain it better, but I think I'm not too far off. :laughing:

Explanation is good. :beer:
 
Thought I'd follow up...

Ended up with the D rated 37x12.50s just because of availability. I've been running them since the end of march which has been around 5K miles. I've done 4 days in Moab as well as 21 road and they have been great off road around 8-10 PSI. On the road I've done a few road trips towing my little camping trailer and they run down the highway just fine, in fact they are quieter than the old school MTRs they replaced. I run them around 20 PSI on the road but I may burp that down a bit for experiment's sake.

Mounted up on 17x9 steelies they are about 115# each. The 35" MTRs on alloys they replaced were 65#. My jeep is in no hurry with these tires and 4.88s.

All in all I am very pleased.
 
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