New Shoes for the Wrangler and XJ: Cooper Discover STT Pro Tires

New Tire Smell

There is nothing quite like the sweet aroma of new rubber. The kind that comes on a set of new tires. Especially a set of Cooper Discoverer STT Pro tires.

Last August, I was fortunate enough to have Cooper Tires supply a beautiful, beefy set of 315/70R17 tires for the Jeep Wrangler. Measuring 34.57 inches tall and 12.6 inches wide, and weighing in at 66 pounds each, these tires were much bigger than my stock tires.

They have a triple-ply side wall so they’ll resist punctures really well. And the tread on these tires is so aggressive and has a great design just made for grabbing onto the road whether it's asphalt or rocks and mud.

A few months before the tires arrived, I'd installed a 2.5” lift kit and added 1 ¼ inch wheel spacers so I was already set for the tire installation.

The Install

Mounting and balancing tires is a job for the professionals, so I went to Dirt Trenz off-road custom shop to have the new tires mounted on the stock rims. They had all the equipment for the job and everything turned out perfectly. If you're in the San Diego area, I highly recommend these guys—they were nothing but professional and do amazing work.

For the rear tire carrier, all I had to do was add a 1 ½ inch G2 wheel spacer. That brought the tire out a little and the wheel size fit perfectly between the bumper and the third brake light so I didn’t have to make any modifications.  I also don’t have any clearance issues with closing the door. I was very pleased with how this worked out.

After the install, we checked to see how the new tires worked with the 2.5 inch lift I'd previously installed and there were no issues with the tires hitting the fenders. The only problem was the rear tires were hitting the backs of the rock rails, so we had to trim off about an inch of those, but that was an easy project and not a big deal.

One of the questions I had going into the install was if I was going to need to adjust my tire pressure running a larger tire, but Dirt Trenz recommended your stock tire pressure.

With my stock tires, I'd measured 18 ½ inches  from center line and the front differential  9 ¼ inches. After, the center height measured 20 ¾ inches and the differential was almost 11 inches. This meant I was going to get some great clearance on the trail with these big tires.

Once the install was done, I was completely happy with how things turned out and I absolutely love how these tires look on my Jeep. 

The Wheels on the Jeep Go Round and Round

After breaking in the tires, I have to say they're everything I expected and more.

These tires are made for hitting trails, getting muddy, and crawling over rocks. No doubt about it. They are also tame enough that you can commute with them. And I do both. The Jeep is my off-roading, adventure-seeking rig and it's also my daily driver, so it gets a lot of miles on and off road.

Hitting the trail with these tires has been a blast. From sand to rocks and climbing, these tires are just really fun!

I usually air them down to 18 psi and it makes going over obstacles so much easier. The way they grip onto rocks and hug trails is so much more noticeable than the stock tires. Thanks to the aggressive tread on the Cooper tires, I was climbing all over obstacles with no problems.

The Asphalt Jungle

My daily commute is 60 miles round trip and I was worried about two things: road noise and comfort.

You put bigger tires on and you’re going to get more noise just because there’s more contact to the ground. That's the trade off. I was expecting it to be really loud because I’d heard horror stories about people putting other brands of tires on their Jeep and it resulting in an insane amount of noise.

Is there road noise with the new tires? A little bit. But, I can barely hear it and I didn't even have to adjust the sound level on my radio. The first time my wife road in the Jeep after the install, I asked her what she thought about the noise and she said, “what are you talking about.?” She didn’t even notice it. I might be a little hypersensitive to it just because I know how it was before and how it is now. It’s not obnoxiously loud. It’s perfect.

How comfortable are the new tires? I did drop the psi down to about 34 psi which did soften out the ride and after 25,000 miles and six 5-tire rotations the tires are wearing is excellent and I still have many more miles of use left.  It also handles just fine. It's smooth down the road, steers just straight, and drives perfectly on my commute with no issues.

Is Bigger Better? Having bigger tires has a lot of benefits when it comes to taking your Jeep off-road, but there are a few things to consider if you're thinking of adding some new rubber to your rig.

Acceleration is one of those things. You put on 66 pound tires and your rotating mass just got heavier. That’s going to slow things down a bit and your engine is going to work a little harder. It’s not as significant as I expected because I do have the 4:10 gears, but there’s a little bit of difference and I notice it. Especially when I’m accelerating up hill onto the freeway.

I may end up re-gearing down the road to something a little bit higher, but I haven’t decided yet. Right now, it’s functioning just fine so I'm good. If I had the lower gears, like the 3:73’s, then I’d probably be in a hurry to upgrade a little sooner.

The other thing is gas mileage. Normally, with my roof rack on, I’m getting 16.5 miles to the gallon. Well, that’s dropped down to 15.5, but that’s to be expected. I knew I was going to lose some gas mileage and I actually thought I was going to lose more than I did, so I'll take 15.5 and call it a day.

Project Jeep Cherokee XJ Overland

When we upgraded the tires on our XJ Overland Project, Cooper Tires once again supplied our new wheels. These are the same tires I’ve been running on my Jeep Wrangler, except these are 32x11.5R15.

I know there are a lot of opinions about tire sizes, and I chose the 32s for several reasons. First of all, we are building an overland rig, not a rock crawler. Our main goal with the XJ is to take it long distances and hit some moderate trails—maybe some that are more difficult once in a while, but nothing crazy. We want to hit the Mojave Trail, Death Valley, maybe Moab. We also want to do some cross-country trips and visit trails in other states, so we want to keep this Jeep tame to avoid straining our drive train and engine on those long trips.

The second reason we chose the 32s is because we put a four-inch lift kit on the XJ and 32s are what’s recommended. I could have gone with 33s and cut the fenders, but I’m not ready to do that yet. Actually, I don’t know that I’ll need to go to 33s to be honest. I’m a firm believer that with good tire placement on obstacles, a durable tire with good tread and rubber compound—along with a good set of lockers, you can go just about anywhere. I’m confident these Cooper Discoverers will get us where we’re going.

The final factor in my decision was rotating mass. Installing the 32s increase our rotating mass by quite a bit. The original tires weighed in at 51 pounds—our new tires weigh in at 71 pounds. That’s an additional 20 pounds per wheel. Bigger tires would’ve been that much more rotating mass and that means the engine’s going to work that much harder. When your engine works harder, you’re going to decrease your gas mileage and we definitely don’t want that on a vehicle we plan on using for long trips. It just doesn’t make sense.

The Cooper Tires on the XJ not only look amazing, but I’m completely happy with their performance.

What Do I Think?

So, what do I think of my Cooper Discoverer STT Pro tires? On both the Wrangler and the XJ, they are spot on! I love the look, I love the drivability, I love the off-road traction, and they just perform really well.

If you’re looking for a new set of tires, you want to consider a set of Cooper tires.??