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What concessions are made when adding big tires?

Posted in How To: Wheels Tires on December 14, 2015
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Big tires are one of the cornerstones of the Jeep lifestyle. They increase ground clearance and allow us to go places that stock vehicles fear to tread. And let’s be honest: huge meats look awesome. However, what concessions do we make to run those big, aggressive tires? That is exactly what we intended to find out with our ’06 Wrangler Unlimited Rubicon.

This is a Jeep that serves as a daily driver but also makes regular excursions over the Rubicon Trail, so it must retain good street manners, yet still be capable and reliable off-road. To accomplish these varied tasks, we had added a Highline Kit from American Expedition Vehicles (AEV), which opened the fenders to fit 35-inch tall tires while retaining a stock appearance. As much as we love this kit, unfortunately AEV recently discontinued it in order to focus on the extremely popular JK and Ram truck markets.

Even more unfortunate is the decrease in acceleration and increase in braking distances gained with the addition of our new 35-inch Toyo Open Country M/Ts on 17x8.5 AEV Pintler rims. The new rolling stock is 60-percent heavier than the tires and wheels they replaced. We think that the compromise is worth it to gain the ground clearance and traction to tackle obstacles we avoided in the past, but we aren’t entirely content to just live with decreased performance. Instead we will be looking to the best that the aftermarket has to offer to gain back our lost acceleration and braking power in future issues. Here’s how our story begins, but stay tuned to learn how you can have your cake and eat it too.

The Toyo Open Country M/T has a reputation for providing great traction on the trail while also being smooth and relatively quiet on the road. These attributes fit perfectly with the theme of our daily driven Jeep that gets wheeled hard on the weekends.

The Open Country M/T is a Load Range E tire with a 10-ply rating. This provides excellent durability and puncture resistance, but it does help account for the weight of the tires.

Tipping the scales at 106 pounds, our new tire and wheel combination was 60 percent heavier than the rolling stock replacing. Seventy pounds is a result of the Toyos, and the remaining 38 pounds comes from the AEV Pintler wheels.

We started by performing acceleration and braking tests with the original tires and wheels, then switched to the new Toyo Open Country M/Ts and AEV Pintler wheels, and repeated the tests.

To measure 0-60 times we used a Diablosport Trinity tuner. The Trinity offers a host of functions from monitoring your Jeep’s vital signs, to reading and clearing DTCs, to adding more power and fuel economy through Diablosport’s tuning. We used the factory tune for these tests, but this gives you a hint as to what we have in store for our Jeep’s future.

Acceleration with the larger, heavier tires and wheels was better measured with an hourglass than with the Diablosport Trinity tuner. The Jeep’s 0-60 mph time with the Toyo tires and AEV wheels decreased by 59 percent.

The larger, heavier tires and wheels smoked our brakes after only one pass. The stench indicated that the brakes were fading under the pressure of the extra rolling mass and put brake upgrades on the top of our priority list.

We brought the Jeep up to 60 miles an hour and started braking at a set of cones. Distance from the cones to the front tire of the Jeep was recorded using a wheel counter after each run.

All tests were performed on a closed course for safety and to eliminate variables between various runs. Here you can see the rubber we laid down during our braking test.

The 35-inch Toyo Open Country M/Ts give us confidence to travel over terrain that we previously wouldn’t have attempted in our LJ. We had to air the new Toyos down to 12 psi to get them to bulge on the trail. Without beadlock rims, we didn’t air them down further and risk blowing a bead.

Jeeps already have very good approach and departure angles when compared to most other vehicles on the market, but there is still room for improvement. The increase in approach and departure angle is just one of the benefits of running larger tires.

We also measured ground clearance under the differentials with both sets of tires and wheels and found that we gained 1 3/4 inches under both pumpkins. The added height is great for ground clearance, but the leverage needed to turn the tires is greater with the taller tires, making the engine and transmission work harder. We’ll have to do something about that.

Tire & Wheel Combo 265/75R16 Goodyear Duratrac on factory 16x7 Rubicon wheels 35x12.5R17 Toyo Open Country M/T on 17x8.5 AEV Pintler wheels
Weight 66 pounds 106 pounds
0-60 Aceeleration 18.6 seconds 29.6 seconds
60-0 braking 137 feet 218 feet
Mileage 15mpg 9mpg
Approach Angle 45 degrees 55 degrees
Departure Angle 40 degrees 45 degrees
Clearance Under Differentials 9.25 inches 11 inches

Sources

AEV
Commerce Township, MI 48390
248-926-0256
http://www.aev-conversions.com
DiabloSport
Delray Beach, FL
561-908-0041
DiabloSport.com
Toyo Tires
800-442-8696
www.toyotires.com

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