Tire Testing - Size Matters

    Can You Run Different Size Tires?

    Harry WagnerPhotographer, Writer

    For decades, hot rodders have run big tires in the back to put horsepower to the ground and small tires up front for less weight and easier steering. But hot rodders don’t have a transfer case, so could this same idea be applied to a 4x4?

    We wanted to find out, so we rounded up three Toyo Open Country M/Ts of different sizes to test on our ’98 Toyota 4Runner. The Open Country M/T was perfect for our test since Toyo offers them in some unique sizes not offered by most tire manufacturers, including the skinny ones we tested.

    We rotated a pair of 255/85R16 (33.5x10.2) Toyos with 285/75R16 (33x11.6) and 265/75R16 (31.8x10.8) Open Country M/Ts at each corner of the 4Runner to test not only width differences but height differences as well.

    You can think of the tall and skinny 255/85R16 tires like Paris Hilton. They provide the most ground clearance, but don’t think that they are without “issues.” They won’t burst into tears or anything like that, but you might be crying if they leave you buried in soft terrain where a wider tire would provide more flotation.

    The 285/75R16 tires are nearly as tall as the 255/85R16s, but they are wider, more like Beyoncé than Paris. The 265/75R16 tires are the shortest of the group but not the skinniest, kind of like Snooki from Jersey Shore if Snooki came in metric sizing.

    Normally, running different-diameter tires on a 4x4 is a bad idea. Something has to give if the front tires aren’t traveling the same speed and distance as the rear tires. That something could be the transfer case, a ring-and-pinion, or traction giving way. Our testing was performed in 4-Hi on sand and mud, where traction was limited and differences in size could be qualified. Different tire sizes when run on high-traction surfaces such as rocks will find the weak links in your drivetrain. Spoiler alert: We didn’t blow up the transfer case, but we did learn a lot in the process.

    Why We Wanted to Run Different-Size Tires
    Given the small difference in diameter, we chose to run the tall skinny tires on the front of our 4Runner and the tall wide tires in the rear after completing our testing. Why? The narrower tires up front are lighter and limit traction to the CVs, which have a nasty habit of breaking when the front ARB Air Locker is on and the tires are bound up off-road. In addition, the narrow tires clear our custom front suspension components without protruding excessively outside the fenders. Out back the wider tires provide excellent traction and floatation, particularly in soft terrain like sand. Like Goldilocks, we now have a combination that is just right.

    Who Won WWII Anyway?
    Refuse to use the metric system? The following information can help you decipher that jumble of numbers and letters found on modern tires. Let’s take the 265/75R16 Toyo Open Country M/T used in our test. The first number (265) is the tire’s section width in millimeters. The second number (75) is the sidewall height expressed as a ratio of the width (75 percent of 265). The last number is the rim diameter, which thankfully is still listed in inches.

    Tire height in inches = 265 mm x 0.75 x 2 (tire above and below rim) / 25.4 mm per inch + 16 inches (rim diameter)

    Tire width in inches = 265 mm / 25.4 mm per inch

    Tire Size Height (in) Width (in) Weight (lb) Rotations Per Mile Air Pressure to Achieve 15 Inches From Ground to Center of Hub
    265/75R16 31.8 10.8 59.2 634 20
    255/85R16 33.5 10.2 61.2 602 10
    285/75R16 33 11.6 65.7 611 12