Oversize Tires – A Good Idea, Or No?

December 2nd, 2015
Truck Tires in Gettysburg, PARolling down the highway in your lifted truck…it’s just cool. You have a commanding view of what’s ahead, you get respect from other vehicles on the road and, of course, you have plenty of ground clearance to get over and around things when you take it off the highway. There’s a down side, though. 
 
The lift kit by itself isn’t enough; if you’ve still got the same stock-sized tires and rims, you won’t have enough ground clearance for the front and rear differentials. The only way to achieve that is with oversize tires and rims, and this is where things will start to get complicated. 
 
  • Brakes: The bigger, heavier tires mean more rotating mass and more unsprung weight, which is more than what your stock brake system was designed for. You’ll start to notice longer stopping distances, overheating and premature wear of pads and rotors. This can really become dangerous when you’re hauling a heavy load or pulling a trailer, both of which put an even greater demand on your brakes. You will need to consider a brake upgrade, including possibly bigger, thicker drilled or slotted rotors, multi-piston brake calipers and high-performance brake pads. You might even need longer aftermarket braided-steel brake lines to compensate for the added height and suspension travel that go with your lift kit.
  • Final Drive Ratio: It’s simple math; the bigger-diameter tires are going to raise your drive ratio. Your stump-pulling truck is suddenly going to feel like it has highway gears and will lack the low-end torque and acceleration it once had. Consider having the rear end gearing changed for lower gears. You can determine the new gear ratio by calculating new tire diameter divided by old tire diameter, multiplied by the current axle ratio. Remember also that the lower the numerical value of the ratio, the higher the gears will be.
  • Body Work: So you put your big ol’ tires on, and now they rub on the inside of your fender wells. You might need to do some trimming to expand them, but remember that things will settle in time and you may need to do that job more than once. 
  • Suspension Geometry: All the bulk added toward the outside will throw your suspension geometry off (along with whatever tweaks the lift kit did to it). Chances are you’re going to need an alignment, and possibly more than one to find a spec of alignment angles that will work. You might also see premature wear of wheel bearings and wheel studs, both of which are stressed by all the excess weight.
  • Speedometer/Odometer: Again, simple math shows that speedometer and odometer readings are going to be thrown off by oversize tires and rims. The speedometer will read slow; along with potential speeding tickets, this can throw off the PCM computer and cause changes in traction control, ABS performance and transmission shift points. Aftermarket kits are available to recalibrate the speedometer and Vehicle Speed Sensor, while older trucks will need a different drive gear for the transmission-mounted speedometer cable. 
 
Still want to go with oversize tires? Don’t be discouraged – it can all work out just fine, just bear in mind all these factors. If you’re thinking about a lift kit and big tires for your truck, give us a call or schedule an appointment at L & M Tire & Wheel in Gettysburg, PA and let one of our consultants help you plan it out so it’s done right! 
  Posted in: Tires 101