Are you considering changing new wheels for your car or truck? Aftermarket wheels are a great way to customize your ride. Upsizing or switching to a staggered fitment can totally change the look of a car or truck. When someone is changing their wheel’s size, they often ask these questions: “Does changing the wheel size affect the speedometer?”. The answer is yes, but it doesn’t have to.
HOW YOUR SPEEDOMETER WORKS
The speedometer was designed and calibrated at the factory for the stock size tires and wheels that would be installed before the vehicle left the line.
The calibration was designed according to the gear ratios in the drive cable, the final drive ratio in the differential, and the tires’ diameter.
That last item is vital. See, for every revolution of the tire, the wheel covers a specified distance. The distance that tire covers in one spin are equal to its circumference.
Circumference = diameter x π (in case you forgot pi = 3.14159)
A 20″ wheel will cover 62.83 inches in one spin. Substitute with 24″ wheels, and now you’re covering 75.40 inches, but your speedometer won’t feel the difference. So, you see how changing wheel size affects the speedometer? But it doesn’t have to happen. Just follow the original combined diameter of the wheel and tire, and you should be good. Here’s how.
CHANGING WHEEL SIZE WITHOUT AFFECTING SPEEDOMETER
In practical terms, let’s assume you are lucky enough to own a 2018 Lexus GS350. When you can manage to pull the ladies off you and your car long enough to get online, you start shopping for some new badass wheels. You’ve got the stock 17″ wheels on there now, and you want more.
So, you look at 18″ inch wheels, and you are obsessed with the Cruiser Alloy Obsession. The bolt pattern, backspacing, and offset are a perfect match. You love the way those mirrored spokes extend to the rim, and the black accents are the bomb. But what’s going to happen to your speedometer if you go up to 18″ wheels? Will you attract as many cops as chicks because you can’t gauge your speed? At 17″, each revolution is covering 53.41 inches of road. At 18 you’re up to 56.55 inches. That’s almost 6% more with only one revolution.
Here’s what you do so that changing the wheel size won’t affect the speedometer. All you need to do is change the standing height of the tire. In other words, since you added an inch to the wheel, you can subtract an inch from the tire’s standing height. With a softer sidewall, you may even find that Lexus even handles better.
PLUS 1, PLUS 2, HUT HUT
So, when you hear gearheads talking “plus 1, plus 2, or plus 3” they aren’t getting ready to snap a football. They’re using shorthand to refer to the process I just described earlier. Plus 1 means that they’ve taken a stock wheel and tire combination and increased the wheel size 1 inch. When they say “plus 2” the wheel size has gone up 2 inches and the tire profile has been decreased accordingly. Same thing for plus 3. It’s how you go about changing wheel size without messing up the speedometer.
And you really don’t want to ever go more than plus 3 without serious modifications. The additional mass of the larger tires will wreak havoc with your fuel efficiency, and you don’t want problems with your suspension. There are other rules of thumb for upsizing, but you need to convert inches to millimeters, and I know you wouldn’t want to do some calculations. There’s an easier way to know for sure.
JUST ASK IF THE NEW WHEEL SIZE AFFECTS SPEEDOMETER
If you don’t want to stress about all the math and geometry and stuff and just want to focus on getting the biggest, baddest wheels that won’t mess with your ABS or speedometer, just ask the pros at Waysize Customz. Just tell them about your ride and the wheels you want. It’s that easy.