Ensuring an Accurate Measurement
Park the car on a level surface where it’s less likely to roll. Ideal locations include paved driveways and garages on flat, level ground. Set your parking brake before exiting the vehicle to best prevent it from rolling. Parking on a driveway will also make it easier for you to make markings on the ground later on. If you’re measuring the wheelbase of a rail vehicle, leave the vehicle on the tracks and apply the brakes to keep it from inadvertently moving.
Make sure the wheels are straightened out. Straighten your turning wheels so that they are pointed directly forward. Your front and rear tires should all be parallel to each other, as well as to the rest of the vehicle body. Most likely, your turning wheels will just be your front 2 tires. Use the steering wheel to turn these tires until they’re neatly aligned with the rest of the wheels.
Look on the door sticker for the factory wheelbase first. The sticker on the inside of the driver door will include the factory specifications for the vehicle, including the wheelbase. Knowing this figure will allow you to compare your own measurement to the factory’s and gauge whether you’ve taken your measurement correctly. The wheelbase will be indicated on the sticker by the letters “WB” followed by a number. This number will be the measurement of the wheelbase in inches. If you need to know your vehicle’s wheelbase in order to purchase replacement parts, this is the best way to get an accurate measurement.
Identify the center of your tires to know where you’ll measure from. This is usually the spot in the middle of the lug nuts or screws holding the tire in place. The wheelbase is the distance between the centers of the front and rear tires of both road and rail vehicles, so you’ll need to measure from 1 center to the other to find the wheelbase. If your vehicle has more than 2 axles (e.g., an 18-wheeler), the wheelbase is considered to be the distance between the steering axle and the center of the driving axle group. If you’re measuring the wheelbase of a rail vehicle, locate the points where the wheels contact the rail instead of the center of each wheel. The wheelbase of rail vehicles is measured between these locations instead of the wheel centers.
Taking the Measurement
Place a steel square on the ground and align it with the center of the tire. Place the short end of the steel square or framing square on the ground. Slide it along the ground until the long end is aligned directly with the center of the front tire. For best results, align the opposite edge of the long end (i.e., the edge further away from the short end) with the center of the tire.
Mark on the ground where the square aligns with the tire center. Use thick chalk to make a mark where the bottom of the long end meets the ground. Pull the steel square away and make the mark slightly thicker so it’s easier to see. Don’t make the mark too thick or draw it out as a line. This may actually make it more difficult for you to accurately measure the wheelbase. Stick to a thick circle no larger than ⁄2 inch (1.3 cm) in diameter.
Repeat this process with the rear wheel to make a second mark. Use the steel square and chalk to make a mark on the ground where the center of the rear axle is. Make sure your marks are both on the same side of the vehicle. You should now have 2 marks on the ground: 1 for the steering axle and 1 for the rear axle.
Use a tape measure to determine the distance between these marks. Place 1 end of your tape measure on the mark by the steering axle and extend the tape down to the mark by the rear axle. This length is the wheelbase of your vehicle. Note that this measurement is typically recorded in inches.
Repeat this process on the opposite side of the vehicle. It’s important to determine whether the wheelbase is the same on both sides of your vehicle. If the wheelbase is longer on 1 side than on the other, this will cause the vehicle will drag to the side and may even pull the rubber off of your tires. You can take your vehicle in to many body repair shops to have the wheelbase altered.
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