If your average time is off by 3 seconds or more, your speedometer is likely in need of re-calibration. If you have changed out the tire and wheel package, the OD and resulting change in revolutions per mile is likely the cause.
Call Toll Free: Please try again or click the Checkout button! How a Change in Tire Size Affects Speedometer Accuracy When you change out your tires and wheels for a larger wheel, you always want to respect the overall diameter OD of the original tire. Click to Call Toll Free.
Tires-Easy Canada has the largest selection of tires, from premium to quality, discount brands that you can buy online in Canada. We offer fast, low cost shipping from warehouses in Canada. Useful Links. Sign Up For Savings. Aspect Ratio All Aspect Ratio So a tire with a diameter of 20 inches will cover about A tire with a diameter of 30 inches will cover more ground -- about Calibration adjusts for these variances and is done by the manufacturer, which sets up the speedometer gear to correspond with the factory-installed ring and pinion ratio and tire size.
A car owner may have to recalibrate his speedometer if he makes changes that make his vehicle fall out of factory specifications see the sidebar below.
Recalibrating a speedometer can be done by manipulating the hairspring, the permanent magnet or both. Generally, the strength of the magnetic field is the easiest variable to change. This requires a powerful electromagnet , which can be used to adjust the strength of the permanent magnet in the speedometer until the needle matches the input from the rotating drive cable.
No speedometer can be percent accurate. In fact, most manufacturers build speedometers so they fall within a fairly narrow tolerance range, no more than 1 percent to 5 percent too slow or too fast.
As long as a car is maintained at factory specs, its speedometer should continue to register vehicle speed within this range. But, if a car is modified, its speedometer may need to be recalibrated. Changing tire size is one of the most common things car owners do that can affect speedometer accuracy. Consider the example below. Newton's Second Law dictates that the force on an object is equal to its mass multiplied by its acceleration.
So, increasing your wheel size will decrease the driving force from your wheels which will culminate in a decrease in acceleration of said wheels. This can also affect your odometer and speedometer as larger tires will have a larger circumference, causing you to travel a little bit further per each complete tire rotation. This also will cause your odometer to register fewer miles than you are actually traveling. Electronic Speedometer Determine the distance of the test drive needed to recalibrate your speedometer.
Press and hold the calibration button on the speedometer, start the vehicle and release the button. Press the button again and drive the distance prescribed by the speedometer manufacturer. And the wider the tire the higher the rolling resistance is and the harder the engine has to work to move the tire , thus decreasing the car's fuel efficiency.
Larger tires can in fact, increase a vehicle's gas mileage if the vehicle is regularly traveling with consistent speeds over 60 miles per hour. Any reputable mechanic who records results properly and can produce a valid report may run a speedometer calibration on your vehicle.
Up-sizing or Down-sizing Up-sizing, or installing a taller tire, will lead to a speedometer reading that is slower than your actual speed. This is because a taller tire will have a larger overall circumference, which will cause it to travel more distance per revolution than the original equipment tire. For example, larger tires decrease your fuel economy because they are heavier, while smaller tires increase fuel efficiency.
Bigger tires also have a higher rolling resistance than smaller tires which means they require more resistance and effort to get them rolling. Divide your old tire diameter by your new tire diameter. Subtract from 1. If your vehicle odometer registers miles and it takes 16 gallons to fill…. If your wheel and tire package ends up being heavier, this will affect acceleration and fuel economy.
Acceleration will be less and so will fuel economy. Steering may also become heavier. Depending on the axle, the next lowest ratio from a 4. Because of the extra weight associated with off-road tires , we usually recommend going with a performance-minded gear ratio for any tire size above 35 inches. No speedometer can be percent accurate. But, if a car is modified, its speedometer may need to be recalibrated. Changing tire size is one of the most common things car owners do that can affect speedometer accuracy.
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