WheelTryOn

Tire size calculator.

Compare two tire sizes side by side. See the diameter difference, sidewall height and how far off your speedometer will be.

Current setup

Current setup

225/45R18, 18x8 ET45

New setup

New setup

245/40R19, 19x9 ET35

CurrentNewDifference
Overall diameter660 mm (25.97")679 mm (26.72")+2.86%within the usual ±3% rule
Sidewall height101 mm98 mm−3 mm
Tread width225 mm245 mm+20 mm
Revolutions per mile777755-22
Speedometer shows 60 mph60.0 mph61.7 mph+1.7 mphyour actual speed with the new size
Ride height (axle)+9.4 mm
Outer lip (poke)69 mm92 mm+22.7 mmsits further out toward the fender
Inner edge (clearance)159 mm162 mm+2.7 mmcloser to the suspension and brakes
Backspacing6.27"6.38"0.11"

A 245 mm tire usually suits a 7–9" wide wheel (about 8" is ideal). Your 9" wheel is in range.

hub facestrutfenderbrake+22.7 mmouter lipcheck fender clearance+2.7 mminner edgecheck strut clearance
CurrentNewLooking at the wheel from the front of the car, to scale. Car side on the left, street on the right. The strut and fender are a mock-up placed around your current setup; the change between the two is what's real.
See the new wheels on your car

Calculated from the sizes you enter; real tires vary by brand and model. Clearance also depends on your car's suspension, brakes, ride height and fender shape, so treat this as a guide and confirm fitment with your wheel and tire seller.

Common plus-size swaps

Bigger wheel, shorter sidewall, almost the same overall diameter. Tap one to load it into the calculator.

Tire size questions.

How do I read a tire size like 245/40R19?

245 is the tread width in millimeters, 40 is the sidewall height as a percentage of that width (the aspect ratio), R means radial construction, and 19 is the wheel diameter in inches.

How much can the overall diameter change?

A common rule of thumb is to stay within about 3% of the original diameter. Bigger changes affect the speedometer, odometer, ABS and traction control calibration, and gearing.

Why does my speedometer read wrong with bigger tires?

The speedometer counts wheel revolutions. A taller tire travels further per revolution, so you're going faster than the speedometer shows. The calculator shows your real speed when the speedometer reads 60 mph.

What is plus sizing?

Going up in wheel diameter while lowering the sidewall so the overall diameter stays about the same, for example 225/45R18 to 245/40R19. You get a bigger wheel and a sharper look without upsetting the speedometer.

What wheel width suits my tire?

As a rough guide, a tire fits rims from about 75% to 95% of its tread width (in inches), with around 85% ideal. Tire makers publish the exact approved range for each size, so check that before you buy.

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