Outer edge movement
+22.7 mm
Toward the fenderThe wheel's outer edge moves 22.7 mm toward the fender.
Wheel & Tire Fitment Calculator
Enter your current and proposed wheel and tire sizes. See how far each wheel edge moves, how the tire diameter changes, and what that does to ride height and speedometer reading.
Compare your setups
Current setup
Baseline, dashed225/45R17 17x7.5 ET+45
Advanced input optionsSize parsing · measured width
225/45R17, 225 45 17 or 225-45-17. Fills the tire fields only.
Diameter x width, such as 18x8.5. Does not change the tire.
Signed millimetres or ET notation. Apply updates Offset ET.
3 to 24 in, step 0.5. Arrow keys adjust; Shift for larger steps.
Optional. Measure including flanges; backspacing needs it.
Proposed setup
Compared, solid245/40R18 18x8.5 ET+35
Advanced input optionsSize parsing · measured width
225/45R17, 225 45 17 or 225-45-17. Fills the tire fields only.
Diameter x width, such as 18x8.5. Does not change the tire.
Signed millimetres or ET notation. Apply updates Offset ET.
3 to 24 in, step 0.5. Arrow keys adjust; Shift for larger steps.
Optional. Measure including flanges; backspacing needs it.
Comparison updated. Outer edge movement +22.7 mm, toward the fender; inner clearance change −2.7 mm, less clearance; tire diameter +2.98%.
Comparison summary
Compared with your current setup, the proposed wheel moves 22.7 mm farther outward and leaves 2.7 mm less inner clearance. Its nominal tire diameter is 2.98% larger.
Geometry only—not a vehicle-specific fitment verdict.
Key changes
Inner clearance change
−2.7 mm
Less clearanceThe inner wheel edge leaves about 2.7 mm less clearance.
Tire diameter change
+2.98%
TallerThe proposed tire is 18.9 mm taller.
Ride-height change
+9.5 mm
HigherThe axle sits about 9.5 mm higher before tire deflection.
Speedometer effect
103.0 km/h
Higher actual speedIndicated 100.0 km/h → estimated actual 103.0 km/h.
Visual comparison
Detailed measurements
Tire geometry
Swipe to view more, if needed
| Measure | Current | Proposed | Change |
|---|---|---|---|
| Tire width | 225.0 mm | 245.0 mm | +20.0 mm |
| Sidewall height | 101.3 mm | 98.0 mm | −3.3 mm |
| Overall diameter | 634.3 mm | 653.2 mm | +18.9 mm (+2.98%) |
| Circumference | 1992.7 mm | 2052.1 mm | +59.4 mm |
| Tire envelope, inner side Nominal width centred on wheel; position from mounting plane | 157.5 mm | 157.5 mm | 0.0 mm |
| Tire envelope, outer side | 67.5 mm | 87.5 mm | +20.0 mm |
Wheel geometry
Swipe to view more, if needed
| Measure | Current | Proposed | Change |
|---|---|---|---|
| Wheel width (nominal) | 190.5 mm | 215.9 mm | +25.4 mm |
| Offset (ET) | 45.0 mm | 35.0 mm | −10.0 mm |
| Spacer | 0.0 mm | 0.0 mm | 0.0 mm |
| Effective offset Offset minus spacer | 45.0 mm | 35.0 mm | −10.0 mm |
| Inner wheel edge Bead-seat extent toward suspension | 140.3 mm | 143.0 mm | +2.7 mm |
| Outer wheel edge Bead-seat extent toward fender; change also describes nominal outer poke | 50.3 mm | 73.0 mm | +22.7 mm |
| Inner clearance change Positive means more space | n/a | n/a | −2.7 mm |
| Backspacing Mechanical, original offset; needs measured overall width | n/a | n/a | Needs both widths |
| Effective backspacing Includes spacer | n/a | n/a | Needs both widths |
| Track width (axle centreline) Assumes the same change on both sides of one axle | n/a | n/a | +20.0 mm |
Speed and revolutions
Swipe to view more, if needed
| Measure | Current | Proposed | Change |
|---|---|---|---|
| Revolutions per km | 501.8 | 487.3 | −14.5 |
| Revolutions per mile | 807.6 | 784.2 | −23.4 |
| Actual speed at indicated 100.0 km/h | 100.0 km/h | 103.0 km/h | +2.98% |
This comparison describes dimensional changes from nominal sizes. Real compatibility also depends on suspension, brakes, steering, fenders, hub bore, load ratings, alignment, vehicle modifications and the tire maker's published dimensions.
Speedometer and diameter explained
Overall tire diameter
Rim diameter plus two sidewalls. The calculator shows the change in millimetres and as a percentage of the current diameter.
Ride height
Half the diameter change, the theoretical shift of axle height with all else equal. Real tires deflect under load and vary by manufacturer, so treat it as an estimate.
Speedometer difference
A larger tire covers more road per revolution. If the gauge was accurate on the current tire, actual speed at a given indication scales with the diameter ratio. Choose a reference speed in either unit to see a concrete number.
Example fitment comparison
Current 225/45R17, 17x7.5 ET45 against proposed 245/40R18, 18x8.5 ET35. Every value below is computed by the same engine the calculator uses.
Swipe to view more, if needed
| Measure | Current | Proposed | Change |
|---|---|---|---|
| Sidewall height | 101.3 mm | 98.0 mm | −3.3 mm |
| Overall diameter | 634.3 mm | 653.2 mm | +18.9 mm (+2.98%) |
| Revolutions per km | 501.8 | 487.3 | −14.5 |
| Inner wheel edge | 140.3 mm | 143.0 mm | +2.7 mm |
| Outer wheel edge | 50.3 mm | 73.0 mm | +22.7 mm |
Compared with your current setup, the proposed wheel moves 22.7 mm farther outward and leaves 2.7 mm less inner clearance. Its nominal tire diameter is 2.98% larger.
How to compare wheel and tire fitment
- Enter the tire size on the placard or sidewall of your current tires, either field by field or pasted as 225/45R17.
- Enter the current wheel diameter, nominal width and offset. Add a spacer thickness if one is fitted.
- Fill in the proposed setup the same way. Use Copy current to proposed to change one value at a time.
- Read the five key changes, then check the visual comparison and the detailed tables.
Every change is proposed minus current. Results stay hidden until every required field holds a complete number in range, so a half-typed value never produces a misleading answer.
Understanding your fitment results
Outer wheel position
How far the outer bead-seat edge of the wheel moves toward the fender, measured from the hub mounting plane. A positive number means the wheel sits farther outward. Tire shape and wheel lip design change what you actually see from outside, so this is a reference for comparison, not a poke measurement.
Inner clearance
The inner edge moves toward the suspension when the inner position grows. Clearance is the opposite: more inner position means less relative space. Brakes, struts and arms sit differently on every vehicle, so measure on the car.
How wheel width and offset work together
Offset is the distance from the mounting face to the wheel centreline. Width spreads the wheel equally either side of that centreline. A wider wheel at the same offset therefore grows both inward and outward by half the width difference. Lowering the offset, or adding a spacer, moves the whole wheel outward. In practice most changes combine both, which is why the calculator reports the two edges separately.
How tire size affects fitment
Tire width in millimetres sets the nominal envelope either side of the wheel centre. Aspect ratio is sidewall height as a percentage of that width. Raising the rim diameter while lowering the aspect ratio often keeps overall diameter close, but the wider tire still moves its envelope. The tire envelope is shown separately from the wheel edges because a tire is not a rectangle and manufacturers differ from nominal.
How the calculations work
- Sidewall height = tire width x aspect ratio / 100.
- Overall diameter = wheel diameter x 25.4 + 2 x sidewall height.
- Circumference = pi x diameter. Revolutions per km = 1,000,000 / circumference in mm; per mile = 1,609,344 / circumference in mm.
- Effective offset = offset minus spacer thickness.
- Inner edge = half wheel width + effective offset. Outer edge = half wheel width − effective offset, both from the mounting plane.
- Inner clearance change is the negative of the inner position change. Track width change assumes the same swap on both sides of one axle.
- Backspacing appears only when you enter a measured overall width including flanges. Nominal width is not substituted.
Calculations run in metric with full precision and are rounded only for display. Imperial output is a conversion, not a second formula set. See the calculation methodology and testing and accuracy pages.
Important limitations
This comparison describes dimensional changes. It does not say a setup fits, is safe, or will work on your vehicle.
Real compatibility can depend on suspension, brakes, steering, fenders, hub bore, wheel and tire load ratings, alignment, vehicle modifications and the tire manufacturer's actual dimensions. Verify with a qualified fitter before buying.