Calculation results
Results update in the browser and are recalculated by PHP after submission.
| Measurement | Current front | New front | Front difference | Current rear | New rear | Rear difference |
|---|---|---|---|---|---|---|
| Nominal width | 120.0 mm | 120.0 mm | 0.0 mm | 180.0 mm | 190.0 mm | 10.0 mm |
| Sidewall height | 84.0 mm | 84.0 mm | 0.0 mm | 99.0 mm | 104.5 mm | 5.5 mm |
| Overall diameter | 599.8 mm | 599.8 mm | 0.00% | 629.8 mm | 640.8 mm | 1.75% |
| Rolling circumference | 1,884.3 mm | 1,884.3 mm | 0.00% | 1,978.6 mm | 2,013.1 mm | 1.75% |
| Revolutions per mile | 854.1 | 854.1 | 0.00% | 813.4 | 799.4 | -1.72% |
| Revolutions per kilometer | 530.7 | 530.7 | — | 505.4 | 496.7 | — |
| Axle height change | 0.0 mm | 5.5 mm | ||||
| Indicated | Estimated actual | Difference |
|---|
Estimated rim-width range
| Position | Selected | Estimated range | Ideal estimate | Status |
|---|---|---|---|---|
| Front | 3.50 in | 2.50–3.50 in | 3.00 in | |
| Rear | 6.00 in | 5.00–6.00 in | 5.50 in |
Estimated remaining clearance
| Location | Remaining | Status |
|---|---|---|
| Front side | 18.0 mm | Acceptable estimate |
| Front vertical | 27.0 mm | Acceptable estimate |
| Rear side | 9.0 mm | Limited clearance |
| Rear vertical | 17.5 mm | Acceptable estimate |
| Chain side | 7.0 mm | Limited clearance |
| Swingarm | 10.0 mm | Limited clearance |
| Fender | 19.5 mm | Acceptable estimate |
| Position | Estimated static load | Tire capacity | Usage | Margin |
|---|---|---|---|---|
| Front | 150.0 kg | 236 kg | 63.6% | 86.0 kg |
| Rear | 150.0 kg | 387 kg | 38.8% | 237.0 kg |
Pressure conversion
| Position | psi | bar | kPa |
|---|---|---|---|
| Front cold | 36.0 | 2.48 | 248 |
| Rear cold | 42.0 | 2.90 | 290 |
| Compatibility check | Result |
|---|---|
| Proposed construction pairing | |
| Tube and rim systems | |
| Front speed rating | |
| Rear speed rating |
Scaled tire visualization
Gray outlines show current sizes. Blue outlines show proposed sizes.
Saved comparisons
Saved locally inside this browser.
Formula used
Core formulas behind dimensional and rotational estimates.
Tire geometry
Sidewall height: width × aspect ratio ÷ 100.
Overall diameter: rim inches × 25.4 + two sidewalls.
Circumference: π × overall diameter.
Revolutions per mile: 1,609,344 ÷ circumference millimeters.
Revolutions per kilometer: 1,000,000 ÷ circumference millimeters.
Speed and gearing
Actual speed: indicated speed × new circumference ÷ current circumference.
Actual distance: displayed distance × new circumference ÷ current circumference.
New RPM: reference RPM × old circumference ÷ new circumference.
Final drive: rear sprocket teeth ÷ front sprocket teeth.
Axle change: new radius minus current radius.
How to use this calculator
Use verified measurements wherever possible.
- Select a general preset or keep custom values.
- Enter current front and rear tire markings.
- Enter proposed front and rear tire markings.
- Add manufacturer diameter or measured circumference.
- Enter actual rim widths and rating symbols.
- Measure chain, swingarm, fork, and fender clearances.
- Add rider, passenger, cargo, pressures, and gearing.
- Review dimensional, gearing, load, and electronics results.
- Export the report for professional review.
- Confirm final fitment before mounting any tire.
Detailed tire selection guide
Practical explanations for every major comparison category.
Understanding nominal tire width
The first number in a metric motorcycle tire marking is nominal section width. It is not a promise of exact mounted width. Tire design, measuring rim, inflation pressure, and manufacturing tolerances influence the measured result.
Understanding aspect ratio
The aspect ratio is sidewall height expressed as a width percentage. A 55-series sidewall is approximately fifty-five percent of nominal width. Actual profile shape still depends on tire construction and rim width.
Rim diameter requirements
The rim diameter identifies the bead-seat diameter in inches. Tire and wheel bead-seat diameters must match exactly. Similar-looking overall diameters cannot compensate for an incorrect bead-seat diameter.
Radial and bias construction
Radial and bias-ply tires use different carcass arrangements. Their flex behavior, heat response, and profile characteristics can differ. Only use mixed construction when the motorcycle or tire manufacturer approves it.
Rim width and tire profile
A narrow rim can pinch the tire profile. A wide rim can flatten the crown. Either condition can change steering feel, footprint shape, measured width, and available edge clearance.
Speedometer effects
A larger rear rolling circumference travels farther per revolution. Wheel-based speed calculations can therefore indicate a lower value than actual road speed. Factory display bias must also be considered.
Odometer effects
Odometer distance can change with rolling circumference. A larger circumference may cause actual distance to exceed displayed distance. Corrected distance can improve fuel-economy and service-interval calculations.
Effective gearing
Rear circumference acts like a small gearing change. A larger tire generally produces taller effective gearing and lower engine RPM at equal road speed. A smaller tire generally produces shorter effective gearing.
Sprocket equivalence
The calculator estimates a sprocket equivalent for comparison. It does not model chain length, axle position, or full drivetrain losses. Use exact sprocket and chain calculations before modifying hardware.
Ground clearance
Changing tire radius changes axle height. Front and rear changes can affect ground clearance differently. Suspension sag and loaded tire deformation can reduce the static change.
Seat height
Rear and front radius changes may influence seat height. The relationship is not one-to-one because chassis geometry and suspension position intervene. Treat any seat-height figure as an estimate.
Rake and trail
Unequal front and rear radius changes alter chassis pitch. That pitch can influence rake and trail. Precise geometry requires steering-head angle, fork offset, tire radius, suspension position, and wheelbase.
ABS ratios
Many motorcycles compare front and rear wheel speeds. A changed tire pair can alter the normal ratio. Some systems tolerate variation, while others may flag faults or intervene unexpectedly.
Traction control
Traction-control logic may use wheel-speed differences and learned tire behavior. Diameter changes can affect those signals. Manufacturer-approved size combinations remain the safest reference.
Load index
Load index maps to a standardized maximum capacity under specified conditions. It does not replace motorcycle gross vehicle weight or axle ratings. Tire load capacity must exceed realistic dynamic demands.
Speed symbol
A speed symbol represents a controlled test category. It is not a safe riding recommendation. Vehicle limits, tire condition, inflation, load, temperature, and local law remain controlling factors.
Passenger and luggage
Passenger and cargo mass often increase rear loading disproportionately. Simple static distribution is only a screening estimate. Use motorcycle payload limits and axle ratings for final decisions.
Cold inflation pressure
Recommended street pressure is normally specified cold. Pressure rises during use as the tire warms. This calculator converts units and compares entered values but does not prescribe pressure.
Hot pressure rise
Hot pressure rise can indicate changing tire temperature and load conditions. A universal percentage target is inappropriate across all motorcycles and uses. Follow the tire and motorcycle maker’s guidance.
Clearance measurement
Clearance must be checked around forks, swingarm, chain, belt, shaft housing, fenders, brakes, and exhaust components. Measure both sides. Include manufacturing variation and wheel alignment.
Dynamic clearance
A tire moves under suspension compression, acceleration, braking, cornering, and wheel flex. Static garage measurements can miss dynamic interference. Consider full suspension travel and steering movement.
Tire growth
Some tires increase diameter slightly at speed. The amount varies with construction, pressure, temperature, and speed. Use manufacturer data when tire growth is important.
Off-road knobs
Knobby tread can add meaningful effective height and width. Mud and stones require extra clearance. Worn and new tread dimensions can differ enough to affect packaging.
Chain adjustment
Rear axle movement changes proximity to swingarm structures and fenders. A tire fitting at one chain adjustment position may rub elsewhere. Check the complete allowed adjustment range.
Actual circumference
Measured rolling circumference often improves calibration estimates. Mark the tire and ground, load the motorcycle consistently, and measure several revolutions. Manufacturer rolling data is preferable when available.
Tire wear
Tread wear gradually reduces diameter. Speed and gearing differences therefore change slightly through tire life. Large knobby tires can show more variation than shallow street patterns.
Front and rear balance
Changing only one tire diameter alters chassis stance and wheel-speed ratio. Changing both can preserve one relationship while disturbing another. Evaluate the pair rather than one tire alone.
Wider tire myths
A wider tire does not automatically provide more useful grip. Compound, construction, temperature, pressure, profile, load, and suspension setup also matter. Excess width can slow steering or create poor profile.
Narrower alternatives
A narrower approved tire may improve agility or clearance. It can also reduce load capacity or alter rim profile. Approval and rating checks remain essential.
Manufacturer variation
Two tires carrying the same nominal code can measure differently. Published specification sheets often list width, diameter, and measuring rim. Use those figures whenever possible.
Legal considerations
Approved tire sizes and rating rules vary by jurisdiction. Inspection, insurance, and registration requirements may apply. Confirm local requirements before using a non-standard size.
Professional inspection
A qualified motorcycle technician can inspect the wheel, valve, tube, bead, clearances, alignment, and electronic-system implications. Calculators cannot physically inspect these conditions.
Frequently asked questions
Important fitment questions and concise answers.
Can I install any tire with the same rim diameter?
No. Rim width, ratings, clearance, construction, and vehicle approval also matter.
Is a wider motorcycle tire always better?
No. It can change profile, steering response, weight, and clearance.
Why do identical size codes measure differently?
Manufacturers use different molds, carcasses, tread shapes, and measuring rims.
Does rear tire diameter change RPM?
Yes. Circumference changes effective gearing at a given road speed.
Will a tire swap change the speedometer?
It can when speed is calculated from wheel rotation.
Can tire size affect ABS?
Yes. Front-to-rear wheel-speed ratios can move outside expected ranges.
Can radial and bias-ply tires be mixed?
Only when the relevant manufacturers explicitly approve the combination.
Should measured circumference be used?
Yes, when measured carefully or supplied by the tire manufacturer.
How much clearance is enough?
There is no universal value. Dynamic conditions and manufacturer requirements control.
Does load index include passengers?
The tire carries part of total load, but vehicle axle limits still apply.
Can this calculator guarantee fitment?
No. It cannot inspect the motorcycle or authorize a tire substitution.
Can I use a tube inside a tubeless tire?
Only when the tire, rim, tube, and motorcycle guidance permit it.
Does tire pressure change size?
Yes. Pressure and load can alter operating radius and measured shape.
Does tread wear affect calculations?
Yes. Worn tread reduces diameter and rolling circumference.
Should I trust alpha-size conversion exactly?
No. Alpha conversions are approximate and must be checked against specific tire data.
Safety notice
All calculations are estimates. Final selection must follow the motorcycle manual, tire manufacturer data, wheel specifications, legal requirements, and qualified professional inspection.