Four Motorcycling
Motorcycle gearing, fuel range, and speed in gear
Enter sprocket teeth, a tank size, or a tire stamp. The calculator returns a final-drive ratio, miles of range, or estimated MPH in each gear.
All tools
Motorcycle Gearing Calculator
Front and rear teeth, plus an optional stock pair, become a final-drive ratio and a percent change.
Speed in gear
RPM, primary ratio, gearbox ratios, sprockets, and a tire size become MPH in each gear.
Fuel range
US gallons and MPG return miles to empty, with an optional reserve field.
RPM at speed
The inverse of speed in gear: enter MPH and one gear to estimate engine RPM.
Engine displacement
Bore, stroke, and cylinders become cubic centimeters and cubic inches.
Sprocket Calculator
Two sprocket pairs, a percent change, and the MPH difference at the same RPM.
Tire size
A motorcycle size such as 180/55-17 becomes an estimated circumference.
Chain length
Pitch, sprocket teeth, and center-to-center distance become an even link count.
Trip fuel
Distance divided by MPG, in US gallons.
Guides
Final drive and cruising RPM
What a shorter or taller sprocket pair does to launch and to highway RPM.
How to read a motorcycle tire size
Width, aspect ratio, and rim diameter, and how this site turns them into circumference.
US MPG on this site
Why the default gallon is the US gallon, and how the metric switch reports km/L.
Why speed in gear is an estimate
Slip, tire growth, and the difference between a model and a GPS reading.
Questions riders ask first
Where does the tire circumference come from?
If you enter a motorcycle size such as 180/55-17, the calculator treats the first number as width in millimeters, the second as sidewall height as a percent of width, and the last as rim diameter in inches. Overall diameter is the rim plus two sidewalls. Circumference is π times that diameter. You can also type a measured circumference in inches on the speed-in-gear page.
What is the difference between primary ratio and the sprockets?
Primary reduction sits between the crankshaft and the gearbox. The sprockets are the final drive: rear teeth divided by front teeth. Overall reduction is primary × the gearbox ratio for that gear × final drive. The speed table needs all three.
Which gallon does the fuel calculator use?
The default is the US gallon, 3.785 liters. If you switch the page to metric, you enter liters and kilometers per liter instead.
Why is there no ready-made gearbox for my motorcycle?
Gearbox ratios vary by year, market, and even by a later-service sprocket change. The reliable source is the number stamped on the bike or printed in the manual you already have. You enter those numbers here.
Does the speedometer show the same figure as speed in gear?
No. The table is a kinematic model from RPM, ratios, and circumference. A speedometer may be calibrated to a different tire, and a GPS reading includes slip and lean. Use the table to compare gearing, not to replace a road measurement.
Can I run the tools without a network after the first load?
Yes. The formulas run in the browser. Once the HTML, CSS, and JavaScript have loaded, the fields keep working offline.
Do the tools remember the sprockets I entered?
Yes, in this browser only. Front and rear teeth, the tire size, the primary ratio, and the fuel figures stay on the device so you can move from final drive to the speed table without typing them again.