Calculators for the bike you just found
After you pick a listing, check power-to-weight, sprockets, sag, and premix so the classified matches the bike in the dirt.
01 / Performance
Performance
Horsepower, torque, gearing, and how fast the bike actually goes.
Horsepower
Convert crank torque and RPM into horsepower and kilowatts. Use a dyno torque reading or a manufacturer peak-torque figure.
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Torque
Back-solve torque from horsepower and RPM. Useful when a spec sheet lists peak HP but not the matching torque figure.
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Power-to-Weight
Compare bikes the way they actually feel: horsepower against wet bike weight plus rider. Higher hp/lb (and W/kg) means a snappier chassis.
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Top Speed
Estimate gearing-limited top speed in high gear at a given RPM. This is the speed the sprockets and tire will allow — not a drag-strip prediction.
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0–60 Acceleration
A power-limited estimate of 0–60 mph time from horsepower, ready-to-ride weight, and drivetrain loss. Ignores wheelie, traction, and aero.
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Gear Ratio
Turn gearbox tooth counts (or published ratios) into overall ratio per gear, including primary and sprockets.
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Final Drive Ratio
Final drive is rear sprocket teeth divided by countershaft (front) sprocket teeth. This is the ratio you change with a sprocket swap.
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RPM
Find engine RPM at a given road speed from overall gearing and rear tire diameter.
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Speed vs RPM
Build a speed table for one gear across the rev range. Use it to see where a shift lands or how a sprocket change moves road speed.
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Wheel RPM
Rear-wheel revolutions per minute from road speed and tire diameter. Independent of engine gearing.
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02 / Gearing & Sprockets
Gearing & Sprockets
Swap sprockets, compare ratios, and size a chain before you cut it.
Sprocket
See how a front or rear sprocket change moves final drive, acceleration, and theoretical top speed.
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Front/Rear Sprocket Ratio
A clean ratio readout for any front and rear tooth combination, plus equivalent swaps that keep the same ratio.
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Gear Ratio Change
Compare an old sprocket pair to a new pair. Reports percent change, equivalent tooth moves, and how much taller or shorter the bike feels.
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Sprocket Size Comparison
Put two complete drivetrains side by side: tooth counts, final drive, and relative acceleration / top speed.
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Chain Length
Estimate chain links from sprocket sizes, center distance, and pitch (420 / 428 / 520 / 525). Rounds to an even link count.
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Gear Speed
Road speed in every gear at a chosen RPM. Enter up to six gearbox ratios the way the service manual lists them.
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Countershaft Sprocket
Changing the front sprocket is the fastest way to move gearing. See the equivalent rear-sprocket change and the percent effect.
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03 / Engine & Maintenance
Engine & Maintenance
Displacement, premix, valves, oil, and hour-based service intervals.
Engine Displacement
Swept volume from bore, stroke, and cylinder count. Output in cc, liters, and cubic inches.
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2-Stroke / 4-Stroke Displacement
Same swept volume math, plus a power-stroke comparison: a two-stroke fires every crank revolution, a four-stroke every other rev.
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Bore & Stroke
Solve the missing dimension. Leave bore at 0 to find bore from displacement and stroke, or stroke at 0 to find stroke from bore.
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Compression Ratio
Static CR from bore, stroke, head chamber, piston dome/dish, deck height, and head-gasket volume.
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Piston Displacement
Swept volume of one piston, plus mean piston speed at a chosen RPM. High mean piston speed is a durability red flag.
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Engine RPM
Engine speed from wheel speed when you already know final drive and the gear you are in. Tire diameter in inches.
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2-Stroke Premix Ratio
How much oil to pour for a given fuel volume and mix ratio. Works in gallons or liters, with common MX ratios on tap.
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Fuel-to-Oil Mix
Work backwards from oil already in the jug, or scale a mix to a larger can. Same math as premix, aimed at mixing benches.
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Valve Clearance
Shim-under-bucket math: new shim = old shim + (measured − spec). Too tight needs a thinner shim; too loose needs a thicker one.
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Oil Capacity
Look up a typical wet-sump fill for popular MX and enduro bikes, or enter a custom capacity. Includes a top-off from the dipstick/sight window.
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Spark Plug Gap
Convert plug gap between millimeters and inches, and compare against typical 2-stroke and 4-stroke dirt bike ranges.
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Engine Hours Maintenance
A practical MX / enduro service calendar from current hours and engine type. Intervals are conservative race-use numbers, not dealer marketing.
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04 / Suspension & Setup
Suspension & Setup
Sag, spring rate, travel, and ride height for race or trail.
Sag
Sag is how far the bike settles from fully extended. Measure from a fender mark to the axle with the bike on a stand, then on the ground.
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Race Sag
Race sag (rider sag) is measured with the rider in full gear, balanced on the pegs. Most MX bikes want about 100–108 mm on ~310 mm travel.
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Rider Sag
Front and rear rider sag together. Enter fender-to-axle (or a zip-tie on the fork stanchion) for each end.
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Static Sag
Static sag is bike-only, no rider. Too little static sag with correct race sag means the spring is too soft (you used a lot of preload). Too much static sag means the spring is too stiff.
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Spring Rate
Estimate fork and shock spring rates from rider weight, sag targets, and linkage leverage. A starting point for ordering springs — not a replacement for a tuner.
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Fork Spring Rate
Two fork springs share the front load. Convert between N/mm and lb/in, or size springs from rider weight and target sag.
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Shock Spring Rate
Size a rear shock spring from rider weight, target sag, and linkage leverage. Convert N/mm ↔ lb/in.
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Suspension Travel
How much wheel travel is left after sag, and how a zip-tie on the fork relates to percent used.
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Ride Height
Front vs rear ride height from fender-to-ground or axle-to-fender measurements. Use it after sag so the bike is not kicking or pushing.
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Suspension Setup
One worksheet: race sag, static sag, suggested spring direction, and a starting clicker map from rider weight.
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05 / Fuel & Range
Fuel & Range
How far a tank goes, what a ride costs, and two-stroke mix on the truck.
Fuel Consumption
MPG, L/100 km, and gallons per hour from fuel used, distance, and hours on the bike.
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Fuel Range
How far the remaining fuel will take you from tank size, current fill, and economy.
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Fuel Cost per Hour
What an hour on the bike costs in pump gas (and premix oil, if you run a two-stroke).
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Fuel Cost per Ride
Price a moto, trail loop, or haul to the track from hours or miles, plus pump price.
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Tank Range
Full-tank distance and time from capacity and either mpg or gallons per hour.
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2-Stroke Premix Fuel
Mix a whole jerry can or a tank: pick ratio, fuel volume, and get oil in ounces, milliliters, and a marked mixing-bottle line.
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06 / Racing & Riding
Racing & Riding
Lap times, race fuel, jump distance, and hill-climb math.
Lap Time
Average lap from a session, or lap time from track length and speed. Accepts seconds or m:ss.s.
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Average Speed
Average speed from distance and time. Time can be minutes, or a lap in seconds.
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Race Fuel
Fuel to put in for a moto or enduro loop: duration × burn rate × safety margin, capped by tank size.
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Race Distance
Total race distance from laps × track length, or laps remaining from a time limit and average lap.
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Riding Time
How long a loop takes at a given average speed, with an optional rest factor for trail days.
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Jump Distance
Projectile-motion estimate of jump distance from takeoff speed, lip angle, and landing-height difference.
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Jump Takeoff Speed
The other way around: what speed you need at the lip to cover a known jump face-to-face distance.
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Hill Climb
Grade, climb angle, vertical gain, and a rough power figure to hold a speed on the hill (no wheelspin assumed).
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07 / Tire & Wheel
Tire & Wheel
Diameter, circumference, pressure, and size-to-size comparisons.
Tire Size
Decode a size like 80/100-21 or 110/90-19 into diameter, sidewall, and circumference.
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Tire Diameter
Overall diameter from a metric dirt-bike size, with a second path if you already measured the tire on the bike.
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Tire Circumference
Rolling circumference from diameter or from a metric size. This is the number a speedometer calibration cares about.
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Tire Wheel RPM
Wheel RPM and distance per revolution from speed and tire diameter — the tire-side version of the performance wheel-RPM tool.
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Tire Pressure
A starting PSI/bar map from rider weight and terrain. MX pressures are low on purpose — this is not a street-tire load table.
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Tire Size Comparison
Two dirt-bike sizes side by side: diameter change, speedometer error, and the gearing change it feels like.
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59 calculators indexed