The calculation, without hidden assumptions
Engine RPM reaches the road through two reductions—the selected transmission gear and final drive—then through tire circumference. This owner solves either road speed or engine RPM and keeps the combined ratio visible, making it useful for cruise checks and drivetrain comparisons without pretending to predict real top speed.
How to use this calculator
Enter the selected transmission gear ratio, final drive and loaded tire diameter.
Choose whether to solve road speed from RPM or RPM from road speed.
Treat the result as geometric drivetrain speed and compare scenarios rather than as a guaranteed vehicle top speed.
Where people use it
- •Estimating highway cruise RPM
- •Comparing final-drive changes
- •Checking theoretical speed at a shift RPM
Example: 0.80 top gear with a 3.55 axle
The combined reduction is 2.84:1. With the same tire, changing either the transmission ratio or axle ratio changes engine RPM at every road speed in direct proportion.
What the result does not assume
- •The 336 formula is a conventional inch/mph approximation. Tire loaded radius and real rolling circumference can differ from nominal diameter.
- •Converter or clutch slip, wheelspin, tire growth, aerodynamic drag and engine power are excluded, so calculated speed is not a guaranteed achievable top speed.
Frequently asked questions
What is overall gear ratio?+
For this calculation it is the selected transmission gear ratio multiplied by the final-drive or axle ratio.
Do larger tires lower cruise RPM?+
For unchanged gearing and road speed, a larger rolling diameter generally lowers engine RPM.
Can this predict top speed?+
It predicts geometric speed at an RPM. Real top speed may be lower because of power, drag, traction or rev limits.
Semantic next steps
Continue the calculation
These links move to a different input, formula or project stage rather than a keyword variation of this page.
Tire Size Calculator — Compare Diameter, Clearance & Speedometer Error
Compare two P-metric tire sizes side by side for sidewall, diameter, circumference, axle clearance and theoretical speedometer error.
OpenRatio Calculator
Simplify integer or decimal ratios, solve a missing proportion value, scale a ratio, and split a total into proportional shares with visible working.
OpenSpeed Converter
Convert nonnegative speed between meters per second, kilometers per hour, miles per hour, knots and feet per second.
OpenDew Point Calculator — °C/°F, RH & Reverse Solve
Calculate dew point, relative humidity or air temperature with the Alduchov–Eskridge Magnus approximation. Work in °C or °F and inspect dew-point depression, vapor pressure, reverse solving and humidity scenarios.
OpenHeat Index Calculator — NWS Feels-Like Temperature
Calculate feels-like temperature with the full NWS heat-index decision procedure: simple screening formula, Rothfusz regression when applicable, and the official low/high-humidity adjustments. Results show °C and °F, method branch, adjustment and heat-category context.
OpenWind Chill Calculator — NWS Formula, °C/°F & Wind Units
Calculate NWS wind chill from air temperature and wind speed with °C/°F plus mph, km/h, m/s or knots. The calculator enforces the official weather-use range and shows substituted working and wind-speed scenarios.
OpenDensity Calculator — Solve Density, Mass or Volume + Units
Solve density, mass or volume from any two known values with SI, metric and US customary units. See equivalent density units, specific gravity and substituted working.
OpenMolarity Calculator — Concentration, Moles, Mass or Volume
Solve amount concentration (molarity), moles, solute mass or final solution volume. Supports M, mM and µM plus mass-based calculations using molar mass.
OpenMore in this calculator collection
Browse nearby calculators in the same topic cluster so related pages reinforce each other instead of sitting as isolated URLs.
Free publisher widget
Put this calculator on your website
Give readers the live calculator without rebuilding the math. Copy the responsive embed in one click, or customize width, height, border and corner radius before publishing. The branded MAXScanner attribution stays visible.
Calculator embed HTML
Paste this code into your page. Focus the code box to select it manually.
Keep the result connected to the real job
MAXScanner keeps the formula and assumptions beside the result so you can verify the number before using it in a drawing, estimate, specification, worksheet or document. Where a supplier, manufacturer, drawing or applicable standard owns a requirement, that source remains authoritative.