⚡ Speed & HP Calculator

Calculate top speed, gear ratios, and horsepower estimates for CT70, Z50, and clone engine builds.

Top Speed Calculator

MPH = (RPM × π × Tire Diameter) ÷ (Primary × Gear Ratio × Sprocket Ratio × 1056)

Engine RPM (peak)

Front Sprocket (teeth)

Rear Sprocket (teeth)

Tire Diameter (inches)

Transmission

— Estimated Top Speed (MPH)

⚠️ Safety Warning

CT70 and Z50 frames and drum brakes were designed for 30 MPH. If your build targets 45+ MPH you MUST upgrade brake shoes and tires before riding. Speed kills on bikes with stock brakes.

Horsepower Estimator

Engine Build

Carb & Exhaust Upgrade

— Estimated Horsepower

— Estimated Torque (ft-lb)

Quick Reference — Speed by Build

Setup	Gearing	3-Speed Top	4-Speed Top
Stock 49cc Z50	14/37	~28 MPH	~32 MPH
Stock 72cc CT70	15/35	~38 MPH	~44 MPH
88cc Kit (15/35)	15/35	~42 MPH	~48 MPH
108cc Stroker (15/34)	15/34	~48 MPH	~54 MPH
140cc Swap (16/34)	16/34	~52 MPH	~59 MPH
190cc ZS (17/32)	17/32	~58 MPH	~66 MPH