Calculate top speed, gear ratios, and horsepower estimates for CT70, Z50, and clone engine builds.
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.
| 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 |
| 108/117cc Stroker, regeared (17/33) | 17/33 | ~55 MPH | ~61 MPH |
| 125cc Clone Swap (17/35) | 17/35 | — | ~56 MPH |
| 140cc Swap (16/34) | 16/34 | ~52 MPH | ~59 MPH |
| 190cc ZS (17/32) | 17/32 | ~58 MPH | ~66 MPH |
— = not applicable. Lifan/YX 125cc swaps are 4-speed only, no 3-speed semi-auto option. 125cc figure is a real-world rider-aboard test result (17/35 gearing), not a calculated estimate. The regeared 108/117cc row (17/33) reflects riders swapping to a smaller rear / larger front sprocket to use the extra torque for higher cruising speed, per community reports — the stock-gearing row above it (15/34) is the more conservative baseline.