On flat, stock bikes, the Kawasaki Z125 Pro generally reaches the higher top speed than the Honda Grom, with typical figures clustering in the low-to-mid 70 mph range for the Z125 and about 60–65 mph for the Grom. Real-world speeds vary with rider weight, wind, and any modifications.
Stock top speeds
Testers and manufacturer data for stock, unmodified bikes show the following typical top speeds on level ground with standard rider weight.
- Honda Grom (MSX125): roughly 60–65 mph (97–105 km/h) on a flat, level road with a rider around 170 lb.
- Kawasaki Z125 Pro: roughly 65–75 mph (105–120 km/h) on a flat, level road with a rider around 170 lb.
These figures reflect stock configurations. Real-world top speeds can differ based on market-specific tuning, weather, rider weight, and condition of the bike.
Technical context: power, weight and gearing
Although both bikes are built around 125cc engines, their power delivery and overall weight influence how quickly they reach their top speeds. The Grom is lighter and tends to have a lower peak power versus the Z125 Pro, which often pulls to a higher top speed in the same conditions. Gear ratios and final-drive setup also shape the actual speed attained at highway cruising RPMs.
Key considerations
Keeping this in mind helps explain why the Z125 Pro often edges out the Grom in top speed tests, while real-world performance can vary with small changes in equipment or posture.
Factors that affect top speed
Top speed is not fixed. Here are the major variables that can push the numbers up or down for both bikes.
- Rider weight and aerodynamics (position on the bike, gear, height)
- Gearing and final-drive ratio (affects acceleration and peak RPM at speed)
- Wind resistance and altitude (air density reduces power delivery)
- Engine condition and fuel quality (stock vs. tuned, octane, maintenance)
- Modifications (exhaust, intake, ECU remapping or fuel management)
- Tire selection and tire pressures (rolling resistance and grip)
In practice, a rider can notice noticeable differences between bikes in the same class, especially when swapping parts or riding in high wind conditions or at different altitudes.
Summary
Bottom line: In stock form, the Kawasaki Z125 Pro typically posts a higher top speed than the Honda Grom on flat ground, with common ranges clustered around the mid-60s to mid-70s mph for the Z125 and about 60–65 mph for the Grom. Real-world results are influenced by weight, wind, and modifications, so expect some overlap under certain conditions. Both bikes remain popular choices for urban riding and light highway use, delivering nimble handling in a small-engine package.