One of the modification category in automotive field is a speed offroad type. Speed offroad is a kind of race with characteristic in speed competition based on limited time, for speed offroad competitions conducted on the track not on the street in general. The main component component of the differential on Suzuki Katana is : drive pinion, pinion shaft, side gear, differential pinion, ring gear and differential carrier, adjusting, oil seal and the rear wheel axle shaft. The working of the differential on Suzuki Katana is the crankshaft rotation of the engine through transmission by the propeller shaft is minimized in accordance with the power that continues the drive pinion the ring gear, otherwise the moment increases and the transmission to the direction of origin. The differential work process can be disrupted if there is an operational disruption to the component. This can be identified damage checks that occur. Disturbances that often occur in the differential is usually by component-components that have been damaged among others. The objective why the differential is turned off is to add the responsive of back wheels spin to help the machine upgrade to be more responsive. The results of the axle engine performance aperture becomes increased when done dynotest because it is done pantek gardan.