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Discussions Question and Answer Forums Razor Electric Scooter, Bike, and Go Kart Modification Forum

Faster Razor MX650 by changing engine sprocket

I'm would like to have a faster top speed by changing the 11-tooth engine sprocket with a 15 or 16-tooth sprocket.  That should speed up the bike about 30% more.  Any one has done this?.  Please comment.

With a higher gear ratio the Razor MX650 dirt bike's motor is capable of powering the bike to speeds faster than 17 MPH on flat ground however with an increase in gear ratio the torque at the rear wheel will be decreased so the bike will not be as good at climbing hills or traveling through loose dirt, grass, mud, or sand. If the bike is only used on flat and hard packed or paved ground then it should work however if the bike is used on uneven or hilly terrain or to go through loose material then it might not be that good of an idea.

You are absolutely right. The bike is used on paved mostly flat ground.  Do you have the specifications for the engine sprocket and where can I order it from?

The largest motor sprocket made for the MX650 motor has 13 teeth and is our item # SPR-2513C sold on this page: https://www.electricscooterparts.com/sprockets25chain-motor.html

Some of our customers have successfully installed 15 and 16 teeth plain bore sprockets on the type of motor that the MX650 has by drilling the sprocket's bore to 12mm and installing it on the motor shaft. We carry plain bore 15 and 16 tooth sprockets with 8mm bore that can be drilled out to 12mm. If going this route I recommend to drill dimples or file flat spots on the motor shaft where the set screws will make contact with it for a secure attachment. Or a small hole could be drilled all the way through the sprocket and motor shaft for a roll pin to go through for a very secure attachment.

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Thanks for the answer. I would like to know your recommendation for what is better and easier changing the front sprocket or the rear one? The rear sprocket is 80 teeth. Are there smaller sprocket that fits?  The other question is there a need to change the chain too when changing the front or the rear sprocket?  Thanks

Changing the motor sprocket to one that has a double-D bore and bolts right on is the easiest way to go. Changing the wheel sprocket is the second easiest way to go. And drilling and installing a plain bore sprocket onto the motor is the most difficult way to go.


Smaller than original wheel sprockets for freewheels are available on our wheel sprockets for #25 chain page and will fit since they are smaller, however, a shorter length of chain will then be needed since one of the sprockets is smaller. Changing to a smaller wheel sprocket may also affect how the chain tensioner works with the chain as the chain will then be in a slightly different position than it originally was.

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