A few weeks ago while looking for a better motor for Liam’s go kart, I came across these electric dirtbikes on some forum. The idea of an electric dirtbike in my neighborhood seemed like a good plan. I have always wanted to get a dirtbike or enduro-style bike to ride around on. Two stroke bikes are loud and would annoy the neighbors really fast. With a little more research I found that a used Razor MX500 would be a cheap initial investment to get into the world of electric bikes. One weekend of searching craigslist allowed me to pick up (3) MX500’s for $175.
The first bike I picked up worked but the freewheel on the back was shot so the motor could not engage the back wheel. This freewheel seems to be the problem with the Razor dirtbikes. A new freewheel was like $12 from some scooter site. While waiting for it to arrive I decided to use the MIG to weld the freewheel solid. It might not be the best solution but it allowed me to be able to ride the bike for a quick test.
After the first test my first impressions were that the bike was kinda slow. Being that it was made for a rider less then 170lbs and I weigh 165lbs, I figured the bike was made for a smaller person. So we rolled the bike back into the garage and let it charge completely over night. The next morning I decided to try it before work, not thinking anything would be different. After a full charge the bike took off pretty fast, and reached a decent top speed. I need to check my max speed, but it definitively surprised me with its power and speed. The bike feels like an under-powered pit bike.
While searching for the first bike, I replied to a couple of different adds on craigslist. The first bike I got for $100 from some kid about 15mins away. He wanted $150 but asked if he would take $100 because I thought I would have to buy a new rear wheel; overall the bike was in decent condition. The second two bikes I got from one person way out by Eureka for $75. These bikes were a little rough with surface rust but looked like to good a deal to pass up. The add asked for $150 because only one of the bikes worked. Later he sent me an email saying he couldn’t get either running and would take $75 for the pair, so I agreed. We picked both bikes up and brought them back to the garage to see what was wrong. One bike just had a faulty brake cable that wouldn’t let the motor engage. Once the cable was fixed that bike worked fine. The batteries and the freewheel was also shot on the second bike. I also noticed later that the chain was also missing.
This whole time I was already researching how to make it more powerful. Various people have done extreme things to these little bikes. Stock the MX500 runs at 36V with a 500watt motor. I tried adding one battery from the second set of bikes to the first to make it 48V. It ran faster but I returned to 36V in fear of ruining the different sets of batteries. I really wasn’t too concerned about speed as I was the torque. The 500watt motor really did not have that much acceleration. I decided to try finding a bigger rear sprocket first instead of new batteries, motor, controller, etc. Currie makes a 90 tooth sprocket that would have to be modified for use on the MX500. Someone posted on a forum to have one custom cut for the bike. A company out of Ketucky, Rebel Gears custom cuts aluminum sprockets. So after a few calls I had a 95t and 100t sprocket on order for the MX500. It took almost two weeks but in the meantime I worked on modding the frame.
First I decided to cut the top battery tower support.
Then a flat piece of steel was welded to the rectangular tube.
Then the whole piece was welded to make it look like top battery tray was just extended.
I also began to weld extra steel rod around the back for looks. They still need more grinding to make them look better; I have only had the MIG welder for a few months.
I also decide to chop the handlebars and use and old MTB bar welded in place.
After all of the welding the rear sprockets finally arrived. After rigging some chain together the sprocket went together easily.
Below is a comparison with the new 100t on bottom and the stock rear sprocket on top. Its quite a bit bigger.
Here a few more pictures of the bike at its current state.
I the future I would like to get the frame powdered coated; I am not really of fan of the red. Tried painting the plastics with Krylon’s Fusion paint. I need to do a few more light coats, but it seems to work ok.
Next comes the 48V setup…….