Razor SX500 VS MX500**
While these Razor bike platforms are very similar and often lumped together in conversation, the stock chassis bikes do actually have quite a few differences. The Razor SX500 is certainty our preferred model, but that is not to say that the MX500 doesn't have its own strengths!.
Frame:
The Razor SX500 frame cavity is much larger, allowing for easier placement of larger battery and controller. The MX500 frame top tube has a pretty aggressive downward slope, and this is what shrinks the battery cavity. This sloped top tube also puts the rear shock bracket in a location that can easily impede on larger battery placement. (Silver = SX500, Red = MX500 in photos)
Swing Arm/Shock:
Both swingarms are the same length from frame bolt to rear axle bolt (14.5”), but the geometry is different. You can physically swap them, but it would likely be more of a detriment because the frame and swingarm geometry would be mis-matched. The MX500 has a slight advantage here because the swingarm has 2 mounting holes, which allows you to slightly raise the seat height without swapping the shock. The Razor SX500 swing arm shock mount sits further back, which requires a longer shock. But when upgrading, this will allow you to choose a shock with more travel.
Wheels:
The Razor MX500 comes stock with a 12” chrome front spoked wheel, and 10” chrome rear spoked wheel. The Razor SX500 comes stock with 10” front and rear wheels. The white/red models came with chrome wheels with red hubs, and the lime green models came with black wheels with lime green hubs. The SX wheels look super cool, but the razor wheels in general are known to be “untrue” out of the box and wobble pretty good.
Plastics/Body Work/Saddle
The Razor MX500 comes with plastic very similar to the original Honda XR50, and many folks have found ways to use XR50/CRF50 plastics and seats on their MX500 models. The MX500 stock seat is pretty cushy and comfortable enough, but the Razor SX500 seat is hard as a rock. The Razor SX500 does have body work that I find more attractive then the MX, but this is subjective and personal preference.
Here at Momentum Worx, we have had them all! We started with 3 MX500 bikes originally, and we moved on to purchase some Razor SX500 models as we came across them on the market place. The Razor MX500 is certainly more plentiful as it has been in production longer, so I personally believe they are easier to find for a good deal in the used market. A lot of folks purchased these bikes for their kids, and then kids grown up and the bikes rot away in the garage until someone decides to list them on the Facebook marketplace. Purchasing new is also an option as well, but this comes at a pretty significant cost premium.
If you are building one of these bikes as an adult, the only thing you are likely going to keep from the original bike is the frame & swingarm, and maybe the plastics. With that being said, I think that makes the Razor SX500 the better bike to build if you have the choice to pick one or the other.
**MX500 and MX650 are pretty much identical other then plastics colors (Red vs yellow), minor changes in the front forks, and then the MX650 comes with a 650 watt motor over the 500 watt motor in the MX500. Considering you are likely going to change the forks and motors, this then becomes irrelevant.