KX500AF feedback (2019-2023 KX450 conversion)

Joko
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Joko

I’m considering converting my 2020 KX450 chassis to fit a KX500 engine with AJ’s Built chassis mods, and adding MX Tech suspension, but would like to hear any actual reviews from anyone who may have done this conversion with the 2019-2023 KX450 and has some feedback on its performance, compared to the std 89-04 stock chassis? Was vibration same or better than stock KX500 chassis? Was there a weight increase with the KX450 chassis vs stock ? How did handling change? Turn better, stability improve? Thanks! 

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toomanykaws
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toomanykaws 6/24/2026 11:44pm
6/24/2026 11:44pm
Built my own AF500 but used an early chassis. Have rode other riders AF. An 09. 11 and a 14. That’s as new as I can say. Feels lighter than a steel frame bike. Definitely stiffer frame being Alum. Hard to compare handling between the two so much. The steel frame is very stable and has a relaxed head tube angle. Keeps itself in a straight line. If you are primarily going to track ride it. An AF would be easier to dial in. Vibration between the two seems similar to me. They all have it. A well Balanced Oem crank is really the cure for either bike. Some engines from the factory were better than others. Luck of the draw on Oem balance. Brakes are way better on the newer bike. But can easily retrofit them onto the steel frame. Especially with a tripple and fork swap.
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scootscheerer 6/27/2026 7:28am
6/27/2026 7:28am

KX500 parts are much harder to find and more expensive so that pushed me away from the 500/450 conversion.

I found the BRC YZM500  swap and went that route. Still spent a ton for a complete do over but its gonna be a badass bike. Just waiting on the Lectron Pro 40mm to come in and button it up. Should be in the 70hp range.

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Joko
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Joko 6/27/2026 3:18pm
6/27/2026 3:18pm

The YZ500 is a great build, I’ve thought about it, since I really liked the stable handling and exc suspension of the YZ250. Are you using the std transmission or the YZ X trans with the taller 4th & 5th gears? Post a ride review after you get it out, would like to hear how it goes!

scootscheerer 6/29/2026 12:40pm
6/29/2026 12:40pm
Joko wrote:
The YZ500 is a great build, I’ve thought about it, since I really liked the stable handling and exc suspension of the YZ250. Are you using...

The YZ500 is a great build, I’ve thought about it, since I really liked the stable handling and exc suspension of the YZ250. Are you using the std transmission or the YZ X trans with the taller 4th & 5th gears? Post a ride review after you get it out, would like to hear how it goes!

I used the standard 5 speed. I'm guessing the Lectron may be a couple weeks but its ready to go other than that.

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