KX500 Chassis Setup for motocross?

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8/12/2021 2:45 PM

What is the hot setup for these old bikes?

Most important, what's the sag and fork height setting that makes a good starting point?

I've read old threads, magazines, etc saying that aftermarket linkage dog-bones are a big improvement in cornering. I'm seeing the 132.5mm length everywhere I look, so I plan to try a set of those.

I am building a 1990 model with a set of modern forks.
I'd love to hear your experience if you've owned and raced one of these old green machines.

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8/12/2021 3:17 PM


Photo

2014 YZ250F KYB forks.

Emig Racing lower triple clamp with custom Luxon Engineering upper triple clamp.

Emig Racing dog bones.

Frame and subframe gussets added throughout, plus mounts to accept KX450 foot pegs.

2 piece clutch cover mod.

Moto Stuff 280mm front rotor.

Guts Racing +1" firm seat foam.

The list goes on and on...



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Do It In The Dirt!

8/12/2021 4:20 PM

New forks is a good start.

I ride a lot of sand, prefer the 06-08 KX450 clamp with more offset. I don't go less than +5mm fork height and 120mm on sag.

Enjoy and don't forget to short shift!

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8/12/2021 4:31 PM
Edited Date/Time: 8/12/2021 4:31 PM

Do anything you can to make it turn and stop better. They have no problem going fast in a straight line.

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8/12/2021 8:34 PM
Edited Date/Time: 8/12/2021 8:35 PM

Zeke27G wrote:
Photo

2014 YZ250F KYB forks.

Emig Racing lower triple clamp with custom Luxon Engineering upper triple clamp.

Emig Racing dog ...more

What's your clamp offset?

OEM for the 500 was 25mm plus a 30mm fork lug offset.

The 48mm KYB Yamaha forks are 32mm offset, so a 23mm clamp would bring you to stock KX500 spec.

I machined my own 7075 clamps for some Yamaha forks with a 22mm offset. That gives me 54mm offset, one millimeter less than stock. Initially I'll be running the same valving as my YZ250 and a 0.49kg/mm spring rate.

I'm planning to make a set of dog-bones to try next week in the 132.5mm length (same as the Emig parts)


Adam43, is the 06-08 a 23mm offset? I believe all those KX-F forks were a 33mm lug offset.
If I'm correct, that gives you 56mm total which is +1mm from the stock KX500 spec. I'll write down 120mm as a starting point for sand.

nytsmaC, Solid advice on the brakes, that OEM Kawi front brake was junk. I will be running a 270mm Galfer rotor on a YZ wheel with a Honda CRF-450R front brake assembly.

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8/12/2021 8:40 PM

Some photos of my work so far... Clamps, 3-bolt peg mount for YZ pegs, frame gussets, etc.
I have the bottom end done and I'm working on the top-end tonight.
With any luck I'll get this thing out to a local track called Ward Creek on the 22nd for a little test-n-tune.

A buddy suggested 13:50 or 13:49 gearing.
What are you fellas running for medium terrain tracks and for hard-pack?

Photo
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Photo

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8/12/2021 10:05 PM

13 tooth is a little small for a kx500. 14/48 would be a gold track setup. 3rd gear starts. Ride most the track in 3rd

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8/12/2021 11:13 PM

toomanykaws wrote:

13 tooth is a little small for a kx500. 14/48 would be a gold track setup. 3rd gear starts. Ride most the track in 3rd

Thanks, I'll pick up a 14 tooth and a couple of different rears.

The stock gearing was 14:47 for that year, I think maybe he got confused on the front sprocket size.

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8/13/2021 5:30 AM

toomanykaws wrote:

13 tooth is a little small for a kx500. 14/48 would be a gold track setup. 3rd gear starts. Ride most the track in 3rd

14-48 is what I run as well.

Can't remember the triple clamp offset, but it was what Emig Racing recommended.

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Do It In The Dirt!

8/14/2021 12:28 AM

Search for the videos on YouTube where Doc Wob built a 500 for Ryan Hughes to race at the Farleigh Castle VMXdN, Ryan wanted the bike WAY stiffer in the suspension department and then started to work back, softer, softer, softer back to where they started with the settings he ran back in the 90s... I run my 500 quite soft, they are not modern 450s, the back end will want to dance all over the place with out a soft squat under hard acceleration... awesome fun to ride though.
Photo

Here’s my old girl.

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8/14/2021 12:36 AM

Yeah the rough part about them for me is getting them to stop. The stock front rotor is pretty pathetic, I honestly can’t believe a bike like that was sold with it lol. I also have the hydro clutch on mine and I like it quite a lot

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8/14/2021 10:52 AM

Have a few extra rear brake caliper holder swingarm mounts for kx450 wheel/brake conversion for sale, $125/ea Photo

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8/14/2021 10:56 AM

Sidecar wrote:

Search for the videos on YouTube where Doc Wob built a 500 for Ryan Hughes to race at the Farleigh Castle VMXdN, Ryan wanted ...more

When I did a few laps on my small home track, the shock and seat felt like a comfortable easy-chair, super plush. The 41mm inverted fork felt like a couple of cooked spaghetti noodles. I rebuilt the shock with stock valving and I'm going a lot firmer on the fork as a starting point. I tend to ride the front end a lot and that stock 1990 stuff was not safe at all. If my fork is initially too firm, I'll change springs and or valving.

Eventually I'd like to build a shock with a high speed adjuster. The compression adjuster in these old KYB shocks changes both low and high speed compression at the same time.

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8/14/2021 11:53 AM

with a dialed suspension these bikes are a lot of fun.

Looks like the start of a nice build cwtoyota

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8/14/2021 3:36 PM
Edited Date/Time: 8/14/2021 3:36 PM

nytsmaC wrote:

Do anything you can to make it turn and stop better. They have no problem going fast in a straight line.

a CR500 is the answer to both of those points. (:

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