Potential front brake upgrade

[Chopperpilot]

I'm about to go get a 2009 KLX250SF and start turning it back into a dirtbike from a factory super moto. I realize that may sound stupid, but it's a better deal than on any KLX230 or TTR230 that I was looking at for my daughter or my GF to ride along with me. Key points being lower seat, and not much happening if you twist the throttle all the way.
Well the 250SF comes with 43mm USD forks on it and a 300mm brake rotor, 17" wheels all around. The fork lugs are definitely different than the regular KLX lugs, but I'm pretty sure I saw that familiar old 15mm KDX/KLX axle sticking through them. I figure I have all the parts to turn this back into a dirtbike mostly because I have the KDX 21" front wheel. But that got me to thinking, what about the brake rotor? Well it looks like both the 250SF and KDX/KLX650R all use a 4 bolt rotor mount. So I'm betting that the 250SF 300mm rotor would bolt onto a KDX hub. Then you'd just need to machine out a spacer for the caliper. The guy who SM'd my KLX650R had one done up and I'm hoping it's for a 300mm rotor (stands to reason that's a common size). When I get the bike, I'll see if the rotor mounts onto the KDX rim and see if my brake spacer is made the right way to space it out, and then post pics!
It's been so long since I had the SM wheels on the KLX that I forget some things exactly, and the wheels were mag wheels from a Suzuki SV650 (IIRC), so the caliper spacer might have an offset to it that wouldn't work anyway, but we'll see.

[Chopperpilot]

Ok, bought the bike, and it's a go! The KLX250SF (Super Moto) does use the KDX/KLX front axle and a KDX front wheel fits right in there. The giant 300mm rotor has the same 4 bolt pattern as a KDX. I'm wondering if the KLX250SF front brake could just be swapped over to the KDX (and most other) forks with it's larger spacer. I think this bike will be great for my daughter to poke around on....... when you twist the throttle, not much happens!

[assquatch20]

Could be promising news. I've thought about getting sumo wheels for the KDX down the line and wondered about brake upgrades.

I'm curious about something else, though. Is the KLX rear axle the same as the KDX you think? Or maybe the KX250F? That would be ideal for something I'm considering to try.

[KDXGarage]

KX250F rear axle is 25 mm diameter. Check out bearing inner diameters when comparing axle diameters.

[assquatch20]

KX250F rear axle is 25 mm diameter. Check out bearing inner diameters when comparing axle diameters.

I'm not trying to derail the thread but where did you find the ID for the bearings? I don't even know the diameter on the KDX. What I'm wondering is if I can hook up my single wheel trailer with the KDX. The maker uses a skewer on hollow axles and makes the hardware to mount to the KX250F so I thought it might be an easy adaptation.

[KDXGarage]

You can just look up the bearing info. 2003 and newer KX went up to 25 mm inner diameter.

KDX and older KX's for many years were 20 mm inner diameter.

The axle inner diameter would go up as well.

[Chuck78]

...and it's a go! The KLX250SF (Super Moto) does use the KDX/KLX front axle and a KDX front wheel fits right in there. The giant 300mm rotor has the same 4 bolt pattern as a KDX.

I'm wondering if the KLX250SF front brake could just be swapped over to the KDX (and most other) forks with it's larger spacer.

I looked up that caliper bracket, and it fits 2009 and 2010 models like you have as well as 2021 and newer KLX300 SM & KLX230 SM models.
I attempted to cross reference part numbers on the inner lower left fork tube to see if it was the same as the common KLX300 off-road model fork that is swapped to the KDX regularly, because that caliper mounting is exactly the same as the KDX caliper mounting at least through 2008/2009&ish from the mid/late-1990's.
No luck on the cross reference, as it appears the color was different for the Supermoto version, so of course the part number is going to be different. It still could potentially be the same brake caliper side axle lug, however, or at least the same rotor mounting positions, but obviously a different color. It would make sense to only have a different caliper mounting bracket to accommodate the larger rotor so they would not have to manufacture another variant of the fork axle/brake lug.

I am going to assume that the axle lug brake caliper mounting points are going to be in the exact same position as the KDX fork in relation to the KDX axle, however I'm not quite 100% certain.
Chopper, if you get a chance to test this and check the brake pad alignment on the rotor by swapping wheels and caliper over for a mock-up, that would be greatly appreciated.

https://www.partzilla.com/product/kawasaki/43044-0026

I never have found any issue with the functionality of my KDX brakes, but then again, I don't ride supermoto and don't ride wide open terrain very often, only short durations of straight sections of trail with no trees in the way...

I do have a pair of 2024 KX450X forks however, not yet swapped on to either bike, but these forks I believe run a 300mm rotor stock, so having a spare wheel and being able to switch between both of my bikes might make things convenient if I had all 300mm rotors and 20mm axles (the 2019+ or earlier even 2006+ KX 4-stroke use I believe a 22 mm front axle or possibly larger. I'm already going to have to make some adapters to run the wheels that I have on this 2024 Showa fork in order to be able to have all my wheels swappable, no biggie.

[Chopperpilot]

OK, took the fork tubes off of the KLX250SF today to do new seals and see what I could do with the valving. They use the same shim setup as the KDX, but instead of 10 x .10 shims, it had 3 x .20 shims. I decided to remove 2 of the .20's and replace them with 4 x .10s, we'll see? I was able to bolt the front caliper and bracket to the kdx fork tubes, so it seems this would be an option for larger brakes. I suppose that the SF bracket/fork lug mounts could place it in some weird relationship to the front axle compared to the KDX, but it probably doesn't. I put kenda 270 tires front and rear on it (5.10r and 4.6f). It developed a head shake around 60mph after I lowered the pressure in the tires to around 20psi? I adjusted in a little more sag and with new seals and fork oil in the front, I guess we'll see if that fixes it. It feels like this thing has a real steep head angle like the KDX, so I'm curious to see what a 21" front wheel will feel like on there. Then maybe later, some longer 43mm fork tubes (I have some spares now!)

Well dang! It seems Kawasaki has 2 different 43mm fork seal/tube types. I got the wrong ones and put them on and completely wasted all that time (except that fixing it won't take near as long).

[KDXGarage]

OOPS. Oh well. Keep at it.

[kdxdazz]

OK, took the fork tubes off of the KLX250SF today to do new seals and see what I could do with the valving. They use the same shim setup as the KDX, but instead of 10 x .10 shims, it had 3 x .20 shims. I decided to remove 2 of the .20's and replace them with 4 x .10s, we'll see? I was able to bolt the front caliper and bracket to the kdx fork tubes, so it seems this would be an option for larger brakes. I suppose that the SF bracket/fork lug mounts could place it in some weird relationship to the front axle compared to the KDX, but it probably doesn't. I put kenda 270 tires front and rear on it (5.10r and 4.6f). It developed a head shake around 60mph after I lowered the pressure in the tires to around 20psi? I adjusted in a little more sag and with new seals and fork oil in the front, I guess we'll see if that fixes it. It feels like this thing has a real steep head angle like the KDX, so I'm curious to see what a 21" front wheel will feel like on there. Then maybe later, some longer 43mm fork tubes (I have some spares now!)

Well dang! It seems Kawasaki has 2 different 43mm fork seal/tube types. I got the wrong ones and put them on and completely wasted all that time (except that fixing it won't take near as long).

I have some experience with supermoto conversions and steep rake angle, drop the forks in the tubes as much as you can then take front sag numbers, on the stock kdx forks I have around 55mm, you then most likely will need to add lots of preload on the front forks to raise the front, I had to do it to my drz when I fitted a taller rear tyre