Dirt bike front suspension

Maybe I’m wrong in thinking this way; but I never put much effort into fine tuning the front suspension on my other bikes. For example, on my 74 Z1, I bought progressive suspension brand front springs, put them in with the pvc spacers… it was stiffer, so I thought, “cool, feels good, done”. I didn’t technically measure preload. Anything was better than before so it was an improvement and I was happy.

On the dirt bike, I feel like it matters more to attempt to tune the suspension. Ya know… Jumping shit. Wheelies past friends.

On my 1979 IT250 here’s what I did

  • Racetech front springs: .43kg stiffness. I weigh 175 on a good day. I said it before but Racetech is great since you can choose different spring rates.
  • Terry Kit vintage dampening rods. eBay find. Apparently these give you 1″ more of fork travel and make for a more plush ride at high speed on bumps? Can’t find much info.
  • I set preload to just under an inch
  • used 300mm of 20 weight fork oil
  • new all balls fork seals

So will these improvements make the IT feel better? Who the fuck knows. I want to see how it feels without doing modern front $200 Racetech emulator cartridges.

Front combined with my beefed up rebuilt YZ250 rear monoshock should be good.


So how exactly do you measure preload? It’s pretty simple. When you screw the top cap on, it’s how much you are compressing the fork spring. My manual calls for about half inch but I went with just under an inch. Preload below.

Below pic is from Racetech website… The Terry kit dampening rods had less holes, but the holes were bigger I think? I find the dampening rods the most confusing part.


3 responses to “Dirt bike front suspension”

  1. Colin says:

    That is the problem with old school (orifice only) dampening… in newer stuff that isn’t cartridge based, the holes in the dampening rods work in conjuction with the shim stack at the other (upper) end of the rod. Most older stuff doesn’t have a shim stack which is why the racetech gold valves are so good, they are basically just an adjustable(tunable) shim stack. So you can really dial in your high and low speed compression, instead of just one end… But if you fuck around with oil viscosity enough you’ll get closeish. maybe…

  2. Ed says:

    I want to see how good I can get it without spending another $200 on the Racetech emulators.

  3. Mike R says:

    I’m restoring a 1992 ATK 604 MX bike and I go back and forth on dropping in heavy springs on the existing vintage forks or grafting on a modern MX bike’s triple clamp so I can use upgraded forks and brakes. How did all of these upgrades feel once you got it off road and jumping off things?

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Published - Apr 29, 2019

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