How do I stiffen up the front suspension?

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You can do a few things:

  • Race Tech springs Look at the Race Tech calculator even if you're not getting springs from them. Note that the spring rate for some (un-heavy) people is lower than what Race Tech actually sells. For example, their calculator lists .65 kg/mm as the correct rate for a 120 pound street rider, while the lightest spring they sell is .70 kg/mm. In this case you will want to contact Sonic Springs for custom springs, or check out the EX500 springs option.
When calculating, the dry weight of the EX250F is 305 pounds, and the the curb (wet) weight is 350 pounds. Race Tech calls for 'semi-wet' weight, which they say means ready-to-go with half a tank of gas. That's about 335 lbs.
For the EX250J, the weights are 335 dry and 375 wet, so semi-wet would be about 360 lbs.
  • Sonic Springs Sonic sells springs for most motorcycles. We like Sonic, and their springs are generally inexpensive. If you're under about 185 lbs you should contact them directly. Sonic's calculator doesn't work real well for light people on light bikes; it doesn't go below .70 . They routinely do custom-rate springs (under .70 kg/mm) if you're a bantamweight. For about $80, a Sonic springs order comes with two springs and the appropriate washers and spacer material. And some stickers.
  • This link will tell you everything Race Tech makes for your bike. This one shows their 250-specific products as well. It's geared toward the EX250J, but most of the parts will also apply to the F. Hint: Searching for Race Tech products at other stores may save you some money. This link tells you what you should actually get from Race Tech for your Ninja.
  • Send your forks to Aftershocks, and they can do anything from changing the oil to a complete re-valve.
  • Note on aftermarket springs: Don't be surprised if the new springs you get are much shorter than the stock ones. The springs aren't designed just to fit the 250; they go in many different bikes. This helps make them more affordable. A preload spacer of the right length makes up the difference. See the preload spacer article for information on cutting the spacers.
  • The stock EX250F springs are part #44026-1362 and have a 0.440 kg/mm spring rate. Their free length is 463.8mm. The minimum service limit is 455mm.