250f vs 450f spring rates and valving different?

14 replies to this topic
  • mavis0826

Posted March 23, 2008 - 02:18 PM


Are the spring rate different between a 07 250f and 450? Would the valving be different?

  • maddogyz250f

Posted March 23, 2008 - 03:19 PM


yes and yes.

  • mavis0826

Posted March 23, 2008 - 06:33 PM


whats different?

  • todds924

Posted March 23, 2008 - 07:01 PM


whats different?

Spring rates and valving are heavier on the 450. Stiffer everywhere. Just like the valving and spring rates are different between the 250f and 250 2 stroke.

  • mavis0826

Posted March 23, 2008 - 07:08 PM


is there somewhere that i can compare the difference between the two?

  • grayracer513

Posted March 23, 2008 - 07:18 PM


Go to Race Tech and look up the spring rates, or download both manuals and do it that way.

What is it that you are specifically trying to find out?

  • todds924

Posted March 24, 2008 - 02:39 PM


Go to Race Tech and look up the spring rates, or download both manuals and do it that way.

What is it that you are specifically trying to find out?

He probably wants to use some 250f forks on a 450 or the other way around. If he's a bigger rider, the 450 stuff would probably work ok on the 250f..

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  • mavis0826

Posted March 25, 2008 - 10:52 AM


I'm actually putting the 250f fork on a 07 wr450. The stock wr fork sucks. I score a brand new fork off a 07 250f for 400 bucks complete with trees. the only problem is the different caliper on the 250f. But I found one on ebay complete with mastercylinder for 70 bucks. I don't want the fork to be as stiff like for mx but a little softer for offroad.

  • grayracer513

Posted March 25, 2008 - 11:18 AM


What you will want to be careful of here is two things:

> You will most likely find that the brake won't work well until you add the matching '07-'08 YZ250F master cylinder or the '08 YZ4540 master cylinder. Both these use a different brake lever than the old ones did, BTW.

> The 250F top tube is about 12mm shorter than the YZ450. This is made up for by the forks being shorter as well. That will make for quicker cornering, but may cause trouble at speed.

In addition, while the damping may be OK, I think you'll find the spring rates are just too light for the weight of the WR. Even so, your project should be workable, and a big improvement over stock.

  • mavis0826

Posted March 25, 2008 - 11:43 AM


I did get the matching mastercylinder off a 08yz450f. I weight 175 without gear, can you change the preload on these forks?

  • grayracer513

Posted March 25, 2008 - 12:07 PM


Your WR currently has .46 kg/mm springs. The '07 YZ250F comes with .44's. Race Tech's calculator calls for .455 in an '07 WR450 for desert/trails at your weight. That's close, but they still may be too soft. You could try it and see what you think, and they aren't hard to change later on.

There is no method provided for changing the preload of the springs to any significant degree, which is one reason the forks are made to be installable at differing heights in the clamps.

  • mavis0826

Posted March 25, 2008 - 01:02 PM


are the spring the same in both style of shocks ie. length, diameter and so on?

  • mackenzie14

Posted March 25, 2008 - 01:03 PM


no they are the same

  • grayracer513

Posted March 25, 2008 - 01:16 PM


No. The springs in your YZ forks are 43.6 x 450 mm, and the WR fork springs are 43.5 X 461 mm. Before you ask about it, shortening a spring increases the spring rate, although here, it's only a two percent change. I still don't recommend it, but if you decide to go that way, take 5mm from each end with an abrasive saw.

  • grayracer513

Posted March 25, 2008 - 01:17 PM


no they are the same

What does that mean?

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