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Fork spring rates WR450/250F

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Guys,

A while back I tried to set up the race sag on my '08 WR450F.

Got the back end set ok at 100mm, but was unable to achieve enough sag on the front. (To my surprise I appear to require softer fork springs than OEM.)

I've been living with the issue ever since but now it's starting to bother me. I want it right.

I have been told that the '08 WR250F has lighter fork springs than those on the equivalent 450.

Rather that buy new aftermarket springs I'd like to try sourcing a pair of 2nd hand OEM 250 springs and give them a try if they will provide me with additional sag.

Your thoughts?

Greg

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How did you maeasure front sag? It is not necessary to measure that. If you are something between 75-85kg, springs will fit you. You can also adjust the spring preload with spacers.

I am not sure about those -08 springs but -07 models have 4.4N in 250 and 4.5N in 450.

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Thank you for your response Jusa.

I have always checked both front and rear race-sag with a tape-measure, all my riding gear on, standing in the "attack position" on the bike.

I believe it is absolutely necessary to measure both front and rear in order to balance the springs at each end.

Cheers,

Greg

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Greg, I am suprised you are not getting enough sag with the stock springs, the bike should sag quite a lot under its own weight, the Wr forks are very soft, are you sre the forks are not bound, or the bushings are gone etc

How much does it sag uder its own weight?

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My thoughts are that the WR's would handle even worse with a softer fork spring to match the 5.5 shock spring that the Australian model comes with. If anything I would prefer to go up a rate on the forks (with a little more preload as well) or down a rate on the rear, depends on your weight but I think they are a little unbalanced in stock form front to rear and what you are talking about will make it even worse. And I never ever waste my time trying to measure fork sag, too many variables distorting the results.

Save your money on the lighter fork springs and invest in getting a Gold Valve and the mid valving sorted out on those forks, thats where your money is better spent since you asked for our thoughts.

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Guys, firstly, thank you for your responses/feedback.

I hear what you are saying and I've always felt the same way, the stock WR450F forks feel "soft". I was bottoming them often.

I increased the compression damping on the stock valves and this was improved but they started to feel a bit harsh in the rest of the stroke.

I fitted a Gold Valve kit a few weeks ago and it seems to have improved things a lot.

I decided to check the race-sag, not because I have bottoming issues (they seem to be gone now, with nice action everywhere else after the Gold Valves), it's just that I want to set the bike up properly and have recently lost 10kg and I'm now 75kg.

Previously, during the bottoming issues, I had always assumed I would need heavier springs and was ready to turn up some preload spacers as an experiment before I spent money on springs.

I did the sag measurements "by the book" (ie. the way the experts recommend).

The back end was easy, nailed it.

I was only able to achieve 93-94mm from the front.

I even went to the extent of (many may not have heard of this method, it comes from roadrace setup) taking two measurements (with me sitting on the bike and a friend dowing the pushing/lifting under load) and averaging the two to eliminate stinction factors:

1. Lift up and drop the front end, measuring when it settles.

2. Push down and let it spring back up, measuring when it settles.

Even when pushing down on the low point of the seat (very un-scientific, but simply to get a "feel" for it) the rear sags visibly more than the front.

Once again, I know everyone thinks the 450F forks are under-sprung, me included (until now).

Doing the measuring seems to indicate the opposite for someone my weight.

Go figure!

Greg

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At 75kg I would keep the stock fork springs. The rear linkage will always move easier than the forks and be sure to measure your sag with you standing on the pegs, not sitting, otherwise you are doing it correctly. With the forks, if you removed your forks bleed screws you could end up with different results. Once your forks pump up a little, different results again. Check your bottom fork clamp torque settings and the WR's are often set with binding at the axle due to the speedo drive getting in the way when fitting the front wheel so check that as well. But again I wouldn't bother trying to check the sag, but I would add a little preload as in stock form they have very little for a big bike.

With the Gold Valves fitted some midvalve work (and possibly a cartridge mod) is also beneficial but without access to a range of shims you might be stuck, also taking the KYB midvalves apart is a little tricky if you have not worked with them before. The stock setup relys on a heavy shim stack even though the valve lift is high. But this is where you need to focus on if you have some harshness as you now have additional damping at the base with the Gold Valve and shimstacks. A single stage stack works better on the Gold Valves on these bikes in my opinion.

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