Fork Spring Preload

5 replies to this topic
  • bmah

Posted March 14, 2008 - 04:26 PM


Hi Guys/Gals,

I just had my new '07 WR450F delivered today. There is still a lot of snow around, so I figured that I would get a lot of the detail work done before I ride my new steed.
It is pretty clear how to set the 'Race Sag' for the rear shock, I've not found much info on the fork. I would imagine that I will need some preload on the fork spring, (I'm 6'4" and 205lb) but, I'm not finding much info on how to go about this. When I checked the sag on the rear, I also checked the front and found it to be stiffer than the rear (ie, cable tie method of determining loaded and unloaded fork travel.) Is there a convention for setting the sag on the fork in relation the the rear shock?

As an aside, my bike will be plated, I added the Trick Dual Sport Micro Kit which is enough to make my bike legal here in NH. I also added the Moose Hand Guards, rejetted the carb, de-snorkled, de-pea-shootered and removed the grey wire. Still left to do is regrease the steering head bearings and the swingarm and suspension linkage bearings.

I am in full on "New Bike Psych mode:busted: !"

  • ww44wrf450f

Posted March 15, 2008 - 04:49 AM


I am in the process of buying a new 06 wr450f , I have a plated 05wr250 and I found that the front spring rate is to soft for a 230lbs. So on the new 06 i will get a higher rated springs in the front -- check the manual there is a chart for spring rates? i will go to the 2nd heaviest? and then play with the oil weight and the level of oil?

  • clark4131

Posted March 15, 2008 - 10:30 AM


If you're not going for the full treatment on the suspension and are happy to do springs and fluid yourself, you can use the Racetech site to get in the ballpark as to what spring rates you should use, front and back. They tend to set things a little light, so the recommended way is to go one setting heavier than what Racetech recommends...SC

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  • bmah

Posted March 15, 2008 - 01:04 PM



What I meant to ask was what should the 'race sag' be for the forks. The manual specifies 90-105 mm for the rear (I think, don't have the manual handy at the moment) I could not find a number for the forks at all in the manual. Is it the same as the rear?

  • RickSanson

Posted March 17, 2008 - 04:31 AM


I'm thinking it should be around 25mm - 30mm but is hard to measure (stiction). I had my suspension done by Jeremy at MX-Tech and fork race sag has never been much of a topic.

  • bmah

Posted March 17, 2008 - 09:04 AM


I have been perusing the manual and found that Yamaha has a part # for a preload spacer for the fork spring. With the standard spring installed, the manual says that up to 3 of these 2.3mm spacers can be installed in each fork leg. I have heard no mention on this forum or elsewhere of adding spacers to the forks to obtain more spring preload for the proper 'race sag'. I'm planning on setting my forks up with 25% sag in the fork with my weight on the bike and a 1/2 tank of fuel. If the spring sag is too much, I'll just make my own spacers from PVC tubing to make it right. According to Race Tech's site, my weight (205) requires a spring value that is more than the stock spring value, but, less than the next heavier spring. I'm hoping that "penny-tech" will prevail on this issue.
I will be doing the sag measurements again in the next couple of days, I'll report back my findings.


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