Working the Dwight_Rudder formula.

[tgrundy131]

Bike :2008 RM250 (not 'z')

Rider: 225 lbs with gear.

Available travle front and rear 310mm (per manual)

Forks: .47 springs

34mm static sag (41-45mm target per formula)

66mm race sag (75-79mm target per formula)

Shock: 5.5 spring

36mm static sag (34mm target per formula)

112 race sag (105mm target per formula)

So it looks like I am close in the back, but the forks need softer springs. Any suggestions on rate? I have also a set of .43's and was wondering if I could mix a .47 and .43 to generate a .45 overall rate.

Looking forward to any input...Thanks

Thomas

[GDI70]

you'll save some money that way. but check your sag numbers after the swap. also, measure the free length of each spring. there may be a difference that you'll have to address with a spacer.

i just fixed a rider up with some .46's on a 04 rm250. 212lbs. he was really close in the numbers. had a large tank on the thing. he's running 105mm sag.

[Dwight_Rudder]

Yes, Try one .43 spring. You are close. You can also reduce preload since both are on the tight / stiff side.

On the rear decrease your static sag to about 32mm (within the +-2mm variance) and see if your rider sag is down to 107mm or less.

Bike :2008 RM250 (not 'z')

Rider: 225 lbs with gear.

Available travle front and rear 310mm (per manual)

Forks: .47 springs

34mm static sag (41-45mm target per formula)

66mm race sag (75-79mm target per formula)

Shock: 5.5 spring

36mm static sag (34mm target per formula)

112 race sag (105mm target per formula)

So it looks like I am close in the back, but the forks need softer springs. Any suggestions on rate? I have also a set of .43's and was wondering if I could mix a .47 and .43 to generate a .45 overall rate.

Looking forward to any input...Thanks

Thomas

[tgrundy131]

Yes, Try one .43 spring. You are close. You can also reduce preload since both are on the tight / stiff side.

On the rear decrease your static sag to about 32mm (within the +-2mm variance) and see if your rider sag is down to 107mm or less.

I have never run spacers in my forks for preload, should I? Is there a way to reduce preload on the front springs when I have no spacers to remove?

[Dwight_Rudder]

There are some preload spacers probably under the springs if not on top. You can cut some out of PVC pipe. I don't suggest cutting the stock spacers. Save them for later.

[mog]

is this for moto , sx or woods ?

[tgrundy131]

is this for moto , sx or woods ?

Woods. The fork worked very well in whooped out sections, but was using very little travel, and was not turning as well as I want it to. In addition to changing the one spring, I plan on removing a face shim from the mid valve to increase float and soften up the mid. A tuner said that I could also increase float by placing a shim under the midvalve collar, but in looking at it, I fail to see how that would work. The midvalve clamp shim will still be contacting the shims under the collar. I thought I needed a taller collar, but will settle on removing a face shim.

I am new at this, so If I am heading down the wrong path, then feel free to chime in.

Thanks for all the replys.

[kan3]

You want a shim that's the same size as the collar which is probably a 8mm OD and 6mm ID. This will obviously act like an extension of the collar.

[mog]

I would remove a shim , you want to make a big change that you can feel

[tgrundy131]

You want a shim that's the same size as the collar which is probably a 8mm OD and 6mm ID. This will obviously act like an extension of the collar.

Now THAT makes sense. Seems like the midvalve clamp shim might get hung up on the shim collar transition. Prolly just thinking too much about it.

[tgrundy131]

you'll save some money that way. but check your sag numbers after the swap. also, measure the free length of each spring. there may be a difference that you'll have to address with a spacer.

i just fixed a rider up with some .46's on a 04 rm250. 212lbs. he was really close in the numbers. had a large tank on the thing. he's running 105mm sag.

GOOD idea on the free length of springs. There was a 3mm difference between the .43 and .47. THANKS!

[tgrundy131]

I would remove a shim , you want to make a big change that you can feel

But I do not want too much of a difference. Do you think a 20mm face shim, or one of the 17's toward the bottom of the stack? Effect of float should be the same.

[mog]

go for the 17 then

[Dwight_Rudder]

go for the 17 then

[kan3]

Now THAT makes sense. Seems like the midvalve clamp shim might get hung up on the shim collar transition. Prolly just thinking too much about it.

If you put it on top of the collar, the shim will sit in the piston recess so no shims will slide over it.

[tgrundy131]

If you put it on top of the collar, the shim will sit in the piston recess so no shims will slide over it.

Good thinking, I will get a couple 8 mm shims next time.

[tgrundy131]

In measuring the front sag, I am having a awful time with stiction and getting a good measurement. Here is what I have done...Forks in the clamps and aligned till the front axle spins freely in both lugs, installed front wheel and secured axle in the left fork lug, right lug bolts loose to eliminate any fork alignment issues.

When measuring, forks only move when applying the front brake (just bouncing on foot peg from the side will not do it) and there has been as much as 15 mm diffrence between measurements. I am looking for some consistancey in my measurements. How do you guys do it?

[kan3]

You can try some lubrication to help remove some stiction. Also, have you inspected your bushings to make sure they're in good condition?

[mog]

most forks will not compress without the front brake , take rider and static sag readings and report back

[PMK]

FWIW, I seldom if ever measure front sag for those exact reasons.

Unfortunately to dial in the front it often comes down to actually testing with different springs.

If you want to go the front sag route, either do it with dry forks with no seals, or pry out the dustwipers to minimize seal drag.

FWIW, in regards to my own bike used for off-road, I fabricated a very short wrench to adjust the preload on my KTM. Depending upon the day and the dirt, I may give a small adjustment if needed to dial in the front.

Once you find your preference for rear sag, try and deviate very slightly when needed, for the forks, get those set and use the rear sag if needed to help the bike turn, obviously triple clamp offsets and fork tube height will give more options.

Ultimately it all must balance to be good.

I respect Dwights accomplishments and experience, but will never advise a rider to lock into something semi abstract as sag to be carried down the mountain on a stone tablet for all to follow exactly the same. Way to many variables, but it does provide a baseline to build from.

PK