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How do I set the sag

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This is the simple way:

1) Put bike on stand. Measure distance from a reference point on rear fender to center of rear axle. Make sure to mark the reference point.

2) Take bike off stand have someone support and sit on bike with all your riding gear on. Some say with feet on pegs some say with feet "dangling" just in front of pegs. Take the same measurement as in step one.

3) Sag = measurement 1 - measurement 2. This measurement should be ~100 mm on a 250F. Use shock preload rings to adjust if necessary.

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At the very back of your manual there is a decent set up section dealing with sag. It also has spring rate information if you need to make a change from what you have.

Generally though, you need about 3.5" of sag on the rear when you're on the bike with full riding gear.

My bike has the 5.1 spring but I need to go stiffer. My sag is about 4.5" to 5" even though my spring pre load is maxed. I weigh about 220 with gear and am going to try the 5.3 or 5.5 spring. I also hope it gives the front end a bit more bite.

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Heres some stuff from

http://www.off-road.com/dirtbike/mar99/db101/db101shock.html

Sag should generally be set at about 1/3 wheel travel. This means about 100mm for most full size dirt bikes. Some bikes have an adjustment range of around 90mm to 105mm. The less the spring is compressed does not necessarily mean the softer the ride will be. Due to the progressive ratio designed into the linkage, setting the spring stiffer can make the ride softer…..

Say what?!?

The linkage is designed to move the shock less as the suspension moves through its travel. This makes it soft at the beginning of the movement and stiffer as it goes through towards the end. This makes it more resistant to bottoming but still allows it to be plush over smaller bumps at full extension. So if we set the spring stiffer, it will move the ride height into the softer ratio part of the travel. This is one reason a "too soft" spring rate can give a dead feel to the rear of a bike (compared to how it should feel).

Once you get the sag set, you can check to see how close the spring rate is for your weight. Check the sag again without a rider aboard. This is known as static sag. You should get between 15mm and 25mm if your spring rate is correct for your weight. If the static sag is less than 15mm, your spring is too soft for your weight. If the static sag is more than 25mm, your spring is too stiff for your weight. I know this may sound backwards, but this is due to the preload applied to the spring to get the rage sag correct for your weight.

and more from

http://www.transworldmotocross.com/mx/how_to/article/0,13190,591886,00.html

Last but not least, while you are still sitting on the bike grab a buddy and have them help you check the sag. Start by taking a measurement (in millimeters) with the bike on the stand. Put one end of the tape measure in the axle hole, and go straight up to the fender. (You should end up pretty close to the seat.) Make a small mark on the fender where you take your measurement, and this will be the same place to measure from when the rider is seated.

Note the reading, then have the rider (that's you!) sit on the bike, fully geared up with boots and all. Now take the same axle bolt-to-fender mark measurement you made when it was on the stand, and write that number down. The difference between these two numbers is your sag.

Consult your owner's manual for your bike's precise numbers, but normally Hondas and Suzukis are in the neighborhood of 105mm, while Yamahas and Kawasakis are about 95mm. If you are over the number, turn the shock counter-clockwise to take tension off of the spring. If you are under, do the opposite until you reach that magical number. Well, that's it…now all you have left to do is go enjoy your new bike!”

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