setting the sag

[hod928]

I have a 2002 yz250f. I'm going to have the suspension sent in to mcr suspension here soon. Gonna have them redo everything and set it up for my weight. Once i get them back how to i set up my bike for the sag. I was told to shoot for 2 inches. What do i need to adjust to adjust it?

 

[sharky243]

The rule of thumb for race sag is 3.5-4 inches of sag. To set it, all you need to do is first, put the bike up on a pit stand so the suspenssion is fully extended. Put a piece of masking tape on one of the side number plates along the back edge. Take a measuring tape and measure from the center of the rear axle up to the tape. Pick a round number (ex. 24 inches). Put a mark on the masking tape at the number you pick. Record this number. Now loosen the lock ring on the rear shock spring pre-load adjustment. Put the bike on the ground, and sit on the bike in the normal riding position. It is best if you are wearing your riding gear as this will add some weight to your body. Bounce on the bike afew times to settle the suspenssion. Have someone measure from the same 2 points, and record that measurement. Compare this measurement with the first one. There should be a 3.5-4 inch difference. Adjust the pre-load ring as necessary to get the desired setting. You may have to change the springs to match your body weight. Stock springs are good for a rider of around 175 pounds give or take. There should be a spring chart in your owners manual to help you choose the right springs. If you must change the spring, you have to do both the forks and the shock.

 

[rmc_olderthandirt]

The exact numbers on how much sag can vary a lot from source of wisdom to the next. I was told that the sag with you sitting on it should be ~100 mm (about 4 inches) and 25mm with just the weight of the bike.

To adjust the sag you need to adjust the pre-load on the spring. Take a look at the shock and you will see that the body is threaded and there is a large nut that adjusts the pre-load on the spring. On a Yamaha there will be a second nut that locks the pair in place.

To adjust the pre-load you need to first back off the locking nut. Use a punch and hammer to loosen the lock nut.

To adjust the pre-load, simply reach in and grab the spring and turn it. When you turn the spring the adjusting nut will turn as well. Do not attempt to turn the adjusting nut by hitting it with the punch, that will just lead to a lot of frustration. Turning the spring is easy. I recommend making a mark on the spring so that you know when you have made one full turn. Expect to get about 20 mm of sag adjust per turn.

Like sparky said, when you measure the race sag (with your weight on it) sit on the bike and bounce up and down a little bit, then let the bike settle. Be sure you are sitting in the normal place, hands on the handlebars, feet on pegs. I like to be up next to a wall so I can balance by pushing my elbow against the wall, otherwise you need help to hold you upright.

With the race sag set, measure the "static" sag, the amount it sags just from the weight of the bike alone. This should be about 25 mm, or an inch. If you are heavier than the expect MX rider (170 lbs) then you will have cranked in extra preload for race sag and your static sag will be low. If you are lighter then you will have backed out the pre-load and the static sag will be more.

If the static sag is way off then you may want to consider changing the spring.

To get the most out of your suspension you will need to adjust the compression and rebound rates for both the forks and shock (rear). These are done with the "clickers", the little flat blade screwdriver slots that you see on the shock and forks. The forks should have two, one at the top and one at the bottom. There may be a rubber plug covering the clicker at the bottom. The rear shock may have two or three. Two adjustments are for compression and rebound. A third adjustment may be provided to provide separate adjustments for "high speed" and "low speed" compression. Note that the speed does NOT imply the velocity of the bike, it implies how sharp the bump is. Hitting a curb is a high speed compression. Hitting a dip is a low speed compression, even if you are going fast.

Before you do anything, figure out where they are set so you can set them back if needed. Turn them in (clockwise) until they bottom. Gently, do not force them! They should "click" every 1/4 turn. Count the clicks in, write it down, then back them out to where you started.

I am sure that a pro rider can take a lap around a new track then bring the bike into the pits and tell the pit crew "I need two more clicks on the fork compression and back the shock rebound off 1"

I can't do that. The only way I know of to adjust is to pick a section of track/trail as a test area. Take a lap with the bike the way it was. Make one adjustment, hit that section again. Decide if it got better or worse. If it got better, leave that adjustment and go on to the next. If it got worse, try it one click the other way. If it is still worse, put it back where it was, go on to the next adjustment. Repeat until you are either exhausted or you can't make it any better.


Rod

 

[longtime coming]

hod928,

Order yourself a factory service manual. It will more than pay for itself very quickly. It will tell you almost all you need to know to set up your bike and maintain it properly. Worth its weight in gold. I think you mentioned something about racing next season on another thread. Do yourself a favour and get that manual. The owner's manual can be handy too.

my 2c