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setting sag


ducati448

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Setting sag is frequent dirt rider issue yet not one I've attended to as street rider. Dirt riders typically look for 1/4 to 1/3 of total suspension travel as static sag; with my XR's 12 inches of rear suspension travel, I've set rear sag @ four inches by first measuring distance between rear axle (or similar center of wheel point) and rear fender mount (again, any fixed point near rear of seat) with bike on box (center stand would do), then same measurement with me on bike (bike off stand); difference between these values constitutes rear sag which is adjusted by rear spring preload.

I'm curious if this issue is attended to by other street riders.

 

Wooster w/age induced rear sag

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ShovelStrokeEd

Just a comment, it would be better if you adjusted the sag via spring rate change with the preload set in the lighter 1/3 of its range. You can then fine tune as the spring wears or load changes with the preload adjuster. It's a far more expensive way to do things but you wind up with a better performing suspension.

 

Same deal in the front.

 

The way it goes is that a too light spring will still collapse too much during riding and leave you at the bad end of the shock travel. Preload won't compensate for this as the force per unit travel does not change on the spring with preload, unless, of course, you are using a progressivly wound spring. Even there, it is no substitute for one with proper rate.

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Please allow me to chime in here and I'll tell you what I do. Static sag-distance a bike compresses with weight on it, rider sag is with rider. Start with the rear shock and try to get all measurements w/in a 1/16". ANd get a total of 3 people if you can.

Pick 2 points to measure at like the tip of your axle and somewhere on the subframe if you can, or at least an exact spot on the plastic bodywork. First find the full extension by having 2 guys pull up on the footpegs to fully extend the rear to where the wheel almost comes off the ground. Record this distance on a sheet of paper.

Now have one guy balance the bike while another settles it by pushing up and down. Measure again. The difference between these two measurements is your static sag. I am not sure what it should be for a BMW telelever but most experts say you should have a good 5-10mm static sag. Now sit on your bike and have a guy balance it for you, but first bounce up and down a few times again, and while all your weight is on the bike and somebody is holding it for you, have the other guy make a measurement [it helps to have the same guy on the tape each time]. Always measure at the same exact spots. Record this measurement.

Subtract your rider sag measurement from your full extension measurement for the rear sag. YOU need have at least 30mm of sag. If you have too much sag turn your preload adjuster in. Do the same for the front as you do for the rear. YOU want about 20mm free sag and 35mm at least for rider sag on the front. I hopw this helps you get a baseline to start from and adjust to your own comfort level.

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Please allow me to chime in here and I'll tell you what I do. Static sag-distance a bike compresses with weight on it, rider sag is with rider. Start with the rear shock and try to get all measurements w/in a 1/16". ANd get a total of 3 people if you can.

Pick 2 points to measure at like the tip of your axle and somewhere on the subframe if you can, or at least an exact spot on the plastic bodywork. First find the full extension by having 2 guys pull up on the footpegs to fully extend the rear to where the wheel almost comes off the ground. Record this distance on a sheet of paper.

Now have one guy balance the bike while another settles it by pushing up and down. Measure again. The difference between these two measurements is your static sag. I am not sure what it should be for a BMW telelever but most experts say you should have a good 5-10mm static sag. Now sit on your bike and have a guy balance it for you, but first bounce up and down a few times again, and while all your weight is on the bike and somebody is holding it for you, have the other guy make a measurement [it helps to have the same guy on the tape each time]. Always measure at the same exact spots. Record this measurement.

Subtract your rider sag measurement from your full extension measurement for the rear sag. YOU need have at least 30mm of sag. If you have too much sag turn your preload adjuster in. Do the same for the front as you do for the rear. YOU want about 20mm free sag and 35mm at least for rider sag on the front. I hopw this helps you get a baseline to start from and adjust to your own comfort level.

Using a center stand to get the wheels off of the ground might be a little easier than have two guys lift the bike by the pegs.

 

There was a one page blurb on setting sag in a magazine I read. I thinkn it was Motorcyclist. Not excactly sure. They had a turbo V-ROD and a a turbo Rocket III in the same issue if that helps.

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