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Setting Race Sag - The STS Way

06 Apr 2010 2:24 PM | Anonymous

This is the first in a series of suspension and bike setup tips from Ellis Tull of STS Suspension.  Thanks very much to STS for supporting the NMA and taking the time to educate us on the importance of this these topic.

The most important step in suspension set up is setting your race sag, the first thing to do take your bike for a little ride through the pits just to get all the stiction out of the suspension put your bike on the stand and take a measurement from the rear axle to a marked point on your rear fender, slightly left of vertical, record your measurement (I use mm because you don’t have to work with fractions).

Have the rider with full gear on sit on the bike in their normal riding position, have someone hold the front of the bike take another measurement from the same 2 spots as the first one, record the measurement. The difference should be approximately 100mm (for most bikes, however check your owners manual to verify correct race sag for your bike).

If it less than 100 mm you need to undo the preload lock ring on the shock and turn the shock collar counterclockwise to take some preload off the shock spring, if the second measurement is say 94 mm mark the preload ring with a Sharpie pen then turn the  preload ring counterclockwise 2 revolutions (each complete turn on the ring is equal to 3 mm) after you get 100 mm you need tighten the preload lock ring and then check your free sag. This can be done by having your bike on the ground under its  own weight and push down on the rear of the bike and let it come up on its own, take  a measurement from your axle to the same point on the fender the number you get is your free sag. It should be between 30 and 40 mm.

This measurement tells you if your spring rate is correct or not, if the free sag # is more than 40 mm you need to get a softer spring, and if the # is less than 30 mm the spring is to stiff.  This may seem backwards but if your race sag is set at 100 mm and the spring is to stiff you will have had to turn the preload ring close to the top of the usable threads on the shock body to achieve your 100mm number, once you drop the bike to the ground to check the free sag the bike will drop down considerably under its own weight as there is very little preload on the spring thus you free sag # will be quite high. On certain bikes such as KTMs you will need to run 110-115 mm of race sag and with mini bikes the race sag should be 85-95 mm.  The most important thing when setting your sag is to take your measurements from the same spots both times. Setting you sag may seem difficult but you are wasting your time trying to do anything without doing this first. Once you get used to this procedure it should take only 5 minutes. I do this pretty much before every ride.

Contact STS at (250) 722-2639 or info@stsracing.ca if you have any questions.

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