XS650: Sag   Leave a comment

Your body can and will tell you all about this. In time. Some parts more than others. Size. Weight. Time. Wear. All, factors.

The harder they come the harder they’ll fall, one and all

 

Amount of change in your motorcycle’s suspension travel with the rider on board-varies around 30% of your total suspension travel. Helps you choose correct spring rates. And correct spring pre-load.

Because suspension works under both compression and dampening a certain amount of preload prevents topping or bottoming out.

First check your springs. Correct rate. Not too progressive. Fork oil. Seals. Bearings. Set your gearing. Half tank of gas. Load when touring.

Have a look at this. For help choosing springs. From here. May need separate springs for touring or carrying a passenger. Or riding conditions.

Static Sag.

Best with a couple of mates. 1 to help you hold the bike up. The other to measure.

Paul Thede from Racetech advises to allow for stiction. Friction and inertia. Both serve to complicate correct measurement but can be compensated for.

Mark 2 points front and rear. Axle centres..2. Frame..2. One each above and below the spring. Front-lower triple clamp. Rear-as close to perpendicular as possible.

  • L1. Set the bike on it’s centrestand. Or racestand not interferring with the swingarm. So both wheels are at full suspension extension.

Measure and record.

Set the bike on the ground. Sit the rider on the bike. In riding position. With full gear.

  • L2. Push down on the suspension. 25-30mm. Slowly release. Measure.
  • L3. Liftbike and rider. 25-30mm. Slowly lower to rest. Measure. Average. This is Static Sag.

Static Sag … L1- L2 + L3/2

Free Sag

Sag from bike alone. Only makes sense after Static Sag is set. Push down. Slowly release. Measure. Lift. Slowly lower. Measure. Split the difference. This is Free Sag. Used mostly setting up rear suspension.

Don’t ignore your stiction result L2-L3. This shows suspension condition. Front should be 10-20mm. Rear, 2-3mm. More or less than these? Time to start getting intimate with your bouncies.

Recommended Sag Measurements: mm …from Racetech

Road Race Street Dirt-full size Dirt-mini
Front
Sag 25-35 30-35 60-75 55-65
Preload 5-25 10-35 3-15 3-10
Stiction 5-15 5-15 10-25 10-20
Rear
Sag 25-35 30-35 90-100 80-85
Free Sag, Top-out bumper 2-8 2-8 15-40 10-25
Free Sag, negative spring 10-15 10-15
Stiction 2-5 2-5 2-5 2-5

Correct Sag numbers are personal. Will vary depending on the type of bike you ride, your individual riding style, your weight of the day, surface conditions….. This may help you get a baseline. Fine tuning is up to you.

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Posted February 15, 2011 by xscafe in Frame - Forks, Frame - Handling

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