I've been trying to learn as much as possible lately about suspension, and correct sag is the first step in setting up suspension, so in light of our new suspension and brake section, I thought I'd share what I've learned.
What is sag?:
Sag is how much your suspension is compressed while not moving. Race sag, (also called rider sag, or actual sag), is how much your suspension is compressed with the rider on board, in full gear. Static sag (or free sag) is how much your suspension is compressed under the weight of the bike. The sag specs for front and rear are very important to how your bike handles. They affect steering geometry, indicate whether you are using the correct spring rates, and much more.
Measuring sag:
You will probably need a helper to get accurate measurements, but the process itself is very simple. Pick arbitrary points on the fork, and the axle to tail, and take your measurements. You should be in full riding gear, and place most of your weight on the footpegs, in your "attack position".
Race sag = spec fully extended - spec with rider.
Static sag = spec fully extended - spec under bike's own weight.
Measure measure race and static for front and rear.
Setting sag:
Now that you know what you have, it's time to set your sag correctly. This is done by changing your preload settings. Changing preload on the rear is done with the large nuts on the spring. Some forks have preload adjustments, but other's don't. In that case, you need to make correct preload spacers for the springs. Obviously that requires you to tear down the forks.
Always set your preload to achieve correct race sag, never set for static sag. Once you have correct race sag, the subsequent static sag will tell you if you have correct spring rates.
Always set rear sag first!!!!!!!
I finally found good info on what sag should be for different types of bikes, here it is:
Offroad and MX bikes:
Front Race sag: 22-25% of travel (65-75mm on most bikes).
Rear Race sag: 30-33% or travel (95-100mm on most bikes).
Front static sag: 25% of race sag
Rear static sag: 30% of race sag
Street bikes:
Front Race sag: 28-33% of travel (30-35mm on most bikes).
Rear Race sag: 28-33% of travel (30-35mm on most bikes).
Rear static sag: 0-5mm
Roadrace bikes:
Front Race sag: 23-27% of travel (30-35mm on most bikes).
Rear Race sag: 23-27% of travel (30-35mm on most bikes).
Rear static sag: 0-5mm
Once you set your correct Race sag, go back again and measure everything. If race sag is correct, check your static sag. If your static sag is too little, your spring is probably too soft for your weight. If your static sag is too much, the spring is probably too stiff. This may sound counter-intuitive, but for example, if your static sag is too little, that means you had to apply too much preload to achieve the correct race sag, and vice versa.
Another method of course is too use online spring rate calculators, that is especially helpful with forks. It's really difficult to get accurate measurements with the high levels of static friction on fork tubes.
Springs are the most important part of your suspension, and only then can you work with dampening to get really good performance. Sag is the key to correct spring rates and preload.
If anyone has anything to add or has questions, dont be shy.
What is sag?:
Sag is how much your suspension is compressed while not moving. Race sag, (also called rider sag, or actual sag), is how much your suspension is compressed with the rider on board, in full gear. Static sag (or free sag) is how much your suspension is compressed under the weight of the bike. The sag specs for front and rear are very important to how your bike handles. They affect steering geometry, indicate whether you are using the correct spring rates, and much more.
Measuring sag:
You will probably need a helper to get accurate measurements, but the process itself is very simple. Pick arbitrary points on the fork, and the axle to tail, and take your measurements. You should be in full riding gear, and place most of your weight on the footpegs, in your "attack position".
Race sag = spec fully extended - spec with rider.
Static sag = spec fully extended - spec under bike's own weight.
Measure measure race and static for front and rear.
Setting sag:
Now that you know what you have, it's time to set your sag correctly. This is done by changing your preload settings. Changing preload on the rear is done with the large nuts on the spring. Some forks have preload adjustments, but other's don't. In that case, you need to make correct preload spacers for the springs. Obviously that requires you to tear down the forks.
Always set your preload to achieve correct race sag, never set for static sag. Once you have correct race sag, the subsequent static sag will tell you if you have correct spring rates.
Always set rear sag first!!!!!!!
I finally found good info on what sag should be for different types of bikes, here it is:
Offroad and MX bikes:
Front Race sag: 22-25% of travel (65-75mm on most bikes).
Rear Race sag: 30-33% or travel (95-100mm on most bikes).
Front static sag: 25% of race sag
Rear static sag: 30% of race sag
Street bikes:
Front Race sag: 28-33% of travel (30-35mm on most bikes).
Rear Race sag: 28-33% of travel (30-35mm on most bikes).
Rear static sag: 0-5mm
Roadrace bikes:
Front Race sag: 23-27% of travel (30-35mm on most bikes).
Rear Race sag: 23-27% of travel (30-35mm on most bikes).
Rear static sag: 0-5mm
Once you set your correct Race sag, go back again and measure everything. If race sag is correct, check your static sag. If your static sag is too little, your spring is probably too soft for your weight. If your static sag is too much, the spring is probably too stiff. This may sound counter-intuitive, but for example, if your static sag is too little, that means you had to apply too much preload to achieve the correct race sag, and vice versa.
Another method of course is too use online spring rate calculators, that is especially helpful with forks. It's really difficult to get accurate measurements with the high levels of static friction on fork tubes.
Springs are the most important part of your suspension, and only then can you work with dampening to get really good performance. Sag is the key to correct spring rates and preload.
If anyone has anything to add or has questions, dont be shy.