Looking to set the sag on your dirt bike?
Setting the sag for your suspension is real important. To handle your weight and riding style
To improve the ride and handling of your dirt bike
So to start with maybe you’re wondering
What is Dirt Bike Sag
Now sag refers to the amount the suspension sags. Or how much the shock gets compressed.
When the rider sits on the dirt bike.
Or how much it sags under it own weight by its self
There is Different Types of Sag
- Free Sag
- Race sag
- Static Sag
Is when the bike is on a stand. Tires are off the ground, and no weight on the suspension.
Or also known as rider sag.
Which is when the rider is on the bike, and how much the suspension sags.
And then you have
Which is when the bike is on the ground under its own weight standing straight up and down.
Just keep in mind
When you’re setting sag for any type of bike.
Refer to your specific dirt bike service and or owner’s manual.
To get the exact instructions, and specs for where the sag should be,
More Sag vs Less Sag
If you have
It will handle better at higher speed straight line stuff
Because the rear end of the bike will sit lower which might be good if you’re more of a desert style racer
And, if you have
It will raise the rear of the bike
So. it will help give the bike better steering cornering characteristics
Which, you might want if you’re running a track.
Though you will have to figure it out what best fit your riding style and terrain
By changing the sag
You are essentially just setting the preload on the shock spring
Tightening or loosing it to fit your needs
Now some of the
Dirt Bike Sag Tools You Will need
You might want it to have metric measurements on it
You will have to convert from inches to mm.
Because if you use a standard tape measure you will need to do some math
So you might be a good idea
To keep a piece of paper handy to write the figures down. So you don’t forget as you go along
Now using a
Sag Scale Tool
Can allow you to measure easier.
As it fits in the centerline of the rear axle
And you can adjust it, and set it to 0 (zero) on your reference mark.
That you make on the fender.
Then once you’re done lock it in place. Rather than trying to hold a tape measure still.
And also so you don’t have to do the math.
Some people like to use a
To make a small reference spot (dot) on back fender
So you’re able to measure back to the same spot
But, if you don’t want a small spec of marker on your fender/plastic
Might need to find something else
You hear of some people using a small piece of masking tape (painters tape) to put a mark on.
But use whatever works best for you.
Now you will also need a
Or a shock preload adjuster tool, or a spanner wrench
However some people use a long flat head screwdriver
To be able to loosen up/tighten, and turn. The shock lock nut, and preload adjustment nut.
Might need a
To tap on your punch tool to get jam nut loose on the shock
Though keep in mind
Might Need a Friend or Two to Help You
To hold the bike and stabilize it
And to read the measurements while you sit on the bike
No fiends around the
Motool Slacker (Digital Sag Scale)
Is a good option
The Motool Slacker can allow you to set dirt bike sag by yourself. Turning a couple people job into one.
Make sure the rider of the bike will
Have All the Gear On
That they would normally be riding with
Helmet, boots, etc
And if you wear a backpack or tool belt. Have that on as well.
Also make sure to have a full tank of gas.
So you can get an accurate sag reading
Ok so before we get into how to set the sag.
Here is some different tip’s on how to measure.
How to Calculate Dirt Bike Sag
Not to get to off topic here. But this could come in handy
If you want to know
How to Convert (mm) to Inches
There is 25.4 mm in one inch so take the amount of
To convert mm to inches take amount of mm the divide by 25.4 to get inches
50mm ÷ 25.4 = 1.968”
And then here’s
How to Convert Inches to (mm)
Multiply the amount of inches times (multiplied) X 25.4
1 ¾ “ (1.75” x 25.4 = 44.45mm )
And then to convert back to inches take 44.45mm ÷ 25.4 = 1.75”
.125″ | 1/8” | 3.175mm
.250″ | ¼” | 6.35mm
.500” | ½” | 19.05mm
0.750” | ¾” | 20.65mm
0.875” | 7/8” | 22.23mm
0.938” | 15/16” | 23.83mm
1.0” | 1” | 25.4mm
To Calculate an Average Measurement
Take and add all measurements together.
Then divide that number by how many measurement there were
Say for example: 75mm, 77mm, 80mm (75 +77+80=232 ÷ 3 = 77.33mm)
When Using a Tape Measure
Standard or Metric
You will need to subtract the smaller (shorter) number from the bigger (longer) measurement
If you have 600mm free sag
Then when the rider is on the bike it’s 500mm. So you have 100mm of sag
This will give you the amount of sag
Now with all that out of the way
Let’s move on to
How to Measure Dirt Bike Sag
Now something to keep in mind is to take your time
And have the same person measure for you. So that things stay as consistent as possible.
It’s a good idea to measure few times
And then take the average of measurements
First let’s look at
How to Check The Free Sag.
So with the bike up on a stand. With no load on the suspension at all.
The swing arm is hanging down.
Make a mark on the rear fender.
With your Sharpie marker, or whatever you choose to use.
Creating a reference point.
So you can go to the same point every time. For an accurate measurement.
You can hook the tape measure in or on the axle if you can.
Or measure from the center point of the axle. To the reference point on your rear fender.
Though remember if you’re using a tape measure.
You will want to write your measurements down.
Because, you will have to do some math.
Once you have that done. Take the bike off the stand.
And lets move on to
How To Check Rider Sag (Race Sag)
Ok so now with the rider sitting on the bike.
You want the rider to be a little bit forward of centerline of the bike toward the tank
But of course need to be in a comfortable riding position of the bike seat
Just remember if you move forward or backwards on the bike seat.
It will change your sag measurement.
Standing Up vs Sitting Down
In a comfortable riding position, is the best way to balance weight. From the front to rear of the bike.
And most of the time
You will get a more consistent measurement.
But if you normally ride
It might be best to check the sag with you sitting down
Pay attention to where you are sitting on the seat. And how your feet are on the pegs.
Make sure to be consistent where you sit. So that you stay in the same spot.
Ok so as the rider is sits or stands on the bike.
Press down, on the back of the seat. To compress the suspension and then let off.
Do this a couple of times
This helps settle the shock. And get rid of and shock stiction
(Don’t push on the fender. It could move or bend. Moving your reference mark)
Take your tape measure or sag scale
And measure from the center of the rear axle. To the reference mark again.
Keep in mind you need this number. To be within sag specifications.
For whatever the bike calls for.
So be sure to always check your owner’s manual
But generally most bikes 250cc to 450cc. Will probably be around 100mm (+ -)
30-33% of the total shock travel. Which is up to about 4 inches on a 12 inch shock
So if you’re out of the specs on your measurements.
Then make adjustments as needed.
You will have to loosen, or tighten the spring preload.
Depending where you’re at.
How to Adjust the Rear Shock Spring
First you need to loosen the rear shock spring for adjustment
But keep in mind
Some bikes like KTM or Husqvarna will have plastic nut and a pinch bolt clamp.
You have to take the pinch clamp loose to spin the nut.
But on most bikes.
They have a double nut setup. To adjust the spring preload.
The upper nut is the jam nut. Which keeps the bottom adjuster nut from coming loose.
So you will need to break the top nut free,
And once it’s loose.
Most of the time you should be able to spin it up by hand.
Though if does get a little stiff. From gunk build up on the threads
Just put some WD40 on it. Then let it sit a minute. Though you still might have to work it a bit.
But if it’s free take the lock nut up a few threads higher than the bottom nut.
To give yourself some adjustment room.
Also on the adjustment nut.
You can make a mark on one of the tabs of the nut with a Sharpie marker.
So, you can tell when you make a full revolution with the nut.
Helping you keep track of each turn you make.
Ok now loosen or tighten the nut. Until you get to the desired height
Loosening the nut will lengthen the spring height. (less spring preload)
And it will lower the bike in the rear
Tightening the nut will compress, and shorten the spring height
Adding more spring preload
Which will raise the bike in the rear.
And keep in mind one full turn of the nut is roughly 2-3mm in height adjustment
Once you adjust and recheck sag
Move on to
Checking the Static Sag
This is the sag the bike has when it’s sitting on the ground under it’s own weight (No Rider)
So, you will again measure with your tape measure, or sag scale.
From the center of the rear axle (or same spot as you measured from before)
To the mark or reference point you made
Now if you’re using a tape measure.
Keep in mind
You will need to subtract this static sag measurement. From the original free sag number.
Most of the time bigger cc bikes have roughly between 30 to 40mm of static sag.
But always check your owners manual. For your bikes specific sag specs.
Because every bike is different.
Let’s say for example you’re specs do call for a 30 – 40mm static sag
Now if you are outside the specs for your static sag. You might have to go with a stiffer or softer spring
Because what the static sag is telling you.
Is that you’re outside the parameters of the proper preload on the spring
This is contingent on the fact you set the race (rider) sag properly
Now if you do have,
Too Little Static Sag
This happens if you have to crank down on the spring too much.
To raise the race (rider) sag back in in spec.
If you’re trying to help accommodate the riders weight
But by doing that you’re adding a lot of preload to the spring itself
And now lets say for example you’re at 20mm or less static sag.
Which is not enough static sag,
If, it’s, supposed to be between 30 – 40mm to be in spec.
So, you will ultimately need to upgrade to a stiffer spring.
Or maybe you have,
Too Much Static Sag
So if you had to loosen the spring too much to lower the race (rider) sag
To try to keep it in spec. The opposite will occur.
You now could have too much static sag.
Lets say for example.
You’re at 50mm static sag. So, you will need to change to a softer spring.
To help bring it back in specs.
Though you want to keep in mind. If you have to go with a way stiffer spring rate.
You’re going to have to change your valving to match the stiffer spring rate,
That’s a different topic for another time.
Button it up
So once you get everything where you want it.
Just tighten back down that upper jam nut. Or, the pinch clamp bolt.
Depending which style/setup you have
And now you’re ready to go ride.
Ok if you want to know what to do
Setting Dirt Bike Sag by Yourself
You will need to use the MoTool Slacker
But first you will need to find the arc of the swing arm/axle
Then make a mark on the back of the bike for a reference point to measure off of and a string
Find the Arc of the Swing Arm and Make a Mark
With the bike on a stand.
And the wheel off the ground
Find the arc of the swing arm
By taking a string (cord) and putting one side at the pivot point of the swing arm, (at the frame)
And hold it there
Run the string along the swing arm
Until you reach the centerline (point) of the rear axle
Then pinch it with you fingers.
While keeping the left hand in place
Holding the string in the center of the pivot point of the swing arm.
Keeping the string taught (but don’t stretch it)
Lift up your right hand (if your on the left side of the bike)
Until you reach the rear fender (back of the bike)
To see where the string intersects the rear of the bike
So wherever you’re right fingers holding the string land
You know where to
Place your reference point. (Mark)
With the Sharpie marker (or whatever you choose to use)
Now this is the arc or travel path of the axle (swing-arm)
Put the clamp on over the mark
Then connect your MoTool slacker on the axle it’s magnetic
Now attach the hook on the string. Up to the clamp on the reference mark.
Make sure the MoTool Slacker is pointing in a straight line. To the clamp on the reference mark.
Zero out the scale with the free sag
Hook up your handlebar mount display. Connect the wire to the main unit.
Take the bike off the stand gently
Hold the bike straight up and down
Check the Static Sag
Lean it up against a wall. To help you balance the bike.
Standing up in riding position. Bounce a couple of times.
Let the suspension settle then
Check the Rider Sag
For a more accurate reading. Double check it couple times
Now, having the rear sag set is the most important and needs to be done first
Once you get the rear sag dialed in and wondering
This is how to
Check the Front Fork Sag on a Dirt Bike
First like above you need a
You can measure from the center of the axle. Or from the bottom of front fork casting.
Up to the wiper seal surface. Or a reference point on the front fork body.
Or triple clamp whatever works for you
As long as you keep measuring in the same consistent place.
Now start with
Check Front Fork Free Sag
By measuring it on the stand first. With the wheels off the ground.
Then take the bike off the stand
Check Front Fork Rider Sag
Sit or stand on the bike. (Just stay consistent with what you’ve been doing.)
With all your riding gear,
Make sure the gas tank is topped off. Like mentioned earlier for the rear sag.
Now to find a constant resting place.
Push down the forks. And then let it come up slow, and let the forks settle and measure.
Then pick up a bit on the front forks let go slowly. Then let the front forks settle and measure.
So you might want to do that a few times.
Then take average of the up and down measurement to get your figure
Ok so now
Subtract the new measurement. From the free sag measurement.
To get your front fork rider sag.
Most of the time
Front Fork Rider Sag should roughly be 22-25% of the total fork travel
Then without the rider
Check Front Fork Static Sag
So, hold the front brake. Lift up and push down the front forks and let go
Repeat a couple of times. Then let the suspension settle
Now with the bike brakes off
Having someone hold the bike straight up and down.
Then take the measurement
Take this measurement and subtract it. From the first free sag figure. To get total static sag.
Check your specs in your dirt bike owner’s manual.
But most of the time
Front fork static sag. Should land roughly between 5-10% of the total fork travel
If you don’t have the right amount of rider sag. You can try to adjust the preload on the springs.
If you have the right amount of rider sag and in spec. But the static sag is not within the specs.
You are going to need a different spring rate. To set the bike up properly for your weight.
You need to make sure that the forks are straight. And that the front wheel is installed properly. As sometimes the forks could be in a bind on the axle. Causing more stiction on the fork tubes. Check more on that here
Double check, and make sure it’s where you want it. Before and after making adjustments
Then once you get the sag set. Now move on to adjusting compression and rebound.
Also as an
Tape Measure Tip
Starting with the bike on a stand rear wheel off the ground (for free sag)
Take a metric tape measure.
Hold the tape measure.
With the body (case) of the tape measure at the bottom somewhere on the swing arm at the axle
And then extend the tape hook up, and out past the reference mark, on the fender
Until it gets to the 10cm (100mm) mark on the tape measure
Then lock the tape in place
Make sure to first set and lock it to the free sag on the 100mm mark
Then have the rider get on the bike
Stick the tape measure body (case) back up against on the same spot of the swing arm at the axle.
With the tape hook sticking up past the mark on the fender.
Then however much it goes down on the tape measure
Will be the amount of sag you have
Set on 10cm/100mm
When the suspension sags down
And it works its way from 100mm down to 110, 120, 130, and so on
So from 100mm to 190mm would be
90 mm sag
This is a method that can take the place of a using a sag scale tool.
And can keep you from having to do some math
But then again its still most of the time easier, to use a Motion Pro Sag Scale
Or if you’re by yourself use the MotoTool.
As it can sometimes be hard. To hold the bike steady, and tape measure still.