How To Set Dirt Bike Sag

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

 

So,

Free Sag 

Is when the bike is on a stand.  Tires are off the ground, and no weight on the suspension.

 

Race sag

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

Static Sag

 

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,

 

Now

More Sag vs Less Sag

If you have

More Sag

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

Less Sag

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

 

Like a

Tape measure

You might want it to have metric measurements on it

Or

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

Sharpie marker

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

Punch Tool

 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

Hammer

 To tap on your punch tool to get jam nut loose on the shock

 

Though keep in mind

You

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.

 

Also

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.

And

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

 

For example

 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   

 

 For example

  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

 

Also

To Calculate an Average Measurement

Take and add all measurements together.

Get total

Then divide that number by how many measurement there were

Say for example: 75mm, 77mm, 80mm     (75 +77+80=232 ÷ 3 = 77.33mm)

 

 

Now,

When Using a Tape Measure

 

Standard or Metric

You will need to subtract the smaller (shorter) number from the bigger (longer) measurement

For example

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.

 

Then,

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.

 

Now,

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.

 

Also

Standing Up vs Sitting Down

 

Now

Standing up

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

Sitting down.

It might be best to check the sag with you sitting down

However,

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)

 

 

Now

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.

Ok, so

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

Ok,

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.

And now,

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,

But

That’s a different topic for another time.

 

Alright lets,

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

When

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

 

So let’s

Find the Arc of the Swing Arm and Make a Mark

Now

With the bike on a stand.

And the wheel off the ground

And to

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.

 

Now

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.

 

Now

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

But

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

Reference Mark

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

And now

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.

However

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.

 

 

Note

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

 

 

Final Thoughts

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

Extra Bonus

 

Here’s another

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

 

For example

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.