Dirt bikes are a specific part of the motorcycle world, and riding them brings a lot of joy, especially if you are a skilled rider who knows what he wants and takes the maximum out of his bike. These bikes have some characteristics that every rider needs to give extra attention and your dirt bike’s suspension sag is one of them.
If you own a dirt bike, you need to know how to adjust your suspension sag correctly and if you are not familiar with how it needs to be done, or you just want to check your knowledge, then this is the perfect article for you since we will explain how you need to adjust your suspension sag.
So how do you adjust the dirt bike’s suspension sag? As a general rule, you need to add more preload or spring tension if the sag is over 100mm. On the opposite, if your sag is less than 100mm, which indicates that the sag is too little and your bike needs less preload. Either way, you need to measure the sag to see if it needs more or less preload.
If you want to learn more about your dirt bike’s suspension sag, continue reading as we will explain all in depth how it needs to be done and what things you need to pay attention to.
Table of Contents
What Is Suspension Sag?
Suspension sag is the distance between how much your dirt bike settles on its rear suspension and what is the range from the rear suspension to the full extension. The sag can be measured in two ways:
- Race Sag: This is the sag measure when the rider sits on the dirt bike.
- Static Sag: This is the sag measure when there is no rider on the dirt bike, but the bike stays still under its own weight.
Dirt bikes that have too much race (rider) sag will result in dirt bike sitting further in the suspension stroke than it should, and it will cause the bike to have a lower steering response which is not very pleasant to feel during off-road rides. Your bike’s steering rack will increase since the rear part of the bike has squatted as it spun around the front axle.
On the other hand, if there is too little of the sag, the opposite will happen. A rider will notice that the steering is too quick, and your dirt bike seems like it is nervous when the bike is on its nose, and the steering angle is also much steeper.
How Do You Measure Suspension Sag?
Measuring your dirt bike sag is a simple task to perform. All it takes is some tools, math knowledge, and help from a friend. You will also need a sag scale or tape measure if you want to spare your time from math calculation. In this case, I will take a tape measure to show you how it needs to be done using math.
If your dirt bike is Japanese, you will also need to use a hammer and punch for adjusting the spring. European dirt bikes require the matching Allen key that you will need to loosen the adjuster clamp, together with hammer and punch to shift the spring adjuster.
Place your dirt bike on a stand and start measuring from the rear axle spot to the rear fender. Take your time, and don’t hurry, so you are sure that you measured it correctly.
Tip: Take measurements from the same spots in the process to be sure that the measurements are consistent and precise. I like to use a sharpie or a knife to mark the spots from which I take measurements. You need to measure it in millimeters and note that on a piece of paper.
Now you need to sit on a dirt bike while it is still on flat ground and ask a friend for help to hold your motorcycle for you so you can put both of your legs on the motorcycle pegs and place your hands on the handlebars.
Place yourself in a neutral position on the motorcycle seat and make sure you are not too far back or forward but right in the middle. If you don’t position yourself in the middle, but you are a little bit too forward or back, it will affect the measurements and lately on your handling.
Note: Make sure you get all the gear along with a helmet, backpack, chest protector, and everything you use while riding because every single pound can make a difference and influence the measurement.
Bound your bike a couple of times while you sit on it, and that way, determine the settling point. You will also need a friend’s help to measure the distance between these two points. The reason why you can’t do it alone is obvious. You cant be sitting on the dirt bike and measuring at the same time.
You need to take away this measurement while sitting on the dirt bike from the measurement you took first while the bike was placed on the stand. The number you will get is your Race Sag. You want your race sage to be close to 100mm, but to be exactly sure, take your motorcycle manual and check the proper race sag measurements written in it.
You can adjust suspension sag to fine-tune your bike’s handling. To get your bike more stable off-road, you need more sag, while to ensure faster handling on the track, you need less sag.
Note: Although it may seem unbelievable at first, only a 5mm range change can make a significant difference.
How Do You Adjust the Suspension Sag?
Once you have measured your suspension sag, it is time to adjust it correctly, and this is how it needs to be done.
If your dirt bike has too much suspension sag, which means that the sag is higher than 100mm, you will have to add more spring tension or more preload. If your dirt bike has too little suspension sag, which means that the sag is lower than 100mm, your motorcycle needs less preload.
Look for the spring preload locker and loosen it. The spring preload locker is a clamp on the European dirt bikes or a jam nut on the Japanese dirt bikes.
After you have loosened the spring preload locker, loosen or tighten the preload adjuster according to the needs of your dirt bike. A tighter preload adjuster means more preload and reduces the sag, while a looser preload adjuster means less preload and increases the sag.
Each complete rotation mainly changes the sag for 2-3mm, but it depends on the bike’s spring rate and the shock body thread pitch. Adjust the rider sag one more time and adjust it.
After you have adjusted the rider sag correctly, you will have to measure the static sag. You will determine if your spring rate is proper by measuring the static sag. After correctly setting the rider sag, the static sag should be in a range between 30 to 50mm. Measure the same spots while the bike is off the stand and without the rider sitting on it, calculate the difference between the motorcycle on and off the stand.
If the number you get is outside the required static measurement range, you need a softer or stiffer spring. If the number you get is bigger than 50mm, you need a softer spring. On the opposite, if the number is lower than 30mm, you need a stiffer spring.
After you have adjusted the rider and static suspension sag correctly, you need to tighten the preload adjustment locker, and that means that you are done with adjusting the suspension sag.
Now that the suspension sag is set correctly notice if there are any differences in handling your dirt bike. I certainly think you will see the difference.
Here is an excellent video from Rocky Mountain ATV MC that is a youtube channel with a ton of helpful videos, and this one is about adjusting your dirt bikes suspension sag:
Final Thoughts
Dirt bikes are a special category of motorcycles (and by special, I mean that they can give you so much fun, especially on off-road terrain, and that is why they have a special place in my heart) that are loved by every rider (at least that I know) that has ever tried riding a dirt bike. Maintaining and servicing dirt bikes is also important, as is servicing “normal” road bikes like cruisers and sportbikes. Suspension sag is one of many characteristic things about dirt bikes that you need to consider when preparing your dirt bike for both road and off-road rides.
This article has covered all the important things you need to do and prepare for adjusting your dirt bike’s suspension sag. I have tried to write it as simple as possible, so the riders who may come with this process for the first time don’t have any problems performing it. We hope that this article has helped you adjust your suspension sag successfully, and if you struggle with some parts, I advise you to get back to the text and look for the solution because this process was written to the very last detail.