The basic motorcycle suspension setup is easy. It might look hard. But really it is not. The rewards in handling are substantial!
BOTH sags (static and rider sag) need to be in the correct range to get your suspension to work properly.
Sag is the amount the bike sags at standstill. It is needed to make sure the wheel is able to move down when it passes over a hole in the road. If there is no sag, the wheel can only move up compromising safety, comfort and speed (you know how important it is to keep the rubber down!)
If your weight is between 70kg and 85kg you should be able to set both sags correctly with the original spring.
You will need
(You will notice I like my lists!)
This page is focused on enduro or MX bike suspension setup because the negative effects of bad setup are bigger when the suspension has a long stroke like on off road bikes. But the same principle applies for adventure bikes, mini bikes and road bikes. The sag range differs but you can find that in your manual.
So this is how you start your motorcycle suspension setup:
Mark a point vertically above the rear wheel axle on the rear mud guard. Measure and note the distance between the axle and that point.
This measurement is your suspension fully extended (FE)
Now remove the bike from the stand. Push down on the seat a couple of times so that the suspension moves up and down. Then let the bike settle under its own weight. Measure again the distance between the axle centre and your marked point.
This measurement is your suspension sagged under the bikes weight (BW)
The difference between the first measurement and the second is called static sag.
FE - BW = Static Sag
Motorcycle suspension setup: static sag range
Linkage bikes 25-50mm.
Non linkage bikes 30-40mm.
Now sit on the bike in your riding gear and let someone hold you in a balanced position while you bounce up and down a couple of times with weight on the foot pegs. Then sit feet on pegs in your normal riding position. Let your friend measure the distance between the axle and your marked point.
This measurement is the suspension sagged under the rider weight (RW)
The difference between the first measurement (fully extended) and this measurement is called rider sag.
FE - RW = Rider Sag
Motorcycle suspension setup: rider sag
Linkage bikes 95-105mm rider sag.
Non linkage 100-110mm.
If in doubt you can also look up the right range for your sag in your manual.
If you are within the zone for rider sag AND for static sag then your spring rate is fine for you. Congratulation! You making good progress with your dirt bike suspension setup. You can go on to check if your bike is balanced. That is the next most important sep to get your suspension dialed.
If you are not in optimal zone then you need to adjust the sag by
changing the preload. The spring preload is the amount (mm) the spring
is compressed by the preload adjuster. Where is the preload adjuster and
how does it work? "Read your f.... manual!" (That was the answer I used
to get from my first source of information - a KTM mechanic in Graz). Otherwise you can also refer to this article: Get familiar with your adjusters.
For safety reasons it is necessary to stay within the sag recommendations!
If you need to change the rear spring in order to get your motorcycle suspension setup properly your dealer can tell you the next harder or softer spring rate available for your bike. You have to change both springs front and rear at the same time. Otherwise your bike won't be balanced front to rear and that creates other handling problems.
It is also possible but not recommended. Forks tend to have a lot of internal frictions and measurements are not consistent.
This motorcycle suspension setup as mentioned above refers to dirt bikes. For road bikes or mini (80cc)bikes or any other motorcycle for that matter the rider sag (by rule of thumb) should be approximately one third of the wheels stroke (measurement of suspension fully extended (FE)). 85cc with 210mm (FE) should have around 70mm rider sag. Check what the manual recommends as static sag and stay within a couple of mm around that value.
If you have problems interpreting your sag results (like I get the right rider sag but my static sag is out etc.) then check out the article on spring rate and sag.
If you have the right springs and the sags are set then you can check out how to work with your click adjusters.
If you still experience handling problems like headshake you can check out the article about how to get rid of headshake.
In the RACING section I also have an article about worst mistakes people do to their suspension and how to fix them. Good if you want to avoid your next crash.
The Dirt Bike Garage Manual
HOW TO GUIDE for "do it yourself" riders