One of the best ways to improve the handling of your bike is to adjust the rear preload settings of your suspension. And with most bikes, it’s something you can change using the tools that come with your toolkit. It’s a free upgrade! And while you can adjust your rear preload settings through trial and error, the best way to change your rear preload is to properly understand it, take some measurements and then test.
Just to clear up any confusion – adjusting rear preload in no way either stiffens or softens your rear suspension. It also does not change your spring rate. All it does is change up or down the initial position of the suspension, either when you’re sitting on it your bike or not – these terms are known as Rider Sag and Static Sag.
When you sit on your bike, you’ll note that the suspension compresses a bit. This is what you want to happen, but depending on your weight it may compress too little or too much. Ideally, you want the majority of the suspension travel to be available for actually riding – not supporting your weight. This is why it’s necessary to adjust rear preload as bike manufacturers obviously set their sag amounts on what they deem is an average person’s weight.
So how do you correctly set your rear preload? We need to take three measurements. For all three measurements you need to measure from the center of the rear axle (marked with a yellow circle below) and a fixed point above the axle. I’ve placed a mark on the pillion grab rail, marked below with a blue circle.
Our first measurement we take is to see what the fully unloaded, or unweighted length of the rear suspension is. This measurement only ever needs to be taken once, even after you change the preload settings.
To measure it correctly, there can’t be any weight on the rear wheel. If you have a center stand the you’re in luck. If not, you’ll need to improvise. You can’t use a paddock stand as weight will still be going through the rear swingarm where the paddock stand attaches to. In the picture above, I chocked the front wheel and used a car jack under the bike with some styrofoam to prevent any scratches. If you’ve got some strong friends, they could hold the rear of the bike up while you perform the measurement.
Our next measurement gives us the normal suspension length, or the length of the suspension under the bike’s own weight. Place the bike back down like you’re parking it but try to have it as upright as possible (i.e. not leaning on its side using the kickstand).
The final measurement we take will provide us with the fully loaded length of the rear suspension. This is the length of the rear suspension when you sit on the bike. To be as accurate as possible, it’s best to put on all your riding gear and sit on the bike just as if you were on the road. You’ll need some help here, as you won’t be able to make the measurement while sitting on the bike and also to help balance the bike while it’s off the kickstand. Make sure your feet are on the pegs and not the ground to get an accurate measurement.
Now, let’s use those measurements and convert them to our Rider Sag and Static Sag figures.
Rider Sag = A – C
Rider Sag is how much the bike ‘drops’ when you sit on it. The ideal figure for Rider Sag is between 30mm and 40mm. Some prefer to be as close to 30mm as possible, but for general street riding and the occasional track day, around 35mm should be fine.
If your Rider Sag is above 40mm then it means your rear preload is too soft and conversely, below 30mm means it’s too hard.
Static Sag = A – B
Static Sag is how much the bike’s own weight acts on the rear suspension. The ideal range here is between 5mm and 10mm. If your static sag figure is more than 10mm it means your springs are too soft whereas a figure less than 5mm means your springs are too hard for you.
Once you have your figures you’ll then know if you need to dial in more rear preload or less of it. Each bike will be different when it comes to preload settings so consult your owners manual. Cheaper bikes offer limited settings which makes it harder to get the preload accurate.
As mentioned before adjusting rear preload does not change the stiffness or softness of your springs. So you may very well find that even if you get the Rider Sag in the sweet spot of 35mm, your Static Sag may still be outside the ideal range. Try your best to ensure you have a bit of static sag, otherwise your suspension can top out. Therefore, you may need to increase the Rider Sag to 40mm just to get the Static Sag up to 5mm, or any other number of combinations.
Once you made the adjustments, take the bike for a ride. Don’t go on the smoothest piece of bitumen you can find as that doesn’t let the suspension go through its range. Hit the twisties and see how it feels. If you’re not happy with it, adjust it again and measure B and C and see how that goes.