Loads of people think that working on your suspension equals rocket science. But adjusting the preload for the rear suspension isn’t that hard at all. Of course you need to measure some and you need to calculate the measurements. Using this formula it will be reduced to childsplay.
Rider Sag = A – C
Remember that formula and all will be OK when you want to adjust the preload. That’s it. Now we just need to aquire ‘A’ and ‘C’. Also that is not hard to do. Follow me in the text and watch the video 😉
To measure the ‘A’ and ‘C’ you need for the preload formula and calculate your bike’s Race Sag you need the following:
- Bike stand or centre stand. (including 1 or 2 assistants in the mix makes it alot easier)
- Assistant to balance your bike when you’re on it.
- Measuring tape or a yardstick.
- If your anything like me with adding and substracting: Calculator.
After you searched the garage for all the above, take your bike out and start the proces below.
First mark a fixed point on your bike to measure from. I’ve put some masking tape on the passenger gripbar for my upper fixed measuring point. For my lower measuring point I used the top of the rear axle bolt. Then push in and let out your rear suspension a few times to remove any stickyness still in there.
To get an idea if you need to make your preload higher or lower first we need to measure the ‘0 point’. This means you need to put the bike on the centre stand so that the rear wheel is free from the ground. If you don’t have a centre stand then you have to improvise. For example you could put your bike in a bike stand and jack up the rear. Just make sure you do it safely and keep a stable platform. Later we will put the bike back on its wheels. That is also the point where your assistant(s) come in.
To get measurement A, elevate the rear wheel of the ground and just let it hang. Measurement A stands for the most extended state of your suspension. Measure between the fixed points and write down the measurement.
Mine was: 62.5 cm
Almost ready to adjust the preload! Just a few more measurements! Ok. Put the bike on it’s wheels again. Let one of the assistants balance the bike out and keep it upright. Now we measure ‘B’ between both fixed points. Now we can make the following formula:
Bike Sag = A – B. The Bike Sag should be around 30 mm for the Vstrom 650 (Check your owner manual of course)
Mine came out like this: 62.5 – 59.5 = 3cm (30 mm)
Adjusting the preload is getting close now! one last obstacle. Go and sit on the bike with all your gear and luggage you will be using on the trip! Don’t forget to get assistant number 2 to hold the bike in balance and let assistant number 1 measure between both fixed points again.
I only have one girlfriend so I used my toes to keep the bike balanced. Of course this will take some accuracy off but in my case, I don’t mind.
Mine came out at: 55.5 cm
Rider Sag = A – C
As I stated above, this is the formula we now use to get that preload slammed in! This was my result:
62.5 – 55.5 = 7cm ( 70 mm of Rider Sag ) For my V-strom 650 this should be around 40-50mm so I have to be making my preload HIGHER. If your number comes under your recommended preload setting you have to make your preload LOWER. This actually has nothing to do with the tension in your spring but it makes your bike higher or lower on the spring. This makes for a shift in weight.
Now we can set it! On the V-strom 650, and most adventure bikes, there is a knob you can turn to adjust the preload. Yeah, shut up BMW riders…. we don’t have a button for that on your handlebars. Turn it the way you need to and check the Rider Sag in between. Do this until you hit the correct Rider Sag.
If your springs preload doesn’t go low or high enough you might need another kind of suspension in the back. In that case check out: