Archive of BMW Motorrad Club Cape (2006 - 2019)

What I was told on our training session with PererO was to turn it all in (big knob) and then turn five turns (clicks) out for road and another 5 clicks for graver/sand.

I did it and it is much better. I weigh 115kg so go according to that.

The big knob is called preload, and a side-effect of making it stiffer is the bike rides higher.  But it is not a height adjuster!  It adjusts the amount of tension in the rear shock spring by preloading it.

The small screw at the base of the rear shock is the damping adjustment screw.  It controls how quickly the oil in the shock is allowed to flow between two chambers.  This controls how much the shock stops 'bouncing', and a side-effect of damping is that when you compress the shock (by pressing down on the back of the bike), the bike comes back up slowly or more quickly depending on the setting.

With the damping screw turned closed (all the way clockwise), the bike returns to normal after pressing it down the way a civil servant walks to the filing cabinet to fetch your ID book (sloth-like).  With the damping fully open (fully anti-clockwise), the bike jumps up like a student hearing the words 'free beer'.

So, these are the trade-offs:

1. Damping too little (screw too open), the bike bounces for a while after going over a bump.  Off-road this can make the bike unstable and throw you off.
2. Damping too much (screw too closed), after hitting a bump, the suspension does not return in time to normal, and the next bump really nails you.
3. Preload too little (spring too soft) and the bike will wallow around corners like a hardly dangerous, big bumps will bottom out the suspension..
4. Preload too much (spring too hard) and there is no room for the back wheel to move down into depressions - so you end up losing traction at speed on bumpy ground and corrugations, and the ride itself is hard and unpleasant.

On top of all that, the two settings affect each other.  When the preload is high, the damping is reduced  (bounce increases).  This is because a stiffer spring can push the oil through the valve quicker for a given setting.  So typically if you increase the preload, you should turn the damping screw closed a bit.

How to adjust your preload and damping

1. Set the preload first, with the bike fully loaded.  A rule of thumb is that with a correct setting, the fully loaded bike's suspension will be 70% compressed (compared to unladen).
2. Now unload the bike (because you are measuring how quickly the back wheel can track the unevenness in the road, with the body of the bike moving in a straight line.)
3. Holding the bike upright (sidestand out for convenience), by the back bracket, with an assistant standing by to help if you lose it, press the back of the bike down as far as you can and release it.
4. Watch how quickly or slowly it rises.  If it is like a sloth, the damping is too much, open the screw a quarter turn and try again.
5. If there is no evidence of damping at all, and it jumps straight up, then you need to close the screw by a quarter turn.  You should just be able to see that there is damping, but it must not be intrusive.

The above is rule-of-thumb.  Personal preferences vary, and changes depending on the terrain:

• For offroad and sand:  harden the preload to deal with bigger bumps and give a more responsive ride,   The damping should be reduced a bit to improve tracking of the ground, and since you often only adjust the preload in the field and don't have the screwdriver handy, the harder preload automatically reduces the damping without adjustment.
• For road riding: softer preload for more comfort with the harder tyres and sitting.  Increase the damping slightly to prevent wallowing around corners.  (Again this happens automatically when you soften the preload).

HTH

Leon, it depends also on the bike model, the age and state of the shocks, the weight, load and load distribution of the bike, your weight, and the riding conditions you are under.  Also, your instructions sound like the preload will be stiffer for road than for off-road, and this is the opposite of what I learnt at Country Trax.

Ok I've done the unthinkable ... I've read the manual.

Forget the theory.  For the 650s turn the knob thingy fully in ie clockwise and then back it off 5 clicks for offroad riding, then back it off 3-5 clicks for onroad.

For the 1150 turn the knob clockwise in the "High" direction for offroad and back off in the "Low" direction for onroad.

It appears that my understanding of suspension concepts was right, but the understanding of the word preload was wrong.  Increasing preload doesn't increase the stiffness of the spring!  It increases the amount of load it takes to start compressing the spring.

Have a look at this article ... excellent for inquisitive academics and (I think) rocket scientists

Refer Manual : "For offroad riding, increase spring preload at front and rear." "Low" setting for solo, "High" setting for off-road or two-up with luggage.

This is another good article:

http://micapeak.com/bmw/gs/gs_tel2.html

I've deleted some of my responses because they would only add confusion.

Leon, hopefully I said "turn the knob fully in, back off 5 clicks for offroad and another 3-5 clicks for onroad"  If I got it the wrong way round my apologies, but that's the advice from Countrytrax instructors and it's what I do on my Dakar.

This tip is supported by the 1150 manuals, though the 650 manual is useless in this regard.

A further tip is that if the back wheel bounces over the bumps and refuses to grip, you've probably added too much preload and can back off a bit.  As mentioned previously in this thread, age, weight, luggage etc etc all influence your settings and there's a lot of "meet en pas" involved in getting it right for each individual.

Useful question Verooch.  I got myself totally confused while going through the answer and it forced me get to the bottom of it for my own peace of mind

Nice link Pete.  After reading it, it seems that the rebound damping has a lot to do with 'hardness' of the ride.  If the shock is being hindered from rebounding (and therefor also harder to compress quickly), it will be harder (regardless of the preload setting).

So, when the Electronic Suspension Adjustment (ESA) on the offroad setting makes the suspension higher and softer, it is increasing the preload (making the bike higher), and reducing the rebound damping (making the suspension softer).

One thing I was taught on the Honda offroad course, was that you should check that the front and back settings match.  You do this by standing on the bike (with someone helping balance the bike), and compressing the suspension with your knees (i.e. a little bounce with your body).  Both the front and back should respond evenly.  The front or the back should not be stiffer than the other, and should not lag behind the other in responding.