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Setting sag on your TM
#1
First stop on setting the suspension up for your bike is to set the sag. If you don’t know what this is, sag is the amount the suspension goes down under the weight of the bike alone and under the weight of you sat on the machine. This forms a baseline from which you can adjust everything else.und. Measure from a point on the swing arm somewhere close to the spindle to a point on the rear mudguard or the top of the number boards. Mark this point you are using with a bit of Gaffer tape so that you come back to the same point.

SIT ON THE BIKE AND GET SOMEONE ELSE TO MEASURE BETWEEN THE SAME POINTS


Then put on all your riding kit including your helmet and boots.  Take the bike off the stand and sit on it and bounce up and down a few times to overcome any what’s called ‘stiction’, then get a friend, partner, intelligent child or passer by to measure between the same two points.  Subtracting the second measurement from the first will give you the sag – simple. For most dirt bikes, a rule of thumb is around 100mm, but you should check your manual for the recommended figure.


IF THE LOCKING RING IS PLASTIC, TAPPING IT CAN BE RISKY. USE A SPECIALIST TOOL IN THE OEM TOOLKIT


If the sag isn’t at the required level, you are going to need to adjust the preload of the shock spring.  Release the pre-load collar lock  bolt, and if the sag was more than recommended you will need to tighten the pre-load adjuster – hence compressing the spring – commonly using a bar of drift and a hammer.  This approach is really risky if the shock has a plastic especially on older bikes where it may have become brittle, so ideally use a specialist tool from the OEM toolkit instead.
If the sag is less than the recommended level, you will need to slacken off the spring pre-load. In either case, be gentle as you are moving the adjuster and look to do it slowly rather than with jerks on the OEM tool or massive clouts with a drift. Keep sitting on the bike between adjustments to take more measurements until you reach the require sag.


THE FREE SAG IS WITH THE BIKE UNDER ITS OWN WEIGHT

The final stage of the process is now to measure the free sag, which will tell you if the spring in your bike is correct for your weight. With the bike off the centre stand and no rider measure the difference between the previous two points, ideally with someone else holding it upright. Compare this to the static sag, which will tell you how much the machine sags under it’s own weight.  If it’s between 20mm and 30mm then you can be confident that the spring is right for your weight, and you can retighten the pre-load collar.


DiFFERENT SPRINGS ARE NEEDED FOR DIFFERENT WEIGHT RIDERS.


If however it’s less than this it’s likely that the spring is too soft, as to achieve the required sag has required too much pre-loading of the spring.  If it’s more than the 20-300mm ideal, then it’s because the spring is too hard. Both scenarios will mean that you need to get another spring for your shock, but that said if you are 20 stone and the average weight is 12 stone, you might have guessed that!  Companies like Hyperpro or K-Tech provide a wide range of springs to cope with both lighter and heavier riders. Fitting a new spring is not difficult if you have both the tools and the knowledge of what is required. If you don’t have both, leave it to a professional.


FACTORY RIDERS HAVE THE SETTINGS RECORDED ON THE LABELS ON THE FORKS


When it comes to the front of the bike, the process is nothing like as easy or indeed as achievable for the average rider.  Most conventional forks don’t have any way to adjust the preload on the springs, so the same level of tuning is not possible. That said, enduro bikes will sometimes have pre-load adjustable via a nut on the top of the fork and the modern breed of air forks have almost infinite adjustments, all of which are possible with nothing more complex than a pump. You do however need to make the adjustments in the correct order, or you risk reducing the travel and totally messing up the suspension! If in real difficulties, you could always read the manual …
As a rule of thumb, your sag and free sag should be roughly the same as the figures you used for the rear, otherwise the bike is going to be unbalanced straight away.
If this is not the case, setting up your forks is best done by a specialist who will be able to identify whether you need pre-load spacers or totally new springs to get the bike to behave correctly. Pay up and look big.



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