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Discussion Starter #1
Hi,
There's a hole in my knowledge when it comes to setting the preload on bike suspension. (Perhaps because previous bikes haven't made it as easy to change it?)
I know to increase the preload when I'm loading the bike up more, particularly the rear when I have a passenger or a lot of luggage, but I don't really know how *much* is right.

Could someone explain how I can tell when I have the front and rear preload set correctly? I realise I don't want the bike to be sitting really low when loaded up, but on the other hand, I don't know what to look for when it's set too high. And of course I want it to feel reasonably level.

I'd be interested in hearing what settings you use, too.

Thanks in advance.
 

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:devil_3:
Well, I am not terribly heavy despite what my wife says, I tip the scale at 75kg, so normally I don't use any preload. On the old bike, I would get it so it would sag about 1" when coming off the centre stand. I would run about 7psi in the forks since I liked a stiffer front end. the rear as the bike aged would get dialed up at the time of the accident it was normally set at 2.
:confused:
When the wife would ride with me (52kg) I would dial up the back to 3 or so, the front I wouldn't adjust. My main goal was to keep the "feel":green_lol: of the bike on the road the same. It took some experimenting, but I got the old girl to be comfortable whether I was by myself or with the wife.
Now with the 650 the experimenting will begin again.
 

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The preload settings change the sag...the height the loaded bike sits on its suspension. The goal is to get the bike in the position on its suspension so you have equal chance of avoiding topping or bottoming the suspension when you hit a big bump hard.

40 mm (plus or minus a coupl'a mm) sag works well on our stroms, both front and back. A helper makes the job much easier.

Front--Raise the front tire off the surface and slide a cable tie around the upper fork leg down against the dust seal. Tire on the ground, you on the bike wearing riding gear, let the suspension settle. Get off, raise the front, and measure the distance the cable tie slipped up the fork tube. Adjust the preload adjusters or the spring spaces to get close to 40 mm.

Rear--Tire off the surface, measure vertically from the axle to a point on the fender or rack. Get on the bike holding the bike upright. Measure how much the bike sags. Crank the preload adjuster to get close to 40 mm. Change the setting if the weight on the rear changes due to heavy luggage or a passenger.
 

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Discussion Starter #5
Thanks for the link, Greywolf. That'll help get it right when I'm at home in the garage, at least, and helps me understand what's going on. I swear I've read that page before, and it's just slipped out of my memory since then :/

Thanks to others too - so the key message is that I need to have a bit of "sag", around 4cm from totally unloaded. If the bike barely goes down at all when I load it up, then the preload is too high. If it sits *really* low, or I can feel it bottoming out on bumps, then the preload is way too low.
 

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The link Greywolf sent is the one I used.

Good stuff. :thumbup:
 

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Advanced Sag Setting

I agree with Grey Wolfs link on setting the sag. I would add one thing though...

(...and I learned this through the Lee Parks Advanced Rider Control Course).

In a word - Sticktion. (the resistance between the fork seals and the forks which causes sticking)

Setting the rear sag can be done as described because the diameter of the shaft on the shock is small and creates a relatively small resistance with the seal. However, on the front forks, the resistance between the fork seals and the forks can be significant.
To properly measure front fork sag you do need friends (or your own children used as slave labour when you don't have friends).

Sit on the bike as described with full riding gear, etc. Have 2 friends balance the bike for you. The friends then compress the front forks as much as possible and s-l-o-w-l-y release the comression. Measure that distance (to the triple tree). Call this FC (front compressed).
Then do the same except the friends now lift the front end and s-l-o-w-l-y let it down. Call this FE (front extended).
Now do the math:
(FC + FE) / 2 = front sag

On my Wee the diffference between the two was 14 mm. What this does is save taking multiple measurements at the front only to have a different number come up each time.

Hope this helps...
 

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View attachment 116474

SAG measurement. Click on the file.
I do not know how to get this shown as a picture. Sorry.

With help of my son :yesnod:. He is 11, but wants a bike already.
Preload front at 5 and rear at 6, 11, 16, 21 and 26 clicks.
Preload front at 4 and rear at 6, 11, ..., etc.
Front at 1 we did not do since I do not to use this setting at all.

You can see that preload rear at 20+ affects the front SAG too.
You can calculate what a 1 click does in mm.

At front 3 and rear 16 I added a topcase of 10 kg. That gave 4 mm more SAG.
So if I use the topcase and fill it up I need to turn the rear preload up 3-4 clicks (cw).
Bike SAG is 40 mm front and 32 mm for my bike. Adding me gives the values in the attachment.

The 25-33% is hard to get. That would be 40-53 mm.
There are some preloadcombinations that give equal front/rear SAG.
Like 5/6, 4/11, 3/11 and 2/16.

For now I have my preload set at 3/15.
In combination with front in/out at -12/-9 clicks and rebound rear at -1,25 this gives me a bike that steers great and is comfortable enough.
 

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My opinion, is more importantly than setting the pre load correctly, is to first swap out the springs and get springs that are correct for how you "normally" ride.

Then use pre load as conditions and your load change to make minor adjustments.
 
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