General Guide to Setting Static & Loaded Sag - Suspension

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QuickDraw
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General Guide to Setting Static & Loaded Sag - Suspension

Post by QuickDraw » Mon Aug 12, 2013 12:28 am

I used this as reference when setting up mine and I was blown away by how good the results were. I did it on my own (ie. no extra hands to help as suggested). I tied string around fork tubes to measure front, and for the rear set up a height scale using clamps, a bit of rod and a metre rule.

Article quoted from www.TRXuk.TRX850.com:

STATIC SAG
The one main thing that most suspension articles miss is the most crucial - setting the sag correctly.
The sag range will be the same for everyone but some will find that they need to change springs to get
into the right range. Race bikes, generally, need harder setting than road bikes as they ride on smoother
surfaces. Road bikes have a huge range of dips, bumps and potholes to cope with so need to set slightly
softer.

Most people will have different preload settings, thanks to differing weight but all will need to be in the
same range for your suspension to work at it's optimum range, namely it's middle third.
Without the sag set right the damping will never be able to work at it's best, as it will be trying to
overcome the effects of a badly set spring. Don't forget that your pride and joy has been designed to work
with a hugely varying type of rider on board. It has to cope with very heavy riders to very light riders.
Aggressive riders to steady riders and all points and weights in between. Basically it's a compromise.
It's amazing that people will spend hundreds, even thousands of pounds on suspension components and
twiddle with them all day and night but never take the time to set the sag correctly and never get the bike
handling any better!

So what is sag? There are two types;
• Static : the amount the bike settles under it's own weight.
• Loaded : the amount the bike settles with a rider on board.

You need to set both the static sag AND the loaded sag, just doing one or the other is only getting half the
story. To do this you will need.
• A tape measure.
• A pen and paper.
• Tools to adjust the front and rear preload.
• Three strong friends.

Setting Static Sag
Setting the static sag is easier than the loaded but it will still need a set of strong hands to keep the bike
off the floor while you take your measurements.

Front
1. Lift the front of the bike off the floor using the same side stand method. Measure from the bottom yoke
to the top of the stanchion. This is measurement A.
2. Drop the bike back onto two wheels and take the reading again. This is measurement B.
3. Subtract measurement B from A. This is your front static sag reading. Keep a note of it just in case you
want to change it back. Ideally you are looking for 10-20mm on a race bike and 20-25mm on a road
bike. Either compress the spring or loosen it off to get in this range.

Rear
1. Lift the back wheel of the bike off the floor by pulling the bike over on its side stand.
2. Measure from the centre of the rear wheel spindle to a point on the tailpiece that is directly above the
spindle. (Mark that point on the tailpiece for the future reference)
3. Write down the measurement and call it reading C.
4. Put the bike back down on it's wheels and hold it upright. Let the bike settle under it's own weight.
Measure the distance from the spindle to the tailpiece. This is reading D.
5. Subtract D from C and this is your rear static sag. Keep a note of it just in case you want to change it
back. Ideally you are looking for 5-10mm on a race bike and 15-20mm on a road bike. Either compress
or loosen off the spring to get into this range.

Loaded Sag[/u
]Now to take into account the rider's weight. Sit on the bike and have one friend steady the front, one
steady the back and the other ready to measure. Sit the bike upright. Now WITHOUT touching the front or
rear brakes bounce up and down a few times in the seat and then assume your normal riding position.

Front and Rear
1. Measure the front of the bike as for measuring the static sag. This measurement E. Subtract E from A
and try to obtain 25-35mm on a race bike and 35-50mm on a road bike
2. Measure the rear of the bike using the same mark as previously. This is measurement F. Subtract F
from A and this is the rear loaded sag reading. Try and get between 20-25mm on a race bike and 30-
40mm on a road bike by adjusting the preload as before.
If you can't get in these ranges for BOTH Static and Loaded then you will need to change the spring for a
harder or softer one. Harder if you're outside the range and softer if you are inside the range. Now go and
ride and feel the difference!

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Re: General Guide to Setting Static & Loaded Sag - Suspensio

Post by Snod Blatter » Mon Aug 12, 2013 12:51 am

I was just getting around to looking at setting up the rear, this is going to be mega useful!
'95 4NX with K&N filter, Motad Venom cans, YSS PD valves, Ohlins fork springs, 530 C+S, Green CDI, 11/16 radial master cylinder, +30mm jack up dog bones. Enjoyable money pit.

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Re: General Guide to Setting Static & Loaded Sag - Suspensio

Post by alextrx850 » Mon Aug 12, 2013 7:34 am

Wow, explained well...will go for this. =D>

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Re: General Guide to Setting Static & Loaded Sag - Suspensio

Post by cobbadiggabuddyblooo » Mon Aug 12, 2013 8:08 am

A good way to retain all measurements is to use a length of masking tape . Stick it to the rear frame and place a small mark on the swingarm edge as your tape reference point . Lift the rear and mark. Mark again when settled then mark when setting loaded sag. You have all your measurements recorded on the masking tape. And work from there.. A small cable tie around the forks will give you a measurement reference point by lifting the front and pushing it against the dust seal . Measure this, it will travel up the forks once the bike is settled under its own weight , measure , then the same for your loaded sag.
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Re: General Guide to Setting Static & Loaded Sag - Suspensio

Post by dfh » Tue Oct 08, 2013 8:11 am

Food for thought guys.

Set your loaded (bike & rider) sag first. Forget static (bike only)

Those nordic types at Ohlins recommend loaded sag (ride height in Ohlins speak) figures of 25 to 35mm rear & 30 to 40mm front.
I suggest starting by setting the loaded sags in the middle of those ranges ie rear 30mm front 35mm.

Once this is done now measure static sag (bike only or free sag in Ohlins speak) Ohlins recommends static sag figures of 5-15mm rear & 20-30mm front.

DO NOT ADJUST PRELOAD as advised by brettmcgaw to bring your static sag in range. Why? Because static or free sag is a diagnostic measurement.
If you can achieve the target figure of 35mm loaded sag on the front fork by using the preload adjuster and the measured static sag comes in at 15mm (less than the target range of 20-30mm)
then the spring rate is too soft. In other words the too soft spring has to be over-preloaded to set loaded sag & the sign of this is the loss of static sag.
If the spring is too hard then the preload would need to be backed off to achieve the loaded sag figure & static sag would become excessive.

The thumbnail fact sheet runs like this.
Front loaded sag target = 35mm. Correct spring is installed if static sag is 20 to 30mm. Spring too soft if less than 20mm, too hard if more than 30mm after preload adjusted for loaded sag.
Rear loaded sag target = 30mm. Correct spring is installed if static sag is 5 to 15mm. Spring too soft if less than 5mm, too hard if more than 15mm after preload adjusted for loaded sag.

Why is it important to understand that even though it is possible to preload an incorrect spring to the target loaded sag it is a bad idea to do so can be seen by looking at the rear suspension figures above. The minimum static sag figure is 5mm, so it is quite possible that a spring that is only a little bit soft could be adjusted over-preloaded) for correct loaded sag with little difficulty. The problem is if you end up with no static sag the spring still contains force as the shock tops out on rebound, with risks of shock damage & loss of grip plus excessive tyre wear.

Hope this helps
Now with 140,000 on the clocks, X-mas tree didn't kill it & I still love it.

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Re: General Guide to Setting Static & Loaded Sag - Suspensio

Post by Snod Blatter » Tue Oct 08, 2013 11:21 am

That makes a lot more sense to me, thanks! Where did you find it though, Ohlins don't seem to hand out this kind of useful information?
'95 4NX with K&N filter, Motad Venom cans, YSS PD valves, Ohlins fork springs, 530 C+S, Green CDI, 11/16 radial master cylinder, +30mm jack up dog bones. Enjoyable money pit.

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Re: General Guide to Setting Static & Loaded Sag - Suspensio

Post by Rexie » Tue Jan 17, 2017 4:18 am

great write dfh explained in simple terms. Thanks

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Re: General Guide to Setting Static & Loaded Sag - Suspensio

Post by cobbadiggabuddyblooo » Tue Jan 17, 2017 10:09 am

Remember go for a ride and do this when the bike is hot too ...
Not so you burn yourself but to heat the oil on your forks and rear shock.
I know Racetech recommend that you for example take your sag measurements then press down on your forks and let the bike settle under its own steam.
This measurement may be say 5 mm different than the previous so you take the difference between the 2 and this allows for any friction or drag.... Do the same on the rear shock..
laughter is the best medicine

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