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Discussion Starter · #1 ·
Hi guys need your opinion I think my rear shock might be toast.


So I am 74kg and set the front sag to 28%, I'm very happy with the front dive now and road handling got much better also adjusted compression/rebound.


The rear I noticed is too soft during my 5300km in Norway with camping gear, needed the preload to 35 and I know everyone found the same thing, the
problem is the other day I tried measuring when I don't have luggage, the correct preload for 30% sag under my own weight.
Bike on center stand 0 preload, from chain plastic protection to left passenger peg got 15cm, then bike down me on it 11cm so only 18% sag and to make
it worse then cranked preload to 35 and I get about 11.6cm so 6mm difference with 35 clicks, which is 15% sag !!!


That's really baffling since while riding I feel it's too soft, but can only get maximum 18% sag, this is totally against logic, am I missing something here ?
 

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I think you are not measuring sag correctly.

% sag is the ratio of the rear wheel spindle vertical movement under rider load expressed as a percentage of the total wheel spindle movement available due to shock travel.
Do it like this:
On centre stand place one end of a tape on rear wheel spindle and the other at a convenient spot vertically above , say near pannier mountings. Record that distance.
Now load the bike as you intend to ride it, put on your riding gear and sit on the bike. Get someone to take that same measurement again with you balancing on the bike so that you don't have weight on your feet.
Now lets say the first measurement was 630 mm and the second was 530, that means the sag was 100mm.
Now you need to work out the percentage sag.
The total spindle movement possible for the AT is 220mm. So % sag is 100 divided by 220 which is 45% sag. That's too much so you need to wind up the preload. I have the ATAS and have set my sag to 29 clicks and 33%. I weigh 16.5 stone plus lightly loaded OEM panniers. Hope this helps
 

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Discussion Starter · #3 ·
I think you are not measuring sag correctly.

% sag is the ratio of the rear wheel spindle vertical movement under rider load expressed as a percentage of the total wheel spindle movement available due to shock travel.
Do it like this:
On centre stand place one end of a tape on rear wheel spindle and the other at a convenient spot vertically above , say near pannier mountings. Record that distance.
Now load the bike as you intend to ride it, put on your riding gear and sit on the bike. Get someone to take that same measurement again with you balancing on the bike so that you don't have weight on your feet.
Now lets say the first measurement was 630 mm and the second was 530, that means the sag was 100mm.
Now you need to work out the percentage sag.
The total spindle movement possible for the AT is 220mm. So % sag is 100 divided by 220 which is 45% sag. That's too much so you need to wind up the preload. I have the ATAS and have set my sag to 29 clicks and 33%. I weigh 16.5 stone plus lightly loaded OEM panniers. Hope this helps
I know what you're explaining, I live alone and don't have anyone to assist me so that's why I measured like I did, but the rotation of the swing arm shouldn't be that huge of a difference,
on such a small displacement at the spot I used, so I'm still really surprised about the 6mm.
 

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Going from 7 clicks to 29 clicks my sag at spindle changed by 32mm.
The place where you are measuring is probably less than half way along the swingarm so you get a sag of 34 mm and that's a true fig of say 80mm. That's 36% sag based on 220mm.
Also measuring at the spindle gives less margin for error as the numbers are bigger. Get a mate round !
 

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I have found a way of taking these measurements on my own
Buy a 1 meter steel ruler and tape one end to the plastic roughly vertically above the spindle. I actually use a point further in towards the centre of the bike so I measure the distance along the arc described by the spindle as it pivots around the swing arm spindle
Now rest the steel rule on cir circular flange of the axle nut and use a loose tie wrap to keep it balanced there. With Bike on Centre stand make a note of where the rule just kisses the circle. It’s easier to judge than you think.
Use your phone on a box or ideally a mini tripod to take a video of where the ruler ends up with you sitting on the bike
Mike
 

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Discussion Starter · #6 ·
I have found a way of taking these measurements on my own
Buy a 1 meter steel ruler and tape one end to the plastic roughly vertically above the spindle. I actually use a point further in towards the centre of the bike so I measure the distance along the arc described by the spindle as it pivots around the swing arm spindle
Now rest the steel rule on cir circular flange of the axle nut and use a loose tie wrap to keep it balanced there. With Bike on Centre stand make a note of where the rule just kisses the circle. It’s easier to judge than you think.
Use your phone on a box or ideally a mini tripod to take a video of where the ruler ends up with you sitting on the bike
Mike
Thanks great ideas, I'll figure something out !
 

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Discussion Starter · #7 ·
Well I checked at axle properly and setting correct sag required 30 clicks, not much left for luggage !

But still the difference between no and full preload, makes only a diffence of 25mm, pretty ridiculous.
 
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