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Rear suspension sag - for road use

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seeyalater
Trackday Trickster



Joined: 15 Sep 2019
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PostPosted: 18:41 - 22 Mar 2020    Post subject: Rear suspension sag - for road use Reply with quote

Hi guys. I was browsing the interweb to see if there is anything I should be checking on the bike.
suspension lag came up so I checked mine on the rear. Its 40mm ish.
So my question is, is this mostly for the track bikes and not really a worry for normal road use.
Il add a photo which to me looks like a normal ride. I'm a 17st 4lbs 5'10 fella and was curious if the bike would need to be adjusted for my weight. It is a 650sa bandit.
cheers
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martin734
Spanner Monkey



Joined: 28 Aug 2019
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PostPosted: 19:23 - 22 Mar 2020    Post subject: Reply with quote

I go for sag figures of 25-30mm at the rear. To adjust the sag you adjust the compression preload on the shock. Some shocks have a much greater range of adjustment than others, some have a screw collar that is infinitely adjustable between its top and bottom limits while others have a collar that adjusts in steps, usually 5-7 steps between max and min preload. to set the correct sag you first need to measure the static sag. Stand the bike upright with its full weight on the wheels and measure the height of a fixed point on the bike above the ground and make a note of the measurement. Then sit on the bike and measure how much it sags and adjust the preload to give you the desired amount of sag.
Once you have set the sag you should then adjust the rebound damping if you can. To do this, stand the bike upright off its stand. Press down firmly on the seat and release, watch how the suspension rises. The suspension should take approximately 1 second to return to the original ride height and stop. If it rises past its static sag point and then falls again you need to increase the rebound damping and if it takes longer than 1 second or doesn't return to its static sag height at all then you need to decrease the rebound damping.
If you have compression damping then this is best adjusted to personal taste after riding. If the ride is harsh or jarring then you should decrease the compression damping and if the ride feels soft and wallowy then increase the compression damping.
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seeyalater
Trackday Trickster



Joined: 15 Sep 2019
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PostPosted: 20:11 - 22 Mar 2020    Post subject: Reply with quote

martin734 wrote:
I go for sag figures of 25-30mm at the rear. To adjust the sag you adjust the compression preload on the shock. Some shocks have a much greater range of adjustment than others, some have a screw collar that is infinitely adjustable between its top and bottom limits while others have a collar that adjusts in steps, usually 5-7 steps between max and min preload. to set the correct sag you first need to measure the static sag. Stand the bike upright with its full weight on the wheels and measure the height of a fixed point on the bike above the ground and make a note of the measurement. Then sit on the bike and measure how much it sags and adjust the preload to give you the desired amount of sag.
Once you have set the sag you should then adjust the rebound damping if you can. To do this, stand the bike upright off its stand. Press down firmly on the seat and release, watch how the suspension rises. The suspension should take approximately 1 second to return to the original ride height and stop. If it rises past its static sag point and then falls again you need to increase the rebound damping and if it takes longer than 1 second or doesn't return to its static sag height at all then you need to decrease the rebound damping.
If you have compression damping then this is best adjusted to personal taste after riding. If the ride is harsh or jarring then you should decrease the compression damping and if the ride feels soft and wallowy then increase the compression damping.


Thanks. I followed a slightly different approach, but it does make more sense to measure on its wheels.
The video I saw, the guy measured with the wheel off the ground, so its maximum drop.
Then he measured with the rider on the bike, pressed down, released and measured again. Then lifted up released and measured again.
He got the average from the lift and drop to get the average and took this from the maximum first measurement.
I would bet if I measured with the bike sat on its wheels, then me sat on it the sag is more like 25mm. Will try it tomorrow.
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stinkwheel
Bovine Proctologist



Joined: 12 Jul 2004
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PostPosted: 21:48 - 22 Mar 2020    Post subject: Reply with quote

In an ideal world, you'd calculate the correct spring rate, fit the correct spring then set static sag. Rider sag would take care of itself.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.
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seeyalater
Trackday Trickster



Joined: 15 Sep 2019
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PostPosted: 14:12 - 23 Mar 2020    Post subject: Reply with quote

Done the rear again but carefully. more like 35mm

Just checked the front and its 50mm. Seems a lot and it's at is highest preload, well it had 1 more turn in it.

Set the rear to 5 instead of 4 and damper to 3 instead of 2.
Not really sure I will see much difference at that but worth a shot. The reason I still increased rear is I wasn't wearing full kit when tested the weight. Will measure again.

I do need to research more about the damper on the bottom of the shocker.


Last edited by seeyalater on 16:13 - 23 Mar 2020; edited 1 time in total
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stinkwheel
Bovine Proctologist



Joined: 12 Jul 2004
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PostPosted: 15:42 - 23 Mar 2020    Post subject: Reply with quote

seeyalater wrote:

Just checked front and its 50mm. Seems alot


Rider sag or static? If static, yes, thast's a fair bit.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.
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seeyalater
Trackday Trickster



Joined: 15 Sep 2019
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PostPosted: 16:14 - 23 Mar 2020    Post subject: Reply with quote

Quote:
Rider sag or static? If static, yes, that's a fair bit.


Rider sag. The first measurement was forks extended. 2nd with me sat on it.
I do feel there should be a middle ground though with a measurement with the bike under its own weight
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seeyalater
Trackday Trickster



Joined: 15 Sep 2019
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PostPosted: 11:28 - 28 Mar 2020    Post subject: Reply with quote

for anyone else who pops on this thread looking for answers, here is a great video about adjusting and checking REBOUND and SAG on your suspension.
https://www.youtube.com/watch?v=lo0kv_6hG-0&list=LLVQmNfs8PoIM3eymVAZgDhg&index=5&t=0s

He doesn't show how to check it but this video does.
https://www.youtube.com/watch?v=ZtzTyCKh5fY
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