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Rider Sag

DaveRSV

DaveRSV

Joined Nov 2007
839 Posts | 0+
Northampton
No, not the baggy around the bum leathers!!

I'll start this tale from the beginning so that it makes sense. After the pipes/map job I was finding the front was getting skittish quite frequently. Spoke to Iain at Forza about a steering damper and he said he'd set up the suspension before I went spending money. Being an impatient bleeder I decided to take the plunge into the world of suspension settings.

Tried softening off the compression/rebound from the manuals standard setting and it made a slight difference to the better but not to the amount I was after.

Started off reading all I could on the 'net about sag etc. Thought in for a penny in for a pound and set up the sag yesterday. Went out for a ride today, meeting up at Yaxley - briefly!, and the bike is bloody wonderful now. It seems really glued to the road, not so twitchy, doesn't shake it's head hardly at all and I look at a corner and it's round it!! (Not that it was bad with corners before, just better now).

Still got a bit to do with the front and then, if necessary or for the sake of experimentation, I'll fine tune with the rebound/compression.

So, if you're like me and always thought that suspension is a mysterious world best left to others I'd say get in there and have a go. The cardinal rule seems to be to record the settings that the bike is on now so that if you don't like the results you can put it back how it was.

Anyone interested here's the two links I used ONE TWO
 
DaveRSV said:
No, not the baggy around the bum leathers!!

I'll start this tale from the beginning so that it makes sense. After the pipes/map job I was finding the front was getting skittish quite frequently. Spoke to Iain at Forza about a steering damper and he said he'd set up the suspension before I went spending money. Being an impatient bleeder I decided to take the plunge into the world of suspension settings.

Tried softening off the compression/rebound from the manuals standard setting and it made a slight difference to the better but not to the amount I was after.

Started off reading all I could on the 'net about sag etc. Thought in for a penny in for a pound and set up the sag yesterday. Went out for a ride today, meeting up at Yaxley - briefly!, and the bike is bloody wonderful now. It seems really glued to the road, not so twitchy, doesn't shake it's head hardly at all and I look at a corner and it's round it!! (Not that it was bad with corners before, just better now).

Still got a bit to do with the front and then, if necessary or for the sake of experimentation, I'll fine tune with the rebound/compression.

So, if you're like me and always thought that suspension is a mysterious world best left to others I'd say get in there and have a go. The cardinal rule seems to be to record the settings that the bike is on now so that if you don't like the results you can put it back how it was.

Anyone interested here's the two links I used ONE TWO
Click to expand...

So what did you set them to Dave?
 
Theres also an articule in this months RIDE mag about setting up SAG :thumbup Going to check mine out too
 
Badger said:
So what did you set them to Dave?
Click to expand...

According to the racetech (2) link both front and rear should be set between 30-35mm. However, the other link (1) states 35-48 for the front and from my experimentation appears a lot more realistic.

I ended up increasing the rear preload by 3 full turns, about 9-10mm. Seemed so much I was a little concerned how it would feel, but on riding see above! This gave around 33mm of sag.

Trying to get the front down to 30-35mm I was no where near and had 10 full turns of preload on the forks. As my Aprilia manual states 6-9 for racing and 8 for street this caused me some concern. I then checked the other site (1) and saw their recommendations and turned it back to 9, which is how it was when I rode it. I've now backed it off to the standard 8 and I'll let you know tomorrow when I've been out on it again, think it 'may' turn a little quicker but probably not that noticeably.

What I'm going to try next is to put the cable tie around the fork leg to see how much travel I'm using. Basically this has put the bike more on it's front end and I know you have to be careful not to cause instability in a straight line in this way.
 
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I have 11.5 turns of preload in the front ohlins of my bike. It's only really an issue if you run out of preload and still have too much sag or vice versa. then you need spring changes.
 
That's interesting spoonz. Mind you, if I up the preload at the front it's going to take something away from the quickened steering, which I like.
 
The rider sag should really be set for your weight and then the suspension damping tailored to suit.

The turn in ability of the bike has a lot to do with the compression of the suspension and weight transfer from rear to front when you get on the brakes. The suspension has a sweet spot in it's damping that it's critical to run in. The damping curve ramps up steeply in and around that last inch of travel. The preload is the natural settling point for the bike with you on it. If your running too little preload you will be running in that high damping area and the front will feel quite stiff and should you hit a pothole mid corner when your suspension is most compressed there will be little travel left to absorb it. Always set it in your gear as it adds about a stone to your weight.

suspension is very much a personal thing but it has some key points which is why Badger mentioned the rider sag. Well worth seeking the services of someone like Southern cross if you can.
 
I think i need new springs, I use up far too much just under the sag and was pushing the cable ties to the bottom of the forks when riding even with preload on full.
 
gaz said:
I think i need new springs, I use up far too much just under the sag and was pushing the cable ties to the bottom of the forks when riding even with preload on full.
Click to expand...

This is where it gets complicated Gaz. The preload should not determine how much travel you use in total. Just how much travel you use with you on the bike without outside influences ie- bumps.

It's actually a good sign if you use all of your travel as that's what it's for. what you don't want is to be using 90% of your travel before you hit a bump or hit the brakes which is why you set the rider sag. If you can set the sag correctly via the preload adjusters then leave them at that and don't touch them again.
Once set you alter the damping to suit the track or style of your riding.
Don't forget that how much travel you use has a lot to do with weight transfer. The weight transfer has a much to do with the rear extending as it does the front compressing.
 
never seen sag adjusted like this, with rider on. sag is only there to stop the suspension topping out hard under spring force and damaging internal components.
static sag should be set buy getting someone to lift the bike, rear. to take the weight of the bike, and then you measure from a fixed point, say bottom of the number plate to the ground. now bounce the rear suspension and allow it to settle in its natural position. measure the same point as before. take one measurement from the other, and this is your static sag. repeat process for the front.
Too much preload, zero sag means the spring is always forcing the suspension to its max limits. not good for internal shock components or handling.
once sag is set ride the bike and adjust compression and rebound settings until you get a set up you are happy with. using cable ties on the front fork legs gives you an idea of travel length, if with your preferred settings you bottom the forks, or you cant reach a preferred set up due to suspension bottoming out then new weight springs required. expect to use almost all of the travel of the forks under hard braking. never adjust static sag in an attempt to remove fork bottoming out.
always remember too, that if you are a small rider and you are not using as much suspension travel as you should softer springs may be required.
after changing spring weights always reset static sag.
 
You are confusing static sag and rider sag. Both are relevant

Static sag makes no allowance for the rider at all. It would mean a 20 stone rider gets the same sag as a 10 stone rider if that were all that is set.
Static sag is the starting point for rider sag.

The bike suspension has to be at the correct level with you on it. If it sits fully compressed when you sit on it that has nothing to do with static sag or the damping setup it is purely down to the preload of the springs for your weight.

have a look here

http://www.biketweakers.com/staticsag.html

http://www.roadracinghelp.com/TechArticle/April/basic_spring_and_sag_setup.htm

http://www.motionpro.com/tech/articles/folding_sag_scale/
 
Static sag makes no allowance for the rider at all. It would mean a 20 stone rider gets the same sag as a 10 stone rider if that were all that is set.
Static sag is the starting point for rider sag.

I disagree, with 20mm of static sag on a bike i can ashore you that if i measured the rider sag of a 10 stone rider and a 20 stone rider they would be significantly different. If you then attempted to adjust the rider sag to the same for both riders by increasing the preload for the 20 stone rider, you run a real risk of having a bike with zero static sag. this is a situation you do not want to have. you will destroy rear shock and fork internals, and make the bike very dangerous to ride. rider sag, if it causes a problem with full suspension travel should be adjusted with harder/softer springs.
one other thing worth mentioning is the huge difference between setting a bike up for a super smooth race track and setting up for poorly surfaced public roads. if you want to learn how to set a bike up for the road, talk to an IOM TT racer. set up is as soft as you can get away with. all about keeping the wheels in contact with the road for the greatest possible amount of time. without passing the deflections through the bars/seat to the rider. much more like wet weather track settings
 
I agree with you and it was a bad analogy on my part because a 20 stone rider would not run the same springs as a 10 stone rider.

But how would you know that you were under or oversprung. you can't rely on the amount of travel you are using as that just tells you the extemes and not your usual ride height

If you set your rider sag and you can't achieve it without 20 turns of preload at one extreme and 2 at the other then you know your springing is wrong.
A bike with the correct spring rate for a given rider weight would not run the extremes of preload to give the top out that would destroy components.

The point i badly tried to make was that say i have my bike set to 20mm static sag then i have no top out issue granted. But i may be on the heavy side for my springs and my bike squats heavily when i get on in my gear. That means my suspension is already 2/3 compressed before i even set off and i constantly lounge in that last 1/3 of travel. How do i know that ?
I can have my sag set perfectly for my weight and still use the same max amount of travel as someone who is 5 stone more and on the same springs.

As i said before it's a black art and there will be a scenario to backup every theory. To my mind though rider sag is a great tool for the average guy in the street to determine how well his bike is sprung for his weight.
 
sprocker said:
Theres also an articule in this months RIDE mag about setting up SAG :thumbup Going to check mine out too
Click to expand...

Good on you sprocker... its all getting very confusing :roll. If i ever need to set mine up ill leave it to the experts :thumbup
 
spoonz said:
The rider sag should really be set for your weight and then the suspension damping tailored to suit.

The turn in ability of the bike has a lot to do with the compression of the suspension and weight transfer from rear to front when you get on the brakes. The suspension has a sweet spot in it's damping that it's critical to run in. The damping curve ramps up steeply in and around that last inch of travel. The preload is the natural settling point for the bike with you on it. If your running too little preload you will be running in that high damping area and the front will feel quite stiff and should you hit a pothole mid corner when your suspension is most compressed there will be little travel left to absorb it.
Click to expand...

My front is towards the lower end of the 35-48 range mentioned in one of my original links. The other link I posted puts the rider sag at 30-35 back and front, this is what I disagreed with, the front being the same amount as the rear.

You have answered one thing for me spoonz, I was thinking that the front was diving a bit quickly when moving slowly in traffic where it's a lot more noticeable and it's interesting to know that the damping increases further down the fork travel, I won't mess with that now (using the "it ain't broke don't fix it thought process!")

Anyhow, I'm ecstatic with the way the bike now feels/handles so I'm going to leave the sag well alone.

For anyone following this thread, the tolerances I used were 30-35mm rider sag at the rear and 35-48 rider sag at the front.
 
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If you look at the Ohlins PDf Dave there is a damping curve for the forks which demonstrates it quite well.
It's not for the fork in your aprilia but i have the correct manual and it shows that you need just under 150kg of force to travel the first 50% of the available travel and 250 kg of force to travel 2/3 of the travel but almost 500 kg to go 100% based on the normal oil level in the forks.

50 % of the total damping is in the last 1/3rd.
 
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Before undertaking the recent adjustments that document wasn't so interesting (forgotten I had it in fact), thanks for pointing me in the direction of it spoonz, lot more interesting now :thumbup
 
Final Chapter.......... I think!

To assist anyone else trying to sort thier suspension I thought I'd record my last couple of days.

The rear compression/rebound is set to standard settings and feels fine.

The front rebound/compression/preload was also standard at this stage, giving front rider sag around 41mm. As I stated above the front felt like it was diving too much, although the bike rode nice. I popped into Forza's at Silverstone yesterday to get some oil to do an oil change. Iain remembered he was going to look at the suspension for me and I relayed what I'd already done. Iain wanted to have a look at the bike and believed it needed more rebound on the front as it returned very quickly, more noticeable when someone else is compressing the forks and I could watch from the side of the bike. He increased the rebound damping by 4 clicks. On the way home from there, by a longer but favourite route of mine the forks felt harsh to me.

Remembering Spoonz comments above I wondered whether the forks needed to be more in the 'sweet' spot. I upped the preload to 10 turns which put the rider sag to around 38mm. I took the bike out today and it felt 'high' at the front and not very confidence inspiring. As the forks had felt harsh yesterday I had taken the tools out to adjust the forks during the ride (once stopped that is :biggrin) On stopping for petrol I put the preload back to 8 turns (38mm rider sag) and the rebound down 2 clicks. The bike now felt a lot more confidence inspiring and the forks didn't feel harsh. They did still seem to dive too much though. In for a penny in for a pound as they say. The next stop I increased the compression damping 2 clicks and on riding home the bike felt absolutely lovely. The forks felt like finely engineered precision with lots of feel, the bike went into corners smoothly and tracked really well. So, I think mine's about there!!

For my preferences at 14.5 stone in riding kit I've ended up with the following settings: -

Fork
----
1) 8 turns of preload giving 41mm of rider sag which is pretty central in the 35 - 48mm range.
2) 10 clicks out from fully closed on compression
3) 10 clicks out from fully closed on rebound

Shock
------
1) 3 additional turns of preload (original length between centres was the standard 313mm) giving 33mm of rider sag which again is pretty central in the 30 - 35mm range.
2) 1.5 turns out on compression from fully closed which is standard
3) 20 clicks out from fully closed for rebound which is standard.

I now love the way the bike feels and rides and I hope this helps someone get their bike feeling better :thumbup
 
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