Basic Suspension Stuff...

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Basic Suspension Stuff...

Postby Shakti Stunter » Wed Sep 28, 2005 5:43 pm

Very Basic Suspension Stuff….
by Shakti Stunter / Kali7

Ok, after having done two supension schools with Steve Brouggy’s Superbike School, watched and sometimes helped a suspension guru (Zenostoic), talked with peeps like Josh Brookes (thought I would name drop that here…. though I probably have only spoken to the lad half a dozen times if that…), and with anyone who has any interest in suspension at all…. I thought I would finally write a layman, ignoramous version of the how to suspension hoohah…. if I have made mistakes, or misnamed stuff…. too bad…



Suspension set up is made up of three components; namely the geometry, the spring setup (sag/preload), and the compression/rebound dampening.

When it comes to geometry, you’re looking at things like ride height etc, these things can be changed with suspension settings... but are starting to get a little techie for my simple article here.

As for springs, most of them tend to be whats called ‘straight rate’ springs, called that because they give you the same amount of resistance in the first few centimeters of travel (up/down movement) as in the next. Once you have set you bike up properly, if you have to dramatically add or reduce your preload on the fork, you need to think about re-valving and changing quality and level of fork oil (i.e. see a professional) or for the rear, you need to replace your shock spring (or make sure it has gas…..). So what do your springs or shock absorbers do? They DAMPEN vibrations…. you know when you ride over a bumpy section of Old Road….

Preload
Refers to what is called the amount of static tension that is applied to the fork or shock springs. Any static tension will cause an increase in spring rate. Spring rate refers to the amount of weight needed to compress a spring an inch (you know, your old highschool physics formula? Force = Mass x Acceleration).

There are two ways to alter the preload. The first one, unless you are mechanically minded, probably not a good idea to play with because you need to muck around with the internal spacer inside the fork (and to add to this, for the mechanically minded: this spacer is what the suspension builder will cut down or add to that provides your adjustment range for your external preload adjusters – often when the external preload adjuster will not allow proper sag to be achieved, it’s because the internal preload spacer has been cut incorrectly).

The second is one you should be familiar with. The external preload adjustment is usually situated on the top of your forks. In plain English, it’s the large knob that requires a 14mm or 17mm socket or wrench to adjust. On a shock, preload is adjusted via the collar that is on the top part of your spring. If you have a standard spring, chances are you have to use that funny looking ‘C’ shape tool in your standard kit. If you were sensible person and spent money on suspension first instead of bling, you don’t need a tool… you can laugh while others struggle with tools and shit, and click away…Oh, and when adjusting think of a tap, on for more, off for less….

Now for some terminology….

Now, you will often find different places and people mixing up the term “static sag� with either ‘free sag’ or ‘rider sag’. I have chosen to opt for what seems to be the consensus on correct terminology and call rider sag, static sag.

Free Sag
This is the amount of travel (up/down movement) used by the motorcycle when under its own weight. You work out free sag by measuring the difference between the bike fully lifted up (suspension tops out under gravity) and the bike at rest.

Static Sag
Is how much the suspension settles with you on the bike. Static sag is derived by measuring the difference between the bike at rest and with the rider sitting on the motorcycle in a natural position (or full race position if this is your track bike).

Static sag provides the ‘give’ during the riding of flip/flop corners, when the road turns hilly, or when doing the straights real fast without having to tax the suspension.

Total Sag
The combined travel used when the free sag and static sag are added together.

Rebound Dampening
Refers to how fast or slow your bike shocks or forks go up to and from rest position or ‘rebound’. Here you can adjust the rate of how fast or slow. On the forks, this will be the small adjuster on the cap of the forks, here you can use a flat head screwdriver or 5 cent coin… (make sure you do this in quarter turn increments…)

Compression Dampening
Where rebound dampening refers to UP, compression refers to DOWN. This is the adjustment on your shock or forks that controls how fast or slow your bike goes down or compresses.

Stiction
Ever wondered how you can tell if your wheel was not put on correctly after getting a new tyre, or if your forks or triple clamps are bent? Or if you forks simply need a service? Chances are your forks will have too much (or abnornally small) amount of stiction. Stiction refers to the measured difference between compressed and extended forks from the rest position. So, to measure stiction, you first compress the forks and slowly let them come back up, you then measure the position of the fork dust seal. Next, lift the front end up and slowly let the forks return to the at rest position. Measure the position of the fork again at the same place. The difference between the two is the stiction.

Whats the point of measuring this shit?
Firstly, you want to determine if your springs and forks work properly, and secondly, if you need to change or service them (DOH!!!!!)

Measuring the forks

A couple of golden rules…. always measure from the SAME point (think about it!!!), and secondly cable ties give you that easy reference point…..

Now, traditionally forks are measured from the base of the triple clamp to the shoulder of the lower fork leg, and on upside down forks can be measured from the shoulder of the upper leg to the end of the chrome tube where it enters the axle casting… or just use the cable tie….

Free Sag

• Bounce on the front forks several times so they can move freely, and maybe dislodge any sticky oil or road shit. Then give them a little break.
• Place and line up the cable tie with the fork dust seal.
• Carefully have the two helpers lift up on the handlebars until the forks “top out�.
• Measure the distance between the cable tie and the top of the fork dust seal. That’s your free sag. Call this measurement L1 (yep, because there is a formula coming up…. woohoo….)
• Typical free sag for the forks is 15mm to 35mm.
.
Static Sag

• Put on your regular riding gear and sit on your bike in normal riding position (or race position if this is your track bike.
• Have one friend hold up the back of your bike so that you can keep both feet on the pegs, while your second mate, does the same measurement thing as with the free sag (make sure he pushes up the front first and give it a few seconds to settle. This measurement you are going to call L2
• And woohoo…. you guessed it, your poor mate at the front this time pushes DOWN the front end, allows the bike to settle, measures, and calls this L3. Typical static sag for the forks is 10mm to 30mm.

Why did I just do this shit?

And now for the forumla…. sag = L1-(L3+L2)/2

As a general principle, the front fork SAG should be approximately 25 (race track stiff) to 35mm (bumpy road tourer). If there is more than 35mm, preload can be added. Turn clockwise (like a tap) to add preload. If all the available preload is added and the resulting number is still greater than 35mm, then the fork springs are too soft and need to be replaced…… (just call Zeno)

So to quote some one who knows what they are saying: “Street bikes run between 25 and 33 percent of their total travel, which equates to 30 to 35mm. Roadrace bikes usually run between 25 and 30mm. This method of checking sag and taking stiction into account also allows you to check the drag of the linkage and seals. It follows that the greater the difference between the measurements (pushing down and pulling up), the worse the stiction� (Paul Thede)

Measuring the shock

Free Sag
• Bounce on the rear of the motorcycle several times then let it settle.
• With the help of a mate, get the rear wheel completely off the ground, then allow it to rest.
• Measure the distance from the axle vertically to some point you have marked out with tape or whiteboard pen. Make sure you measure exactly vertically, otherwise you will end up with a lower number. This measurement is L1.

Static Sag
• Now without bouncing the bike (this is kind of important), do the rider thing, just like you did on the front. using your marked point as a reference to get L2 (lifting up then to rest) and L3 (pushing down then to rest). Then do the formula thing again.

If you have too much sag you need more preload (see notes under preload….. this is where if you have your whizz bang new shit you can laugh at people trying to chisel their spring collar in the hope it will move…..whilst you twist the dially thingie…) Now, if you have too little sag you need less preload. For roadrace bikes, rear sag is typically 25 to 30mm. Street riders usually use 30 to 35mm.

References:
Suspension Workshops, Eastern Creek with Australian Superbike School.
Paul Thede, “Beyond nuts and bolts�
Marcus McBain, “Basic Spring and Sag Setup�
May a flea climb up my ass find happiness.
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Postby Uncle » Wed Sep 28, 2005 11:51 pm

lol got glue?
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Postby STREET ELITE ALEX » Thu Sep 29, 2005 1:18 am

boooooorrrrring............boooooorrrrinnng. if its broke take it to the shop thats my philosophy...........hang on but im not a philosofist. d'oh
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Postby STREET ELITE LUCAS » Thu Sep 29, 2005 1:52 pm

I don't think setting my suspension is going to help my handling with the flat front tyre :lol:
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Postby Shakti Stunter » Fri Sep 30, 2005 2:06 pm

glue, boring and flat front tyres..... says it all really.... :roll:

I mean we wouldnt want REAL stunters to get the reputuation of being mistakenly called stoooopid now would we? 8)
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Postby STREET ELITE LUCAS » Fri Sep 30, 2005 3:49 pm

But my front is flat so that it stoppies better.
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Postby BlueHeeler » Fri Sep 30, 2005 8:19 pm

To be honest, I have never ridden a stunt bike with decent suspension.

Whats the point??? Isnt the front wheel meant to be in the air anyway?
"SUZUKI: Common choice of ride amongst wellhung Motorcycle riders. Owners tend to be more skilled and less full of bulls*** than other riders ie, Honda, Yamaha" (urbandictionary.com)
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Postby HYPE » Fri Sep 30, 2005 8:49 pm

BlueHeeler wrote:To be honest, I have never ridden a stunt bike with decent suspension.


hey.. nuttin wrong with the CBR susp ..........now! :)

BlueHeeler wrote:Whats the point??? Isnt the front wheel meant to be in the air anyway?


well i guess youve got a point.. when you're running 10-20psi the suspension doesnt really need to be 'tuned' just set to soft/medium... setting the sag and the likes are not as important as track/road racing etc... but still relevant for those interested...

if you want your forks sorted for better endos you want to see 'Zenostoic' (Jimmy) ...he's tried & tested and i swear by his expertise... before revalving/rebuilding, whenever i landed a minger it would go into instant slappers and when jammin the front breaks endo's were suicidal!
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Postby BlueHeeler » Fri Sep 30, 2005 10:36 pm

Thats what I meant. Guess I could have elaborated a little more.

And I definately know the benefit of decent suspension on a stunter. I was nearly a victim of one of those tank slappers.
"SUZUKI: Common choice of ride amongst wellhung Motorcycle riders. Owners tend to be more skilled and less full of bulls*** than other riders ie, Honda, Yamaha" (urbandictionary.com)
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Postby STREET ELITE ALEX » Sat Oct 01, 2005 1:28 am

sorry shakti didnt mean to sound rood :( when i got my bike it was leaking a bitta oil out the right front fork. i took it to the bike shop to getr the front tyre changed, the mechanic rang me up to tell me that when he jacked up the bike, the front tyre stayed on the ground untill the brake line took up the tention only then did the wheel come off the ground. :shock: so i trailered the bike away as he wouldnt let me ride it home. in the garage i disconnected the callipers and pulled the front wheel down about a foot oil going every where.
This is after i had been trying to wheely out the front.
Now that would have been quite a moment if the front wheel had have fallen off!!!

I think i could have done with zinodampers expertise.
all sorted now though
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Postby Uncle » Sat Oct 01, 2005 4:51 pm

Shakti Stunter wrote:glue, boring and flat front tyres..... says it all really.... :roll:

I mean we wouldnt want REAL stunters to get the reputuation of being mistakenly called stoooopid now would we? 8)

A.Yes it sure dose
B.I already have a reputuation for being stooopid so whats your point?
oh thats right I am not a REAL stunter am I :roll:
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