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Old 12-16-2010, 09:19 PM   #1 (permalink)
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Default If anyone is interested in suspension help

Ok it's winter and cold so I thought I would make a help/how too thread on tuning suspension. one of only a few subjects I know anything about, so if you have any questions of feel your bikes is doing something weird as far as handling ask away!

this is a sag "how too" I did for guy on another board




SAG #'s

I like
Front 35mm with 20mm free sag
Rear 30mm rear with 5-10 mm free sag

SAG Definitions

Free Sag= the amount the bike will settle under its own weight from its fully extended position

Rider Sag= the amount the bike will settle with rider from its fully extended position


i.e. if you have 20mm of FREE SAG on the front, the bike should only settle an additional 15MM with rider for total sag of 35mm


I recommend that you set your rider sag 1st and then check free sag #'s this will help you to determine if you need different springs or not





Now let’s get your bike tuned!

SETTING SAG

setting sag is the MOST important thing you can do, it balances your bike and without it you will run into geometry issues.

for all this you will need at least 1 friend but it's better with 2,one to steady the bike one to take measurements


first you need to get your front tire off the ground I use a "triple tree stand", if you don't have one you can use the kick stand trick! just put your bike on the kick stand and pull it over so the front is in the air with the rear tire on the ground {sounds hard but it's easy!!} you want to gently pull the tire down while it's in the air, you want you suspension FULLY extended!!


next I use tape to hold the "Measuring tape " in place! this will ensure your measuring from the same point every time!



now measure to the bottom of the fork tube uncompressed as you can see I'm at 220 mm uncompressed {this # will very depending on were you tape your "Measuring tape at” wright that # down in a note book. take your bike off the stand, now with you on the bike you want the tape to read 180mm {or -40mm from your fully extended #}



now do the rear: note in the pic's it's on the rear stand that because I had no one to hold the bike as I took the pic's you can use the kick stand trick to get the rear in the air as well, but this time just push the front tire to the ground as you pull the bike onto the kick stand! and have a friends measure the bike uncompressed! but 1st.......
pick a point and tape your "Measuring tape " on to the tail directly above the axle




use a fixed point on the swing arm! I like to use the top of the inside of the axle! this measurement should be done Uncompressed {back tire hanging under it's own weight}



so you can see {if my back tire would have been in the air not on the stand my # let's say would be} 660mm now with you on the bike that # should read 625mm REMEMBER all measurements are from fully extended or "uncompressed' and then with you on the bike in a natural riding position!

So front you want 40mm from full extended **street** 35mm track
rear 35mm from fully extended **street** 30mm track





.................................................. .......................................



it os also VERY important that you have enough FREE SAG


free sag in how much the bike sags under it's own weight, you want 20mm in front and 5-10 in the rear!

why is free sag important?

think of it as reach! it's how far the bike can reach out and make contact with the pavement! if it can't reach out at all, your tires will continually loose contact with the ground and ANY interruption in traction is NEVER a good thing! free sag is just as important as sag! and the only way to get the 2 right is by getting a spring that works well for you weight


.................................................. .............................................




There are NO magic #'s NEVER set your bike to what works for rider (A) unless you ride exactly like he does.... and you don't, you will sometimes see test riders settings in magazines THERE JUNK and there not going to work for you, don't use them!



think of you tire as a basket ball, only with this basketball you do not want it to dribble you want it to stay firmly planted on the ground, ( a tire in the air has zero traction}





compassion:

this one is fairly basic it's adjust how hard or soft your bike reacts after hitting a bump, too soft your bike will give you no "feel" and will allow the tire to became air born under hard bumps

too hard: your tire has to act at a suspension component and this will over load it from all the extra work your asking it to do, you asking it to give you optimum traction and to flex to absurd the bumps that your compassion damping is not being allowed to do, this will also make your bike rough and feel harsh


rebound:

rebound is how fast or slow the suspension will push the tire back to the ground after a bump you want this is be fast, go too fast on rebound and your bike will pogo causing poor handling go too slow and you will get what is called "packing" the suspension can not return to a neutral state



ride hight :

raising or lowering the rear


The whole reason for raising the rear of a bike is to adjust your swing arm angle, but your sprockets will have squat and a anti squat characteristics as well + you need to take in account the placement of your rear axel in the sliders, so there are a few things that go into proper geometry set up! But I have always heard and found that 12.5 degrees is a good place to start when it comes to rear geometry……. now manufactures do things for the masses so they want a bike to be safe and very compliant and a flat swing arm angle give you just that

rase the rear of a bike too high you will have under steer after apex ( the bike will run wide) and no traction on the gas

lower it too low you will have over steer after apex ( the bike will run the corner too tight) and tons or traction on the gas

the happy place is, good solid on the gas traction and being able to hold a tight line as well





raising and lowing the front




all though this is not the best way to effect your "turn in" ( you are better off having adjustable ripple clamps) you can rase and lower the forks, this will depending on what you bike needs in the way of turning NOTE: not all bikes need there front ends lowered case in point the 2010 BMW S1000RR needs the front end raised 12mm



to all this there are many schools of thought I have always gone by the school that you adjust the front for "turn in" adjust the rear for "drive out"
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Last edited by AMRRA12; 12-17-2010 at 10:28 PM.
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Old 12-17-2010, 02:38 AM   #2 (permalink)
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Good write-up, do you elaborate somewhere on the adjustment side of it - as in how to get to these numbers?
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Old 12-17-2010, 11:15 AM   #3 (permalink)
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Originally Posted by Dshred View Post
Good write-up, do you elaborate somewhere on the adjustment side of it - as in how to get to these numbers?
added ......./\ like that or do you want more detail? I have tons of time at work today if you do.
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Old 12-17-2010, 12:13 PM   #4 (permalink)
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I believe that AMRA meant he likes 35mm SAG,, that would be 20mm due to the bikes weight, plus a further 15mm with him sat on the bike (front)

His 220-180 to get 40mm sag would be for road riding so he is setting 5mm more for street use.
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Old 12-17-2010, 12:25 PM   #5 (permalink)
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Using the figures in AMRA's write up

FRONT:

Tape readings
Wheel in air (suspension unloaded): 220mm
Free (static) sag due to bikes weight: 200mm (220-200) = 20mm
Rider sag (rider sat on bike with all gear): 185mm (track) (220-185) = 35mm


REAR


Tape readings
Wheel in air (suspension unloaded): 660mm
Free (static) sag due to bikes weight: 645mm (660-645) = 15mm
Rider sag (rider sat on bike with all gear): 630mm (track) (660-630) = 30mm
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Old 12-17-2010, 02:35 PM   #6 (permalink)
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i will go through it and clean it up a bit, most of it was done from my Iphone so it may be a bit jumbled
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Old 12-17-2010, 02:48 PM   #7 (permalink)
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As always AMRRA#12, another great technical post... Thanks...
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Old 12-17-2010, 04:35 PM   #8 (permalink)
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As always AMRRA#12, another great technical post... Thanks...
thanks man I cleand up alot of it!
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Old 12-18-2010, 11:46 AM   #9 (permalink)
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If anyone is interested I can do a how too on how to measure swing arms angles.
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Old 12-18-2010, 12:59 PM   #10 (permalink)
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I'd pay for someone like yourself to come over and help me set my suspension up to suit me.I weigh bugger all (70kg's) and get bucked off my seat over big bumps,and I've got a track day in 3 weeks,so it would be nice to have it set right.
I'll try to get the sags done but I feel I'll need a softer rear spring.
Great write-up!!!
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