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If anyone is interested in suspension help

62K views 141 replies 43 participants last post by  Chloe 
#1 · (Edited)
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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#5 ·
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
 
#6 ·
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
 
#7 ·
As always AMRRA#12, another great technical post... Thanks... :D
 
#10 ·
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!!!
 
#13 ·
Yes on mine the front was pushing even before I raised the rear (a sure sign of too must weight on the front tire)


NOTE: if this is all done with stock springs once you match springs to your weight and riding style, this will all change!

Suspension is a never ending battle as you get faster or you change somthing on your bike you ask more from your suspension and therefore you need to adjust it.
 
#16 ·
^^^^ Tires are factory Bridgestone BT-016,have done a Phillip Island track day and they felt really good,very grippy.Don't race,but have another P.Island track day in 3 weeks.As for my riding abilities,23 years experience,only accidents I've had have been when I'm trying too hard and survival instincts have kicked in and gone for the brakes,instead of looking around the corner I was going into.I think I've been able to overcome that problem.
Done 3 track days in total with my best times around the high 1:40's low 1:50's,so maybe at a guess I'd say I'm average to slightly above average.
 
#17 · (Edited)
1st thing is set your sag, then count all you clicks on comp and rebound front and rear

i.e. ( front comp hast 13 clicks im at 5 clicks from full stiff) post that up, this will make it easer to see if you have any blatant adjustment problems
 
#18 ·
this post is absolutely brilliant. I've read zillions of how-to's on suspension setups, and this one puts it in nice plain English. Thanks!
 
#22 · (Edited)
+1 but changing out springs track side may not be an option, and if it's not, there are a few things you can do to get better traction.


1st thing is you need to have GOOD notes on where is bike is set up currently (because your changing that and you want to get back to that point when the rain stops}

bikes work best with a cretin amount of traction, and it's not what most people would think: "more traction is better ,right?" NO traction is just like anything else too much is never good! you want your tires to grip but they also MUST be able to give, slide,push and spin.

so on a wet surface you have one factor that just sacrificed your traction for you and now you need to get some of that back, the best way is to lower the rear of the bike a bit.. either by backing off spring pre-load of dialing out compression or if your shock has it (and most good after market shocks do) low speed compression ..this will give you more "squat" out of the swing-arm, basically it will put more weight on the rear tire as soon as you crack the throttle and flatten out the contact patch a bit pushing more tire onto the ground.

now for the sacrifice you just made by doing that

more rear squat will lighten the front tire on the throttle, this will cause the front to loose some of it's contact patch (after apex on the gas) and the bike will want to run wide


but when your tuning for the weather it's all a matter of acceptable losses
 
#23 · (Edited)
This {how too} does not go into "sticktion #'s" and this weekend ..well my weekend tue,wen,thur, off. I will try to do a wright up with pics to cover this.

it's very easy to check and to account for but hard to explain without pics

basically "sticktion" is taking into account the amount of friction internal shock/fork parts play on setting sag#'s

if you are setting you sag continue to do so and you can check stiction at a later point


+ this should help demonstrate JUST HOW important setting your sag truly is, when you want to take into account the role of just a few MM of friction plays into the process!
 
#26 ·
Hello,

Thanks for the great post.

Today, mainly because bored with the snow preventing a ride, I adjusted the sag on my S1RR (I weigh 95kg without the gear) so I did the following adjustments to preload :

Front +2 "notches" Rider SAG is now 40mm (25 free + 15) which is on the high side of BMW user manual recommendations (probably needs a bit more).

Back : 3/4 turns and SAG is now 35mm (13 free +22) which is pretty much in the middle of the suggested range.

The manual suggests that Compression damping and rebound should be adjusted if SAG is changed. Considering that I can't really test with the current weather, what starting point would you suggest me to set them at (front and rear) ?

I got the bike for track days but there's a fair chance I'll be using it more on the twisties (it's registered on the same numberplate as my K13R so I know I won't resist riding it). The roads here are generally very good (quite like a track surface in fact).

Thanks for your inputs.

PS: this is the 1st time I try to set my suspension (ESA on teh other and previous bikes).

Cheers
Marc
 
#27 ·
Me too!
I'm 187 lbs all up, and have just added 1.5 notches on front (4 left showing) to give me:
Front 25mm free, 13 rider, total 38 sag
And 0.5 turn on the rear to give:
Rear 14mm free, 18 rider, total 32 sag

I found it tough getting an average from sticksion but repeAted the process until the wife got board:)

Question: I seem to have more free sag than most (25 vs 20 front, 14 vs 10 back ideal) even though I'm the BMW design weight and the bike is only 700 miles old.
What effect would too much free sag have?

Great thread, thanks for the advise, it's got me right back into it.
 
#33 ·
G'day AMRRA#12,hope you had a good Xmas.I finally got around to doing some measurements and here's what I've got.
Front 15mm free sag
20mm rider sag
Rear 5mm free sag
20mm rider sag
Front rebound is 5 clicks from full soft
Preload is at std setting 14mm from top of adjuster.
Compression damping is at 10 clicks from full soft.

Rear rebound damping is 2 turns out from full hard.
High speed comp damping 2 3/4 turns out from fully seated
Low speed 2 1/4
Hope you can make sense of this and advise me of what if anything I should be tweaking a little or a lot.
Thanks for your input.
 
#36 ·
I would go out 8 clicks = ( 2 turns) it's hard saying but I’m willing to bet your way to slow on rebound and the rear shock is packing (this is a Gen2 ZX right?) have you raised rear ride height? I have never seen a Gen2 to not benefit hugely from 5mm more ride height in the rear
 
#42 · (Edited)
Hi,
Thanks for a really god thread!

Question; (Sorry for my not perfect english...)
The numbers for front and rear sag in the first post, were they for street, trackdays or racing?
I normally drive trackdays but are increasing speed and want right figures from the start before I do the rest of the settings.

Edit;
I also have the feeling that I am a little bit to heavy for the front fork. I weight about 87 kg / 192 pound without gear and the fork is going way to much down during hard breaking even if I increase the compression. I will start with the sag adjustments and see what the will tell me, but can I solve a soft front fork with more oil or should I get a stiffer spring?

Best regards
Peter
 
#45 ·
AMMRA12 I just wanted to thank you for your help with setting my suspension up.Even though I didn't have to change anything too much,knowing that I was in "the ball park" gave me a lot more confidence to ride a bit harder on my track day.It has also given me a better understanding of what I can change to suit different conditions.
Here's a pic of the left side of my back tyre after 2 sessions at Phillip Island.

Tire Automotive tire Synthetic rubber Auto part Wheel


Thanks again for taking the time to help a fellow rider.:D
 
#47 · (Edited)
AMMRA12 I just wanted to thank you for your help with setting my suspension up.Even though I didn't have to change anything too much,knowing that I was in "the ball park" gave me a lot more confidence to ride a bit harder on my track day.It has also given me a better understanding of what I can change to suit different conditions.
Here's a pic of the left side of my back tyre after 2 sessions at Phillip Island.

View attachment 4339

Thanks again for taking the time to help a fellow rider.:D

any time man! and the tire looks real good! very smooth on the throttle!

here is a pic from my tire after a long tuning session and yours looks better than mine!!
[/IMG]
 
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