Basic rules for suspension
From years of doing tuning, I've almost always found that it's best to aim towards developing a "tuning plan" or a consistent series of steps that ends up allowing you to derive the perfect tuning settings (or as close as you can be) for the intended usage of the vehicle.
That holds true with suspension, dynamometer design, carburetion, bike control setup, engine building, chassis development and whatever else you are trying to assemble into a "good working pile" of parts and pieces.
By structuring testing and other evolutionary / empirical processes, you will be training yourself to rapidly identify problems, recognize trends and patterns and be able to create a possible path to improving whatever you are working on.
In suspension, the basic path is to do the spring rates and preloads and then do the damping.
Springs setup, front and rear, is to simply set "spring" both ends of the bike so that when you push down on the footpegs (where most of your weight is when you aggressively corner), both ends of the bike NEED to go up and down exactly evenly, both in travel and rate.
Select a rear spring that will just bottom out
over your harshest bump that you are riding over with "normal" sag.
Soften it up till it just bottoms out, then tighten preload 1/4. Check
the sag and see if it's in general range of 35mm to 20mm.
Select front fork springs that allow the front
end and the rear end to travel equally and evenly when you bounce on
the footpegs (helps to have someone hold the bike upright). That's after
you have set the rear spring as in the above step.
Rear rebound: Use just barely enough to prevent
wallowing in high speed sweepers.
Front rebound: Use just enough rebound to keep
the front end from topping out and drifting wide when exiting low speed
corners at full throttle.
Compression damping, front and rear: The goal is to use as little as possible. Use the proper, perhaps heavier than stock spring to do the major work during non-braking mode riding - but never use a front spring that is stiff enough to be stronger than and mismatched than the required rear spring.
Use compression damping to trim if necessary and only if required.
Excessive dive under braking: Use increased oil level to firm the front end under hard braking. 5mm is a significant change in modern forks.
Goals are to always use the softest rear spring that works within "sag" range limit.
Use just enough rebound damping to control the springs.
Use as little compression damping as possible and only
when required. Not everybody has a supply of alternate fork and shock
springs, so you will probably have to improvise and use a bit of extra
preload or a bit more compression damping to compensate for too soft
of a spring.
2007 July 12
After years of paying suspension experts I set up my own suspension, using your guidelines.
My bike is a 04 SV 650 with conventional GSX-R 600 forks and a Penske shock.
The local suspension experts recommended a 600lb rear spring and a set of .95 front springs. With that set up the bike worked ok and I rode it that way for a few years. It would not turn in as fast as I would have liked and raising the rear resulted in slightly quicker turning but poor tire wear.
As I am 215lbs the tire did not spin noticeably.
I tried a 450 rear spring and .78 springs but they were too soft.
I went next to a 485 (used Ohlins) and .85 front springs. I used OEM Suzuki valving for a 04-05 GSX-R 600 which comes stock with .85 springs.
I need a bit more fork oil as I bottom the forks on the brakes at the end of the fastest straight but it's great everywhere else.
The part I find most odd is that the bike turns much faster with the soft set
up and I weigh 215. I am two seconds a lap faster with no other changes. I can change
my line in a corner and can trail brake until my knee is down.
Thanks Very Much,
Thanks! Great to hear that this helped - It's nice to hear once in a while! <winkl!>
Add that bit of fork oil to raise the "air spring" progressiveness and that should address the dive under hard braking and still be supple in mid corner.
As far as the turning easier?
You probably figured that out as you hit "send"... :-)
The .85 front end is now softer than the .95's and when you have the brakes on,
it's more compressed, steepening up the forks - and turning in at a quicker rate
more for a given lean angle.
As far as the rear spring, when you are braking, the rear end is topped out, regardless of the spring being "stiffer" or "softer".
Age helps....... Remember front ends that "don't dive"? Anti-Dive Systems on
the 80's vintage Hondas and Suzukis........
I do -
They were relatively GREAT under hard, straight braking - but, the bike was a bear to turn into tight corners - and now, you may have gained 1% better straight line braking, you lost 5% of your corner entrance speed. So - "anti-dive" - not such a great idea after we tested it - We blocked it off on our 86 and 87 gsxr's.