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Topic: Suspension adjustment  (Read 2049 times)

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Mo Throttle
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« on: March 26, 2012, 12:57:43 AM »

In simple terms what does one do to "soften or stiffen" the ride by turning the knob below the frame or adjusting the screws on top of the forks? Please explain dampening also in soft or harsh ride terms. Thanks so much/
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garry
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« Reply #1 on: March 26, 2012, 06:27:18 AM »

This will be like drinking from a fire hose, but look up the "Dave Moss Unsprung" videos on ustream.tv. They are like an hour each but explain lots about suspension tuning. The engineer in me would prefer more science/physics, diagrams of suspension internals, equations and the like, but it's still good stuff.

We need to know what the knobs you are referring to actually are as there are several. Many ST bikes only provide spring preload and rebound damping adjustments. Sportbikes usually have fully adjustable suspension which includes spring preload, compression and rebound on the forks, plus spring preload, high and low speed compression damping, and rebound damping on the shock. Then there is the stiffness of the springs themselves (the spring rate, and is it linear or progressive). You can't really adjust the spring rate, but you can change springs for not a ton of money if they are too soft or too firm.

Compression damping helps control how the fork/shock behaves when absorbing a bump. Usually referred to as softer or firmer. Basically you are adjusting the size of a hole that oil gets pushed through. The smaller the hole, the more resistance there is.

Rebound damping helps control the forks/shock when it is extending after absorbing a bump. That adjustment is usually referred to as fast or slow. Increasing the rebound damping will slow the fork/shock extension down. If rebound is too fast, the suspension can "pogo"; too slow and it will "pack" (not fully extend before hitting the next bump).

And then there is the issue of oil viscosity. You can choose the weight of the oil to change how your suspension responds (lighter weight such as 5W flows easier than thicker oil so it provides less damping at the same settings).

You use spring preload to adjust how much the suspension sags under your weight (and passenger and luggage if applicable). Since the amount the suspension sags affects steering geometry (mucho sag in the rear makes it chopper-like), it is usually the first step in adjusting suspension. Get the sag/geometry right, then start playing with the clickers to adjust damping.

One last thing that I recently learned is that spring preload does indeed change the stiffness of a linear rate spring. I was always in the "preload only affects sag, not stiffness" camp until doing some research on how springs behave:

http://www.afcoracing.com/tech_pages/spring.shtml

http://www.foremostspring.com/springs_compression_ends.html
« Last Edit: March 26, 2012, 10:50:37 AM by garry » Logged

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« Reply #2 on: March 26, 2012, 08:21:49 AM »

There is no real simple answer so prepare for a novel here:

Just messing with the suspension settings without having at least a basic understanding of what you’re doing can lead to a bike that handles like crap and doesn’t ride any better than when you started. It’s like tinkering with a carb without really knowing what you’re doing; you’ll fiddle with it for days, chasing your tail, and never really get anywhere. It’s a sure-fire recipe for anger and frustration.  Crazy
There are some things you have to have a basic understanding of before you go messing with things: spring rate, spring preload, compression dampening, and rebound dampening. I’m going to assume your bike has fully adjustable suspension (preload, compression, rebound).

-SPRING RATE: spring rate is set by the springs themselves so this is the one thing that isn’t adjustable without changing parts. Most bikes I’ve dealt with are OK as far as spring rate from the factory, assuming you’re not after all out corner burning performance; then they tend to be set up a touch too soft for us thick Americans. Bigsmile It sounds like you after comfort so as long as you’re in between about 150-250lb your spring rate is probably close enough to work with. If you’re exceptionally light or heavy different springs may be in order.
-PRELOAD: preload is a certain amount of tension put on the springs at their “at rest” position. You want the suspension to “squish” a certain amount from fully extended when it’s supporting the weight of the bike and rider at rest. This is called “sag” and is pretty important to set correctly. Too little sag (too much preload) in front will result in “slow” steering response and a harsh ride, too much sag (too little preload) may cause instability in a corner and suspension bottoming (not good).
In the rear, too little sag will result in quick steering but a harsh ride and possible instability issues. Too much sag in the rear will result in slow steering response and possible bottoming and poor handling.
It’s adjusted with the pre-load adjusters (the big adjuster on the top of most forks and a thin “nut” on the shock body in the rear). You want roughly 32-38mm (1 1/4-1 1/2”) of sag in the front and 28-32mm(1 1/8-1 ¼”) in the rear. Since you’re after comfort, I’d aim for the high end on both of those unless you frequently carry a passenger or lots of weight, then go for the smaller number in the rear. If you have problems with the suspension bottoming, bump up the preload.

-COMPRESSION DAMPENING: the compression dampening controls how quickly, or easily, the suspension will “squish down”.  Too little will allow the suspension to compress too quickly and can cause it to bottom too easily. It will also result in a bike that will “nose dive” when the brakes are applied or nose up on takeoff. This excessive “rocking” when on the brakes or on power will result in poor handling in a curve. Too much will not allow it to compress fast enough and will result in a rough ride and a bike that is “unsettled” when you hit bumps in a turn.

-REBOUND DAMPENING: Rebound controls how quickly the suspension is allowed to extend. Too little rebound will allow the suspension to extend too quickly and will result in a mushy uncontrolled ride. It can also cause “wallowy” handling. Too much won’t allow the suspension to extend fast enough and the bike will “pogo” over bumps. That means the suspension will not extend fast enough and the tire will actually leave the ground slightly as it skips off the back of one bump and hits the next. It’s kind of a “chattery” sort of feeling and it DEFINITELY makes the ride rough and unpleasant. It also greatly reduces your control as the tire will not be able to properly “grab” the pavement as it’s skipping along.

This is a VERY basic explanation so if you really want to get into it I suggest some research on the subject.

As far as getting a softer ride; my suggestion it to back off the preload a little and take a few clicks of rebound out (softer). Compression is the last thing I mess with for a softer ride. Look to your owner’s manual if you’re unsure as to where each adjustment is made. Be careful though as going too far can cause some crummy handling characteristics.
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« Reply #3 on: March 26, 2012, 09:57:13 AM »

suspension tuning, while scientific also has an element of black magic.....
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« Reply #4 on: March 26, 2012, 10:03:23 AM »

The book "Total Control" by Lee Parks has a pretty good introduction to the basic principles of suspension adjustment. (Warning: It's a fooking complicated topic!)  Thumbsup
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« Reply #5 on: March 26, 2012, 10:09:19 AM »


(Warning: It's a fooking complicated topic!)  Thumbsup


the problem is there is no "perfect setting" for all around use. tuning is very specific to conditions so what works well on one road is not so good on the next. Years of screwing with suspension settings on my woods bike has me convinved that the best money you can spend is to send it to a proffesional and let them do it for you, the results will be amazing.
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garry
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« Reply #6 on: March 26, 2012, 10:36:46 AM »


the problem is there is no "perfect setting" for all around use. tuning is very specific to conditions so what works well on one road is not so good on the next. Years of screwing with suspension settings on my woods bike has me convinved that the best money you can spend is to send it to a proffesional and let them do it for you, the results will be amazing.


I just sent the forks and shock on my KTM 950 to a shop in NC for a rebuild/revalve and it is big step forward in control while leaned over on bumpy pavement. Good stuff. Money ($500) well spent (stock springs were OK for my weight).
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« Reply #7 on: March 26, 2012, 10:41:02 AM »




the problem is there is no "perfect setting" for all around use. tuning is very specific to conditions so what works well on one road is not so good on the next. Years of screwing with suspension settings on my woods bike has me convinved that the best money you can spend is to send it to a proffesional and let them do it for you, the results will be amazing.

+1 An hour with a good suspension tuner is worth every penny.
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« Reply #8 on: March 28, 2012, 08:07:54 AM »

When you ride your bike, note what you wish was different in how your bike reacts to road imperfections. Then learn how you can adjust your bike to make it deal with bumps and other things better. Adjust in small amounts til you are satisfied.
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« Reply #9 on: March 28, 2012, 11:18:43 PM »

 Until you have the proper spring rate for your weight adjusting preload or damping settings will be a compromise at best. Even with the proper spring rate you'll still be compromising unless you spend the money on fully adjustable suspension, and someone to help you tune it if you can't/won't take the time to figure it out yourself. Yes it is a bit of an art, but time, and tweaking can teach you a lot if you have the tools, and patience.

 Whether it's worth the $$$$ or not depends on what you demand of the bike.
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black hills
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« Reply #10 on: March 30, 2012, 05:11:09 PM »

a common misconception is that softer springs will make it ride softer. this is false, softer springs get you into the mid part of the damping and actually made the ride harsher. get the proper springs (static and rider sag) and go from there.
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« Reply #11 on: March 30, 2012, 05:38:53 PM »


a common misconception is that softer springs will make it ride softer. this is false, softer springs get you into the mid part of the damping and actually made the ride harsher. get the proper springs (static and rider sag) and go from there.


This is very true. My Wee Strom forks were quite harsh. I upped the spring rate a good bit which kept the forks from blowing through their travel. All that fork movement needed to move a lot of oil and the damper rods just couldn't flow enough (hole too small) so the result was harshness. With stiffer springs, the forks didn't compress as much, and combined with lighter fork oil, the hydro-locking from not being able to flow the required oil was mostly gone. Who would have thunk that stiffer springs can create a softer ride...
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« Reply #12 on: March 30, 2012, 05:53:22 PM »

All part of the black magic
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« Reply #13 on: March 31, 2012, 01:24:39 AM »

Like most, when I read a motorcycle specific book and got to the "suspension chapter", my a.d.d. kicked in and I skimmed it really quick or just put it down.  

I finally got the vfr's suspension dialed in.  Over the last few months, I had the shock revalved and resprung and the springs and oil changed in the forks.  My shop (washington cycle works in washington, nj) is great.  They got it adjusted right.  Now, the bike falls in and stands up easy in and out of turns and is quite nimble now.  

Taking a bike to a proper suspension shop is money well spent in my opinion.  There is a lot going on with each end of a bike, more than just adjusting and going for a ride.  Paying someone $50 to adjust it correctly and accurately is priceless.  Thumbsup
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