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Suspension settings interaction


superfist

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Couple comments, purely intended to help ...... 
Forget looking at tire wear to set the suspension.  Tire wear WILL give you some guide about tire pressures, but not sag, rebound or compression damping.  
 
Adjusting preload has ZERO affect on stiffening or softening the spring.  All it does is raise or lower that end of the motorcycle.  It's important to get preload/sag correct as having the bike ride in the correct part of the suspension (roughly 1/3 of available travel), as well as having the correct front to rear height relationship is very important to handling.  However it doesn't make the springs 'stiffer', not one little bit.  Set the front and rear sag correctly, by static measurement in the workshop.  How to do it is well documented in numerous articles you'll find on the internet.  Once measured and set, don't touch it again.
 
So to your question "how does rebound and pre-load interact?  Simple answer, they don't interact at all.  As previously explained the sole purpose of preload is to set the static position of the motorcycle in the suspension travel.  Rebound is to control the rate of return of the compressed spring after it encounters a bump (or anything else that causes the spring to compress e.g. rear squat, front braking, cornering forces).  
 
So in practical terms, set sag by measuring and adjusting it in the workshop.  Set rebound damping on the road to get an appropriate balance between firming it up to remove any wallow in the corners on smooth roads, yet at the same time be fast enough to give an acceptable and compliant ride over rough roads.  It will always be a balance between these two competing objectives that only the individual rider can determine.  
 
Good luck, and if anything needs clarification don't hesitate.
 
P.S. and if your're scratching your head trying to figure why screwing up the preload doesn't stiffen the spring, consider your humble bathroom scale.  Does sticking a block of wood under the scale increase what the scale says you weigh (determined by how much the spring inside the scales compresses) or just increase your height when you're standing on the scales???  The preload adjuster is in principal no more than that block of wood.  Screwing up the preload adjuster just pushes against one end of the spring, bike just goes up, amount spring compressed remains unaffected (solely determined by the weight of motorcycle and rider it is supporting).
 
 

 
I disagree with nearly everything you said.
 
Ps - preload does not change the ride height. It simply preloads the spring (which most are progressive springs these days, this affecting how stiff it will be in its initial stroke).
That's where we probably differ, I disagree totally with everything you said.
 
The ONLY thing altering preload does is alter the height of the motorcycle (with the exception of suspensions with long rebound springs).  
 
"Preload is simply the amount the springs are compressed while the suspension is fully extended"  - [url=]http://www.promecha.com.au/sag_preload.htm[/url]  That is the only time preload has any effect on the spring length, "when the suspension is fully extended".  And that is because this is the only time the spring is 'trapped' between two fixed distance ends.  All other times the spring is free to move the inner fork tube or shock absorber shaft up or down the exact same distance the other end of the spring is shifted.
 
As soon as you drop the weight of the bike (or rider and bike) onto the spring it will compress to EXACTLY the same length regardless of the initial preload.  It must, simple physics.  It will always compress to a length where it exerts a force equal to the weight of bike and rider.  The bike and rider weight do not change when preload is adjusted, so the compressed length of the spring to support that weight will always be the same, it MUST.  The only difference will be the height of the bike (because the position of one end of the spring has been shifted up or down).
 
Another worthy quote from the above link (the authors of that article are one of the most highly regarded motorcycle suspension specialists in Australia)....... "Preload makes the bike sit higher, or lower. It does not make the spring stiffer. So if someone tells you that you should reduce your preload to make the bike feel less harsh, they probably don’t have a clue."
 
 
 
 
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Increasing shock preload increases the height of the bike ...... only until the shock is fully extended. Once the shock is fully extended, the bike cannot go up any higher. From that point, increasing preload starts to compress the spring. Usually, there is a spec how much the spring should be compressed with preload before you even put the shock on the bike. If you crank in more preload after the shock is in full extension, the ride will feel harsher. It is not the spring rate making it feel harsher, it is the extra weight needed to get the spring to start compressing when the shock is fully extended, topped out.
If you have a 100 lb/in straight rate spring with 4 inches of travel in the shock/spring, it will take 100 lbs of force to compress the spring the first inch. However, if you crank in 3" of preload, (an exaggeration for illustration purposes) it will take over 300 lbs of force to start the spring compression from a position of full shock extension. Guess which situation will feel stiffer.
 
A different situation where adding preload may make the ride feel stiffer; If the shock spring has a dual rate, and the softer, initial spring rate is too low for the rider weight, or the amount of travel the spring has in the initial softer rate is too short, adding preload may coil bind the softer, initial rate coils, causing the shock to ride on the harder final rate coils.
 
The key problem in both situations is the spring rates are too light for rider/bike weight, and increasing preload cannot compensate for too weak a spring rate.
 
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Increasing shock preload increases the height of the bike ...... only until the shock is fully extended. Once the shock is fully extended, the bike cannot go up any higher. From that point, increasing preload starts to compress the spring. Usually, there is a spec how much the spring should be compressed with preload before you even put the shock on the bike. If you crank in more preload after the shock is in full extension, the ride will feel harsher. It is not the spring rate making it feel harsher, it is the extra weight needed to get the spring to start compressing when the shock is fully extended, topped out. If you have a 100 lb/in straight rate spring with 4 inches of travel in the shock/spring, it will take 100 lbs of force to compress the spring the first inch. However, if you crank in 3" of preload, (an exaggeration for illustration purposes) it will take over 300 lbs of force to start the spring compression from a position of full shock extension. Guess which situation will feel stiffer.
 
A different situation where adding preload may make the ride feel stiffer; If the shock spring has a dual rate, and the softer, initial spring rate is too low for the rider weight, or the amount of travel the spring has in the initial softer rate is too short, adding preload may coil bind the softer, initial rate coils, causing the shock to ride on the harder final rate coils.
 
The key problem in both situations is the spring rates are too light for rider/bike weight, and increasing preload cannot compensate for too weak a spring rate.

Your purely theoretical example is correct.  If you could (you can't for practical reasons) put so much preload on the springs that the bike doesn't sink even the smallest amount into the suspension travel under the combined weight of bike and rider ..........  the ride would be harsher, because now you have no suspension.   The amount of preload in the spring would need to exceed the combined weight of motorcycle and rider it is supporting.  You would be riding around on a motorcycle with the suspension fully topped out, so not only would it be harsher it would handle like totally crap.
 
Now back to the real world.  Firstly you can't put that amount of preload into a typical motorcycle suspension even if you deliberately wanted to.  As long as the suspension sinks even a tiny amount when the combined weight of rider and motorcycle is added, the spring length will be IDENTICAL regardless of the amount of initial preload.  The only difference will be the amount the spring had to compress before achieving its equilibrium length.
 
If say the combined weight of rider and motorcycle is 100kg, the spring will ALWAYS compress to an identical length where it exerts an opposing 100KG force.   Whether the spring initially sits compressed to 25Kg, 50kg, or 75kg is totally irrelevant to the length it will be when 100Kg of force is applied.  All that will change is the amount of distance it needs to compress to get to its 100Kg length.
 
P.S. The only reason I'm laboring this point is that so many beginning riders falsely believe that altering preload will affect ride quality.   It may have some very minor effect in the final 1/3 of travel due to its impact on oil height, and correctly set prevent the suspension topping or bottoming out.
 
But for all practical purposes ride quality is determined by spring weight, rebound and compression damping, and fork oil height.  Preload only affects the spring length when the suspension is fully extended and we don't ride around much like that.  Just to reinforce one more time, all it does do for practical purposes is alter the static ride height of the motorcycle.
  
If your not going to accept the word of highly regarded experts e.g. [url=]http://www.promecha.com.au/sag_preload.htm[/url], and author with a PhD, I suppose its silly to think you'd believe me.  Perhaps you didn't even bother to read the article.
 
 
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You are assuming everyone has the correct spring rate and preload/rider sag. That certainly is not true in the real world, especially for us 250 lb guys who bought a bike with stock springs for 160 lb rider.
 
 
 
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You are assuming everyone has the correct spring rate and preload/rider sag. That certainly is not true in the real world, especially for us 250 lb guys who bought a bike with stock springs for 160 lb rider.  
 

No, the example you give makes zero difference.  As long as the weight of rider and motorcycle compress the spring, the initial preload on the spring, or the weight of the spring used makes no difference.  If the spring has to support X lbs, it will ALWAYS be compress to a length where it supports X lbs (regardless of whether it is a strong or weak spring).  It can do nothing else but this.  The only difference between a strong and weak spring is how much it compresses to support X lbs.  Partially compressing each spring (preload) prior to applying X pounds won't alter how much each compress, as long as X pounds exceeds the preload tension.  
 
The only time preload can alter how much a spring compresses if is it is greater than the load applied, and in that case the spring doesn't move at all.  In practice you can achieve this with just the weight of the bike (zero free sag) where the suspension is fully topped out with no rider on board (usually a sign of underweight springs for the bike/rider weight).  But if you were able to achieve zero sag with a rider on the motorcycle, you would have no suspension.
 
A 250 lb guy will need to screw up the preload with underweight springs to get an acceptable 'rider sag'.  But this doesn't increase the spring rate one zot.  All it's doing is pushing on one end of the spring to physically lift the motorcycle.   That's all its doing.  In older damper rod forks with no external adjuster you changed the sag by simply cutting a different length internal spacer (a piece of water pipe).  If you wanted 10mm less sag you cut your piece of water pipe 10mm longer than the spacer already in the fork.  Stick it in and it just jacked up the fork to sit 10mm higher.  Spring remained the exact same length once it was supporting the weight of the bike, or rider and bike.
 
 
 
 
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You are talking about when there is sag. I am talking about when the shock is fully extended and there is no sag, which can happen under riding conditions as the shock tops out to full extension. Two different situations.
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You are talking about when there is sag. I am talking about when the shock is fully extended and there is no sag, which can happen under riding conditions as the shock tops out to full extension. Two different situations.
I'm was talking about anytime the suspension is in a state other than fully extended (99.9% of the time when riding).  But yes you would be correct, increasing preload will make the front suspension a tiny bit 'stiffer' at the point of landing after the front wheel has completely left the road, and the suspension was fully extended (a wheelie).  That's the only time it will make any difference.
 
So by all means if you want to soften the landing a tiny fraction when pulling wheelies consider reducing the preload.  I would have though that better throttle and rear brake control would have been way more effective.  But I dunno, I like to keep the front wheel planted firmly on the road (and I'm probably in serious trouble if the rear wheel has completely left the road).  I set preload for what its meant to do, and that is position the suspension correctly in its travel range to prevent it from either bottoming or topping out.
 
 
 
  
 
 
 
 
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Just an FYI, if you set the back too soft and the front too hard, the FJ won't turn. Uh, a friend did this.

 


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The roster: '79 Honda XL 125 '83, Honda Ascot VT500, '84 Kawasaki GPz 550, '83 Honda VF700, '86 Kawasaki Ninja 600, '87 Kawasaki Ninja 1000, '84 Suzuki GSX-R 750, '96 Honda CBR600F, '98 Kawasaki ZX-7R, '85 Kawasaki Ninja 600, '01 Suzuki GSX-R 750, '16 Yamaha FJ-09, '15 Yamaha FJR1300ES, KTM 1290 Super Duke GT

 

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Resurrecting this very old thread....

I just recently noticed that my rear tyre (Michelin Road 5) is showing some uneven signs in the tread pattern.  i.e., the trailing edges are raised while the leading edges are rounded.

Only just noticeable, but noticeable by eye and uniform nonetheless.  If I run my fingers around the tyre the rear edge can be felt clearly raised.  So, after reading some expert opinions on the subject it would appear that a distinct possibility is that my rebound damping is set too hard/fast.

My rear shock BTW is a K-Tech Razor-R that has rebound damping adjustment with a range of 32 clicks.

I was 'sure' that I'd had it set in the middle of that range at 16.

Sure enough, when I checked it was set at 7 clicks out.  Definitely on the harder/faster side of settings.

I've taken it to 16 and will see if that makes any difference on the tyre tread patterning.  Went for a short ride today and really can't say that I noticed a great difference in ride experience but we'll see over the longer term.

Have I diagnosed this correctly?

 

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Daz,

Same loading and tire pressure?  If you reduced rebound normally you'd also reduce compression and maybe play with preload...  Same goes for tweaking the front damping to balance things out.  That is unless somehow you screwed up and just had rear rebound set too high and all the other settings are about where they should be.

It's going to hit mid 70's here tomorrow!  Crazy weather, it's been way below normal and wet.  Too bad I will still be couch bound for quite a while.  It also may be my shoulder surgery was a fail and must be redone!  I can't believe it.  Then there's my neck and other shoulder...

It always could be worse.

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I’ve personally seen too many sets of Road 5’s wear that exact same way: either ragged on the edges and cupped, or just badly cupped. It’s mostly the tire and the types of road you ride IMHO. This is in many different bike models. 
 

set rebound so you like the feel and performance of the bike IMHO. 

or to look at it another way… the Road 6’s are out… wonder why? (Besides marketing that is…)

-Skip

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7 hours ago, dazzler24 said:

My rear shock BTW is a K-Tech Razor-R that has rebound damping adjustment with a range of 32 clicks.

I was 'sure' that I'd had it set in the middle of that range at 16.

Sure enough, when I checked it was set at 7 clicks out.  Definitely on the harder/faster side of settings.

I've taken it to 16 and will see if that makes any difference on the tyre tread patterning.  Went for a short ride today and really can't say that I noticed a great difference in ride experience but we'll see over the longer term.

Have I diagnosed this correctly?

 

Are you sure you have the terms correct?  When you add rebound damping (turn the knob clockwise) it slows the damping movement or what some refer to as "harder".  When you open or lessen the rebound damping- counter clockwise, (soften) it will rebound faster and feel more 'springy'.  Harder/slower and softer/faster depending on the terms you prefer.

Your damping, both compression and rebound is hydraulically controlling how fast the spring moves in either direction, if you open the clickers you would essentially be riding on the spring and if you close the clickers you would have a very harsh ride.

If you open the rebound damping from 7 to 16 you should feel a very dramatic difference, 2 clicks is noticeable.  Here is something to try, turn the rebound fully closed -clockwise- and balance the bike standing behind holding the grab handles, press down firmly and release and see how slow the rear 'rebounds'. Then open (counter clockwise) 5 clicks and see how it speeds up or softens, now try it at 10 clicks out.  When I set up my rebound, I usually start about 5-7 clicks from fully closed and fine tune from there.  You can set a basic setting in the garage but it needs to be setup by feel while riding.

***2015 Candy Red FJ-09***

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^ What Betoney says is correct.

And lots of tyres wear the same, it's more to do with the way the tread hits the pavement than damping set up.

Edited by OZVFR
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