So, the bike is a bunch faster now, and i'm moving on to suspension and handling, i want to know if $60 for prgressive springs is worth the $58 more in difference than the diy fork spacers in the mods section of the main page.  Already have a kat shock on the way, and tires are too new for my cheap ass to get rid of them just becuse they are stock (and i won't have a job untill may) so front fork work is the only thing i have left to do, that i understand will make a big difference. So anyone have any input/ideas/bold faced lies to help sway me one way or the other?

Fork spacers won't stop nose-dive under braking nor will they firm-up the ride.  Forks do not operate like a pogo-stick under normal riding conditions-they sag--and preload spacers only serve to adjust the ride height.  The Kat shock reputedly raises the back an inch or so, which shifts more weight onto the front, so I would think it an especially good idea to go with the Progressives when doing the shock.           

That's what i thought, but just wanted to if i could get off cheap, thanks

Quote from: Gisser on February 21, 2006, 12:28:43 AM
Fork spacers won't stop nose-dive under braking nor will they firm-up the ride. .....Progressives when doing the shock.           

I'm sorry - I have to disagree.  I have spacers in mine and the ride is MUCH firmer.  Like REALLY firm - The forks BARELY bottom when doing a stoppie.

Nose dive is also much less.

Having said that - I would agree that progressives are the way to go and you can't beat the cost..  But if you're a cheap bastid like me  well then...spacers do the job - for now...

Now it's my turn to disagree/agree, depending on your view. I say that fork spacers only help with sag and not nose dive.

The GS uses straight rate springs, which means that it takes the same amount of force to compress a certain distance, no matter how much it is initially compressed.

The simple equation for the force of a spring is:

F = -kx   
where k is the spring constant and x is the distance compressed. The minus sign is there because the force produced when you compress a spring is away from the direction of compression. You push a spring in and it produces a force toward you, in the opposite direction.

So, if you compress the springs a tiny bit with fork spacers then you are only changing the x value, which doesn't make a difference because it will take the same amount of force to compress the spring as it did before. This is because the k value is a constant.

With Progressive springs, they are just that, a PROGRESSIVE winding, which means that the spring constant k changes with x. The more you compress the springs the more force is required to compress it the same distance.

thanks for the explination alpha, but i must say DAMN YOU!!!! I don't have calc untill 6 and you're making me think

if "x" changes, then "F" must change too....they are dependant upon each other.....so if you reduce the spring compression distance, then the the force required to compress the spring will increase....right?

so therefore, using spacers will require more force, be stiffer, and reduce nose dive....(now refute....I haven't done physics or calc in a few years, so I'm kinda rusty.....but I'll ask at work tonight - I work with for a math tutoring facility, and my boss/the owner grad with a degree in math from BC)....

also....I thought they were called progressive fork springs because it was the company's name....learn something new everyday...glad to have that out of the way until tomorrow....

Quote from: mastrind on February 21, 2006, 11:56:55 AM
if "x" changes, then "F" must change too....they are dependant upon each other.....so if you reduce the spring compression distance, then the the force required to compress the spring will increase....right?

so therefore, using spacers will require more force, be stiffer, and reduce nose dive....(now refute....I haven't done physics or calc in a few years, so I'm kinda rusty.....but I'll ask at work tonight - I work with for a math tutoring facility, and my boss/the owner grad with a degree in math from BC)....

also....I thought they were called progressive fork springs because it was the company's name....learn something new everyday...glad to have that out of the way until tomorrow....

Mmkay, so if you change x initially, the change in x (delta x) when you compress the spring will be the same as the delta x as when the spring is not initially compressed.

Let's make this easy. Say the spring constant k is equal to 1, that way we can just disregard it, and that the force F varies directly with delta x.

So:
F = (x₂ - x₁) yes? Change in x.

So let's say the initial spring compression with fork spacers is 10mm, and that you want to compress the spring ANOTHER 10mm to the 20mm mark.

F = (20mm - 10mm) = 10 N (yeah I know the units and whatnot, bite me)

Now let's say that there was no initial spring compression, and you want to compress the spring 10mm from its original position.

F = (10mm - 0mm) = 10N (I told you, units and whatnot are relative here).

So with a straight spring constant the force is the same for the same change in distance.

I think what Mastrind is saying is that he thinks that it requires an additional 10Nm for each additional 10mm of compression, as a cummulative effect, thus stiffer.  But, you're right, it only takes 10Nm to compress an additional 10mm in a straight rate spring.  So if you put 10Nm of preload, it will only take 10Nm to compress another 10mm.  Not an additional 10Nm of force (20Nm) to compress the additional 10mm.  It's just 20Nm to compress 20mm.  The 20Nm is "stiffer".

Another thing to consider is stiction, expecially when the forks become more raked out due to the additional preload.  The more raked out, the higher the stiction, so it seems like it takes more force to dive the forks, when in fact the sliders have to overcome the friction of the stiction just to get moving (sliding up the fork leg, absorbing the bump).

Hmm...Alpha I think you made a small mistake, yes the rate of commpression is constant, however the total force supplied by the spacers at say "20mm" and using F=-kx, where when x=0 the spring is uncompressed, really means that

F=-kx=-1(N/mm)*(20-0)mm=20N of Force

So i you preload your suspension you simple reduce the static sag, and make the whole ride more stiff since you start out at say 20N of force and have to go up from there to compress the suspension vs. stock where lets say you start out at 10N of force.

The adjuster on our rear suspensoin works under the same concept, as you turn it up, you  compress the spring more providing a increased force to compressing it making it stiffer.

Now here comes the down side, depending on how much you preload the spring you will remove the total amount of compression of the spring, so if you had 6 inches of travel before, put the thing under preload by 1 inch, well now you only have 5 inches of travel. I am not sure when the GS bottoms out if it is the springs out of room, or if the forks hit the bottom, I am not sure.

Since coil binding is worse than bottoming (okay it's the same, but manufacturers have to take that into account, so the spring shouldn't bind when the suspension bottoms out), You really still have 6 inches of travel, it's just going to take a greater force to compress the spring.  You compress the spring, but the distance between the eyebolts of the shock should not change (with the exception of sag <- a dynamic).  If you set the preload to max, you will still have 6in of travel.

Quote from: coll0412 on March 05, 2006, 12:00:23 PM

F=-kx=-1(N/mm)*(20-0)mm=20N of Force

So i you preload your suspension you simple reduce the static sag, and make the whole ride more stiff since you start out at say 20N of force and have to go up from there to compress the suspension vs. stock where lets say you start out at 10N of force.

I didn't agree with the Alpha formula as an excercise in mathematics either, but the above statement is simply not true on a street bike and is the reason I say the forks are not pogo sticks. 

As long as the suspension has any sag before absorbing force then (using the given rate) 10N of force will equal 10MM of travel no matter what preload is dialed in.

Pogo sticks, OTOH, must overcome preload with every bounce but how often are the forks fully extended before hitting a bump?  Maybe when  landing a wheelie?  Otherwise, preload adds no stiffness to the spring effect.  Make sense?

Quote from: coll0412 on March 05, 2006, 12:00:23 PM
The adjuster on our rear suspensoin works under the same concept, as you turn it up, you  compress the spring more providing a increased force to compressing it making it stiffer.

Same as above goes for the rear shock exept that less sag and poor stock damping means that the shock is more likely to top out over a series of bumbs and added preload will definitely be felt in that condition.

To recap, preload spacers do not firm up the suspension except (a) to the extent that weight is shifted, and (b) when the suspension is fully extended (common on a dirt-bike but mostly irrelevant on a streetbike with proper sag & damping).

Quote from: coll0412 on March 05, 2006, 12:00:23 PM
Now here comes the down side, depending on how much you preload the spring you will remove the total amount of compression of the spring, so if you had 6 inches of travel before, put the thing under preload by 1 inch, well now you only have 5 inches of travel. I am not sure when the GS bottoms out if it is the springs out of room, or if the forks hit the bottom, I am not sure.

The GS450 has room for about a 1-1/2" spacer before coil-bind.  With the short spring the GS500 uses, it's anyone's guess.