Progressives on new GS500's?

[RVertigo]

You can get straight rate springs here for $109.

They have a weight calculator too...  At 170 they recomend 0.782 kg/mm rather than the stock 0.594 kg/mm.

[Gisser]

Phil and John also mentioned that adding spacers to the front fork only raises the front ride height, putting more weight on the rear wheel.  While this does make the bike bottom less on the front, the reduced spring compression on the front is a result of the shifted weight and not of stiffer front springs.   However, on this last point, I'm not sure if they are correct as so many posters on this forum have indicated otherwise.
O

Heh.  Who are you going to believe?  The specialists who do suspensions for a living, or the GStwin conventional wisdom.     Phil & John have it right, it's been stated here before, but then people have their own theories and the truth gets lost over time.  That paragraph should be included any DIY suspension FAQ.

[registrable]

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[scratch]

Phil and John also mentioned that adding spacers to the front fork only raises the front ride height, putting more weight on the rear wheel.  While this does make the bike bottom less on the front, the reduced spring compression on the front is a result of the shifted weight and not of stiffer front springs.   However, on this last point, I'm not sure if they are correct as so many posters on this forum have indicated otherwise.
O

Heh.  Who are you going to believe?  The specialists who do suspensions for a living, or the GStwin conventional wisdom.     Phil & John have it right, it's been stated here before, but then people have their own theories and the truth gets lost over time.  That paragraph should be included any DIY suspension FAQ.

It is true. Preload does not change the spring rate (.594kg/mm). I went back to the stock spring rate, because it is softer than the .8kg/mm Progressives which are too stiff for my weight (125lbs, which would require a .715kg/mm spring rate as suggested by RaceTech.com's site), and I ride in the rain alot, furthering my need for a softer spring. This is why in almost every suspension thread I include PVD's site, which mentions spring rate.

[Alphamazing]

Soo... hey scratch... whatcha gonna do with those Progressives lying around? Want to sell them to me?

[scratch]

I'm working out, so I may still need them (my target is 135lbs).

[Alphamazing]

I should really get back onto my workout schedule. I weigh 130 right now. Sad thing is, I've LOST weight since I got into college. Mind boggling.

[RVertigo]

I'm trying to stay down to 170...   :lol:

[Gisser]

It is true. Preload does not change the spring rate (.594kg/mm). I went back to the stock spring rate, because it is softer than the .8kg/mm Progressives which are too stiff for my weight (125lbs, which would require a .715kg/mm spring rate as suggested by RaceTech.com's site)

Progressives are dual rate springs, so one wonders if that .8kg/mm is the soft rate or the firm rate?  Oh, well, you tested, it's too firm for your liking.  You could try replacing the preload spacers with short sections of the stock spring and have a triple rate spring.  It would definitely be softer.  

[scratch]

.574kg/mm is the soft rate, but it feels like with even only 3/8ths inches of preload (3 washers), that those coils are used up in just getting the proper Rider sag (1.5inches).

[jbeaber]

When I got my 89 GS, it was bottoming out left and right, any tie I hit a bump (like entering a driveway).  At the same time, the fork seals went.  I brought my bike to Evolution Suspension in San Jose, California (GREAT shop).  So, older GS500s have a much lower volume of oil in the fork than the newer ones.  I forget what year they chaged this.  The design did not change, however, only the volume of oil in the fork.  So, I had some spacers thrown in and the volume of oil increased.  The bike bottoms out very rarely now, only when I enter one particular driveway a little faster than I should.  Cheap fix that worked well with minimal hardware required.

[Gisser]

.574kg/mm is the soft rate, but it feels like with even only 3/8ths inches of preload (3 washers), that those coils are used up in just getting the proper Rider sag (1.5inches).

It doesn't work that way.  Remember the paragraph I quoted:  Preload does not squish the spring, it raises the ride height.  The bike/rider weight squishes the spring and we can make a nerdy looking guestimate how much soft-rate travel is leftover after sag is factored in...

8Kg/mm is 39% firmer than .574kg/mm

Typical spring (GS450)
= 80 coils (78 coil gaps)
= .155 wire diameter
= 20" free length (12" collapsed length)(8" difference)

So 31 coils (39% of total) are "progressively wound."  Let's say these are wound 30% tighter than the firm coils.

Figure the softer spring gaps as...

48X + 30(.7X) = 8"
X = .116"  .7X = .08"

So 30 coil gaps X .08" = 2.4" worth of soft travel.

Figure you have .75" actual preload and 2.250 total sag.  That means 3" worth of spring compression at rest.

Thirty-nine percent (1.17") came out of the soft windings which means 1.23" of soft travel still available.  That sounds generous--the key variables being the actual preload and the percentage tighter the "progressive" coils are wound than the rest.  

Of course, in the real world, the Progressives were still too firm for your liking.  

[scratch]

Is that bike sag (sans rider)? That's why I stated it feels like the remainder of the soft coils are used up in Rider sag.

[Gisser]

That was bike & rider sag.  You know, it doesn't make much sense that a 125 lb rider could max out the initial spring rate before so much as hitting a bump in the road when Progressive's target market must range from average riders between 120-to-180 lbs.  You'd expect to have an extra inch to an inch and a half of .574kg/mm rate travel when all is said and done.  If you know these figures...

1) spring wire diameter
2) number of coils
3) number of closer wound coils
4) spring free length
5) free length of just the closely wound section of coils

......then you can get a good idea how much of the suspension travel is sprung at the .574kg/mm rate.