fork springs/preload * points to ponder*

[Braahp]

A fellow DRN'er sent me a very cool spreadsheet that calculates spring force versus travel. You can change preload and spring rates. Takes a bunch of the guess work out. Take for instance.....did you know that your STOCK .36kg springs with stock spacer giving you 25 mm of preload is actually stiffer than a .40kg spring with 10mm preload all the way up to 125mm of fork travel. This about 2/3 of the travel. Then all the way out to 170mm of travel the .40kg spring is only has 4 more lbs. force. Interesting huh? I never imagined using the stock spacer would give such results. No wonder Fredette recommends lighter springs and oem preload. It all makes sense to me now.

 

[owenlo]

Where???

Where is the spresdsheet and how do I get one???


Obie

 

[canyncarvr]

Fredette recommends 'lighter' springs? Lighter than....stock? Don't think so. Lighter than....other's recs?

Any spring will increase in rate as you compress it. That's how springs work. Problem is, it will also DECREASE in load-carrying ability.

If 125mm (5 inches) = 2/3 travel, that makes the front end good for only 7.5 inches? Guess I'll check the spec sheet......

The idea of taking a too-light spring and 'making up' the difference with a too long spacer (too much preload) makes no sense to me at all.

 

[Braahp]

Did you check out the fork springs calculator yet? I hope you didi get it. Interesting to see the differences huh?

 

[owenlo]

Got It

Great little tool indeed. It will come in handy! ;)

 

[Braahp]

Yeah I meant "lighter" springs than others. I'm experimenting with a few springs to see which suits me and my riding best. Leaving my GV stack and oil level the same I've used a .37kg spring with stock spacer and XR .40kg springs with 10mm spacer....now changed to a .39kg spring with stock spacer to see how that works.

 

[G. Gearloose]

One should aim for about 3/4-1" free sag and an aditional 3/4 - 1" when loaded. this may limit the envelope on how much one can play with spring length, preload, spacers, ect to make the wrong spring similate 'right'. For instance preloading to get the rate your after, can drastically upset the sag.
just throwing this out there for discussion..

 

[dirt bike dave]

IMO, a soft spring with excessive preload will result in an overly harsh ride on small sharp obstacles, yet still be too soft for the big hits. Sort of the worst of both worlds. And the effect on handling of too little free and loaded sag has already been mentioned.