Spring rates - how to determine

[ghunter]

How does one calculate and/or decipher spring rates for an application? I am aware that most spring rates are in kg. which is fine, but should I just convert this to lbs. and get springs that fit my weight, or is there another formula or chart used to decide which spring to use for a given application. I don't mean a chart for a specific bike, but rather a chart that cross references rider weight, terrain, ability, etc.

Or am I getting too specific? I need to respring both ends of my '02 Kx500. For my weight (210 lbs.) the suspension is way too soft and need recommendations. I mainly ride very technical trails and desert, no MX or SX type jumping, and I am an advanced rider.

I paid about $750 to have the suspension on my Husaberg done by Scotts Performance, and I loved it. But I was hoping to replace the springs myself on my KX and save some bucks. Any suggestions? Thanks!

 

[Jeremy Wilkey]

GH,
Fork springs have been a indusrty type thing for years... Forks have simliar geometry and make spring selection a snap. Rate is a function of rider weight and bike weight. Preload is allso factored when say a rider is more or less a percentage of total weight. So say a CR450 will require lighter springs than a xr650, but not propertunalty to the weight diference of the bike. The avergae rider weight stays simliar so rate increases slightly but preload increases even more..


Shocks most tunners have claculated a slope incetcept furmula after they test ideal sag numbers for lighht and havy riders. You can do a quick average based on linkage rate but that may not work out well if you have a very funky linkage.

Also some bike work better or worse based on difrences in chassis geometry or tunner prefrence.

After this base line most tunners alter for SX, or Rocky condtions. Either way the advice will still be influnced by the suspensiuon guy dishing it out..


Regards,
Jer

 

[KawieKX125]

slope incetcept furmula

Whoa, your mind going a bit faster than your fingers there.
Jer, since a slope-intercept form equation is a linear, does that mean that a linkage is linear? I would think an exponential or quadratic equation would work better? Can you clear this up please?
Thanks
Also, what does each part in th equation mean. What does slope= and what does the Y-intercept=? This intrigues me alot since I am very good at math.
Maybe I can prove to my parents(with the fact that fairly complex math is used in suspension engineering) that there is alot to learn in the MX industry.:think

 

[marcusgunby]

From what ive learnt the slope isalmost linear up to the last third of travel then it goes up at a high rate.

 

[KawieKX125]

So it is probably more accurate as an exponential fnction?

 

[marcusgunby]

Aaron i havnt done higher maths since college so im not even going to pretend to know ;)

 

[ghunter]

Back to the original question!

Okay,I am not proficient in higher math, nor do I have the values to plug in to the equations. So while the answer I receive is certainly pertinent to the question, it does me no good. :(

I guess I asked the wrong question so let me make this easier: What would you recommend for suspension changes to my bike? Bike and rider specs in original post.

Thanks. :cool:

 

[KawieKX125]

Call jeremy or one of his associates. I called his east coast guy and he recommended what I use. They are very nice and extremely helpful.

 

[cp380sx]

www.race-tech.com has a good spring calculator.

 

[Jeremy Wilkey]

Kawie,
What I'm saying is this.. We take 2-4 riders of diffrent weights.. We check sag with each rider. After looking at what spring rates actually produce say ideal sag numbers we have points that we could and do plot..

Now you'll see that for oour purpouses a line can be drawn between these points. We make it a straight line.. As it actually is if we could avergae it..

Now we have a simple y= rate of spring

m(Slope of line a function of ratio in static postion)
x(rider weight)
b (yintcecpt) this has to do with ratio and static weight of bike.

Now after have this line we make modifcations to y incecept and slope to satisfy or tuning prefrences..


Regards,
Jer



Ghunter,

.46 and 5.4