matching spring rates

[madEG]

I have two questions:

Here we see the different spring rates for the different rear shocks: http://www.kuhnco.com/SV650/GSXRShockSwap/

1. I assume that if I chose a shock like the zx6r, with a spring rate of #540, that I should get front springs to match the rear's increase. If the rear moved up ratio wise:

From the RaceTech website: SV650 2003 Stock Fork Spring Rate (measured): .670 kg/mm(stock)


430
----- =
540


0.67
------
X


So, uh, X = 84 ?

Assuming I am thinking about this correctly, to be 'even' I need to get a fork spring set that is approx .84.

Does this make sense? That is my first question...


Futhermore...


Also from the RaceTech website:

STREET
Rider Weight: 195 lbs.
Recommended Spring Rate: 0.863 kg/mm(use closest available)

RACING
Rider Weight: 195 lbs.
Recommended Spring Rate: 0.928 kg/mm(use closest available)

FRK SPR 34.7x340mm .85kg
FRK SPR 34.7x340mm .90kg
FRK SPR 34.7x340mm .95kg


2. Second question: Assuming that a "best" spring rate fell between two available springs:

In general, would one prefer to have the front springs softer than the rear? e.g. If I "needed" .87 and all they offered was .85 and .90, which would be less wrong? I understand there may be personal preference, but again, in general...

If I had to guess, extreme examples of a stiffer rear spring make more sense than the obverse (a hardtail bike is workable, but a fixed front with a suspended rear sounds crazy) - but I don't want to guess this way.

What do you guys think?

you should be choosing spring rate to get your static sag correct.
adjust preload to get it close to ideal ,search google on how to do this there lots of articles.

also sv650 has a soft front spring and a hard rear spring.

you hopefully only need to change one end of bike to get it right.

eg a light rider will be ok keeping fron spring but will need lighter rear spring

or heavy rider will need heavier front springs but be ok keeping rear shock.

keep in mind that the suspension on the sv is very basic and can be improve by replacing spring to suit your weight (if needed) and adding gold valves (dampening adjustment) for front and replacing the rear shock with one that has 3 way adjustment (preload,compression, rebound) for the rear.

you are best off changing the front first to springs that suit your weight and some heavier oil me a 15 stone used .9kg springs with 15 wt oil with an air gap of 130mm which suited me perfect the front is a lot balanced then the shock changed to gsxr1000 K3 shock as this suit my weight and it looks trick. Both jobs take about 4hours and transforms your ride.
The info you have got from racetech is correct but you dont go to deep into suspension setup unless your racing. A well setup bike will be goodf enough for the road dont forget the SV is a budget bike not a race bike

[madEG]

Originally Posted by FirePower

you should be choosing spring rate to get your static sag correct.
adjust preload to get it close to ideal ,search google on how to do this there lots of articles.

also sv650 has a soft front spring and a hard rear spring.

I am not arguing with you, but you mean relative to the suspension and its design, no? I see that in the link I gave earlier that certainly, 430# is greater than say a GXSR750's 400ish# - but those numbers are relative to numerous factors: the bike, it's weight, and the suspension design.... etc.

Given all that, is that still so? I have heard many people mention that the stock spring is too light for folks who are 190+ pounds...

Originally Posted by FirePower

you hopefully only need to change one end of bike to get it right.

eg a light rider will be ok keeping fron spring but will need lighter rear spring

or heavy rider will need heavier front springs but be ok keeping rear shock.

keep in mind that the suspension on the sv is very basic and can be improve by replacing spring to suit your weight (if needed) and adding gold valves (dampening adjustment) for front and replacing the rear shock with one that has 3 way adjustment (preload,compression, rebound) for the rear.

I am with you regarding actual suspension setup. Not to pat myself on the back, but I understand all of that stuff from my days of downhill mountain bike racing. I am not an expert, but no worries there. What I miss is a sponsor to pay for the testing of various parts...

For this summer, which will include a few track days, the plan is Springs and oil, and OEM rear shock from either gsxr1000-k3 or possibly the zx6r, as I mentioned above, if that is more appropriate for my weight + leathers...

The drop-in damping rods/cartridge emulators made by Traxxion will happen if money allows, as I recently bought a house and am now poor. If I trip over a bag of money, then the three way penske is also in the cards.

Originally Posted by chris SVK3

you are best off changing the front first to springs that suit your weight and some heavier oil me a 15 stone used .9kg springs with 15 wt oil with an air gap of 130mm which suited me perfect the front is a lot balanced then the shock changed to gsxr1000 K3 shock as this suit my weight and it looks trick. Both jobs take about 4hours and transforms your ride.
The info you have got from racetech is correct but you dont go to deep into suspension setup unless your racing. A well setup bike will be goodf enough for the road dont forget the SV is a budget bike not a race bike

Thanks for the info re: the air gap. I was looking for that info on how much oil. I had initially planned to measure what was removed, and replace with that volume, if the manual did not specifically state a value. Thanks also for your opinion with your weight/sprint rate/rear shock combo that it works for you. That is the type info I am looking for...

Guys, I know that the SV is not a race bike. It is my first bike, that I intend to keep for the here and now. I don't expect it to handle like my friends R6. I would like, however, to stiffen of the front springs as they are too soft for my taste, especially when heavy on the front brake.


So, the two questions were:

1. Should one who does zero commuting (I only back road ride, ever, I work from home, and plan a few track days to go get lapped on...) raise the rate of both springs, front and rear in tandem?

2. Is there a general rule regarding the ratio of stiffness for springs for the front relative to the rear spring? If they could not be "even", which would the general populace prefer to have, a slightly stiffer front spring set, or a stiffer rear shock spring.


Thanks!