Shock length and spring rate versus ride height

[CSpronken]

Shock length and spring rate versus ride height

I have a few questions (marked bold).

How does shock length and spring rate relate to ride height at the rear wheel? I read that on a some type of bike a 1.5mm longer shock would result in a 5mm increase in ride height at the rear wheel. Is this correct and if so anyone know what the ratio is for a curvy? AFAIK a 12mm increase in rear wheel ride height would roughly result in 0.5º less rake (from 25º to 24.5º)?

For instance a 340mm shock length of the ZX6R would be an increase of 3mm over curvy stock resulting in an a rear wheel ride height increase of 10mm at a 1.5 to 5mm ratio? Is this too simplistic, ignoring rider weight and spring rate?

I weight 184 lbs without gear and have a 7 lbs lighter aftermarket exhaust (no regular passenger requirement), what year ZX6R/ZX10R shock would be best for sporty road use? I see fairly little information on '09/'10 ZX6R/ZX10R shocks. I assume these also still require modifications to the battery box?

PS. I have progressive spring in my curvy front.

I cant directly answer your questions on geometry as i havent got round to doing my own shock yet. but if you measure the length and angle of linkages between back tyre and seat and make a sketch it should be possible to figure out the ratio, and also the force of rider weight transmitted through the spring, which would then give you an approximation for the static displacement for a given weight and spring rate. this could also be used to find effective spring rate of a shock not designed for the sv. in fact i was planning to do all this myself when i get round to sorting my suspension, and i would be very interested in your results if you go through with it.

if you havent found it already, the racetech spring calculator is a good resource http://old.racetech.com/evalving/menu/searchstreet.asp

i believe pretty much all shock swaps require a battery box chop, kawasaki more than most because they use a piggyback resevoir

[CSpronken]

Originally Posted by mjc

I cant directly answer your questions on geometry as i havent got round to doing my own shock yet. but if you measure the length and angle of linkages between back tyre and seat and make a sketch it should be possible to figure out the ratio, and also the force of rider weight transmitted through the spring, which would then give you an approximation for the static displacement for a given weight and spring rate. this could also be used to find effective spring rate of a shock not designed for the sv. in fact i was planning to do all this myself when i get round to sorting my suspension, and i would be very interested in your results if you go through with it.

I will see what I will end up with.

if you havent found it already, the racetech spring calculator is a good resource http://old.racetech.com/evalving/menu/searchstreet.asp

Strange things is I get 7.88 kg/mm for the rear shock while curvy stock is apparently 9.1 kg/mm.

http://old.racetech.com/evalving/Spr...ork&bikeid=486

If I enter the same info for a Pointy model I get the same 7.88 kg/mm rear shock while stock is 7.7 kg/mm, so I think the 99-02 curvy calculation is mistakenly using the post 03 pointy input to calculate? Perhaps I should send them an email.

i believe pretty much all shock swaps require a battery box chop, kawasaki more than most because they use a piggyback resevoir

Gonna read up a bit more on this thread:
http://forum.svrider.com/showthread.php?t=46840

[Mr Speirs]

Curvy shock is sprung stiffer than the Pointy's. There is a chart somewhere showing all the springs rate of suitable replacements.

However for Curvy's the only options are the zx6/zx10r shock between 2004-2006 or a Busa shock. All GSXR shock are softer spring rates however I think there is one that is close but still not stiffer.

The best option is the zx6/10 shocks though. Busa shocks are good too but only if you weigh 20st and carry a pillion...they are real stiff.

Zx shock from 2008 onwards are all softer and therefore no use to curvy owners.

How this helps.

[CSpronken]

However for Curvy's the only options are the zx6/zx10r shock between 2004-2006 or a Busa shock. All GSXR shock are softer spring rates however I think there is one that is close but still not stiffer.

Zx shock from 2008 onwards are all softer and therefore no use to curvy owners.

How this helps.

Are you sure about the later year shock. Looking at the chart a 08 ZX10R or a 07/08 or 09/10 ZX6R would do as well, just that spring rate would be the same as 1st gen stock. My guess is between 510 (stock) and 540 would be Ideal for my weight, but that's just a guess.

Originally Posted by Mr Speirs

Curvy shock is sprung stiffer than the Pointy's. There is a chart somewhere showing all the springs rate of suitable replacements.

This one?

[Mr Speirs]

Weird I though the 08 zx10 shock was softer, either way it is on par with the stock spring which is regarded as being undersprung.

07/08 zx6r shock is again the same spring rate don't know about the 09/10 though.

So the shocks you can choose from are:

zx6r from 03-06 or
zx10 04-05 (sorry i said 04-06 in my first post didn't I?)

The 10r's seem to be preferred as they are closest to the original shock length. 1mm more which which raise the rear slightly but not enough to notice or for it to change the handling (in terms of geometry) drastically.

[CSpronken]

Originally Posted by Mr Speirs

The 10r's seem to be preferred as they are closest to the original shock length. 1mm more which which raise the rear slightly but not enough to notice or for it to change the handling (in terms of geometry) drastically.

Handling might improve even with the extra length of the ZX6R shock, thought that was the consensus, not sure.

[CSpronken]

One more question: I read people saying how much of an improvement a ZX6R shock is. How much of this is down to it being a stiffer spring and how much is down to being a better schock? For instance if I would use a '08 ZX6R schock it's 514lbs vs. 510lbs stock. Will I still feel a significance difference in shock performance even if the spring rate is very similar?

I'm still in doubt if I would go for the extra ride height a of ZX6R '08 model or go for the stiffer 05/06 ZX6R shock and see if I need to work with the dogbones to increase the height.

[CSpronken]

Well simple question then: would a ZX10R 04/05 shock be too stiff for my 87kg, 13.7 stone weight with gear? I drive sporty, but not on the limit, almost never with pillion.

simple answers to your questions, stock suspension on the sv is budget with hardly any adjustment
zx/gsxr shocks are better quality and have more adjustent
when you put on any of the above shocks you have adjustment of the rear ride hight (preload) and compresson,
you are just over average weight (what spring rate is concidered standard) so a standard spring on the above shocks can be adjusted to your weight and riding style (id say 1 stone heavier then you are may be out of adjustable compensation), just make sure you take the rear ride hight into cocideration as you have no adjustment on the front, which means rear up turn quicker so id take a mil or 2 of the rear preload from proper sag settings