Spring rate & pre-load on Giant DH Comp

Can anyone advise on the best spring rate for a 73kg rider on a DH Comp? I've got a 450x2.75 at the moment, and I'm having trouble measuring sag accurately (I think I'm only getting about 2cm).

When the owners manual says at least 1mm of pre-load, I presume that means 1 full turn? Also, will more pre-load give more or less sag?

Thanks
 

Tho-R

Likes Dirt
Use this to get a relative spring size
http://www.tftunedshox.com/springcalc.htm

Sag should be about 25-36% sag - best way to measure is on the shock shaft, use the bottom out bumper.

Winding it in will give less sag, less will give it more.

But what im lead to belive that u need at least 2 full turns?

think i have summed everything up.
 

jjperko

Likes Bikes and Dirt
I'm a fraction under 70kgs and have a 500x2.75 however thats not on a platform shock. I assume your DH comp would have a Swinger so that might slightly change things

More preload will give you less sag. As for the 1mm of preload, I'm not sure on this but I assume it means making the spring 1mm shorter by winding it up however many turns.

If your getting 2cm from a 2.75 shock thats about 30% sag which is pretty much perfect for downhill

EDIT: Beaten to it but anyway...
 

spinner

Likes Bikes and Dirt
I think a 450 lb should be about right for your weight. I'm 85ish kg and use a 500lb with a 6 way swinger.
1 turn of preload will be a bit more than 1mm , like 1.2mm ?.......close enough anyway.
 
Thanks for the tips

Thanks for the tips so far.

Sounds as though I'm in the ball-park with sag, 2cm in 2.75" is as someone said 30%.
Although the http://www.tftunedshox.com/springcalc.htm link suggests (73kg, 2.75, 8.25", plush DH) that I might need 350 (4-bar with spv).

Any further info is always helpful too.

Cheers.
 

spinner

Likes Bikes and Dirt
The shock stroke is actually 2.5". The compressed spring length is 2.75". This allows .25" of preload to be applied before coil bind. This brings the TF calculated spring rate down to 424 so maybe you do need a 400 lb spring with a bit of preload ?

On that note , the DH Comp is a linkage driven single pivot so does anyone know if it falls into the single pivot / DW or 4 bar / VPP category ?
 
Mine's an 06 model, but I presume it's the same as the 05. Either way the spring rating has a 2.75 stroke.
I found a second link to calc, but it gives a different answer to the earlier one: http://www.mojo.co.uk/springcalc.html

The Giant website used to have previous models of bikes, and it explained the DH suspension. I recall it being called a 4-bar.

Any suggestions on where to get a 400lb spring cheaply?
 
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spinner

Likes Bikes and Dirt
A 2.75" spring on a 2.75" shock ? Sounds wrong to me.

A mate of mine has a 400lb he's not using , I'll check with him tomorrow and see if he wants to sell it.
 
I've measured the stoke & it's definitely 2.75".
My spring is rated at 2.75 also, so I am wondering if the spring should be more than this length, so that I can apply pre-load? I'm still only getting about 2cm sag.
Does anyone know what the standard spring is on the DH Comps (my bike was 2nd-hand, so I'm not sure if my spring is standard)?
 

S.

ex offender
The shock stroke is actually 2.5". The compressed spring length is 2.75". This allows .25" of preload to be applied before coil bind. This brings the TF calculated spring rate down to 424 so maybe you do need a 400 lb spring with a bit of preload ?

On that note , the DH Comp is a linkage driven single pivot so does anyone know if it falls into the single pivot / DW or 4 bar / VPP category ?
Should go in the 4-bar/VPP category - the singlepivot/DW thing refers to the very linear rate that singlepivots have (as do DW-link bikes), 4-bar/VPPs often have more of a rising rate. Pretty sure the shock stroke IS actually 2.75" (including bottom out bumper, which you never actually use all of) - the spring will be able to compress a bit more than that, it just says 2.75" to avoid confusion between spring length and shock stroke.
 
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