SBK Fork Spring Rates

[csorin]

I just got a set of 996 SBK forks off of eBay for a great price.  The forks came in today and look amazing.  Super clean, no scratches, etc.

According to the seller, they were setup by GP Suspension for a 160 lb rider.  I weigh 175 and plan on putting these on my 04 620.  Any ideas what a 160 lb 996 spring rate is?  Could I just slap these on the Monster and see what happens with sag?  Should I just suck it up and send it out to GP Suspension for a clean up and new springs?  Thanks guys. 

[Raux]

From what I know.. the SBK forks are all stronger front spring and weaker back springs than monsters.

so a 160lb spring rate on the monster would be too weak on a sbk for a 160lb rider.
vice versa a 160lb spring rate on a sbk would be too strong for a 160lb rider on a monster...

since you are 15lb heavier (is that 160lb with gear or just rider).. it might not be a bad setup.

[EEL]

I'd say get new springs. I was planning on doing something similar but the spring rates are REALLY different.. much stiffer on the SBK forks.

[csorin]

Getting new springs was the original plan.  These forks are just in such good shape.  According to the seller, the seals and oil have zero miles on them.  From the looks of it, I'm inclined to believe him.  If this is the case, and the bike was setup for a 996 with a 160lb rider, I'm wondering if it's in the ballpark for my Monster plus 175lb me.

Traxxion had recommended a .90 kg spring when we spoke about respringing the stock forks.  If these 996 springs are close, I might just try slapping them on the bike as is.

[ducpainter]

I'd run 'em.

Check sag and adjust as necessary.

[csorin]

Are spring rates affecting sag more than anything?  In other words, if correct sag can be reached within the pre-load settings, are the springs good to go?

[Speeddog]

Are spring rates affecting sag more than anything? 

No.

In other words, if correct sag can be reached within the pre-load settings, are the springs good to go?

If you can get acceptable free sag and rider sag, then at least they're in the ballpark.

I'm with ducpainter on this, run 'em and see what you think.

[csorin]

On the subject of SBK fork swaps, what should I expect to pay for machining the stock triples?  Cost of having shims made?

[ducpainter]

On the subject of SBK fork swaps, what should I expect to pay for machining the stock triples?  Cost of having shims made?

That varies a lot depending on location.

[booger]

Lots of people out there getting smart and doing this mod. Beats the hell out of spending a ton of money on useless carbon    Before you attack me for being old & cheap I have no qualms about spending for useful carbon i.e BST wheels. 

csorin, I have some half a millimeter aluminum shim stock somewhere, you're welcome to some. Cost of getting a triple bored out varies depending on who you know & whether you have any machinist friends. I don't, but I got lucky and scored a stock triple from an S2R1000(removeable risers) already bored out from another member for $35 shipped.

On a 2004 620 you must remember that the handlebar risers are cast into the triple. You can't really use the stock bars because the forks will stick up ~35mm and interfere with the bars. This means clipons. If you get some stock triples from an S2R the risers are a tad bit taller and you might get away with using bars, however you'll need the S2R bars as well because they're different(thicker) at the risers on that model. You could just remove the risers and go to clipons, but that's more money.

I'd suggest boring your stockers out, milling or cutting the risers off, a nice powdercoat or paint job and clipons. Don't forget you might need some new steering head bearings.

[csorin]

Berg,

Thanks for the suggestions.  The plan was to bore the stock triples and cut the risers off.  In the threads that mention this mod, no one talks about costs.  I don't even know what the ballpark is.

I would really like to get something like this done:



Really like the look of the cut down stock triple.  If cost is prohibitive (I've no metal working tools), I might just bore the triples and hook everything up.

Once the triples are bored, does the surface need to be coated/protected?  I'd hate for rust stains to start dripping down my new (to me) forks.  Can I just spray a clear protectant over the metal if there is such a thing?   

[Drunken Monkey]

Racetech says the ideal spring rate (street) for a 175lb rider on a 403lb Monster is 0.835 kg/mm and for racing it's 0.885 kg/mm

Racetech says the ideal spring rate (street) for a 160lb rider on a 418lb 998 is 0.910 kg/mm.

Given that springs basically come in .05 increments (i.e. .85kg or .90kg) you probably have .90kg springs on there now.

You're in the ballpark.

http://old.racetech.com/evalving/menu/searchstreet.asp

[bikepilot]

csorin, the upper triple is aluminum.  No need to coat it after boring, it won't rust.

[booger]

Really like the look of the cut down stock triple.

That's the example that stuck in my mind. Nice craftmanship and I like the little Corse logo encapsulated in clearcoat.

Just take it off your bike, go to a machine shop and consult. Try to find one that focuses mainly on motos, but machinists are machinists. I cannot imagine it being ridiculously expensive to get done. The important thing is to ensure it's done accurately. If you need to save money, after it's bored out & milled down just prep well and rattlecan it to the best of your ability. Should look great. 

[csorin]

csorin, the upper triple is aluminum.  No need to coat it after boring, it won't rust.

Ah, good news.  The more I can incrementally absorb costs, the better.

Given that springs basically come in .05 increments (i.e. .85kg or .90kg) you probably have .90kg springs on there now.

You're in the ballpark.

This too is good news.  Traxxion had recommended a .90 kg spring for spirited back country, occasional track, and occasional 2-up for my Monster.  Glad this is coming together better than expected.