|   Suspension Gurus: Opinions please... | zedro
Oct 18, 2001 8:13 PM | | So heres whats up. I just installed my Stinky travel upgrade plates and did a parking lot run. Problem is i can blow through my travel purposely by 'throwing' my weight. But by my numbers this really shouldnt be the case. Heres the info:
The plates change the levereage ratio from the stock 2.5 to 3.375
(ie. 6.75" of rear travel). Now i changed the spring accordingly, from a 450# to a 650# (607.5# would be the exact equivalent, so in theory it should be harder to bottom out). Now the angle of the shock has changed, moving closer to 90deg, perhaps causing a bit of a regressive rate which i believed to be either somewhat negligable or at least compensated by the relatively heavier spring. Also i assumed that the compression damping would also stay relative, since the higher ratio = faster shaft speed = more damping blah blah. But now i'm wondering if this is not the case and is the reason why i can bottom out so easily (although my logic still dictates it should work properly).
Another possibility is with the shock itself. It has been sucking a bit of air lately, perhaps crippling my damping.
So what do you guys think? |
| re: Suspension Gurus: Opinions please... | Gutty
Oct 18, 2001 8:35 PM | | You stoked you finally got your plates? Did they come out alright?
Sorry can't help with your problem. Sounds like too much of a falling rate though. Have you got the new longer shock yet? |
| worked out pretty well... | zedro
Oct 19, 2001 8:52 AM | | i had designed a new easy to drill pattern but that'll have to wait. The bearing bore tolerances were maybe a bit on the tight side; there was some metal flaking but the whole build was a success. I guess its just a matter of tunning the bike now and i'll get the longer shock next year (last weekend on the chairlifts :(
The plates look so burly compared to those skimpy little stock ones. I've already generated a bit of interest in the plates, but unfortunatly its for the 2001 type models, meaning back to the drawing board :) |
| re: Suspension Gurus: Opinions please... | Dirt Carver
Oct 18, 2001 8:47 PM | | I have a 2.5 ratio suspension right now(5" travel), and my riding weight is 175+ pounds full riding gear, i use a 500 pound spring, sometimes a 550 on rougher dh stuff. I am thinking you might have a bit too low spring rate of #450 if this is what your basing your longer travel set up on. Maybe the diff between your bike and my Turner RFX (linear) says something for the spring rate, dunno but just a though to consider?
The shock may be suspect depending on how beat it is and hurting. |
| Damper | Dougal
Oct 19, 2001 12:36 AM | | While you've scaled the spring rate you haven't scaled the damper ratios. So your nicely damped bike has turned into an almost undamped bike.
Increasing the leverage ratio actually slows down the damper shaft relative to the axle speed which means even less damping.
A stiffer spring could fix your hassles easiest but a revalve is the best way.
Dougal.8m.com |
| RE: Damper | TK
Oct 19, 2001 8:23 AM | | I would start by checking the sag first. Maybe you already did but I didn't see it mentioned. Your spring rate calculations may be good, but should be double checked in the real world. After you are satisfied that the sag is correct you may want to look into changing the dampening. Given the amount of spring rate change though I would agree that the shock may need to be revalved. |
| doe...im a doofus... | zedro
Oct 19, 2001 8:46 AM | | makes sense about the damping now, thinkin all backwards. The sag is set right BTW.
I think its a combination of factors; the rate change damping effect, my shock which i noticed now looses damping at the end of the stroke (hello rebuild), and probably a bit of a regressive rate, but i think i'll try n map it out and see how bad.
Fortunatly i originally planned this mod with a 8.75"/2.75" in mind, which keeps the same rate in 7" mode, and just slighltly higher rate in 8" mode. But that'll be all for next year.
Thanx for the help guys. |
| Damper | hey Dougal
Oct 19, 2001 7:42 PM | | If the shaft speed is slower, would the damping be more accurate? Or easier to meter against the slower shaft speed? Or is it that a damper is set for a perticular leverage ratio? And is a higher lever putting more stress on a damper and how? Would a Fox shock be a linear damper? or is there really no such thing?
Just some curiousity |
| Damper | Dougal
Oct 19, 2001 11:02 PM | | If you're talking about damping rates (speed vs force) then you'd expect a FOX damper to be linear but they could have been valved to fit any particular OEM bike.
Damping curves can be linear, regressive or progressive. A rising rate linkage speeds the damper up at the end (faster means more force) so a linear damper gives more damping at the end than at the start.
Slower shaft speeds are harder to control, it's better to have a longer stroke shock moving faster, it gives the damper more time and distance to react.
It gets real complex real quick, let me know if you've got any more questions I might be able to answer.
Dougal.8m.com |
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