FOX Podium RC1 shocks - Help
- Thread starter FunJimmy
- Start date
sav0r
Coast to Coast
The larger the shaft generally the greater the (resistive) force you are going to see from shaft displacement. Now canister (or bladder) size matters somewhat as well, but that 5/8" shaft combined with a high PSI charge is why are getting large amounts of spring rate from the shock without the spring. I'm surprised Fox is using a 5/8" shaft, that's a huge shaft for a dual shock rear suspension. My guess is that it's an adaptation from a quad front shock. That said, if you have a shock tool or can gain access to one let those guys down to 120-150psi. You should cut that spring rate of the shock alone in half and you won't see any noticeable difference in performance of the damper itself.
Tune-A-Fish
BOTM LOSER Proudly Deplorable
Stiction
FunJimmy
Been Around the Block
So I sent the photo (above) of the shock compressed on the scale to Fox and asked them to comment. More specifically on the contribution to spring rate of a gas charged shock. This is the responce I received. Doesn't leave a lot of options.
Email:
[size=8pt]Jim
Hope your week was good.
I sent this along to our engineers. Although they understand your thinking here, what you are doing in the picture is not something that gives us information that is helpful in trying to set up the shocks in question to your bike.
Id really like to get you fixed up. At this time, I only have 2 solutions for that; 1- get you the 100lb, 8” spring now and send 85lb if/when they are available. 2- return the shocks (would need to talk to Devin for that).
Whatever you decide is fine. The goal is to get you comfortable and rolling. I’m doing all I can with the resources available. If your satisfaction cannot happen on FOX, I’ll have to live with that. Definitely not my first choice but you can’t win them all.
Have a great weekend.
Stacey Sell
FOX Global Distributor Sales
Email:
[size=8pt]Jim
Hope your week was good.
I sent this along to our engineers. Although they understand your thinking here, what you are doing in the picture is not something that gives us information that is helpful in trying to set up the shocks in question to your bike.
Id really like to get you fixed up. At this time, I only have 2 solutions for that; 1- get you the 100lb, 8” spring now and send 85lb if/when they are available. 2- return the shocks (would need to talk to Devin for that).
Whatever you decide is fine. The goal is to get you comfortable and rolling. I’m doing all I can with the resources available. If your satisfaction cannot happen on FOX, I’ll have to live with that. Definitely not my first choice but you can’t win them all.
Have a great weekend.
Stacey Sell
FOX Global Distributor Sales
FunJimmy
Been Around the Block
Sav0r said:
That's very generious and an thoughtful offer Sav0r but I have no interest in working, adapting and experimenting with these shocks on behalf of Fox. If they have no interest in ensuring their products are right for the market they can have them back. Once I get my money back I will consider other options. Thanks again. You've been a big help.
ideally you want a dual spring LASHUP something like a 250 the shorty one and a 140 the the long which goives a 80/140 rate the bonus being a crossover spacer can be added to tune when the 140 kicks in or whatever rate you choose on the long spring instead of waiting for the short heavy spring to coilbind
the gas pressure indeed carries weight but typically on a decarbon style design (your podiums)is only slightly very slightly progressive and is not a contributer to spring rate in the way a spring is because of that
very easy to calculate how much load the ressi or emulsion pressure will support
for a 1/2 shaft multiply the pressure times .2 @ 250 psi = 50 lbs of simple load support at the SHOCK per shock this is not factoring slr
for 5/8 x .3 250 75lbs support at the SHOCK per shock
but the volume at about 3cc's per inch of 1/2'' shaft travel is slight compared to the ressy gas volume hence not a lot of change
thios is why an true airspring shock has to have a large shaft it would not change rate enough in travel otherwise
an emulsion shock will have a bit more change in gas spring effect cause they are filled without too much extra room for gas,just enough plus a bit
it helps to calculate the SLR you have by my eyeball a 1.2-1.3 slr, the shocks see 1.2 times any weight loads is what it boils down to
and you can also play with the calc formula seen in the images it seems to work accurately for longer travel off road bikes that i have used it for
there is a nice graph on dual springs compared to straight rate
the gas pressure indeed carries weight but typically on a decarbon style design (your podiums)is only slightly very slightly progressive and is not a contributer to spring rate in the way a spring is because of that
very easy to calculate how much load the ressi or emulsion pressure will support
for a 1/2 shaft multiply the pressure times .2 @ 250 psi = 50 lbs of simple load support at the SHOCK per shock this is not factoring slr
for 5/8 x .3 250 75lbs support at the SHOCK per shock
but the volume at about 3cc's per inch of 1/2'' shaft travel is slight compared to the ressy gas volume hence not a lot of change
thios is why an true airspring shock has to have a large shaft it would not change rate enough in travel otherwise
an emulsion shock will have a bit more change in gas spring effect cause they are filled without too much extra room for gas,just enough plus a bit
it helps to calculate the SLR you have by my eyeball a 1.2-1.3 slr, the shocks see 1.2 times any weight loads is what it boils down to
and you can also play with the calc formula seen in the images it seems to work accurately for longer travel off road bikes that i have used it for
there is a nice graph on dual springs compared to straight rate
Attachments
sav0r
Coast to Coast
FunJimmy said:
I was thinking that they were needle type inflation? I tried to find a manual for them but no dice.
As far as the dual rate springs are concerned, I think they are old technology. New dampers can control high and low speed movements in unique ways. As a result dual rates springs really aren't needed or even advantageous. They are a bandaid fix for a problem that we no longer face with modern damper technology. I think Work's continues to sell them because they look cool.
Sav0r said:
when you see it on china shocks thats is a diff fishkettle
ohlins and racetech both top of the line shocks are using progressive wound springs and dual rate lashups
they go hand in hand with the new tech coming about
works has the ars setup which is a splendid design for some versatility
sav0r
Coast to Coast
It absolutely is a tuning feature. Granted the uninformed should avoid playing with it, but for those who have educated themselves changing reservoir pressure is an easy and effective means of change. Anything over 80psi and you greatly reduce hysteresis and cavitation. Greater pressure reduces hysteresis further but has little effect on cavitation. But with dual shock suspension where you see close to 1:1 motion ratios adjusting spring rate via reservoir pressure on two shocks can have a huge effect, especially in this case where the shocks have very large shafts. There's no arguing this, less spring rate would help here and it would have basically no negative effect on damper performance.
Sav0r said:
it cant factored into spring rate directly , only in the initial static rate from then on only testing or calculating the gas spring effect can be used accurately to add to the spring rate
a shock with a 1/2" shaft dia supports 50lbs at 250psi it does not add 50lbs to the spring rate it will add some but very little maybe 8 or ten
as you state correctly it depends on the compression ratio a 1/2 shaft at 3cc per inch would need a very small tiny gas volume to work against to bring the gas pressue up to 500 psi in the next inch of travel from static,then 1500 the next inch that just isnt happening,it is just a factual example of what would need to happen to add the 50lb value to spring rate the volume of any gas shock is too high in the res for much change at all to be usable
the mfgs set their shocks at a pressure that has been engineered to be good in all conditions with included i am sure a very large margin to allow for even some minor leak-out
but it is not a tuning tool
FunJimmy
Been Around the Block
xb33bsa said:
Maybe I wasn't clear when I posted the photo attempting to measure shaft pressure on the scale. I didnt mean to suggest that the nitrogen gas pressure added to the combined spring rate in the way a coil spring does. You said it correctly. The nitrogen charge adds support. Once that initial support (41.4 lbs each) is overcome the rest is basically up to the coils spring but it does impact the ability to setup the correct sag. This issue has always been about an overly stiff shock and the inability to get the correct static sag settings.
sav0r
Coast to Coast
xb33bsa said:
I agree, and that's why it's obvious that less reservoir pressure would help. But you are a little delirious as to how perfect the manufacturers set that pressure. It's just a number and an adjustable one at that. There's nothing holy or untouchable about it. Dampers are tools, change them, if it helps it's a win no matter how you look at it. Can changes have positive and negative aspects? Absolutely, you have to weigh those aspects when making changes. Reservoir pressure, specifically the addition of it, is an effective means of providing "platform" to the motorcycle, though not a great way of adjusting spring rate.
Tune-A-Fish
BOTM LOSER Proudly Deplorable
No gas adjustment in the books... never changed gas pressure at the track B4 or ever after service or rebuild ever
Also not a suspension guru, but gas is not a "normal" suspension adjustment... could a change in spec pressure make a diff in perf... possibly but not many if any rider will know unless a drastic change is made.
http://www.ridefox.com/fox_tech_center/owners_manuals/605-00-117_RevA.pdf
Also not a suspension guru, but gas is not a "normal" suspension adjustment... could a change in spec pressure make a diff in perf... possibly but not many if any rider will know unless a drastic change is made.
http://www.ridefox.com/fox_tech_center/owners_manuals/605-00-117_RevA.pdf