Official Baja SAE Forums Homepage
Forum Home Forum Home > General > Design Discussion
  New Posts New Posts RSS Feed - air shocks stroke/eye-eye (fox)
  FAQ FAQ  Forum Search   Events   Register Register  Login Login

air shocks stroke/eye-eye (fox)

 Post Reply Post Reply
Author
Message
otto View Drop Down
Milling Master
Milling Master


Joined: Oct/06/2011
Location: OR & Colorado
Status: Offline
Points: 100
Post Options Post Options   Thanks (0) Thanks(0)   Quote otto Quote  Post ReplyReply Direct Link To This Post Topic: air shocks stroke/eye-eye (fox)
    Posted: Oct/12/2011 at 4:17pm
for the teams out there that have ran air shocks on their car, what stroke and eye to eye were you running?  Have been speaking with a suspension place and their response (from Fox) was that the longest travel option they could get on a Float R was 5.3 inches with 18.5 inches eye to eye.  Ideally looking for a shock with over 6 inches of stroke, which Fox has in a basic Float 2 at 6 inches, somewhere around 19 inches eye to eye. (no rebound adjust, just air pressure, blah).

Would like a little infos on what other people out there have used in the ways of air shocks.  Not particularly interested in the Float X evols (very $$$, on the heavier side).

Planning on running 12 inches of wheel travel with these, and the smaller stroke means the shock needs to get leveraged more which encroaches on foot room or moves the shocks way up the A-arm which makes loads on the A-arm get much much worse... so if there is some combination out there that affords an air shock with 6 inches of stroke and some rebound adjust I'm all ears.
Cornell Baja 2008-2012, suspension stuff
Oregon State 2012+, saw chain & some more baja
Back to Top
CLReedy21 View Drop Down
Baja Godfather
Baja Godfather
Avatar

Joined: Nov/30/2008
Location: Marysville, OH
Status: Offline
Points: 736
Post Options Post Options   Thanks (0) Thanks(0)   Quote CLReedy21 Quote  Post ReplyReply Direct Link To This Post Posted: Oct/12/2011 at 8:12pm
Float R's.

EDIT:  I know you said they aren't enough, but trust me when I say that they are.

Just compromise a little with your motion ratio if the rebound is important to you.  We're running almost 14" of travel with a Float 2 @ 6.2" of travel, but no rebound.  You gotta remember you'll probably never use that last inch or two of travel so maybe cut your travel a bit if the motion ratio is key to your dynamics but you must have the rebound as well.


Edited by CLReedy21 - Oct/12/2011 at 8:35pm
-Chris Reedy
TTU Alumni
Fourwheeler Drawer



"Quick with the hammer, slow with the brain."
Back to Top
otto View Drop Down
Milling Master
Milling Master


Joined: Oct/06/2011
Location: OR & Colorado
Status: Offline
Points: 100
Post Options Post Options   Thanks (0) Thanks(0)   Quote otto Quote  Post ReplyReply Direct Link To This Post Posted: Oct/12/2011 at 10:04pm
maybe i wasnt too clear.  its not that i think the shock itself isnt "enough" from a damper point of view its that the amount of stroke available from the longest travel version I can get just does not afford me the geometric concessions to place the shock mounts in a reasonable location on the frame.  I'm not worried about leveraging the damper more, its just that by doing so (which is necessary for a fixed amount of wheel travel vs. a shock with more stroke) the inboard mounts or the outboard mounts (both, really) are in a terrible place.  Frame side moves inboard taking up any leg room you may have had and on the a-arm they move further up the a-arm, giving ridiculous bending loads.  We already overbuild our lowers for rocks and such, but mounting the shocks past the middle of the control arm is not really (what i consider) a viable option.

considering getting a custom tune/valving on the float 2's to match a shock that is set up well for our car, or somehow working a float R to the float 2 air sleeve and an aftermarket extra volume chamber... need to speak more with susp dealer

also, the 12 inches of wheel travel is something I am less willing to compromise on, and this is mostly an issue on the front suspension.... dont really need to worry about foot room on the rear susp.

ANYWAY, so chris you guys ran the float 2's and you were not happy with them? or thought that some rebound adjust would have proved to be useful?  did you do any revalving?  Did you jump on the float 2's because they had more stroke?

Fairly certain laval runs the float R... I really just want to know if 5.3 inches is the actual maximum amount of travel you can get out of any of the Float R shocks
Cornell Baja 2008-2012, suspension stuff
Oregon State 2012+, saw chain & some more baja
Back to Top
CLReedy21 View Drop Down
Baja Godfather
Baja Godfather
Avatar

Joined: Nov/30/2008
Location: Marysville, OH
Status: Offline
Points: 736
Post Options Post Options   Thanks (0) Thanks(0)   Quote CLReedy21 Quote  Post ReplyReply Direct Link To This Post Posted: Oct/13/2011 at 1:34am
I understand your dilemma but first off a difference of 1/2" in length and 1" in stroke is fairly negligible.  In our system you're going to see about 1.4" difference in mounting position on the A-Arm between a 5.3" and 6.2" travel shock if you keep the frame mount and wheel travel the same.  Sure your shock angle changes a hair, but that's not the end of the world.  If you don't have half an inch wiggle room on your frame mounting position to account for the length difference then I don't know what to tell you.  That's the kind of distance you can easily take up in tabs.  As far as sending the bending loads through the roof again look back at that number I posted and realize that the 1.4" put its just on either side of being dead in the middle.  I think you have gotten a little too numbers driven with this and need to take a step back and look at it from a macro view and realize it's not much different, especially in a rock ready A-arm.

It's debatable whether or not you'll need 12" of travel, but I ask you to consider this: when was the last time that your car used all 12" of travel on one of the competition courses?  I'd be willing to be the answer is never especially with an air shock.

We ran custom tuned float 2's last year and had good results.  We moved to them for their higher internal volume and lower sear friction vs the float 1's. They had no adjustments besides air pressure and I didn't miss having 37 different settings to mess up.  Laval does run the R's so they can probably give you a good idea on what they can do.
-Chris Reedy
TTU Alumni
Fourwheeler Drawer



"Quick with the hammer, slow with the brain."
Back to Top
otto View Drop Down
Milling Master
Milling Master


Joined: Oct/06/2011
Location: OR & Colorado
Status: Offline
Points: 100
Post Options Post Options   Thanks (0) Thanks(0)   Quote otto Quote  Post ReplyReply Direct Link To This Post Posted: Oct/13/2011 at 3:42am
(eye-eye length has virtually no impact on shock placement, just up/down on frame pretty much, interested in that dimension purely for comparison)

it's easy for me to sound exaggerated on the internets,

confirmed that the shock moves roughly 1.25" on the a-arm moving from 6.00" stroke to 5.3".  Comparing to a shock mounted directly in the middle of the control arm, youre looking at increasing the shock load on the control arm by about 16.5% by moving it that much and the frame reaction load by 33%.  I would say negligible to be in the <3% category.  Whether or not you'll be breaking a-arms every time you hit a railroad tie is unlikely, but any hopes of reducing fastener/joint size frame side are diminishing rapidly.

If you compare to a control arm that has the shock mounted, say, 1/4 of the length down the axis of the arm from the ball joint youre looking at a 66% reduction in load at the frame side and a 33% reduction in reaction load at the shock (compared to a shock mounted in the middle of the control arm, loading occurring at the ball joint).

you still run into the same problem of not using all of your travel even if you reduce your total wheel travel. You're decreasing the leverage on the shock (or increasing motion ratio) by reducing wheel travel, but at the same time reducing the air pressure you need to hit your target ride height so I'm not sure where you stand with the ramp up near bottom out.  What would make the biggest difference would be to have more negative travel (droop) for the same total wheel travel (if your prime concern is losing travel due to progressive air springs). That way you need less air pressure to hit your desired ride height so the stiffness of the air spring at full bottom will be less compared to a set up with less suspension droop.

We have not ran air shocks before, but we frequently run into the foam bumpers on our coil shocks.  Single air chamber means big a progressive spring rate, which isn't necessarily a bad thing considering that sometimes you may run into that 7" curb a little too fast...

in summary: investigating tuning the float 2's, not ruling out the float r




Cornell Baja 2008-2012, suspension stuff
Oregon State 2012+, saw chain & some more baja
Back to Top
ErikHardy View Drop Down
Baja Godfather
Baja Godfather
Avatar

Joined: Apr/12/2010
Location: Hood, Flint, MI
Status: Offline
Points: 939
Post Options Post Options   Thanks (0) Thanks(0)   Quote ErikHardy Quote  Post ReplyReply Direct Link To This Post Posted: Oct/13/2011 at 8:14am

What if you keep the shock points the same on the A-arm and the frame but move the pivot points on the lower arm closer together?

Back to Top
CLReedy21 View Drop Down
Baja Godfather
Baja Godfather
Avatar

Joined: Nov/30/2008
Location: Marysville, OH
Status: Offline
Points: 736
Post Options Post Options   Thanks (0) Thanks(0)   Quote CLReedy21 Quote  Post ReplyReply Direct Link To This Post Posted: Oct/13/2011 at 3:13pm
Some of that math seems suspect to me, but my point is that, for us at least, our A arms are something like 3-4x stronger than they need to be so you can write off a 15% difference in load very easily.  We're using a 6.0" shock but we're also getting more like 14" of wheel travel up front so we're seeing similar shock forces.  We use 1/4" hardware for all the frame mounting and none of it has broken.  My study on the subject a couple years ago showed that the tabs are the weak link there anyways.

When you reduce your wheel travel you simply need to adjust your air pressure and damping values to suit your new operating range and motion ratio.

Summary:  We have different priorities when it comes to the critical parameters of suspension design.
-Chris Reedy
TTU Alumni
Fourwheeler Drawer



"Quick with the hammer, slow with the brain."
Back to Top
Red_Beard View Drop Down
Organizer
Organizer


Joined: May/14/2009
Location: Bellingham, WA
Status: Offline
Points: 269
Post Options Post Options   Thanks (0) Thanks(0)   Quote Red_Beard Quote  Post ReplyReply Direct Link To This Post Posted: Oct/13/2011 at 3:51pm
When I was on the team we ran two types of Walker Evans, a 6"x2.0" stroke , and its smaller brother a 5.5"x1.125" stroke, I can't remember what the eye to eye was on them, maybe one of the guys from the team will chime in.  We struggled to successfully utilize the last .5" of droop travel on the 6" due to integration issues ( tie-rods hitting upper arms and axle plunge restrictions).  We always had the lower mount as far out on the arm as we could (maintaining proper motion ratio, shock angle, ect...), but it was always a struggle to get the last .5" of droop out of the shocks.  We jumped back and forth between 12" and 16" of wheel travel, which in my opinion is about the right amount for our cars.  We always found ourselves using every single bit of shock/wheel travel we had on our cars; I can still remember a couple of the big drops in Oregon bottoming out the shocks (hydro locking) every time I hit it.  So I agree with you on not wanting to sacrifice any wheel travel.

Once we switched to the 5.5" travel shocks things worked a bit better.  We were able to move the arm mount inboard a couple inches to clean up our shock angle, while still maintaining a solid motion ratio, and still able to maintain around 13" of wheel travel.  Here again, we used every last bit of shock travel and wheel travel when we were racing.  With this set-up we were able to set the ride height at about 2" of shock shaft showing (1/3 up travel, 2/3 down travel), which was a struggle with the 6" shock.  We did run into some loading issues with this shock and this set-up, but was easily solved with some custom machining on the shock piston and running a very light weight shock oil.

These shocks are very robust, and can take a ton of beating, so I wouldn't worry about running a shorter stroke shock all while maintaining a higher wheel travel value.  You may sacrifice some ride characteristics, but it'll be negligible (assuming you can get in and mess with the valve stack).

SDSM&T 09-10 Team Lead
2nd & 9th Baja West

Project Engineer
Matrix Service - Bellingham, WA
Back to Top
otto View Drop Down
Milling Master
Milling Master


Joined: Oct/06/2011
Location: OR & Colorado
Status: Offline
Points: 100
Post Options Post Options   Thanks (0) Thanks(0)   Quote otto Quote  Post ReplyReply Direct Link To This Post Posted: Oct/14/2011 at 12:46am
Originally posted by ErikHardy ErikHardy wrote:

What if you keep the shock points the same on the A-arm and the frame but move the pivot points on the lower arm closer together?



If you mean the pivots of the actual control arm then you would be changing your suspension geometry.  I generally don't let the shock mounting drive kinematics but you could probably do some fiddling with track width and such to move the shock around on the frame if necessary.
Cornell Baja 2008-2012, suspension stuff
Oregon State 2012+, saw chain & some more baja
Back to Top
ErikHardy View Drop Down
Baja Godfather
Baja Godfather
Avatar

Joined: Apr/12/2010
Location: Hood, Flint, MI
Status: Offline
Points: 939
Post Options Post Options   Thanks (0) Thanks(0)   Quote ErikHardy Quote  Post ReplyReply Direct Link To This Post Posted: Oct/14/2011 at 8:12am
Indeed it does change the geometry (not necessarily a bad thing) but its an easy way to get more travel.
 
In your case, what is your top priority? Suspension travel, Bump Steer, Camber gain, roll centers, ergonomics, loading conditions etc.? Just curious how other designers work around things.
Back to Top
zmpeck View Drop Down
Organizer
Organizer


Joined: Aug/29/2009
Status: Offline
Points: 40
Post Options Post Options   Thanks (0) Thanks(0)   Quote zmpeck Quote  Post ReplyReply Direct Link To This Post Posted: Oct/14/2011 at 9:04am
Michigan Tech has run Float R's for the last 4 years.  We use shocks for a DS650 application, which have 6.2" of stroke and 19.8" extended length. 

Edited by zmpeck - Oct/14/2011 at 9:05am
Back to Top
BroncoX View Drop Down
Milling Master
Milling Master


Joined: May/29/2011
Location: United States
Status: Offline
Points: 87
Post Options Post Options   Thanks (0) Thanks(0)   Quote BroncoX Quote  Post ReplyReply Direct Link To This Post Posted: Oct/14/2011 at 1:03pm
We run Fox Float Evol Xs. I think i have a .pdf file of all the shocks that fox list for the Baja SAE cars. It shows our shocks as having an eye to eye of 20in.
Cal Poly Pomona

Bronco Racing
Back to Top
Soccerdan7 View Drop Down
Organizer
Organizer
Avatar

Joined: Sep/22/2010
Location: CA
Status: Offline
Points: 780
Post Options Post Options   Thanks (0) Thanks(0)   Quote Soccerdan7 Quote  Post ReplyReply Direct Link To This Post Posted: Oct/14/2011 at 1:08pm
Do you mind sharing that pdf?
Danny

Cornell

(fall'07 - spring'12)
Former Captain / MEng / that guy with all the carbon
10 races, 7 top ten's, 2 overall wins
Back to Top
otto View Drop Down
Milling Master
Milling Master


Joined: Oct/06/2011
Location: OR & Colorado
Status: Offline
Points: 100
Post Options Post Options   Thanks (0) Thanks(0)   Quote otto Quote  Post ReplyReply Direct Link To This Post Posted: Oct/14/2011 at 3:12pm
what danny said, haha

would be much appreciated
Cornell Baja 2008-2012, suspension stuff
Oregon State 2012+, saw chain & some more baja
Back to Top
otto View Drop Down
Milling Master
Milling Master


Joined: Oct/06/2011
Location: OR & Colorado
Status: Offline
Points: 100
Post Options Post Options   Thanks (0) Thanks(0)   Quote otto Quote  Post ReplyReply Direct Link To This Post Posted: Oct/14/2011 at 3:14pm
actually, a little internet searching revealed this: http://constans.pbworks.com/f/Fox+Shox+Specs+and+Sponsor+Info.pdf

is this the pdf you speak of? seems like its from a few years ago, was not aware of sponsorship directly through fox.
Cornell Baja 2008-2012, suspension stuff
Oregon State 2012+, saw chain & some more baja
Back to Top
BroncoX View Drop Down
Milling Master
Milling Master


Joined: May/29/2011
Location: United States
Status: Offline
Points: 87
Post Options Post Options   Thanks (0) Thanks(0)   Quote BroncoX Quote  Post ReplyReply Direct Link To This Post Posted: Oct/15/2011 at 2:16am
Yep that's it! beat me too it. 
Cal Poly Pomona

Bronco Racing
Back to Top
 Post Reply Post Reply
  Share Topic   

Forum Jump Forum Permissions View Drop Down



This page was generated in 0.078 seconds.