[billj]

I must confess that I built my 4-link more based on what fit than by calculation of what would work best........... Though I'm generally happy with the result, there are two things that I'd like to improve.

1) Traction on the front axle during climbs
2) Reduced wheel hop, also during climbs.


From what I've gathered in reading, it would be desireable for AS to go down with droop and be higher in bump. Using the 4-link calculator, I find the curious situation in that AS increased on both sides of static.

- droop = 150%
- static = 110%
- bump = 150%

I've messed with the link positions within the spreadsheet, but this relationship continues. What should I move around to get better AS numbers?? I'm thinking maybe that I've got to get the IC more out in front by making the links more parallel. But this only changes the values, the relationship of both droop and bump being larger than static remains??

My design is nothing extraordinary, so I don't understand why I should have this strange behaviour. Any help would be most appreciated.


EDIT: BTW, the weight and CG values are WAG..........

 

[billj]

Further confusion on my part............

On the "travel" page of the spreadsheet, the calculations for bump and droop are executed. It would seem to me that the values of x, y and z for the link locations would change based on the bump and droop numbers entered by the user. However, some of these x, y, and z values are fixed numbers.

What gives??

 

[billj]

I think that there's an error in the spreadsheet regarding these bump and droop calcs...........

 

[Amund]

 

[Gordon]

1) Traction on the front axle during climbs
2) Reduced wheel hop, also during climbs.

I'll let triaged comment on the calculator, I don't know it that well.

as to number 1) probably the best thing you can do is hook your winch cable to the front axle. It's pretty easy too.

on #2 you need less anti squat not just in droop and compression but especially at ride height. If it was mine and it was a trail rig I would raise the frame side of the upper link mounts a little bit. This will screw up your roll axis a little bit but that is OK for trail use. If you raise them enough the AS will start to decrease in droop.

Another way to controll wheel hop is with shocks, I don't know what you have on there now, but when I went from ranchos to Edelbrock IAS monotubes it made a big difference. There are lots of other good monotubes out there too. If you already have monotubes or coil overs or air shocks some shock tuning might help, but I would start with changing the suspension geometry.

 

[billj]

Thanks for the reply Gordon...........

I already do the winch to front axle thing. It helps but I'm still somewhat unhappy with the traction of the front end. I don't seem to have that "pull" over the top of a ledge, if you know what I mean........

I'll look at the feasibility of messing with the upper link mounts. I'm running air shox, so I also have that variable to deal with.

Thanks again for the tips. Now I'll wait around for Triaged to understand what's going on with the spreadsheet..........

 

[Triaged]

Further confusion on my part............

On the "travel" page of the spreadsheet, the calculations for bump and droop are executed. It would seem to me that the values of x, y and z for the link locations would change based on the bump and droop numbers entered by the user. However, some of these x, y, and z values are fixed numbers.

What gives??

The cells that are yellow are just reference dimensions (the exact same # as elseware but just there to fill up space or copy/paste for me easier). The white cells are all calculated and the blue cells are all user input.

-Do you have your Macro permissions set correctly? (tools/macro/security and set it for medium then close and restart).

-Do you have the solver add-in installed? (tools/add-ins and check the solver box...you might need the CD).

-Make sure you have the latest version (http://home.earthlink.net/~triaged/Files/4BarLinkV3.0.zip)

The bottom 3 white cells that you circled are direct equations (intersection of 2 circles in 'X' and static +-travel in 'Z')
The 3 top white cells you circled (really 4 but one was cut off I,K,O, & Q7) are calculated with the solver using a VB script so there is no equation in the cell (only the final result). If you were to delete the values from these cells it would still update properly when you hit calculate. These only update when you hit the "Calculate" button so make sure you always hit that button. Numbers can be displayed that are not up to date (not correct). Also sometimes the solver can have noticable error in it. This often happens near the point that your suspension is going to invert (not good!) but your real suspension won't travel that far. A quick gut check is to see if the link lengths were calculated out right (are the upper links from static/droop/bump all the same?).

These are the #'s that I get when I run your suspension. I really don't know why the #'s would be so far off?

Static
Anti-Squat 110.174 %
Roll Axis Slope 0.0000 in/in (Roll Oversteer)
Roll Center Height #DIV/0! in
Roll Axis Angle 0.000 degrees (Roll Oversteer)
Instant Center X-Axis 59.800 in
Instant Center Z-Axis 24.000 in

4' Bump
Anti-Squat 118.899 %
Roll Axis Slope -0.1582 in/in (Roll Understeer)
Roll Center Height #DIV/0! in
Roll Axis Angle -8.991 degrees (Roll Understeer)
Instant Center X-Axis 44.842 in
Instant Center Z-Axis 21.177 in

10" Droop
Anti-Squat 111.277 %
Roll Axis Slope 0.4164 in/in (Roll Oversteer)
Roll Center Height #DIV/0! in
Roll Axis Angle 22.608 degrees (Roll Oversteer)
Instant Center X-Axis 214.554 in
Instant Center Z-Axis 102.102 in

I would be less worried about what your suspension does at full travel then what it does right around ride height (like +-2"). You can change the #'s in the blue boxes to both 2 and see what happens. You do seem to have a fairly consistant AS%.

 

[billj]

Thanks a lot for the clarification!!! I'm a "challenged" individual when it comes to computer stuff, so I'll talk with the folks at the help desk, about the Excel configuration.

In any event, it's good to know that my AS is more consistent than I was seeing.

Thanks a lot!!!