Wishbone suspension analysis program by MCdermott
Posted: December 1, 2006, 12:32 am
Click to download. It's from the Yahoo group site. It has a pretty cool diagraming feature, I didn't put in any info, I just viewed the example. I assume that units of measure are inches since the tire height in the example is 20.
http://www.locostusa.com/yahoo/Wishbone_setup.exe
If you have trouble getting it to run on a new system read this:
http://filext.com/faq/run_old_program_xp.php
Below is how I came up with the balljoint locations needed to use this program:
Q: So what's this Fore and aft business?
A: The X field is fore and aft. Visualize an A arm from above. There's two pivots on one end and a balljoint on the other. The fore/aft numbers represent how far these two pivots are apart. The + (forward) is how far one pivot is in front of the balljoint and the - (rear) is how far the other is behind it. Obviously there will be one in front and one behind. Typically the one behind is the larger dimension since that is the direction of the load when a tire hits something.
Once you have all the numbers you just plug them in and go to it. All you are really doing is trying to properly locate the upper chassis pivot point. You want your lower chassis point the same height as the lower balljoint height so no work is needed with that other than moving it in and out and you are going to put it where it provides the best mounting point on your chassis. This will be decided primarily by your chassis width.
Getting that upper chassis pivot in the right place is the holy grail. Where you put it dictates how your suspension works. Moving it around changes your roll center, camber curve, the whole nine yards. Try and get a roll center that isn't too far below your center of gravity and aim for a camber curve that matches your desired range of suspension travel.
It's been debated how important it is to have your roll center stay put and not move relative to the chassis when the chassis is in roll can the wheels in bound etc. I worked extra hard to make sure my roll center moved very little as the suspension moved. A good test for this is the skewed roll. Roll the chassis a few degrees and then introduce some bump and see what happens. If you ever want to get a visual of what's going on hit F6 and look at the graph.
That should be enough to get you started.
I hope this helps!
http://www.locostusa.com/yahoo/Wishbone_setup.exe
If you have trouble getting it to run on a new system read this:
http://filext.com/faq/run_old_program_xp.php
Below is how I came up with the balljoint locations needed to use this program:
The first step is to decide what wheel and tire size you are going to run and work from there. Bolt the Spindle to the wheel/tire combo with ball joints in place and then clamp everything into your intended static alignment on a hard level surface. You want 7 or so degrees of caster and a degree or so (depending on the car's prupose) of negative camber. Once you get it where you want it you need to carefully measure the height from the ball joint centers to the ground. (meaure it several times, it needs to be accurate) Next you need to set up a reference object to symbolize the midline of the chassis on the inside of the wheel/spindle/tire (I used a big carpenter's square) that is exactly 90 degrees to the ground. It also needs to be the distance of 1/2 of your track measurement from the center of the tire. Then you need to measure the distance horizontally from the vertical reference point (symbolizing the chassis midline) to the center of the balljoints. You now have the X and Y coordinates you need to allow you to play with the program and get meaningful results.
While everything is still clamped into place measure the steering arm joint center's location. You'll need that later to set up your steering system. Also measure track width.
The other "chassis points" are wide open. Put them wherever you want ot achieve the roll center you want. I know this all may sound confusing and tedious, but it's really simple once you see the big picure. The hard part is accurately measuring the fixed points that you cannot change, which are the balljoint locations on the factory parts. Once you get these numbers nailed down you are off and running.
Q: So what's this Fore and aft business?
A: The X field is fore and aft. Visualize an A arm from above. There's two pivots on one end and a balljoint on the other. The fore/aft numbers represent how far these two pivots are apart. The + (forward) is how far one pivot is in front of the balljoint and the - (rear) is how far the other is behind it. Obviously there will be one in front and one behind. Typically the one behind is the larger dimension since that is the direction of the load when a tire hits something.
Once you have all the numbers you just plug them in and go to it. All you are really doing is trying to properly locate the upper chassis pivot point. You want your lower chassis point the same height as the lower balljoint height so no work is needed with that other than moving it in and out and you are going to put it where it provides the best mounting point on your chassis. This will be decided primarily by your chassis width.
Getting that upper chassis pivot in the right place is the holy grail. Where you put it dictates how your suspension works. Moving it around changes your roll center, camber curve, the whole nine yards. Try and get a roll center that isn't too far below your center of gravity and aim for a camber curve that matches your desired range of suspension travel.
It's been debated how important it is to have your roll center stay put and not move relative to the chassis when the chassis is in roll can the wheels in bound etc. I worked extra hard to make sure my roll center moved very little as the suspension moved. A good test for this is the skewed roll. Roll the chassis a few degrees and then introduce some bump and see what happens. If you ever want to get a visual of what's going on hit F6 and look at the graph.
That should be enough to get you started.
I hope this helps!
