Front suspension design input needed

[Ron Sutton]

Originally Posted by 358Mustang

So in order to couple with the rear setup I have got.. I am running a home made 3 link in the rear, roll center is about 8". coilover shock behind the axle, with a 300# spring. It needs more roll stiffness in the rear I feel, maybe due to the angle I have my shocks kicked in at... So my plan was to add a rear sway bar to that.

I just mention the rear because obviously I need them to work together. I am thinking I probly want to go with a little stiffer of a spring up front to limit front travel. I am trying to get the CG down and planned on having the motor fairly low. SO I guess that would fall towards the stiffer spring, softer bar category unless you can say why the other way is better..

I am unsure exactly on spring rate, I would thinkg of starting in the 450-500# range... Coilover mounted as far towards the tire as I can within reason

Gotcha. You're going the conventional route.
Based on what you said, it looks like you're looking to travel the front end in the 3/4" to 1-1/2" range (at the crossmember). I should have asked this earlier ... will you be autocrossing, running track days at full size road courses or both?

Regardless, for a low travel/high roll suspension set up …
• If your priority is autocross or the low speed corners of road courses, your target RC should be around 1” in full dive.
• If your priority is the mid-speed corners of road courses, your target RC should be between 1.5” to 2.5” in full dive.
• Of course, you can set it for anything in-between.
• The higher the RC is within the range 1” to 2.5” favors the mid-range corners. Lower favors the low speed corners.
• If optimum lap times matter to you, the answer of what is the optimum roll center will come through testing.
• If you're not that hardcore & just want to have fun running the track hard & fast, pick what makes sense to you & go run it.

P.S. I concur with Mike's tips above. He & I both favor high travel/low roll set-ups, so that influences our designs & geometry settings, including lower roll centers ... and long control arms which tame the geometry changes. The farther you travel the front suspension ... the more the longer control arms help.

I attached an illustration of my Track-Star front suspension which we travel in the 4" to 4.5" range at the crossmember (more at the outer front wheel). I design these custom for each client's particular car, but the LCA's end up in the 23" to 25.5" range & UCA's in the 11.75" to 13" range. This allows us to travel the front end that 4-4.5" and have the optimum geometry throughout the travel.

If you're traveling the front end only a little, then control arm length is less of an issue.