Thanks, Marcus! I should have mentioned Car9, which is another opportunity.
Bent Wrench, if you have a particular vision for a car that the readily available designs don't fit, by all means don't let that stop you. You could sketch it or post pictures of cars that appeal to you, decide on a power train and get the dimensions of the pieces that you'll use. You can use mockups (plastic pipe is great) to figure the sizes of the boxes to use for components and people. You need this information even if you are eventually going to execute your design in CAD.
To design the suspension you must start with the uprights you are going to use, wheels and tires. Don't buy the tires!
These dictate where your outside pickups will be.
As for the inside pickups, that is the tricky part but:
- Width is dictated by the size of components, be they engine, differential, or steering rack.
- Bottom wishbones are either level or pointing up a little to generate a little extra camber gain in the early stages of roll.
- Camber gain is driven by swing angle lengths.
- For a given upright, there is a magic angle for the chassis tube to which inner pivots are attached, which limits roll center migration in bump, roll and combinations thereof at various mounting points for the wishbones. Engineering types could probably calculate it, but us mortals can find it in Wishbone by raising or lowering the upper pivot and moving across the horizontal plane until the sweet spot is found for the desired roll center height.
- KPI affects camber gain, so any simulations should include steering inputs.
Professional automotive engineers are not so concerned about roll centers, opting instead for force-based models. However, geometric roll centers are reasonable approximations of force-based roll centers.
If none of the above makes any sense, that's ok. Keep reading, and plunk your measurements into Wishbone and experiment with them.
OK, that was a fun distraction. I'm working on taxes due Monday.
PS for those who may be wondering about my sudden re-appearance. I took care of aging parents 2007-2010 which took a lot of spare time and killed my accounting practice. Started a business with wife in 2010 (service provider agency for people with developmental disabilities, she is the pro) which is doing nicely now but keeps me busy. I still want to build, but with simplified plans as noted in my sig. I have a new garage with 50 amp service and am currently dismantling my donor. Very excited about some nice Haynes roadsters finished recently!
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I am not sure I remember why I decided to make my own frame design and it has been a huge amount of work. I hope it pays off and honestly it's been help from other people that is making it possible for me.