This is my starting point-a new-to-me '40 Ford coupe. Obviously, you need to take these dimensions before you begin to slice and dice sheetmetal. It's a good idea to have the car on a stock chassis (as shown here) in order to come up with points of reference.
Aside from gassers, low is pretty much right when it comes to hot rods and customs. That's no surprise. But how many times have you looked at a car that, well, looked completely out of kilter? You know-the car that just doesn't sit right. What's even worse is the independent suspension that has been lowered so severely the camber is dangerously skewed (and those guys wonder why their tires have goofy tread wear). Inevitably, out-of-whack cars like this don't work that well either, and that's even more critical than "the look" for a car that sees regular use.
So what's the point? Simple, it's easy to build a car by slicing coils off springs and throwing suspension bits at it, but that's not the best way to do it-even if your car is going to be a pretty standard piece. The right way to do things is to begin with a basic plan coupled with some very basic dimensions; the first thing you need to do is establish the ride height of your ride.
The first thing I had to do was level the car front to back (most built-in-Detroit cars are more or less level along the rocker panel when they leave the factory). As you can see, a simple carpenter's level placed on the rocker panel does the trick.
By establishing the ride height, you can then build the car to suit the components instead of the other way around. You can establish some "knowns" (how high or how low you want it to sit, tire dimensions, rocker panel or running board height, etc.) and then fill in the variables (suspension hardware such as springs, shocks, suspension links, and so on). This way, a car like the '40 Ford in the photos, which will eventually be fitted with 29 1/2-inch and 25-inch-tall rolling stock, will still look right and work right, even after it's lowered as far as mechanically possible.
To get there, I first figured out the rearend width (see the February '08 R&C for more info). Then I determined how high the back tire could go before I ran into body interference, and took the measurements. Pal George Cathey of Pro Designs used my dimensions and laid out a rough draft of the chassis perimeter in Auto CAD. The drawing shown on page 48 isn't complete or finalized, but it is a work in progress as we deal with dimensions. Of course, there are limits to this juggling: Pinion angle, tire clearance, and other factors enter into the equation, but it's still nice to have a real point of reference before you or your chassis builder fires up the plasma cutter.
As you'll soon see, there are no tricks to this scheme. Instead, there are just a few common sense ideas that work. Check out the following photos and copy the concept and you'll have the basics to build a car that not only looks right, but also works properly, too.
Next, I leveled the body side to side. A couple of reference points are handy for this drill; I used the trunk floor opening (as shown), the top of the cowl, and the firewall. If the car isn't level from side to side, shim it (plywood works) until it is. | 
This car will eventually be mini-tubbed, but I didn't want to carve up the body before the new chassis was more or less ready to roll under it. | 
I then determined where the axle centerline was; in my case, there was no original back axle with which to work so I simply used original Ford drawings (Wescott's Auto has them on its Web site, www.wescottsauto.com) to determine the center point. |
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At the rear wheelwell, here's the clearance dimension up top. I'll need approximately 2.75 inches minimum from the top of the tire to the top of the fender mount flange. Now, keep in mind that most coilover shocks available today have a stroke range of roughly 3.00 to 5.50 inches (remember, too, that angling the shock during mounting has an effect on the travel, effectively reducing the actual numbers). |
Next, I measured from several known points (rocker panel, running board, or, better still, the original framerail) to the ground and subtracted the number I obtained earlier (the tire-to-ground dimension). That's the actual frame ride height. I also measured from the back of the frame to the ground. | 
You can make a sketch, copy this drawing, or draw the works in Auto CAD like this. As pointed out in the text, this is an in-progress drawing our buddy, George Cathey, is working on for me. Eventually, the idea is to finalize the blueprint, and then have the framerails bent by Art Morrison (Morrison's PROfile 2x4 setup). | 
With the tire at ride height, we measured from the base of the tire to the ground and recorded this number. Keep in mind the tire will flatten slightly when weight is applied to it, but this number is sufficient for our purposes. |
I repeated the drill at the nose of the car as well as measuring the distance between the framerail at the firewall to the ground. Mark the numbers down and use the plan. You won't be sorry. | | |