Finding ride height?

I have done the searches and I have read the books, maybe I am just too dense but I have still not been able to find a definitive answer to my question. I am getting ready to put the spring hangars on my 9" and I know that you have to find ride height so that you can set the frame at that angle in order to set the pinion angle with the manifold level putting the transmission roughly 3° down then set the rear end parallel at 3° up. My question is if you need the ride height to determine what angle to set the engine and rear end at which determines what angle to weld the spring hangars on at, but you need the spring hangars welded on to get your ride height, how the hell is this accomplished. Before you say find someone with a similar set up and measure theirs, I have tried and failed, probably because I wanted my car to sit low but not crazy low so I decided on an 8" kickup in the rear and a 4" kickup in the front. I am using a pete and jakes style 4" dropped I-beam front end and a ford 9" with a posies model a rear spring and I will make my own ladder bars. here are a couple of pics of the frame.

 

You don't need the spring hangers on to get ride height. You just simply put the frame at the height you want it and build to that. The axle centre line ends up being determined for you with wheel diameter, and you just put your frame at the height you want it at. Your suspension is built to keep the frame at that height. This is overly simplified of coarse. Peter

 

What he said. You don't find ride height, you decide what it will be.

 

Well, that still leaves the problem of getting the suspension set up to have it sit to that predetermined ride height....after all the weight is on the finished car.

riddle me that

 

Lowering blocks...

 

I know the axles are going to set wherever the tires put them, but final ride height is determined by the axle heights plus the rest of the assembled suspension components minus compression from the weight of the engine, body, fuel tank or whatever else. Unless you can build your own springs and stuff how can you just come up with an arbitrary measurement and build to that? Am I over-thinking this shit should I just set the frame at 3° down in the front and build off of that. If I do this and the actual ride height/angle turn out to be different than this what negative effects would that produce?

 

We use 3 1/2" of travel as a baseline to the bottom of the frame at the rear axle kickup. As stated, your rear axle height is determined only by tire size.

Figuring spring compression is a little stickier. If you are using leafs, you can get rated monoleaf springs from the circle track industry. If you already have a set of leaf springs and want to build the mounts to them, run a string between the spring eyes and measure from there down to the center bolt where the spring sits against the axle. That is the "arch". For a light car, subtract about 2 inches, and that is how far you need the frame and shackle eyes from the axle perch height. I use 2" of compression because you can usually get to that fairly easily without a ton of block or messing with the spring pack. For a heavier car (1500+ rear axle weight) use 3" compression.

 

Good info, thanks.

 

Tommy,
You can always get coil springs that will do whatever you want them to. That's the reason we use coilovers in the first place... Once you have the shock "eye to eye" length for the shocks you want to use, build your shock mounts and then pick the coil springs that will work for the finished weight. Always buy springs last...

 

Thanks for the info ex west. I wanted to stay with the traditional rear end set-up ie. transverse rear spring, shocks and panhard which is why I bought the posies spring. So if I measure the distance from a string between the spring eyes and subtract two inches that should get me a close approximation of the spring height under load right. Then to get the height from the spring eyes to the centerline of the axle should I put the shackles on the spring hangars at 45° and measure from the shackle at the spring end to the centerline of the spring hangar bracket. If that is correct it should give me the height of the rear crossmember. Then can I do the same thing for the front end measuring the spring arch and subtracting two inches or does the front spring compress less?

 

Does anyone know how much a monoleaf spring will compress under a 331 Hemi with a T5 behind it in a Model A?

 

Did you ever get the measurement of the front spring? compressed and uncompressed?