The majority of the force from hitting a pothole is taken by the strut rod, but agree with Norm you have braking forces that create a torque about the spindle, as well as the cornering forces from the tires. Turn the tire and you have a different angle of force on the UCA.

I would feel more comfortable with your setup than the dropped crosslink that TCP uses!

 

eZ, I think I've read this post 5 times end to end. LOVE the idea. I'd like to try this myself. Do you happen to remember the part # for the shocks you wound up with in the end?

 

HAL-12-350 for the spring

HAL-DS501 for the shock

 

Sweet! Thanks.

How's the setup been working for you to date?

 

I works incredible! Im going to take it apart for a visual inspection soon. Make sure evrything is well in tact. The 350 spring is great for a stiffer street spring. probably buy a 450 spring if I take it road racing. My rear setup feels too bouncy now though. dont know if I need to go softer or stiffer in the rear

 

I'm aiming for performance street with an occasional auto-cross or run around NJ Motorsports park's tracks, so I'll probably just "spring" (bad pun...) for the 450lb setup. I looked up the coil overs as soon as you posted the numbers. Summit seems the cheapest right now. I was trying to view your thread on your rear setup but I don't seem to be allowed to view any of the pics??? I'm in the process of designing a triangulated 4 link for my brother's 64 Falcon. If that goes well, I'll adapt it to my stang.

 

built a 4 link for my rear...allowed for much wider wheels with mini tub. However I ran a parallel setup. Trying to learn how to make the front and rear setup work together as far as spring setup. Yes summit was the cheapest. Sometimes you can find a 10% off code online. The adjustability of the front coils are awesome. If I was going to drag race a lot I would get the double adjustable. Autocross the single should be sufficient. Actually If I adjust the shock to level 8 Im sure it would be plenty stiff for autocross on 350 springs. I have it set on 4 right now and I corner hell of fast. Right now It has just the right amount of understeer. The rear brakes loose just before the front does. Just how I want it. Now If I can spring for some new tires it may change some things. Going to put some NT-01 up front and NT-05R in the rear.

 

That's either a front vs rear ride frequency issue or the rear shocks are significantly softer than the fronts in the low shock piston speed ranges.

What is the rear spring rate, and what is your front motion ratio (I'm wild-*** guessing from the pics that it's around 0.8).


Norm

 

Norm, what would be an optimum setup front to rear? Do I want the same motion ratio or a percentage of the front for the rear? Just noticed, I'm right down the street from you in Pennsauken...

eZ, what do you have for a steering setup? Still running the stock box and hardware or a R&P? I'm building my own R&P base on a J-car rack. Just need to finish the centerlink and tie rods.

 

The motion ratio is what you need to know to get you from the spring rates to the effective rates at the wheels. From that you can determine things like ride frequencies and front vs rear lateral load transfer distribution (though determining LLTD requires you to know a few other things). It's mostly just a mathematical tool, not something that you target to have any specific front to rear ratio.

Generally, OE short-long arm front suspension MR's for conventional springs are in the 0.6 range. Strut designs are 0.9 to maybe 0.95. Coilovers can be whatever the designer comes up with. Most coil sprung rear motion ratios are 1.0, although arrangements like the Fox body with the rear springs mounted to the lower control arms are less (around 0.7 IIRC), and it is possible to exceed 1.0. Kind of a long way of saying that more information is needed.

A soft spring with a fairly high motion ratio can behave like a much stiffer spring with lower motion ratio. To match a 350 lb/in spring working through an 0.8 motion ratio down at an 0.6 motion ratio would require the springs to be about 622 lb/in (these numbers were not picked at random).

Roughly, you'd like the rear ride frequency to be something like 10% or so higher than the front ride frequency. More precisely, you'd like for one complete rear suspension cycle to end at precisely the same time as one front suspension cycle when you're traveling at maybe 45 to 50 mph (including the time delay before the rear suspension starts moving over the same bump). Depending on your driving environment - your typical speeds and whether you're using relatively stockish or MUCH stiffer springs - you might choose a different speed, which could be either higher or lower.

Figuring LLTD is more complicated, and ultimately has to consider the driver's preferences (some drivers like a car to feel "looser" than others) and driving style. But basically you want a bigger percentage of the LLTD up front than there is weight percent there (IOW, if your car is 56% front weight / 44% rear, you'd probably want 61% or so of the LLTD up front).

These things can be estimated by calculation (the math never really gives you an exact solution; it only puts you in the ballpark, but is a much better approach than just guessing wildly). Fred Puhn's softcover book "How To Make Your Car Handle" has just enough math and formulas in it to get you started.


Norm