Originally Posted by myduster360
Originally Posted by TC@HP2

Originally Posted by myduster360
Originally Posted by Frankenduster
I get that. The car is pretty neutral right now with some slight understeer. I'm fine with that. I am looking to build a similar car within a year or so and was thinking of having it a step or two softer. Again, it is easy enough to do with torsion bars and sway bars due to the diameters/lever arms but....


I used Direct Connection's "neutral handling" methodology to find my Swinger's needed rear leaf spring rate and its a decent starting point. You can do the same using your current car as a starting point since its "pretty neutral" handling is what you want to emulate only "softer".

1) Calculate your current cars Front roll couple. That value will represent 75%-80% the cars total roll stiffness. Thus the 20%-25% remaining will be the range of your CURRENT car's rear roll couple. I'm guessing if you back calculate the leaf spring rate, your MP XHD may be in the range of 110-140 lb/in

2) Now substitute in "softer" TB redo the calcs and see what the rear leafs you'd need. Just error on the side of too soft because a rear bar can bridge the gap and bump up the rear roll couple.


Agree this info provides a good starting point but would remind other readers it is not a set in stone set of values. The neutral handling line was developed from sanctioned competition cars with specific limitations on tire size, overall weight, and biased weight. Street cars can have a much greater variety of variables and a wider range of these variables that can impact where this neutral point occurs.

I'd also add, because of the limited number of torsion bars and sway bars, anyone doing this work should dial in what they want for front rates and then build the rear to compliment it. It much cheaper and easier to modify leaf spring packs for rate than it is to get a custom t-bar size made. T-bars are also limited by the socket size on most of cars to be no more than 1.24, max, unless you are energetic enough to convert ABE bodies to C body sockets, ala the original SCCA TA series race cars.



Ok so the alternative being either
1) Random A$$ Guess
or
2) Rock solid methodology of intrawebs opinion poll??

Seems they'd have far more caveats, what-ifs and could-bees, than using actual data derived from a real vehicle.


I'm not saying don't use the neutral handling line. It is a great starting point. What I'm saying don't be surprised if using it does not immediately produce the desired results because street cars have more variables to contend with.