[DeTomaso] Sway bars

[Mike Drew]

BG,

Your car is stock, 7/8 front and 3/4 rear. The cars were deliberately set up to understeer (push). 

Euro cars had, as an option, 7/8 rear swaybars which made the cars very neutral. 

Back in the 1990s Larry Stock and Jack DeRyke and I conducted skidpad tests with a primitive G-meter using Larry’s black Pantera. We started off with the stock configuration as a baseline, then installed 7/8 rear bar, then 1-inch front bar, then 1-inch rear bar. 

More is always better, right?

Wrong. We saw a HUGE improvement in cornering power going from 3/4 rear to 7/8 rear leaving the stock 7/8 front bar alone. We were surprised to then see a decrease in performance going to a 1-inch front with 7/8 rear, and an even greater decrease going to 1-inch front and rear. 

Jack’s theory at the time was that the stiffer swaybars were imparting loads to the somewhat flexible chassis that it was incapable of withstanding. He had a beautiful turn of phrase: he said he thought the chassis was “acting like an undamped spring”.

The graphs of the cornering G-forces were very smooth and controlled with the smaller bars.  But when 1-inch bars were introduced, there would be sharp spikes and troughs in the graphs, especially with 1-inch front and rear. Instead of delivering a constant .93 gs, let’s say, the graph showed cornering gs rapidly oscillating between .89 and .83 (or something like that).

This was long before anybody ever invented chassis stiffening kits. It stands to reason that once the chassis is stiffened up, cornering performance might be improved by using 1-inch bars. But it’s fairly clear that for a stock body, 7/8 inch front and rear is optimal, with the caveat that you will lose some of the built-in stability imparted by having a smaller stock bar in the rear. 

That means with a bigger rear bar, you can go around a given corner faster, but you need to be a better driver.  With the stock setup, if you go into a corner too hot the car will understeer, or plow/push toward the straight ahead. If you lift off the gas the great likelihood is that the front end will be weighted, the tires will become more effective, and the nose will politely tuck in and the car will safely negotiate the corner. 

With a more neutral setup, you can go whipping around that same corner at a higher speed.  But if you lift off the gas, the rear end will be more inclined to step out, and a spinout could result. 

Note that most aftermarket wheel and tire combos aggravate the understeer/plowing condition, because the width of the tire contact patch is normally increased far more in the rear than the front. This upsets the balance and promotes understeer. So a given car will need a swaybar change to maintain the same cornering balance after switching from old-fashioned stock-sized tires to slightly wider front tires and ridiculously wider rear tires. 

Most people who go the big-wheel route opt for 335-width rear tires, but some have opted for 315 for this very reason.

Mike

Sent from my iPad

> On Apr 9, 2020, at 13:06, The Goyaniuks via DeTomaso <detomaso at server.detomasolist.com> wrote:
> 
> 
>   There is dialogue about sway bar bushings going on right now.
>   I am busy putting my 74 back on the road - Stock body.
>   (upgraded springs, shocks, brakes)
>   Can anyone let me know what the stock sway bar set-up is?
>   I ask this simple question because my FRONT is 7/8 inch and my REAR is
>   3/4 inch. I was surprised by the sway bar thicknesses. I thought that
>   the rears should be the same or thicker than the fronts.
>   Anyway, my second question is:
>   Any performance improvement by leaving my fronts as 7/8 inch and
>   putting 1" on the rear.
>   BG
> _______________________________________________
> 
> 
> Detomaso Email List is not managed by POCA
> Posted emails must not exceed 1.5 Megabytes
> DeTomaso mailing list
> DeTomaso at server.detomasolist.com
> http://server.detomasolist.com/mailman/listinfo/detomaso
> 
> To manage your subscription (change email address, unsubscribe, etc.) use the links above.
> 
> Members who post to this list grant license to the list to forward any message posted here to all past, current, or future members of the list. They also grant the list owner permission to maintain an archive or approve the archiving of list messages.