[DeTomaso] need formula for springs needed-- was shocks for ORR

Wed Oct 10 00:55:30 EDT 2007

 Dennis and Jason,

I freely admit that my opinion comes from a total slacker regarding ORR, but I wonder if stiffer shocks is the right way to go. My understanding is that it is not the shock's job to prevent excessive spring compression-- if that is happening, the spring is too soft. The shock's job is to dampen the spring's natural tendency to continue to let the car bounce up and down once it is disturbed. Indeed, the Brits call them "dampers" because that's what they actually do.

At the risk of boring you to tears, I had an Alfa that was "undersprung", that is, the springs were too soft.? Despite Konis set on full hard so expansion joints rattled my teeth, the car would still "porpoise" when going thru depressions at intersections for water to drain away. The car was "undersprung and overdamped."? In contrast, my MGB was "oversprung and underdamped".? It would also rattle my teeth over expansion joints but never porpoised. However, the ride was "bouncy," where you could feel the car oscillating up and down more than it should after hitting a bump.? So its dampers were not preventing the car from bouncing along in its springs.

What spring rates are you and Jason running??? I have no real world experience at this, but if Jason doesn't bottom out at 150mph, that gives you an idea of what spring rate is necessary to contain a certain amount of kinetic energy. Basically a car encountering a change in road shape is being forced to change its course from straight ahead in the vertical plane to a different trajectory. Inertia wants to keep it going straight, and the springs have to transmit force to prevent it from burrowing into the asphalt.? 

It seems to me that since Kinetic Energy=1/2 Mass x? (V squared), you could get an idea of what spring force would be necessary to keep the same mass from bottoming at a different speed.? I'm afraid my physics is too rusty to give you the formula, but spring strength is measured in pounds, which is a measure of force, mass x acceleration.? The springs have to accelerate the car away from the road. If they are not strong enough, they bottom out and the whole car becomes unsprung weight. So the spring has to have enough strength to not bottom out under this extreme load.? 

Again, I don't have the equations for you, but I suspect everything will drop out of the them and you'll be left with the velocity squared factor-- if the car is going twice as fast the springs will have to be 4 times as firm to prevent bottoming.? 

Meaning you'd be looking at something like:

Jason's spring rate x??? Dennis' speed squared

?????????????????????????? Jason's speed squared??? =? spring rate needed to prevent Jason's car from bottoming at Dennis' speed.? If Dennis' car weights more or less than Jason's, you would correct by a simple proportion, as the M is not squared in the formula.

However, I think this also assumes that the springs in the two cars are the same length and will crush the same distance before they bind, etc, etc. But it should provide a ballpark estimate, I would think.? 

Jack and the other people who really know and don't just make slacker guesses like me?? 

Jim Oddie

-----Original Message-----

From: Jason Eaton <jason.eaton at gmail.com>
To: Mad Dog Antenucci <teampantera at yahoo.com>
Cc: detomaso at realbig.com
Sent: Tue, 9 Oct 2007 6:22 pm
Subject: Re: [DeTomaso] Bigger-Better-Heavy Duty Shocks for Silver State WOOPS - No Slacker Content

You can reduce the unsprung weight by cutting back on the beer and donuts!

We didnt have any problems with compression, but were only going 150
though there. Also I'm pretty sure we are running higher rate spring
then yours. lets compare notes.

On 9/25/07, Mad Dog Antenucci <teampantera at yahoo.com> wrote:
> Off Roaders & JORN IN NORWAY:
>
>  Bilstein and Aldan were wrong.....rebuilding the shocks for the Pantera with 
25% more compression and rebound was not enough to stop full compression at the 
dips (at WOT) at Silver State in the Pantera....you couldn't have pulled a 
greased string out of my backside on the hardest hit so its back to the drawing 
board.;-]>
>
>  In the last ORR I had another great run....engine although it had too much 
compression ;-]> ran great....the Pantera is handling better then it ever 
has.....but hitting full compression broke  the ABS side skirts and bottom of 
the air dam in the dips. Shock mounts and chassis all look good and the Pantera 
stayed straight and true on full compression so no handling problem.  Te ABS was 
meant to provide some added hi-speed stability which it did until it broke ;-]> 
but the ABS was also meant tobe the  'sacraficial lamb'  which it also did but 
bottom line I still got full compression in dips above 145 mph
>
>  So, as part of this winter's projects (MORE engine compression) ;-]> I need 
some customized  shocks with added compression to handle these dips (aka WOOPS).  
I don't think there are any plans in 2008 to regrade the course dips so the 
challenge is to build shocks around the course conditions.
>
>  No Col. I still can't afford those high tech $5 grand computerized units but 
a couple people I spoke too suggested adding a stop on top of springs to 
eliminate the 'full compression'.... the negative to that suggestion is others 
have suggested it could also cause wheel hop 'at speed' on full compression 
which could lead to loss of control and an off road 4x4 excursion. ;-]> So goal 
is to STOP full compression.
>
>  If YOU have a contact name of anyone you have personally dealed with on 
customized shocks for off-road conditions send it to me. I gotta figure those 
guys who are running offroad at 150 mph can help where roundy-rounders can't.
>
>  JORN, SEND ME contact infor on the VIKINGS that ran 200  MPH last week.
>
>  MD
>
>
> Mad Dawg Antenucci
> Team Pantera Racing
>  The 1st & still the only vintage race team in open road racing
> www.teampanteraracing.com
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