[DeTomaso] Shorter front shocks?

[Scott Bell]

I RESPECTFULLY couldn't disagree more with Mike's conclusion here. I work with folks that know a lot more about shock technology
than I will ever know and it is a bit more complicated than simply using a shorter spring.

If the shocks are tool long then a shorter spring will get the ride height down BUT may cause a new issue where the springs become
loose between the perches. A Shorter spring will ONLY work if the spring retains some pre-load when the car is un-weighted.

IF with a shorter spring, the spring is loose when the ride height is adjusted to preference, then the correct solution is a shorter
shock. (You could use a shorter spring with suspension limiting straps)

Most new shocks today have more travel than the same length stock Pantera shocks. This isn't a good thing because we don't need that
much travel. 

The issue Ken is running into is very common for folks that want a lowered car while maintaining a high spring rate.

The only correct solution is to run a shorter shock (when you want a low ride height AND a higher spring rate). We have done a lot
of testing in this area. Running a shorter shock allows you to run a higher spring rate while getting the ride height you want. When
we talk about a shorter shock, we are talking about a small amount. The stock shock runs around 16.4 inches total length. The
shorter shock we are using is 15.2 inches total length. The compressed length is the same for both shocks. With this setup you can
set the shock ride height to be mid travel where it should be.

There is a lot more to ride height and spring rate that the rather simple math used in Mike's example. There is a bit of a science
behind it. Items include SPRING RATE, SPRUNG WEIGHT, SUSPENSION MOTION RATIO, STATIC LOAD, SHOCK RIDE HEIGHT DESIRED, etc...

SPRING RATE:	You should always find the closest spring rate available for your application. When in doubt, choose a lower spring
rate.

It is easier to achieve handling and performance with a lower spring rate and a "stiff" stabilizer bar or shock.

Regards, Scott	
	

-----Original Message-----
From: DeTomaso [mailto:detomaso-bounces at poca.com] On Behalf Of Mike Drew via DeTomaso
Sent: Tuesday, April 05, 2016 8:50 PM
To: detomaso at poca.com
Subject: Re: [DeTomaso] Shorter front shocks?


In a message dated 4/5/16 13 40 50, detomaso at poca.com writes:


> Has anyone done an analysis of the viability of running a bit shorter 
> front shocks?  With the typical length front shocks, and springs on the heavy 
> side, it appears that the nose is a bit higher than I want at the lowest 
> spring position.  I could probably use lighter springs adjusted for the 
> desired height, but I'm not sure that is a good solution.
> 

>>>That is assuredly a bad solution.   Ride height should be controlled by 
spring height, period.   Ride characteristics should be controlled by spring 
rate, period.

Since you have adjustable spring perches, however, if you have your perches 
set as low as they go and the ride height is too high still, the 
inescapable conclusion is that the springs (NOT the shocks) are too tall.   FWIW, 
every adjustable Pantera shock/spring package I've ever seen will allow you to 
lower the car TOO much, which makes me wonder what kind of deal you have 
going on?   Have you started with a tried-and-true combination and then changed 
to longer and/or stiffer springs?

Realize that effective spring force and spring length are interrelated and 
need to be controlled against one another.   If you have a spring of a given 
advertised rate, and you cut it in half, you double the rate.   So what you 
need to do is decide what spring rate AND what length you want/need, and 
then buy exactly that....

It took me a long time to figure out exactly why that was true; intuitively 
it made no sense to me at first.   Here's the explanation:


Say you have a spring that is 12 inches long, with 12 coils on it, and you 
put a 500 pound weight on top of it and it compresses one inch.   That means 
each coil compressed 1/12th of an inch, for a total compression of one 
inch.   The spring rate is 500 lbs/inch.

Now, cut it in half.   Put a 500 pound weight on it, each coil will still 
compress 1/12th of an inch, but since there are only six coils it will only 
compress 6/12ths, or half an inch.   500 pounds compressed it only half an 
inch, so it would take 1000 pounds to compress it a full inch, thus the spring 
rate is 1000 lbs/inch.

Presuming your existing spring rate is appropriate, you may need to buy 
shorter springs with the same rate.   Even if they are two inches shorter, you 
would then have adequate adjustment in your perches to set the ride height 
where you wanted.   

But I'm still skeptical overall of your situation.   Tell us exactly what 
you're using?

FWIW I had Carrera coilovers on my car initially; those springs were 
considerably longer than those on the Konis that replaced them....

Mike