[A4] suspension theory thoughts, questions, etc - grooved shocks

[Grant Lenahan]

See questions below:

On Jan 11, 2007, at 8:40 AM, Taka Mizutani wrote:

> By having adjustable upper and lower perches, you can move the entire
> spring physically lower to the ground in order to lower ride height.

What do you move the upper perch on.  It should be connected only to 
the top of the shock piston. I dont get your point.
>
> With the cheaper setups (like the H&R coilover setup I had on the A4), 
> you
> lower ride height by scrunching the lower spring perch up and 
> compressing
> the spring to shorten the distance.

I dont know the H&R setup, but I do know the Bilstein setups - and have 
for 15 years.  They are actually fairly typical.
  But on any setup where the lower perch moves on the strut body, the 
spring "distance" (whatever the heck that means - I'll assume you mean 
the spring length when under static load) is unaffected. As I have 
posted about 4 times now, the spring compresses from its open, unloaded 
length to its loaded length by an amount that is affected ONLY, repeat 
ONLY by the weight of the car and the spring rate. So this sounds to be 
wrong.

>
> Sorry if I'm not using the correct terminology, but if you take a look 
> at the two
> products I mention above, you should be able to see exactly what I'm 
> talking about.
>
Explain it, p[lease.

> The advantage as I understand it, is that you do not change the 
> effective spring rate
> if you can move the entire spring body in relation to the shock body 
> rather than merely
> compressing the spring to lower the car.
This is correct. And it requires either extraordinary mechanical means, 
or a cleaver advertising copywriter, to do anything else. The ALL do 
this if only the lower perch moves.

The upper perch sit on the shock piston, whcih is freely floating.  It 
rests, loosely, on the top of the spring, held there by gravity. Lots 
of gravity.  The spring length is determined by that gravity.  Moveable 
upper perches are a myth - unless they are somewhat like I suggested - 
camber plates.

Grant

>
> Taka
>
>
> On 1/11/07, Grant Lenahan <glenahan at vfemail.net> wrote:
>> preload a car spring?
>>
>> Grant
>> On Jan 11, 2007, at 7:16 AM, Taka Mizutani wrote:
>>
>> > Adjustable lower and upper perches definitely do exist- they're 
>> pretty
>> > common
>> > on the coilover setups for the Japanese cars- I know I'd get that 
>> type
>> > of setup if
>> > I were to go coilover on the STi. Allows you to separately adjust
>> > spring preload
>> > and ride height, which is really nice. Add two-way adjustable 
>> damping
>> > and camber
>> > plates and you have a really trick setup that's way too adjustable 
>> for
>> > 90% of people
>> > who buy these things. Takes way too much tweaking to get right 
>> unless
>> > you have
>>  > a baseline setup already developed for the car.
>> >
>> > Taka
>> >
>> >
>> > On 1/10/07, Grant Lenahan <glenahan at vfemail.net > wrote:
>> >> > in looking at 'real' "coilover" designs [i too have always 
>> thought
>> >> it
>> >> > funny that they're called coilovers when pretty much every
>> >> suspension
>> >> > i've come across is a shock inside a spring] they do all use the
>> >> same
>> >> > principal - an adjustable lower perch. with the exception of the
>> >> > stasis motorsport coilovers, these look like they have an 
>> adjustable
>> >> > upper perch as well. and they outta at 4grand.
>> >>
>> >> I have never seen an adjustable upper perch. What you may have 
>> seen is
>> >> a camber plate, whcih allows you to adjust CAMBER, but not ride
>> >> height.
>> >> Its a slotted plate you attach the strut top to.
>>