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Traditionally modded suspension vs. Air Ride for thirdgen

 
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Schultzy89GTA
M.R.A. (11sec Club)


Joined: 08 Jan 2004
Posts: 4417
Location: Gresham, OR

1989 Pontiac GTA

PostPosted: Mon Feb 13, 2006 5:17 pm    Post subject: Traditionally modded suspension vs. Air Ride for thirdgen Reply with quote

The Air Ride suspension has been the darling of the magazines for the last few years including several well publicized (thanks Primedia) track days. At these track days, automotive journalists have been allowed to flog Air Ride equipped rides of various shapes and sizes around road courses to demonstrate their capabilities.

I am curious to hear opinions on how an Air Ride suspension would compare performance-wise to a more traditionally modded thirdgen suspension.

-Schultzy

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Red Sled: 89 GTA, 383, TKO, N2O

12.73 @ 109.39, 1.793 60 \ 11.794 @ 121.16, 1.62 60 (old combo)
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Dewey316
The Lama


Joined: 08 Jan 2004
Posts: 7295
Location: Bringing the tech

1990 Chevrolet Camaro RS

PostPosted: Mon Feb 13, 2006 5:34 pm    Post subject: Reply with quote

When was the last time you saw race car, with air ride on the side?

Really, Its one thing to impress the magazine editors (all you have to do is pay them), it also easy to impress Kandied on TGO (all you have to do, is give him the parts to make his car pretty). Now getting the NASA and SCCA guys that race, to run a pair of them, is a whole diffrent matter.

Heck, I may just e-mail Karl Hunter, I'm sure he will have very good technical explanation as to the downside to bags.

I am also going to go out on a limb, and guess that it takes some very signifant shocks, that are valved completely diffrently, to get the most out of air-bags.
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chevymad
Master B


Joined: 11 Jan 2004
Posts: 5476


1987 Pontiac Formula

PostPosted: Mon Feb 13, 2006 8:57 pm    Post subject: Reply with quote

The main problem I see with bags is the spring rates. In order to get good handling you want a low car with stiff springs. But in order for bags to act like stiff springs you need higher air pressure, which jack's the car up. Then if you lower the air pressure the springs get soft and you bottom out even easier. Thing's work exactly backwards from what you want. They've been working on getting this right and have come up with a few adjustable systems. The one adjustable spring rate system I've seen used 3 different add on air chambers plumbed to the bag. Spring rate=pressure and air volume. So by using different size air chambers plumbed through a valve to the bag you can change the air volume seperately from pressure. I guess it works ok, but now you've added 3 air chambers for each spring, a valve for each and the order of complexity just went up a bunch.
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Dewey316
The Lama


Joined: 08 Jan 2004
Posts: 7295
Location: Bringing the tech

1990 Chevrolet Camaro RS

PostPosted: Wed Mar 15, 2006 10:20 pm    Post subject: Reply with quote

Here we go, it took a while, as Karl doesn't check his e-mail all that often. But here is what Karl Hunter had to say.

Quote:
Anyway - about air suspension in performance vehicles...

For a venicle in a performance application air suspension is not the best
choice, and there are many reasons, most of which pertain to "spring rate"

With metal springs it is very easy to control spring rate, and that rate is
very consistent throughout the range of travel within the springs physical
limitations. For example - if you have a metal spring that has a 1000 Lb/In
rate then it will require 3000 Lbs to compress the spring 3 inches, and
another 1000 Lbs to compress it an additional inch and so on.

With air springs, however, the rate is determined by the volume of air
inside the chamber and the dimensions of the chamber - and that rate is
constantly VARIABLE - and according to the ride height with an air bag type
spring, the rate will be different and continuously variable for different
ride height settings. The more volume in the chamber (heigher ride height)
the softer the spring will be. The less volume, the stiffer. The biggest
problem is the non-linear way that an air bag spring responds to changing
loads - it may take 1000 Lbs to compress the spring 1 inch - but the next
inch may be 2000 Lbs depending on the dimensions of the chamber. Also - in a
roll condition the outside loaded wheel will have a rising rate spring
working on the suspension where the inside wheel has a decreasing rate
spring. You follow? Everything is constantly changing with an air
suspension. Setting corner weights becomes almost impossible - and if you
can adjust each corner individually, by the time you get the corner weights
set on the car you could end up with completely different spring rates at
any given corner with no way to resolve the issue, even though the "air
pressure" may be the same. Pressure and volume are both critical, but you
get stuck with the air bags that are supplied and those are what determine
what characteristics the spring will have - and in most cases the air bags
are generic and there is nothing you can change. Ideally, you could set the
air spring to have the correct volume of air (nitrogen would be better) and
then shim the spring (or use a threaded adjuster) to get the correct height
- but this is never the case.

Metal springs are used in racing cars for all these reasons. Consistent rate
- easy to change rate - easy to change geight - linear - etc...

Not to mention that air springs are affected by temperature and
environmental conditions... that and the need for a pump and pressure
monitor - blah blah blah.

Need I go on?

Was there a thread on ThirdGen with a similar subject? Don't be afraid to
tell anyone who says that air ride systems are better than coil springs that
they are a complete moron... then ask them why Formula-1 cars don't use air
springs on the suspension??? (they use titanium torsion bars)

Oh - and coil springs are nothing more than torsion bars that have been
wrapped up in a coil - they operate in the exact same manner. No difference
in performance.

Let me know if this answers your questions.

Karl Hunter
Hunter Motorsports
Vancouver B.C. Canada
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