[200q20v] Re: The 'why' of coilovers - long
b.m.benz at prodigy.net
Sun Oct 29 11:24:02 EST 2000
Thanks for your well considered reply and explanation of your upgrade
decisions. Just what I was hoping for, and I'm sure equally appreciated by
the list. We have a great thread going, sorry that I am leaving the country
for a few weeks and must drop out. Comments below.
> From: Chris Maresca <ckm at crust.net>
> Date: Fri, 27 Oct 2000 22:45:29 -0700 (PDT)
> To: Bernie Benz <b.m.benz at prodigy.net>
> Cc: audi-20v <audi20v at rennlist.org>
> Subject: The 'why' of coilovers - long
> On Fri, 27 Oct 2000, Bernie Benz wrote:
>> Your euphoria over coilovers as being "the glue" is presented sans any
>> quanitive, let alone qualitive justification for the exurberance. Did you
>> increase the spring rate, lower the ride height, alter the bump and/or
>> rebound damping, or just spend money, as you are apparently encouraging
>> others to do in suit?
> Well, I did some of the above before doing this, and, since you asked,
> here are the reasons why I chose to go with coilovers, rather than
> something else.
> In April, my wife and I took one of our two CQ's to Parhump, NV to take
> part in the QC's Driver School at Spring Mountain Raceway. The car we
> took was our mint 1990 CQ (red), which has Delrin's, Koni Yellow's
> (rebound adjustable), stock springs and 6 months old Dunlop SP4000's.
> It was fun, but towards the end of the session, I was really pushing the
> envelope on the CQ, esp. solo. More than a few people, including Lee
> Mitchell (former SCCA Pro and a race driver for +/- 20 yrs), Ron Wood and
> Larry Boyer, commented that I was almost scraping the front spoiler and
> that the inside wheel had lifted more than once.
> Gary Allison told me that I had better get some stiffer springs, since
> pushing harder was just going to cause problems.
> I whole hartedly agreed and had been thinking about doing something
> about the springs for a while. So, I was off to make my suspension
> The Options
>> Do you believe that any of the above suspension adjustments possible
>> with a coilover spring mounting system has any direct or indirect
>> effect on body roll or understeer, and how?
> To alleviate roll and nose dive on a CQ, there are really only two
> Stiffer Springs
> Coilovers (which are stiffer springs, really)
> As far as understeer goes, that was not my main concern, but I believe
> that the enormous weight transfer that occurs when a CQ slows down has an
> adverse effect on turn entry charcteristics of the car. Unloading the
> rear tires and heavily loading the front tires is not a good thing.
> Stiffer springs, with higher rebound shocks, help to keep the front up and
> the rear down, simply put. Better weight distribution across all four
> tires helps alleviate some of the understeer.
IMO, increasing spring rate does not, in the first order, alter the weight
transfer under deceleration, inasmuch as you have not changed the CG height
relative to the axle height. Only the effect of the weight transfer,
reduced ride height in front and increased ride height in the rear, have
been changed, in this case reduced. The tire forces on the ground remain
the same. So, if there is an advantage to reducing suspension travel by
increasing spring rate, it must come from reducing the resultant changes in
suspension geometery, i.e. toe, camber, and bump steer of an imperfect
suspension system. Thus, the justification for for my previous post
statement, "IMO, the stiffer spring suspension "upgrade" is a crutch to
reduce bump steer by limiting suspension travel". (Are we having fun!)
> I had tried stiffer, rebound adjustable shocks and that just was not
> cutting it, ditto with stiffer rubber bits (if anything, these may turn
> out to be a mistake, and that was more of a 'road feel' thing than
> anything else...), as well as a stiffer chassis (I have a front strut
Again IMO, the sole purpose of a shock is to alter the dynamic
characteristics of the spring and unsprung mass mechanical resonant system.
They are totally ineffective in changing the static characteristics of a
suspension system. In the bump direction, an ideal suspension stores the
bump energy in the spring by compressing it with little of this energy
absorbed by damping and thus transfered to the chassis (a soft bump shock).
In the rebound direction, the objective is to return the axle to its normal
static ride height as quickly as possible and without overshoot, i.e. a
critically damped mechanical resonant system. An underdamped system
oscilates, the tire bounces on the ground. With an overdamped system time
is lost in returning the axle to static ride height, and the system is not
ready for the next bump. Rebound damping is the critical shock issue, and
must be matched to the spring/mass system. Again, shock characteristics are
totally unrelated to static suspension issues, such as understeer.
Strut braces. From my experiences designing my strut-to-strut brace, (See
Chris Miller's 200Q-20V site) I was suprised to discover and realize just
how stiff the strut towers on our cars really are relative to the rubber
upper strut mounting, and concluded that a tower-to-tower brace adds nothing
and is redundant. The latteral cornering forces exerted by the strut at the
tower level deflect the rubber strut mounting bushing orders of magnitude
more than is the resultant deflection of the strut tower. Thus, my
strut-to-strut brace accomplishes more than a tower brace in that it divides
this latteral force equally between the two rubber tower bushings for half
> So, it had come down to coilovers or new springs. The springs were a bit
> cheaper, about $150 to $200, but I knew I would need new shocks anyway and
> the biggest difference was going to be in the labor.
> Last year, I had driven Rick Zehr's car, the one with updated springs and
> smaller (?) OD wheels. While I liked the stiffness, I was not pleased
> about the harshness or the fact that the car was lowered. Also, the
> backend was skittish and the car had a tendancy to bottom out.
> Earlier this year, I drove Harrision Blackwood's modified CQ. His car is
> like a solid piece of metal. Between the rollcage, the uber-stiff
> suspension and the racing seat, it's pretty close to being a real race
> car. And it behaves like one. It's hard to describe the skittish
> nervousness the car gives off when driving it. You feel every nuance of
> the road surface, and when you go over something sharp, it doesn't really
> shake because the body is so stiff. It's fun, if you're driving fast, but
> I thought it was a bit much for everyday. It really reminded me of
> driving a race-prepared Peugot 205 GTI or a Formula Ford (yes, I've driven
> both), just with a bit more luxury.
> Anyway, there was another consideration coming into all this. I have both
> a 1990 and a 1991 CQ. I don't know how many people have had the pleasure
> of driving both models back to back for long periods, but the 1991 is
> definetly the more refined car. Quieter, better suspension, easy to drive
> at very high speeds. I don't know why this is, but it's like the 1990 is
> a end-of-the-80's car and the 1991 is a 1990's car, if you know what I
> mean. It's hard to quantify, but several people who have driven the 1991
> got the same impression.
Is your '90 an early one without the wimpy rear anti-roll bar? Could be the
difference. I intend to experiment with trying the 4K and 4KQ front
anti-roll bars (as I remember, 23 and 27mm respectively) to the rear of my
90Q. I think that it should improve the car's understeer characteristics.
But I suspect that the 4KQ bar may be too much.
> And this was the car to get the suspension upgrade. On top of it all, I
> was not too keen on lowering the ride height, since I like to got skiing
> and the car is already low enough to be a snow plow.
> So, nothing was perfect. The coilovers were nice, but potentially too
> stiff. The springs were OK, but perhaps too short, bottoming out and
> lowering the car. Then there was the cost difference.
> The Decision
> Finally, I decided to do the coilovers. The decision was reached after
> many discussions with 2B about keeping the character and comfort of the
> car, keeping the stock ride height, etc.
> I figured that coilovers would give me the best range of choices in spring
> rates if I didn't like what 2B chose, and that I would get to keep the
> ride height. The down side was an additional $500 or so.
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