Reply to: RE>>As ye plow, etc.
As ye plow, so shall ye reap
[ Lotus West trivia question.... who was responsible for the original L/W =
tech tip,
[ which was published many years ago, under the above subject / title???
Rod Bean wrote:
>>1) L/W trivia question: I say Dean Price.
Nope. It was Jim Gallagher! The gist of his article was that with the =
original
7 suspension with the Chapmanesque dual purpose anti-roll bar and upper =
arm
geometry, you simply get too much camber with roll. The solution touted =
by Jim
(and validated by loads of folks... ever notice how competitive 7s at =
slaloms all
seem pigeon-toed?) is to dial in considerable static negative camber, and =
live
with the braking penalty. (Or, to compensate, slow it down by scrubbing =
off
speed while getting it rotated, eh Rod..... ;-) ;-) ;-)
Marty Wilson wrote:
>>> I am after some feedback on setting up the front suspension of my =
Amaroo
>>> Clubman.
>>> I have only run it in hillclimbs so far and the "turn in" on the =
corners
>>> doesnt seem too famous, it tends to understeer. I have been advised =
to dial
>>> in more negative camber and this will cure it.
Steve White replied:
>> What sort of adjustments do you have available to you? Camber, caster
>> and toe? How much adjustment is possible? What sort of tyres are you
>> running, what size and how old are they? What pressures do you =
normally
>> run in them? What sort of compromises are you prepared to live with?
>> .... for instance you might improve the turn-in and make the car really=
>> responsive to steering input, but that might make the car really =
'darty'
>> and tiring to keep in a straight line.
I wrote:
> If it pushes all the time, then more negative camber at the front =
*might* be a
> wise approach.... Everything is a compromise as Steve pointed out.
> Best bet though, might be to begin by getting some tire temperature =
test data,
> to tell you whether the camber is in the ballpark to begin with at the =
front, and
> how the roll stiffnesses are presently set up... before more radical =
measures,
> first consider just using less toe-in at the front.
Well, my tire pyrometer comment was sort of a "motherhood and apple pie" =
idea
of how to proceed to optimize grip at both ends of the car. But I =
suppose that
under unusual circumstances, such as extreme static negative camber (Jim =
was
recommending 3 degrees... yikes) it might be tricky to achieve meaningful =
results
from tire pyrometer testing. Would you actually have to set up =
individual tests
of right turns and left turns.....?
> Depending on the course, and your driving style, you oughta be able to =
get
> away with much less toe-in than you would use on the street. Change it =
a little
> bit at a time!
With regard to toe-in, Marc Nichols wrote:
> I have improved my 7 turn-in by minimizing toe in. In fact, I have run =
up to
> 1/32" toe out. A bit darty, but faster.
Yeah as a matter of fact, Jim Gallagher pointed out in the "as ye plow" =
article,
that some toe-out may be *required* to counteract the tendancy for the =
wheels
to turn in the direction in which they are cambered... in other words the =
more
negative camber you use, the less toe-in (or possibly, the more toe-out!) =
you will
need.....
> You may wish to check the ackerman geometry. Toe in on turns as set up =
for
> street cars may promote understeer under race conditions since the slip =
angle
> on the outside (loaded) tire is higher than the inside. This can often =
be adjusted
> by tweeking the steering arms.
Yeah, fascinating. This bit about Ackerman angles being optimized =
differently
even for road racing or autocrossing has come up before. I don't =
understand
exactly how you go about determining what you need, though.... Marc, =
could
you explain more about this, for our benefit.
> Is the front suspension bottoming? Also, different shock settings may =
need to
> be tried. Try stiffer first.
Yep, I have heard the suspension bottoming issue mentioned before too, in
reference to 7 replicas, on Kitracers.
For instance, Liam Venter wrote:
> Running on the bump stops. (check this first) It happens more often =
than you
> realise and I found I had this problem but it was hard to feel. =
Indication-
> Understeer comes on suddenly, check by putting a tell tale on the bump =
stop. -
> problem can be solved with stiffer springs, increased preload on the =
springs to
> give more bump travel. Longer travel shock absorbers.
Hmm. Yeah that makes a lotta sense, but why are 7s so sensitive to =
bottoming?
Is it just a matter of marginal suspension travel at the front?
Marc Nichols wrote:
> I also found that my 7 was "falling on the front end" at turn in. =
Stiffer front
> springs actually improved turn in and balance.
Oooh boy. Now that is a really subtle one. A stiffer front bar =
*improved* the
turn-in? Wow, that is counter-intuitive, or maybe my poor little brain =
just can't
comprehend all the things that may be going on at the same time, during =
your
car's turn-in transition.
OK, here's a blind stab. Could it be that before, when you were "falling =
on the
front end" you were in fact, hitting the bump stops and thus abruptly =
washing
out the front end. Stiffening the front springs oughta *increase* front =
end load
transfer and thus promote push, but maybe this is moot, if hitting the =
bump
stops were causing a more sudden and dramatic problem?
It all goes to demonstrate, that Liam was on target with his comment:
> The above is my very simplistic over simplification of a very confusing =
( I am
> very confused - the more I try to understand the more I realise I don't =
know)
> subject. Remember a little knowledge is dangerous and more knowlege is
> more dangerous!
Yep. I fully agree. Understanding this stuff properly requires =
considerable
effort.
OK, other opinions on this? Jeremy Braithwaite? Dick Carlson? Ian =
Peters?
Billzilla?
erik.berg@trw.com
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