Quoting W Bell <cbody67tx@xxxxxxxxxxxxx>:
> Yes, bar length and diameter are determiners of basic spring rate, just as
> the number of coils and wire diameter and checking height are on coil
> springs. Lever arm on the control arms is a factor in the mix too.
Yes, we all now agree to that.
> The reply was that he could raise the car with the front torsion bars, but he
> would make it uncomfortable to ride in due to the increased ride rate of the
> torsion bars being twisted as far as they would be. This was in something
> like Motor Trend and printed in the later 1960s.
OK, we agreed that the spring rate is not affected by how high the car sits.
> factory specs as to ride height, the propensity to bottom out is
> significantly reduced and the ride rate is firmer than if it's sitting too
> low. Not to mention the affect the lower ride height has on the great
> steering geometry of the steering linkage.
Again, ride height should not affect the spring rate, and therefore no effect on
the ride. There may be a reason why the "perceived" stifness is changed. But
I can't think of one. But yes, the FSM recommends to re do the alignment every
time you change the T-bar height. From my experience, the effect of small ride
heights is minimal in the alignment.
>
> If the rocker panels are parallel with the ground, the aerodynamics of the
> car are not adversely affected. High speed handling, even with a full load
> in the trunk and a full load of passengers, which might result in a slight
> nose-up condition, have no adverse affects on the handling of those Chrysler
> products at normal highway speeds or even extra-legal cruising speeds. Been
> there, done that.
My experience is opposite to that (i.e, front end sitting high is less stable
car at high speed). Also, this is theoritically supported. As the front end
gets higher, both the lift and the yaw moments coefficients as well as the
overall drag coefficient increase. This has been established by wind tunnel
tests back in the 70's. That means that the front end gets "lighter" and more
affected by cross winds, and your overall high speed performance suffers. By
how much depends on the cross winds and how fast you are really going. The
Imperials being fairly heavy cars are probably less effected than
smaller/lighter cars in terms of stability.
In fact, the Mopar Perf Race Manual recommends that drag
> race cars have their alignment set with the front end jacked up an inch to
> compensate for the acceleration mode they normally are in when drag racing.
That was for different reasons. That was done in order to improve rear wheel
traction at the expense of high speed stability and performance. Remember, a
drag race only lasts a few seconds, and its dead straight. Losing traction at
the low end will cost you a lot more than reducing a little drag at the upper
end. For Imperials that were meant for prolong high speed driving, and with
little chance of losing traction during acceleration (low gear ratios and lots
of weight on the back) the slightly front tilted attitude (like the cars came
stock) is probably more desireable.
> Considering what's behind the front bumper on those Chrysler bodies (i.e.,
> strut mount cross member that acts like an air dam under there), it would
> take quite a bit of raise past the factory spec ride height to get enough air
> under the car to adversely affect handling or fuel economy at normal highway
> speed, I suspect.
I also doubt the ride height would have much of an effect in fuel economy, but
it would in high speed performance. The cross members would make the impact in
overall drag even higher with a jacked up front end. My Sedan is currently
sitting a bit too low at the back end, so the rockers are about parallel to the
ground. I see little stability effect, but probably because I have rigged up
an air dam under the bumper. I will eventually raise the back end a bit, and I
suspect my high speed performance will improve a bit.
As for the inherent advantages of T-bar suspension, there are two, as far as I
know. One, is lower unspung weight. However, in cars like the Imps, I doubt
that's much of an issue as the wheels and in the case of the 67+ the brake
calipers weigh lots of pounds. The second, which I think is what made the
T-bar handle better was more freedon to get a better geometry front suspension.
This is more of an issue in a V8 car with limited space around the fender
wells due to the cylinder banks. The T-bar takes away the spring mounting
requirements from the fender wells, and gives more freedom to the designer to
select the proper suspension geometry while still allowing enough space foe
engine fit and to service the engine.
D^2
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