| Yeah, in the pits......
|
|
| > Can you got right too?? :) Sorry I couldnt resist!!
| >
| > | LOL OMG......
| > |
| > | Dude, I just drive the race car, I don't squabble in here over all
this
| > | technical crap......
| > |
| > | Go fast...... turn left.
---
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Well, tonight all of the ras posts I've been missing all arrived
at once...
The basic problem is that rear drive cars generally require that most of
the roll torque be taken at the front--if you don't do this, then it will
be difficult to accelerate out of corners. It's not usually practical to
get a large roll stiffness entirely from the anti-roll bar on a real car
(things bend!) -- so the engineering solution is to increase the front ride
stiffness (and accept the crappy ride) so that the ride springs provide
part of the desired roll stiffness.
> Thanks,
> Hal
Thanks for that answer. I was confused because I saw the roll stiffness
being handled separately, after the calculation of ride frequency. But
based on what you and Jonny Hodgson have said it seems that you need to
have the ride frequencies be slightly different front and rear (and
presumably with no common modes) in order to prevent cyclic pitching,
and you arbitrarily choose the front as the higher one since you know
that you will need it to be higher when you get to working out the roll
stiffness and roll couple. Does that sound correct?
Thanks,
Hal
> Well, tonight all of the ras posts I've been missing all arrived
> at once...
> The basic problem is that rear drive cars generally require that most
of
> the roll torque be taken at the front--if you don't do this, then it
will
> be difficult to accelerate out of corners. It's not usually practical
to
> get a large roll stiffness entirely from the anti-roll bar on a real
car
> (things bend!) -- so the engineering solution is to increase the front
ride
> stiffness (and accept the crappy ride) so that the ride springs
provide
> part of the desired roll stiffness.
> > I have been working my way through the book "Race Car Vehicle
Dynamics"
> > (which I got out of our company library - it's great working for an
auto
> > company) and I noticed that in the examples around pgs. 580 - 600 or
so
> > it is said that you want the front ride frequency to be higher than
the
> > rear. I did not see any explanation for this. Why would this be
true?
> > Thanks,
> > Hal
1) For road cars, the rear needs to be the stiffer end so that it
'catches up' after a bump (1.0 / 1.1 Hz are the target frequencies we
were given). The exception would be if you wanted to drive in reverse
lots... ;-)
2) Further thought suggests that the car will suffer greater pitching
moments under braking, so stiffer springs at the front allow ride
height to be better controlled as well as permitting the front to be
lower than the rear, as it's usually preferred to be.
Jonny
