rec.autos.simulators

by **Haqsa** » Tue, 04 Sep 2001 00:42:18

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

by **Michael Barlo** » Tue, 04 Sep 2001 01:13:11

This is a completely **Uneducated** guess, I just want to see if I'm
right or not.

While accelerating, the weight of the car is shifted rearward. With the
rear being higher in the first place, while accelerating the car will be
level. Of course while breaking, that theory is shot out the window(?) Now
I'd like to find out how close I am to being right.

by **Haqsa** » Tue, 04 Sep 2001 06:11:11

I think you are thinking of ride height. I'm referring to the natural
frequency of the suspension, i.e. at what frequency would it bounce up
and down if it had no dampers. The Millikens' say the front frequency
should be higher than the rear, and I think I have heard this elsewhere
too, but I would like to know why.

> This is a completely **Uneducated** guess, I just want to see if
I'm
> right or not.

> While accelerating, the weight of the car is shifted rearward.
With the
> rear being higher in the first place, while accelerating the car will
be
> level. Of course while breaking, that theory is shot out the
window(?) Now
> I'd like to find out how close I am to being right.

> > 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

by **Billy Hutso** » Tue, 04 Sep 2001 07:02:55

Maybe because the weight of the engine in the front???

by **Jonny Hodgso** » Wed, 05 Sep 2001 02:40:55

Well no, since the axle weight is accounted for in the nat freq
calculations.

It's the other way round for road cars, to achieve "pitch
cancellation" over bumps - the rear 'catches up' the front so that it
rapidly becomes a bounce mode, rather than pitch, which is more
comfortable.

Jonny

> > 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

by **Billy Hutso** » Wed, 05 Sep 2001 05:35:21

LOL OMG......

Dude, I just drive the race car, I don't squabble in here over all this
technical crap......

Go fast...... turn left.

> > Maybe because the weight of the engine in the front???

> Well no, since the axle weight is accounted for in the nat freq
> calculations.

> It's the other way round for road cars, to achieve "pitch
> cancellation" over bumps - the rear 'catches up' the front so that it
> rapidly becomes a bounce mode, rather than pitch, which is more
> comfortable.

> Jonny

> > > 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

by **Haqsa** » Wed, 05 Sep 2001 06:02:37

Okay the pitch cancellation part makes sense, but I'm still not sure why
the front should have the higher frequency. Can you explain that?

Thanks,
Hal

> > Maybe because the weight of the engine in the front???

> Well no, since the axle weight is accounted for in the nat freq
> calculations.

> It's the other way round for road cars, to achieve "pitch
> cancellation" over bumps - the rear 'catches up' the front so that it
> rapidly becomes a bounce mode, rather than pitch, which is more
> comfortable.

> Jonny

> > > 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

by **Jonny Hodgso** » Wed, 05 Sep 2001 06:17:34

Not really! Does that section refer specifically to, say,
front-engined, rear-drive cars? IIRC there was some general
theorising that the roll couple distribution should reflect the weight
distribution... but then there are anti-roll bars to do that without
upsetting ride frequencies.

Jonny

> > > Maybe because the weight of the engine in the front???

> > Well no, since the axle weight is accounted for in the nat freq
> > calculations.

> > It's the other way round for road cars, to achieve "pitch
> > cancellation" over bumps - the rear 'catches up' the front so that
it
> > rapidly becomes a bounce mode, rather than pitch, which is more
> > comfortable.

> > Jonny

> > > > 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

by **Thom j** » Wed, 05 Sep 2001 06:47:26

Can you got right too?? :) Sorry I couldnt resist!!

---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.276 / Virus Database: 145 - Release Date: 9/3/2001

by **Haqsa** » Wed, 05 Sep 2001 08:52:51

The example that I was looking at was referring to a rear drive, solid
axle car that oddly enough was heavier in the rear. But the statement
on front ride frequency being higher than rear seemed to be a general
statement that did not apply only to this vehicle. And yes, it was
treated independently of roll couple. The examples calculate the spring
rate first, based on ride frequency, and then look at the resulting roll
couple and roll gain and adjust it with ARB's. The interesting thing is
that undamped ride frequency is a function of the static deflection of
the suspension, so that a vehicle with higher front ride frequency would
have lower static deflection in front. While this seems to agree with
some real life setups I have seen, some prominent on-line setup guides
advise spring rates that give equal static deflection front and rear.
That's part of why I'm trying to figure this out. The other reason is
that the examples pretty much give you an easy first cut at how to set
spring rates (or really wheel rates). If you go through the formulae
and charts, it implies that for race cars you want somewhere around 2 to
4 inches of static deflection (wheel deflection due to the car's
weight), with slightly less in front, and maybe about half of that if
you are setting up a car with significant downforce devices. That's a
very handy rule of thumb to have if we can just make sense of it!

by **Ben Colema** » Thu, 06 Sep 2001 05:11:23

Stabbing in the dark a bit, but won't the frequency be related to the
unsprung weight? In which case you can change the spring rates to change
static deflection but the lighter spring is working on the same mass....or
something....and the mass of the drive train makes the rear frequency lower.
(?)

Ben

>The example that I was looking at was referring to a rear drive, solid
>axle car that oddly enough was heavier in the rear. But the statement
>on front ride frequency being higher than rear seemed to be a general
>statement that did not apply only to this vehicle. And yes, it was
>treated independently of roll couple. The examples calculate the spring
>rate first, based on ride frequency, and then look at the resulting roll
>couple and roll gain and adjust it with ARB's. The interesting thing is
>that undamped ride frequency is a function of the static deflection of
>the suspension, so that a vehicle with higher front ride frequency would
>have lower static deflection in front. While this seems to agree with
>some real life setups I have seen, some prominent on-line setup guides
>advise spring rates that give equal static deflection front and rear.
>That's part of why I'm trying to figure this out. The other reason is
>that the examples pretty much give you an easy first cut at how to set
>spring rates (or really wheel rates). If you go through the formulae
>and charts, it implies that for race cars you want somewhere around 2 to
>4 inches of static deflection (wheel deflection due to the car's
>weight), with slightly less in front, and maybe about half of that if
>you are setting up a car with significant downforce devices. That's a
>very handy rule of thumb to have if we can just make sense of it!

>> Not really! Does that section refer specifically to, say,
>> front-engined, rear-drive cars? IIRC there was some general
>> theorising that the roll couple distribution should reflect the weight
>> distribution... but then there are anti-roll bars to do that without
>> upsetting ride frequencies.

>> Jonny

by **Jonny Hodgso** » Thu, 06 Sep 2001 02:26:50

Okay, just thought I'd check.

rear.

When I went for a MonsterRank recently, I started with equal and ended
up with front slightly stiffer... My 4wd, off-road R/C car runs the
back somewhat stiffer I believe, but I also think that's due to the
way tyres are supplied out of their bags - once I've cut'n'shut them,
it moves closer to a sensible spring balance. Perhaps it's time I had
another look at those calculations...

Absolutely! Now, how does it translate to 1/10th scale? ;-)

Jonny

by **Haqsa** » Thu, 06 Sep 2001 10:54:19

Yes, exactly, the frequency is a function of the wheel rate and the
unsprung mass supported by that wheel. But the question is not, "why is
the rear frequency lower?" but rather "why do the Millikens and other
advise that we set the chassis up so that the rear frequency is lower?".
It tends to work out that if the unsprung weight distribution is even
close to 50%, which it would be for many race cars, that you want
stiffer springs in front. This is apart from any roll rate
considerations, so it is not based on trying to get understeer. I'm
wondering if this is related to stability and control, or is it just a
carryover from passenger car design which is based on ride comfort.

by **Haqsa** » Thu, 06 Sep 2001 12:00:15

Whoops, I mispoke there. In the previous message I meant to say sprung
mass and sprung weight, not unsprung. The unsprung mass does not affect
the ride frequency of the vehicle, although I suppose you could
calculate a natural frequency for the suspension based on the unsprung
mass and the tire rate. Also I suppose you could get into coupling
between the sprung and unsprung mass if their natural frequencies are
harmonics of each other, but that is way beyond the scope of what I am
trying to figure out here.

> Yes, exactly, the frequency is a function of the wheel rate and the
> unsprung mass supported by that wheel. But the question is not, "why
is
> the rear frequency lower?" but rather "why do the Millikens and other
> advise that we set the chassis up so that the rear frequency is
lower?".
> It tends to work out that if the unsprung weight distribution is even
> close to 50%, which it would be for many race cars, that you want
> stiffer springs in front. This is apart from any roll rate
> considerations, so it is not based on trying to get understeer. I'm
> wondering if this is related to stability and control, or is it just a
> carryover from passenger car design which is based on ride comfort.

> > Stabbing in the dark a bit, but won't the frequency be related to
the
> > unsprung weight? In which case you can change the spring rates to
> change
> > static deflection but the lighter spring is working on the same
> mass....or
> > something....and the mass of the drive train makes the rear
frequency
> lower.
> > (?)

> > Ben

by **Billy Hutso** » Sat, 08 Sep 2001 09:25:27

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.

> ---
> Outgoing mail is certified Virus Free.
> Checked by AVG anti-virus system (http://www.grisoft.com).
> Version: 6.0.276 / Virus Database: 145 - Release Date: 9/3/2001

rec.autos.simulators

Ride Frequency

Ride Frequency

Ride Frequency

Ride Frequency

Ride Frequency

Ride Frequency

Ride Frequency

Ride Frequency

Ride Frequency

Ride Frequency

Ride Frequency

Ride Frequency

Ride Frequency

Ride Frequency

Ride Frequency

Ride Frequency