rec.autos.simulators

by **Ruud van Ga** » Mon, 06 May 2002 02:09:57

On Fri, 03 May 2002 21:15:24 -0500, Pat Dotson

>Ruud, you might be the man to answer this. In RACER, if you
>put a softer spring on one corner of the car, with no
>other changes. Will that corner see more or less dynamic
>loading than before? RACER puts out those numbers doesn't
>it?

Yes, you could try and check the loads in Racer.
With a softer spring on just one corner, the car would lean more into
that corner, you'd say. Not necessarily meaning more load, just more
suspension compression. Looking at Todd's experiment, it seems the
diagonal takes more of the weight.

As for dynamic loading, you'd think that with a very stiff spring you
get very responsive loads; like from normal (~weight/4) load to a high
load very quickly.
In a soft spring, the car must lean first, and this takes time. So the
average load will be less. Todd's experiment then would suggest the
steady state load is also less, so dynamic load is then less.

Just guessing, but with the softer spring like in Todd's example, the
car leans more, but the weight of the left-rear wheel (and body) keeps
the car from getting the load at the right-front from reaching the
same value as with the stiffer spring (as with the stiffer spring you
get less rotation in the car).

Hope that doesn't clutter things up. ;-)

Ruud van Gaal
Free car sim: http://www.racesimcentral.net/
Pencil art : http://www.racesimcentral.net/

by **Doug Millike** » Mon, 06 May 2002 02:57:04

> The CG doesn't change with anything except a bit with fuel
> displacement, and ofcourse driver displacement (a good way to get more
> grip in a kart is to hang outwards when turning).

In a normal car with suspension, moving the CG toward the inside will
reduce load differences between inner and outer tires, common example is
left-weight offset on oval track cars. Working through the tire load
sensitivity effects, the car will have more grip with the offset CG
(assuming that other things are "equal"...which never actually happens!)

Why should this work opposite (lean out) in a kart? Does it really work
this way?? I have some ideas, but we haven't studied karts in detail so
I'm curious to hear any theories.

-- Doug Milliken

by **Pat Dotso** » Mon, 06 May 2002 15:39:04

> > The CG doesn't change with anything except a bit with fuel
> > displacement, and ofcourse driver displacement (a good way to get more
> > grip in a kart is to hang outwards when turning).

> Why should this work opposite (lean out) in a kart? Does it really work
> this way?? I have some ideas, but we haven't studied karts in detail so
> I'm curious to hear any theories.

I've heard a theory that road course karts that have to
turn left and right need to unload weight from the inside
rear tire to make the kart turn. The driver leaning
toward the outside of the turn isn't increasing grip,
he is reducing drag on the inside rear wheel caused by
the solid rear axle and lack of any stagger.

Pat Dotson

by **Blak** » Mon, 06 May 2002 17:23:19

Yep, The solid Axle is the reason. I used to race Karts for many years and once I learned that I akways let my body lean to the
outsideit lets the inside rear wheel "spin" if the inside wheel gets a good bite the kart pushes off the turns...

| >
| > > The CG doesn't change with anything except a bit with fuel
| > > displacement, and ofcourse driver displacement (a good way to get more
| > > grip in a kart is to hang outwards when turning).
| >
| > Why should this work opposite (lean out) in a kart? Does it really work
| > this way?? I have some ideas, but we haven't studied karts in detail so
| > I'm curious to hear any theories.
|
| I've heard a theory that road course karts that have to
| turn left and right need to unload weight from the inside
| rear tire to make the kart turn. The driver leaning
| toward the outside of the turn isn't increasing grip,
| he is reducing drag on the inside rear wheel caused by
| the solid rear axle and lack of any stagger.
|
| Pat Dotson
|

by **Ruud van Ga** » Tue, 07 May 2002 21:50:41

On Sun, 05 May 2002 01:39:04 -0500, Pat Dotson

>> > The CG doesn't change with anything except a bit with fuel
>> > displacement, and ofcourse driver displacement (a good way to get more
>> > grip in a kart is to hang outwards when turning).

>> Why should this work opposite (lean out) in a kart? Does it really work
>> this way?? I have some ideas, but we haven't studied karts in detail so
>> I'm curious to hear any theories.

>I've heard a theory that road course karts that have to
>turn left and right need to unload weight from the inside
>rear tire to make the kart turn. The driver leaning
>toward the outside of the turn isn't increasing grip,
>he is reducing drag on the inside rear wheel caused by
>the solid rear axle and lack of any stagger.

Ah, that might explain it. I learned it with indoor karting; someone
suggested it to me and it seemed strange at the time. But especially
with slippery understeering karts it helped to get through the turn
with less understeer.

I then assumed it was upto the grip on the outerfront tires, but karts
are funny with their overgrippy tires (depending on the state of the
tires you really have to adjust how you drive, esp. at U-turns).

Ruud van Gaal
Free car sim: http://www.racer.nl/
Pencil art : http://www.marketgraph.nl/gallery/

by **Pat Dotso** » Wed, 08 May 2002 12:52:50

Does it sound right to say that a kart's roll center is
at the outside of the tire contact patch? Seems like
it is since there is no suspension.

I really want to try to come up with a realistic handling
kart in RACER!

--
Pat Dotson

> On Sun, 05 May 2002 01:39:04 -0500, Pat Dotson

> >> > The CG doesn't change with anything except a bit with fuel
> >> > displacement, and ofcourse driver displacement (a good way to get more
> >> > grip in a kart is to hang outwards when turning).

> >> Why should this work opposite (lean out) in a kart? Does it really work
> >> this way?? I have some ideas, but we haven't studied karts in detail so
> >> I'm curious to hear any theories.

> >I've heard a theory that road course karts that have to
> >turn left and right need to unload weight from the inside
> >rear tire to make the kart turn. The driver leaning
> >toward the outside of the turn isn't increasing grip,
> >he is reducing drag on the inside rear wheel caused by
> >the solid rear axle and lack of any stagger.

> Ah, that might explain it. I learned it with indoor karting; someone
> suggested it to me and it seemed strange at the time. But especially
> with slippery understeering karts it helped to get through the turn
> with less understeer.

> I then assumed it was upto the grip on the outerfront tires, but karts
> are funny with their overgrippy tires (depending on the state of the
> tires you really have to adjust how you drive, esp. at U-turns).

> Ruud van Gaal
> Free car sim: http://www.racer.nl/
> Pencil art : http://www.marketgraph.nl/gallery/

by **Ruud van Ga** » Wed, 08 May 2002 19:18:51

On Mon, 06 May 2002 22:52:50 -0500, Pat Dotson

>Does it sound right to say that a kart's roll center is
>at the outside of the tire contact patch? Seems like
>it is since there is no suspension.

Hm, I have no idea. I guess you can see the framework as a very stiff
suspension probably. At least the karts I drive have it seems some
kinds of sturdy plastic that's being used to connect the wheels (with
enough bumping you get extra camber because of the damage, but it
doesn't break as such).

You might see the rods connecting the wheels as the suspension, I
guess.

The very least you need to run Racer at 1000hz then (debug.ini's
timing). I found that necessary (or better) for karts and F1 cars.

Also note that the next version may use instant centers, but those are
reasonably similar to roll centers (you deduce both from the rods).

Ruud van Gaal
Free car sim: http://www.racer.nl/
Pencil art : http://www.marketgraph.nl/gallery/

by **Doug Millike** » Wed, 08 May 2002 21:24:58

Start with the easy situation of a rigid frame (not true for karts, but
useful for thinking about things) on a flat road. Then the only suspension
is the tires.

For SMALL amounts of roll, the outside tire compresses (bump travel) and
the inside tire extends (rebound travel). Since the tire spring rates are
probably about the same (for SMALL deflections) the "ride travel" will be
about equal (but opposite) on each side. So the "roll center" must be on
the ground, in the middle of the kart.

Of course this idea falls apart as soon as one wheel is (nearly) lifted off
the ground, at which point the roll center must move to somewhere near the
outside wheel (karts sometimes "bicycle"). And since the kart frame is
flexible, one end (the rear) can roll more than the other.

A "simple" vehicle is not necessarily simple to analyze...

> Does it sound right to say that a kart's roll center is
> at the outside of the tire contact patch? Seems like
> it is since there is no suspension.

> I really want to try to come up with a realistic handling
> kart in RACER!

> --
> Pat Dotson

> > On Sun, 05 May 2002 01:39:04 -0500, Pat Dotson

> > >> > The CG doesn't change with anything except a bit with fuel
> > >> > displacement, and ofcourse driver displacement (a good way to get more
> > >> > grip in a kart is to hang outwards when turning).

> > >> Why should this work opposite (lean out) in a kart? Does it really work
> > >> this way?? I have some ideas, but we haven't studied karts in detail so
> > >> I'm curious to hear any theories.

> > >I've heard a theory that road course karts that have to
> > >turn left and right need to unload weight from the inside
> > >rear tire to make the kart turn. The driver leaning
> > >toward the outside of the turn isn't increasing grip,
> > >he is reducing drag on the inside rear wheel caused by
> > >the solid rear axle and lack of any stagger.

> > Ah, that might explain it. I learned it with indoor karting; someone
> > suggested it to me and it seemed strange at the time. But especially
> > with slippery understeering karts it helped to get through the turn
> > with less understeer.

> > I then assumed it was upto the grip on the outerfront tires, but karts
> > are funny with their overgrippy tires (depending on the state of the
> > tires you really have to adjust how you drive, esp. at U-turns).

> > Ruud van Gaal
> > Free car sim: http://www.racer.nl/
> > Pencil art : http://www.marketgraph.nl/gallery/

rec.autos.simulators

Physics Questions - Weight Transfer, Tire Grip, etc.

Physics Questions - Weight Transfer, Tire Grip, etc.

Physics Questions - Weight Transfer, Tire Grip, etc.

Physics Questions - Weight Transfer, Tire Grip, etc.

Physics Questions - Weight Transfer, Tire Grip, etc.

Physics Questions - Weight Transfer, Tire Grip, etc.

Physics Questions - Weight Transfer, Tire Grip, etc.

Physics Questions - Weight Transfer, Tire Grip, etc.

Physics Questions - Weight Transfer, Tire Grip, etc.