Left foot braking

Alan Baker wrote:
> In article .com>,
> "Motorhead Lawyer" > wrote:
>
> > Chris V wrote:
> > > Typically this is used in a car that has understeer normally, but has
> > > trailing throttle oversteer (i.e. tends to rotate or spin when you let
> > > off the gas in a corner). Most FWD cars tend to be this way, and some
> > > RWD cars.
> >
> > Sounds like you need to learn a lot more about TTO. I know of *no* FWD
> > cars that will do it. Semi-trailing arm RWD cars (Porsche 911, older
> > BMWs) do, but generally only at higher speeds.
>
> Every car has the same phenomenon. It's just that on some the tendency
> is completely masked by the incredible amount of understeer in normal
> circumstances...

[Don't know why you're deciding to argue with *me* about this; I
thought you were correct - before.]

TTO is not a description of a *tendency*; it is an *effect*. A car
either understeers, oversteers, or it is neutral. A *tendency toward*
one of those from another does not change the *effect* unless it
*exceeds* that tendency. Trailing throttle OVERSTEER is not *partly
mitigated understeer*; it is OVERSTEER. FWD cars don't do it. BMW
E21s and E28s do.

> > > By using left foot braking, you tend to slow into the corner, leaving
> > > one foot slightly on the brake to drag the rears and throw weight
> > > forward, and at the same time get on teh throttle early.
> >
> > None of which follows from what you describe. Slight drag not only
> > does not "throw weight forward"; it allows it to stay rearward as much
> > as at a steady speed equilibrium. Getting on the throttle early then
> > totally negates it by throwing weight *rearward*.
>
> And braking causes weight to be transferred forward. It is an inevitable
> consequence of applying the force below the centre of mass.

Gee; and F=ma. So what? If the braking (negative 'a') approaches
zero, then so does F. Weight transfer with minimal braking is minimal.

> > > By staying on
> > > the throttle through the corner, and modulating the brake with your
> > > left foot, you can mitigate teh throttle on understeer by using the
> > > trail braking oversteer and get a nice, neutral line that can change
> > > easily from a little more of one or the other depending on need in a
> > > particualr corner like a decreasing radius).
> >
> > Maybe you can reproduce all this fine analysis in a wild, sideways,
> > gravel-covered rally slide, but on pavement, it just doesn't work well.
>
> Also, you can achieve the same effect for the most part by simply
> modulating the throttle from engine braking, to no acceleration, to
> acceleration...

Try that in Turn 5 at Road America ...
--
C.R. Krieger
(Been there; drove that)

In article .com>,
"Motorhead Lawyer" > wrote:

> Alan Baker wrote:
> > In article .com>,
> > "Motorhead Lawyer" > wrote:
> >
> > > Chris V wrote:
> > > > Typically this is used in a car that has understeer normally, but has
> > > > trailing throttle oversteer (i.e. tends to rotate or spin when you let
> > > > off the gas in a corner). Most FWD cars tend to be this way, and some
> > > > RWD cars.
> > >
> > > Sounds like you need to learn a lot more about TTO. I know of *no* FWD
> > > cars that will do it. Semi-trailing arm RWD cars (Porsche 911, older
> > > BMWs) do, but generally only at higher speeds.
> >
> > Every car has the same phenomenon. It's just that on some the tendency
> > is completely masked by the incredible amount of understeer in normal
> > circumstances...
>
> [Don't know why you're deciding to argue with *me* about this; I
> thought you were correct - before.]
>
> TTO is not a description of a *tendency*; it is an *effect*. A car
> either understeers, oversteers, or it is neutral. A *tendency toward*
> one of those from another does not change the *effect* unless it
> *exceeds* that tendency. Trailing throttle OVERSTEER is not *partly
> mitigated understeer*; it is OVERSTEER. FWD cars don't do it. BMW
> E21s and E28s do.

And if you are putting enough steering input into a vehicle that doesn't
do it under more moderate inputs, it can suddenly do it too.

>
> > > > By using left foot braking, you tend to slow into the corner, leaving
> > > > one foot slightly on the brake to drag the rears and throw weight
> > > > forward, and at the same time get on teh throttle early.
> > >
> > > None of which follows from what you describe. Slight drag not only
> > > does not "throw weight forward"; it allows it to stay rearward as much
> > > as at a steady speed equilibrium. Getting on the throttle early then
> > > totally negates it by throwing weight *rearward*.
> >
> > And braking causes weight to be transferred forward. It is an inevitable
> > consequence of applying the force below the centre of mass.
>
> Gee; and F=ma. So what? If the braking (negative 'a') approaches
> zero, then so does F. Weight transfer with minimal braking is minimal.
>
> > > > By staying on
> > > > the throttle through the corner, and modulating the brake with your
> > > > left foot, you can mitigate teh throttle on understeer by using the
> > > > trail braking oversteer and get a nice, neutral line that can change
> > > > easily from a little more of one or the other depending on need in a
> > > > particualr corner like a decreasing radius).
> > >
> > > Maybe you can reproduce all this fine analysis in a wild, sideways,
> > > gravel-covered rally slide, but on pavement, it just doesn't work well.
> >
> > Also, you can achieve the same effect for the most part by simply
> > modulating the throttle from engine braking, to no acceleration, to
> > acceleration...
>
> Try that in Turn 5 at Road America ...
> --
> C.R. Krieger
> (Been there; drove that)

--
Alan Baker
Vancouver, British Columbia
"If you raise the ceiling 4 feet, move the fireplace from that wall
to that wall, you'll still only get the full stereophonic effect
if you sit in the bottom of that cupboard."

Alan Baker wrote:
> In article .com>,
> "Motorhead Lawyer" > wrote:

> > TTO is not a description of a *tendency*; it is an *effect*. A car
> > either understeers, oversteers, or it is neutral. A *tendency toward*
> > one of those from another does not change the *effect* unless it
> > *exceeds* that tendency. Trailing throttle OVERSTEER is not *partly
> > mitigated understeer*; it is OVERSTEER. FWD cars don't do it. BMW
> > E21s and E28s do.
>
> And if you are putting enough steering input into a vehicle that doesn't
> do it under more moderate inputs, it can suddenly do it too.

Only if the car is already oversteering can you produce more oversteer
by changing steering input. There are only two possible steering
inputs: more (into the turn) or less (away from the turn). Here's the
effect these have:

If the car is oversteering, less input (what would be called
'countersteer') is required to keep the car on line. More input (into
the turn) will increase oversteer and is likely to spin the car.

If the car is understeering (as all FWDs do - it's the nature of the
beast), less steering input will straighten the car but it will *not*
produce oversteer (unless it's a gross overcorrection that swings the
car the opposite direction, but I'm talking about fine corrections
here, not spectacular and useless mistakes). Likewise, *more* steering
input will not produce oversteer; it will produce *more* understeer.
--
C.R. Krieger
(Been there; drove that)