RE: braking 101 (short)

[Eaton Dave <dave.eaton@minedu.govt.nz>]

200 lines to read.  sigh....

> Date: Wed, 21 Oct 1998 12:10:11 EDT
> From: QSHIPQ@aol.com
> 
> >flame bait to one side.....
> 
> >"on corner entry" meant just that.  not (power on) cornering.  throttle
lift
> >going into the corner.  in this "mode" the braking torque to the front
> >wheels is *increased* (rotating at higher speed), and the braking torque
to
> >the rears are decreased (rotating at a lower speed)...
> 
> Reread that statement.  Are you sure you have this correct?  If the front
> wheels are rotating faster than the rears, where does engine braking
Torsen
> Trg go?   

yes i'm sure scott.  the torsen under "coast" throttle conditions does *not*
act the way it does under acceleration.  you need to re-visit the theory of
operation.  the maths on the bias ratio under braking (coast throttle) is
interesting.  the zexel folks spent  a lot of time to ensure that the torsen
shifted torque under coast throttle conditons.  once again, happy to supply
references since you're clearly struggling here...

> 
> >the point is that the quattro with torsen is able to *remove* engine
braking
> >force from the rears.  this has 2 effects: -
> >1) putting more engine braking through the tyres in the front where the
best
> >adhesion is, and
> >2) leaving more rear tyre adhesion for braking.
> 
> 1)  Sounds good, would you want that if the maximum braking weight
> distribution is 50/50 in the quattro?   What would you need to do to get a
> better actual braking distribution?   What does this mean to those
considering
> springs and braking upgrades to their quattros?  Those with proportioning
> valves?  Those with ABS?  Those with ABS and Torsens?  What does an open
diff
> do with engine Trg and braking?  2)  Given that total braking in the back
is
> - -/= 22% in a quattro, you need ALL the "more rear tyre adhesion for
braking"
> you can get.  I'm with you all the way here.  
> 
> However Mr. Ilkays' point remains.  Mass of quattro (all other things
being
> equal), and where that mass is.  Translate this to a street quattro, it
can
> only send 22% of it's braking force to the rear of the car, this point
becomes
> lost in the mass of the car (and the corresponding lack of mass in the
rear
> brakes).  Add to this, a street car has ABS, both the rwd and the awd car
will
> brake as close to the ideal as the hardware and weight distribution
permits.
> That's a loss to a front heavy abs car with tiny rear brakes when compared
to
> a more evenly distributed rwd car.  
> 

no, once again you're missing the point.  the point is that the quattro
sends less engine braking torque to the rear leaving more rear traction for
actual braking.  this is a win.  references from zexel are numerous. look
them up.

> 
> No, in "coast" mode there is no differentiation, that's 50f/50 r, that's
U.
> If the rear goes into O the torsen will not "remove" (sic) torque from the
> rear until the rear DRIVESHAFT (the ones between the f & r diffs) is
spinning
> as or faster than the front. 

wrong.   once again you don't know how a torsen operates.  mind you there
are various models and they do have some different features.

> 
> >so, by definition better awd braking than a locked centre car (forced to
> >send 50% braking torque rearwards), and less propensity to snap oversteer
> >than the generation 1 car.
> 
> Incorrect statement.  See above.  What happens when the fr/r braking
> distribution exceeds 22%r?  Like in a 90q under braking.  Dave, not sure
this
> is worth discussing yet.  You don't understand chassis dynamics and
braking.
> No big deal, it just makes for a tough discussion.   You don't have the
basics
> yet.
> 
yada yada yada....

[snip a hundred lines]

one final statistic: once again, sorry to let the facts get in the way of a
good meaningless discussion, but what do you think is the reason that the
new s4 brakes better than the e36 euro m3 evo 2 (source autocar 60mph to 0
statistics)?  

luck perhaps?  flaky stopwatches?  myopia?

end of discussion...

dave
'95 rs2
'90 ur-q