rec.autos.simulators

by **Lindsay Adam** » Tue, 10 Nov 1998 04:00:00

I have an apology to make (and a long running debate to sellte for a few
people I suspect!!!)......

a few weeks ago one of the threads here turned to braking, and braking
distaces/ABS etc etc,

>Skidding will stop better in the dry

to which I replied...

"no it won't...... if it did ALL racers would blast up to a corner, lock the
brakes - hey presto, no overtaking under braking and shortest braking
distance...."

... as I find the whole car dynamics etc very interesting I spoke to a
friend/physics specialist/Accident investigator..... and guess what its true
shortest dry braking distance is with locked wheels. Completely uncontrolled
of course but shortest..

So.. sorry Cossie - please accept my unreserved apologies :-)

cheers

-Lindsay

by **John Walla** » Tue, 10 Nov 1998 04:00:00

I'd guess that an accident investigator will look at things from the
perspective of a road car. There is a lot of difference between a
racing tyre (which will be, or should be, at optimum temperature) and
a road tyre which will generally be cool. The reason behind the
"locked tyre stops more quickly" theory is that the act of locking the
tyre generates heat in the contact patch - this heat brings the road
tyre up toward optimum operating temperature and hence improves grip
and stopping power. The drawback being of course that the race driver
will be prepared to deal with such an event whereas the average driver
in the road would get into a world of trouble if the car locked up. On
top of that you have the increased tyre wear, possible flat-spotting,
blistering, loss of control etc.

Overall I'd say that a road tyre _may_ stop more quickly (I don't know
for sure), but with all kinds of horrible complications. A race tyre
shouldn't stop any more quickly (in fact it will be longer), and the
complications would be most unwelcome.

Cheers!
John

by **John** » Tue, 10 Nov 1998 04:00:00

You've been badly misled! Go out and try it for yourself. It's not
difficult.

>I have an apology to make (and a long running debate to sellte for a few
>people I suspect!!!)......

>a few weeks ago one of the threads here turned to braking, and braking
>distaces/ABS etc etc,

>>Skidding will stop better in the dry

>to which I replied...

>"no it won't...... if it did ALL racers would blast up to a corner, lock
the
>brakes - hey presto, no overtaking under braking and shortest braking
>distance...."

>... as I find the whole car dynamics etc very interesting I spoke to a
>friend/physics specialist/Accident investigator..... and guess what its
true
>shortest dry braking distance is with locked wheels. Completely
uncontrolled
>of course but shortest..

>So.. sorry Cossie - please accept my unreserved apologies :-)

>cheers

>-Lindsay

by **John** » Tue, 10 Nov 1998 04:00:00

To put the record straight, early ABS systems could be outperformed
(slightly) in the dry by a skilled driver using cadence braking (but of
course most people panic and lock everything up so they were still much
better in vast majority of real-life situations). Later systems with faster
responses and cycle rates are pretty much as good as the best human input.
Curiously, one of the very few times that locking your brakes actually
benefits stopping distances is in snow as the build up of snow in front of
the wheels will slow you down. This does NOT work on ice! As I said in the
first post, go try for yourself.

John Klemantaski

>I have an apology to make (and a long running debate to sellte for a few
>people I suspect!!!)......

>a few weeks ago one of the threads here turned to braking, and braking
>distaces/ABS etc etc,

>>Skidding will stop better in the dry

>to which I replied...

>"no it won't...... if it did ALL racers would blast up to a corner, lock
the
>brakes - hey presto, no overtaking under braking and shortest braking
>distance...."

>... as I find the whole car dynamics etc very interesting I spoke to a
>friend/physics specialist/Accident investigator..... and guess what its
true
>shortest dry braking distance is with locked wheels. Completely
uncontrolled
>of course but shortest..

>So.. sorry Cossie - please accept my unreserved apologies :-)

>cheers

>-Lindsay

by **Lindsay Adam** » Tue, 10 Nov 1998 04:00:00

show me.... I'm all ears :-)

--
==========================
please remove "nunspam"
to reply by email - thanx
-Lindsay
==========================

>You need to take back the appology and talk to someone who knows what they
are talking
>about. This defies the laws of Physics - Static and Kinetic friction!

by **Lindsay Adam** » Tue, 10 Nov 1998 04:00:00

I race too, and I have to say that my first reaction was that of my first
post - it sure as hell feels like the decceleration decreases (i.e. you go
faster) when you lock up the brakes - well in amy race car I've driven it
does, but according to the info I've been fed that's not so...... the quest
for knowledge continues!!!!

As you rightly say, when racing its not desireable because of all sorts of
other reasons, car balance, control, tyre wear, blistereing etc. but that's
not the issue - I'm talking of a one time stop, shortest distance possible.
Aparently the temp at the contact point doesn't matter because the contact
point is continuosly being left on the road surface (in the form of a black
line)....

I'll endevour to get some data on it, if anyone else has any - let us know !

Cheers

-Lindsay

--
==========================
please remove "nunspam"
to reply by email - thanx
-Lindsay
==========================

>>... as I find the whole car dynamics etc very interesting I spoke to a
>>friend/physics specialist/Accident investigator..... and guess what its
true
>>shortest dry braking distance is with locked wheels. Completely
uncontrolled
>>of course but shortest..

>I'd guess that an accident investigator will look at things from the
>perspective of a road car. There is a lot of difference between a
>racing tyre (which will be, or should be, at optimum temperature) and
>a road tyre which will generally be cool. The reason behind the
>"locked tyre stops more quickly" theory is that the act of locking the
>tyre generates heat in the contact patch - this heat brings the road
>tyre up toward optimum operating temperature and hence improves grip
>and stopping power. The drawback being of course that the race driver
>will be prepared to deal with such an event whereas the average driver
>in the road would get into a world of trouble if the car locked up. On
>top of that you have the increased tyre wear, possible flat-spotting,
>blistering, loss of control etc.

>Overall I'd say that a road tyre _may_ stop more quickly (I don't know
>for sure), but with all kinds of horrible complications. A race tyre
>shouldn't stop any more quickly (in fact it will be longer), and the
>complications would be most unwelcome.

>Cheers!
>John

by **Goy Larse** » Tue, 10 Nov 1998 04:00:00

> To put the record straight, early ABS systems could be outperformed
> (slightly) in the dry by a skilled driver using cadence braking (but of
> course most people panic and lock everything up so they were still much
> better in vast majority of real-life situations). Later systems with faster
> responses and cycle rates are pretty much as good as the best human input.
> Curiously, one of the very few times that locking your brakes actually
> benefits stopping distances is in snow as the build up of snow in front of
> the wheels will slow you down. This does NOT work on ice! As I said in the
> first post, go try for yourself.

It`s still possible to get shorter braking distances in the dry than
what current road-ABS gives you, they are not setup for optimum braking,
they are setup for optimum braking/stability (within that particular
sytems limits of course), hence there is a well known trick amongst
Group-N racers to eliminate about half of the pulses from the wheel to
the ABS system, thus shortenng braking distances, and let the driver
think about stability :-)

Beers and cheers
(uncle) Goy

by **Lindsay Adam** » Tue, 10 Nov 1998 04:00:00

Oh.... okay then - I take back my apology !! :-D

I've just been wandering around the net and found various references to the
fact that I was correct in my first reaction (I guess i should have checked
these first :-( ) one of them's at
http://www.tarorigin.com/art/absscuff/index.html, with loads of links from
there.

so .... I stand corrected on my correction - does that mean I'm all square
now? - or that I just have too much time on my hands :-)

later

-Lindsay

--
==========================
please remove "nunspam"
to reply by email - thanx
-Lindsay
==========================

>You need to take back the appology and talk to someone who knows what they
are talking
>about. This defies the laws of Physics - Static and Kinetic friction!

>> I have an apology to make (and a long running debate to sellte for a few
>> people I suspect!!!)......

>> a few weeks ago one of the threads here turned to braking, and braking
>> distaces/ABS etc etc,

>> >Skidding will stop better in the dry

>> to which I replied...

>> "no it won't...... if it did ALL racers would blast up to a corner, lock
the
>> brakes - hey presto, no overtaking under braking and shortest braking
>> distance...."

>> ... as I find the whole car dynamics etc very interesting I spoke to a
>> friend/physics specialist/Accident investigator..... and guess what its
true
>> shortest dry braking distance is with locked wheels. Completely
uncontrolled
>> of course but shortest..

>> So.. sorry Cossie - please accept my unreserved apologies :-)

>> cheers

>> -Lindsay

>--
> Byron Forbes
> Captain of Team Lightning Bolt

> http://members.tripod.com/~HOSHUMUNGUS

> and

> http://www.frontiernet.net/~godsoe/bolt/home.htm

by **Byron Forbe** » Wed, 11 Nov 1998 04:00:00

You need to take back the appology and talk to someone who knows what they are talking
about. This defies the laws of Physics - Static and Kinetic friction!

> I have an apology to make (and a long running debate to sellte for a few
> people I suspect!!!)......

> a few weeks ago one of the threads here turned to braking, and braking
> distaces/ABS etc etc,

> >Skidding will stop better in the dry

> to which I replied...

> "no it won't...... if it did ALL racers would blast up to a corner, lock the
> brakes - hey presto, no overtaking under braking and shortest braking
> distance...."

> ... as I find the whole car dynamics etc very interesting I spoke to a
> friend/physics specialist/Accident investigator..... and guess what its true
> shortest dry braking distance is with locked wheels. Completely uncontrolled
> of course but shortest..

> So.. sorry Cossie - please accept my unreserved apologies :-)

> cheers

> -Lindsay

--
Byron Forbes
Captain of Team Lightning Bolt

http://members.tripod.com/~HOSHUMUNGUS

and

http://www.frontiernet.net/~godsoe/bolt/home.htm

by **Cossi** » Wed, 11 Nov 1998 04:00:00

It's okay. Actually I should make my statement more clear, under certain
situation (especially at low speed) locking up would make your car stop
better in dry condition, but at high speed it would take a lot longer since
the momentum of the car is so high, it would tkae a lot longer to stop.

>I have an apology to make (and a long running debate to sellte for a few
>people I suspect!!!)......

>a few weeks ago one of the threads here turned to braking, and braking
>distaces/ABS etc etc,

>>Skidding will stop better in the dry

>to which I replied...

>"no it won't...... if it did ALL racers would blast up to a corner, lock
the
>brakes - hey presto, no overtaking under braking and shortest braking
>distance...."

>.... as I find the whole car dynamics etc very interesting I spoke to a
>friend/physics specialist/Accident investigator..... and guess what its
true
>shortest dry braking distance is with locked wheels. Completely
uncontrolled
>of course but shortest..

>So.. sorry Cossie - please accept my unreserved apologies :-)

>cheers

>-Lindsay

by **Cossi** » Wed, 11 Nov 1998 04:00:00

Try driving 2 different car (same kind, 1 with ABS and 1 without) at 30 mph,
slam on the brakes. The one without ABS will stop better in the dry for
sure..

>You need to take back the appology and talk to someone who knows what they
are talking
>about. This defies the laws of Physics - Static and Kinetic friction!

>> I have an apology to make (and a long running debate to sellte for a few
>> people I suspect!!!)......

>> a few weeks ago one of the threads here turned to braking, and braking
>> distaces/ABS etc etc,

>> >Skidding will stop better in the dry

>> to which I replied...

>> "no it won't...... if it did ALL racers would blast up to a corner, lock
the
>> brakes - hey presto, no overtaking under braking and shortest braking
>> distance...."

>> ... as I find the whole car dynamics etc very interesting I spoke to a
>> friend/physics specialist/Accident investigator..... and guess what its
true
>> shortest dry braking distance is with locked wheels. Completely
uncontrolled
>> of course but shortest..

>> So.. sorry Cossie - please accept my unreserved apologies :-)

>> cheers

>> -Lindsay

>--
> Byron Forbes
> Captain of Team Lightning Bolt

> http://members.tripod.com/~HOSHUMUNGUS

> and

> http://www.frontiernet.net/~godsoe/bolt/home.htm

by **John Walla** » Wed, 11 Nov 1998 04:00:00

On Mon, 9 Nov 1998 21:59:13 -0000, "Lindsay Adams"

>Aparently the temp at the contact point doesn't matter because the contact
>point is continuosly being left on the road surface (in the form of a black
>line)....

Everything below the contact point is rapidly going waaaay over
optimum due to friction, thermal transfer and hystersis, so even if it
is "renewed" it will still be well over optimum.

In any case, speed is reduced as momentum is converted into heat - in
the case of a locked wheel this means only the heat generated between
the contact patch of the tyre and the asphalt - the brakes are
effectively doing nothing. If the wheels are rotating then heat is
generated at both tyre/asphalt and disc/pad contact points, and speed
is scrubbed off more effectively. Add into that the fact that tyres
create optimum grip at some point between 0 and 10% slip and you can
see that a locked wheel will not be as effective.

IMO there may not be much in it - a skilled race driver in a racecar
will be able to stop more quickly by himself, but Joe Public and/or
people in road cars may stop better with tyres a'screeching.

Cheers!
John

by **Anssi Lehtin** » Wed, 11 Nov 1998 04:00:00

> "no it won't...... if it did ALL racers would blast up to a corner, lock the
> brakes - hey presto, no overtaking under braking and shortest braking
> distance...."

As you've already been told, the fastest way to stop is not locking the
brakes (in fact, it's just on the edge of locking up). However, even if
locked

PS. I think that your friend (and teachers in traffic schools at least
here in Finland) makes the approximation that most people do not know how
to brake (i.e. brake like wussies) and its better to have them lock up in
panic situations than just barely putting any pressure on the brake in
fear of locking up.

PS. Racing driver dislike lockups because they tend to make the soft tires
"square" by leaving a flat spot (thus destabilizing the car).

--
Anssi Lehtinen

by **Marc J. Nelso** » Wed, 11 Nov 1998 04:00:00

In optimum situations, what happens with the debris that's either 1) on the road
as the tire skids over it (sand, rocks, gum wrappers, whatever), or 2) the
debris that's laid down as the tire skids (marbles)? As the tire skids, does it
not tend to ride-over these unseen objects? - or does the mass of the vehicle
out-weigh the physics involved?

Seems to me that in a vacuum, the skidding tire will stop in a shorter distance
than that of a non-skidding one, but I don't recall the last time I drove in a
vacuum. I suppose though that the amount of debris under the tire is
negligible.

Just a thought - we now resume the regurlarly scheduled debate. =)

Cheers!

Marc

> Everything below the contact point is rapidly going waaaay over
> optimum due to friction, thermal transfer and hystersis, so even if it
> is "renewed" it will still be well over optimum.

> In any case, speed is reduced as momentum is converted into heat - in
> the case of a locked wheel this means only the heat generated between
> the contact patch of the tyre and the asphalt - the brakes are
> effectively doing nothing. If the wheels are rotating then heat is
> generated at both tyre/asphalt and disc/pad contact points, and speed
> is scrubbed off more effectively. Add into that the fact that tyres
> create optimum grip at some point between 0 and 10% slip and you can
> see that a locked wheel will not be as effective.

> IMO there may not be much in it - a skilled race driver in a racecar
> will be able to stop more quickly by himself, but Joe Public and/or
> people in road cars may stop better with tyres a'screeching.

> Cheers!
> John

--
Marc J. Nelson
SimRacing Online - http://www.simracing.com/

* Switch confused.net with concentric.net to reply...Confused-yet? *

by **Byron Forbe** » Wed, 11 Nov 1998 04:00:00

This is probably because the ABS is setup conservatively ie so that wheel locking
braking power is no where near reached.
The statement that a car can be stopped faster with locked wheels than otherwise
probably takes into account the average braking skill of the average motorist. And there
has been some talk of the heating effect that occurs under skidding which leads to better
grip, but I'm still very suspicious of this theory - I'd be very surprised if a heating,
skidding tyre could slow one down as well as someone who knew how to brake properly on
cold tyres. One thing's for sure - in racing applications, locking the brakes is a big no
no, and not just for flat spotting/overheating/tyre wear reasons. It's simply not as
efficient as keeping all four paws rolling!

> Try driving 2 different car (same kind, 1 with ABS and 1 without) at 30 mph,
> slam on the brakes. The one without ABS will stop better in the dry for
> sure..

> >You need to take back the appology and talk to someone who knows what they
> are talking
> >about. This defies the laws of Physics - Static and Kinetic friction!

> >> I have an apology to make (and a long running debate to sellte for a few
> >> people I suspect!!!)......

> >> a few weeks ago one of the threads here turned to braking, and braking
> >> distaces/ABS etc etc,

> >> >Skidding will stop better in the dry

> >> to which I replied...

> >> "no it won't...... if it did ALL racers would blast up to a corner, lock
> the
> >> brakes - hey presto, no overtaking under braking and shortest braking
> >> distance...."

> >> ... as I find the whole car dynamics etc very interesting I spoke to a
> >> friend/physics specialist/Accident investigator..... and guess what its
> true
> >> shortest dry braking distance is with locked wheels. Completely
> uncontrolled
> >> of course but shortest..

> >> So.. sorry Cossie - please accept my unreserved apologies :-)

> >> cheers

> >> -Lindsay

> >--
> > Byron Forbes
> > Captain of Team Lightning Bolt

> > http://members.tripod.com/~HOSHUMUNGUS

> > and

> > http://www.frontiernet.net/~godsoe/bolt/home.htm

--
Byron Forbes
Captain of Team Lightning Bolt

http://members.tripod.com/~HOSHUMUNGUS

and

http://www.frontiernet.net/~godsoe/bolt/home.htm

rec.autos.simulators

unreserved apology to Cossie

unreserved apology to Cossie

unreserved apology to Cossie

unreserved apology to Cossie

unreserved apology to Cossie

unreserved apology to Cossie

unreserved apology to Cossie

unreserved apology to Cossie

unreserved apology to Cossie

unreserved apology to Cossie

unreserved apology to Cossie

unreserved apology to Cossie

unreserved apology to Cossie

unreserved apology to Cossie

unreserved apology to Cossie

unreserved apology to Cossie