Cost of repair Audi BMW Saab...(crossposting)
#41
Guest
Posts: n/a
Re: Cost of repair Audi BMW Saab...(crossposting)
Just exactly the point I wanted to make!
> The rearwheel drive is fun and with all the electronic gimmicks it
> will really do it's job. However at a certain climb angle or even
> slipperyness of the road, the rearwheel drive gives in, then the FWD
> and then the quattro.
> The rearwheel drive is fun and with all the electronic gimmicks it
> will really do it's job. However at a certain climb angle or even
> slipperyness of the road, the rearwheel drive gives in, then the FWD
> and then the quattro.
#42
Guest
Posts: n/a
Re: Cost of repair Audi BMW Saab...(still crossposting)
> Sorry, no. This is contrary to the laws of physics. If you assume equal
> axle weights, as the car climbs it places more weight over the rear axle
and
> less over the front. So a rear wheel drive car would have an advantage
over
> a FWD in climbing. Obviously, an AWD car with the same weight and tires
> would be better than either.
You are now forgetting the most important point here, i.e., as it is
impossible to keep perfectly straight steering - for one thing nothing is
perfect, for another lateral slopes will spoil the rest of any good attempt
at this. This, in practice, in the real world, zillion light years from
where you live, means that when slippery enough and from certain climbing
angles on the RWD will start
swinging its butt so badly that no amount of wheel work will be able to
compensate in order to keep the car on the right path. If you don't
acknowledge this, it is only because you've never experienced that before.
Actually, it does happen even with Quattro, given a sufficient amount of
torque and pressure on the accelerator, and that's precisely because of your
explanation above.
When climbing under those conditions Quattro has no FWD rivals, RWD is
totally out of the question, but FWD is the easiest to handle.
> I have never found a FWD car is better than a RWD car in the snow in
> general. The reason people think that is because at the point that they
> *do* lose traction (and they all will eventually), it is easier for the
> inexperienced troglodyte driver to control the FWD's inherent front end
> plowing understeer than the RWD, which can be made to either under or over
> steer with judicious input on the fun pedal.
The reason FWD is way more effective on slippery ground than RWD can be read
in my previous point. Any attempt at countering this would suggest a
tremendous lack of hands-on experience.
> axle weights, as the car climbs it places more weight over the rear axle
and
> less over the front. So a rear wheel drive car would have an advantage
over
> a FWD in climbing. Obviously, an AWD car with the same weight and tires
> would be better than either.
You are now forgetting the most important point here, i.e., as it is
impossible to keep perfectly straight steering - for one thing nothing is
perfect, for another lateral slopes will spoil the rest of any good attempt
at this. This, in practice, in the real world, zillion light years from
where you live, means that when slippery enough and from certain climbing
angles on the RWD will start
swinging its butt so badly that no amount of wheel work will be able to
compensate in order to keep the car on the right path. If you don't
acknowledge this, it is only because you've never experienced that before.
Actually, it does happen even with Quattro, given a sufficient amount of
torque and pressure on the accelerator, and that's precisely because of your
explanation above.
When climbing under those conditions Quattro has no FWD rivals, RWD is
totally out of the question, but FWD is the easiest to handle.
> I have never found a FWD car is better than a RWD car in the snow in
> general. The reason people think that is because at the point that they
> *do* lose traction (and they all will eventually), it is easier for the
> inexperienced troglodyte driver to control the FWD's inherent front end
> plowing understeer than the RWD, which can be made to either under or over
> steer with judicious input on the fun pedal.
The reason FWD is way more effective on slippery ground than RWD can be read
in my previous point. Any attempt at countering this would suggest a
tremendous lack of hands-on experience.
#43
Guest
Posts: n/a
Re: Cost of repair Audi BMW Saab...(crossposting)
> > But you will need to replace the rear ones much more often, if you enjoy
> > spirited driving on winding roads, that is. We all know it is winding
> roads
> > that are good fun.
>
> And the front-driver SAABs (and Audis, for that matter) will have to
> have their front tires replaced more often than their rears. Even.
Well, Floyd, my argument does not hold true for your 330xi, but the point is
that RWD will render their rear tyres unusable much faster than Quattro will
render either front or rear or both, that's simply because any burst of
acceleration is evenly distributed. You know the worst for tyre life is
drift spinning, and that's the only thing I envy from those driving BMW
RWDs. Of course I must concede RWD on the dry is way better fun than either
FWD or Quattro.
> > I have a set of fully dedicated winter Vredesteins to be able to enjoy
my
> > quattro in the winter, and a set of Sport Contact 2 that my car is
already
> > "wearing" now.
>
> And I have a set of Michelin Pilot Alpines for my 330xi for winter.
> A guy in an S4, parked next to me last winter, said he almost didn't
> make it up the ski hill's road. I said: "get rid of the PZeros."
He certainly wouldn't if he'd been driving an RWD.
JP Roberts
> > spirited driving on winding roads, that is. We all know it is winding
> roads
> > that are good fun.
>
> And the front-driver SAABs (and Audis, for that matter) will have to
> have their front tires replaced more often than their rears. Even.
Well, Floyd, my argument does not hold true for your 330xi, but the point is
that RWD will render their rear tyres unusable much faster than Quattro will
render either front or rear or both, that's simply because any burst of
acceleration is evenly distributed. You know the worst for tyre life is
drift spinning, and that's the only thing I envy from those driving BMW
RWDs. Of course I must concede RWD on the dry is way better fun than either
FWD or Quattro.
> > I have a set of fully dedicated winter Vredesteins to be able to enjoy
my
> > quattro in the winter, and a set of Sport Contact 2 that my car is
already
> > "wearing" now.
>
> And I have a set of Michelin Pilot Alpines for my 330xi for winter.
> A guy in an S4, parked next to me last winter, said he almost didn't
> make it up the ski hill's road. I said: "get rid of the PZeros."
He certainly wouldn't if he'd been driving an RWD.
JP Roberts
#44
Guest
Posts: n/a
Re: Cost of repair Audi BMW Saab...(still crossposting)
"Fred W." <Fred.Wills@allspam myrealbox.com> wrote:
>> The rearwheel drive is fun and with all the electronic gimmicks it
>> will really do it's job. However at a certain climb angle or even
>> slipperyness of the road, the rearwheel drive gives in, then the FWD
>> and then the quattro.
>>
>
>Sorry, no. This is contrary to the laws of physics. If you assume equal
>axle weights, as the car climbs it places more weight over the rear axle and
>less over the front. So a rear wheel drive car would have an advantage over
>a FWD in climbing. Obviously, an AWD car with the same weight and tires
>would be better than either.
You almost got me there
This is going to be a bit longer:
There's sort of a thinking error in your statement. It took me a while
to do the math (i.e. mechanics) but the outcome is, that the ratio
front/rear with regard to the friction force does _not_ change.
Let me elaborate:
The friction is depending on two parameters (yes, this is a
simplification for tires, but it's valid in all cases so bear with
with me): the friction coefficient µ and the force _orthogonal_ to the
surface. The formula for the friction force is Ff = Fn x µ.
The force pressing the car down onto the tarmac in this case is the
mass of the car x g (the earht acceleration 9,81) so you got Fn = mass
x 9,81
Now if you have the car on a level surface and assume a 50/50
distribution then the orthogonal force per tire is basically a quarter
of the Fn. So the result would be Fn/4 x µ.
The |
V indicates the direction of Fn
____
__/ | \__
|_ __V___ _|
____U______U_____
So far so good.
Now the worst case example:
Tilt the road and car 90° (don't sit in the car).
__
| | |
|C \
| | |
| | |
|C /
| |_|
In this case, the car would have to be held by something else, because
for Fr = µ x 0. I.e. there is no acceleration towards the tarmac and
so there is no resulting orthogonal force pressing the tires to the
tarmac and therefore no Friction. The car would slide.
So if you choose increasing angles between 0 and 90°, the orthogonal
force down on the tarmac slowly decreases on all four tires and is
gradually "converted" into a force wanting to push the car
"backwards".
But again, for all tires.
The core message is that the friction force is slowly reduced but
equally on both front and rear tires as long as you don't change the
center of gravity.
Ok, now most likely I have made a complete fool out of myself, but if
you are in doubt, then imagine a 90° sloped road. You'd need to
support the car on the trunk because there is absolutely no way the
tires would be able to hold the car in that position
In your theory, there would be a 100% load on the rear wheels and the
car could still go.
I'd be curious to learn if I am really wrong. Mathematically and
physically I mean.
>plowing understeer than the RWD, which can be made to either under or over
>steer with judicious input on the fun pedal.
I agree. But getting away from a standstill is easier with the FWD
because the RWD just slips sideways if it looses traction and you
can't steer the direction vector.
>-Fred W
>
Regards
Wolfgang
--
1999 Audi A6 Avant TDI
>> The rearwheel drive is fun and with all the electronic gimmicks it
>> will really do it's job. However at a certain climb angle or even
>> slipperyness of the road, the rearwheel drive gives in, then the FWD
>> and then the quattro.
>>
>
>Sorry, no. This is contrary to the laws of physics. If you assume equal
>axle weights, as the car climbs it places more weight over the rear axle and
>less over the front. So a rear wheel drive car would have an advantage over
>a FWD in climbing. Obviously, an AWD car with the same weight and tires
>would be better than either.
You almost got me there
This is going to be a bit longer:
There's sort of a thinking error in your statement. It took me a while
to do the math (i.e. mechanics) but the outcome is, that the ratio
front/rear with regard to the friction force does _not_ change.
Let me elaborate:
The friction is depending on two parameters (yes, this is a
simplification for tires, but it's valid in all cases so bear with
with me): the friction coefficient µ and the force _orthogonal_ to the
surface. The formula for the friction force is Ff = Fn x µ.
The force pressing the car down onto the tarmac in this case is the
mass of the car x g (the earht acceleration 9,81) so you got Fn = mass
x 9,81
Now if you have the car on a level surface and assume a 50/50
distribution then the orthogonal force per tire is basically a quarter
of the Fn. So the result would be Fn/4 x µ.
The |
V indicates the direction of Fn
____
__/ | \__
|_ __V___ _|
____U______U_____
So far so good.
Now the worst case example:
Tilt the road and car 90° (don't sit in the car).
__
| | |
|C \
| | |
| | |
|C /
| |_|
In this case, the car would have to be held by something else, because
for Fr = µ x 0. I.e. there is no acceleration towards the tarmac and
so there is no resulting orthogonal force pressing the tires to the
tarmac and therefore no Friction. The car would slide.
So if you choose increasing angles between 0 and 90°, the orthogonal
force down on the tarmac slowly decreases on all four tires and is
gradually "converted" into a force wanting to push the car
"backwards".
But again, for all tires.
The core message is that the friction force is slowly reduced but
equally on both front and rear tires as long as you don't change the
center of gravity.
Ok, now most likely I have made a complete fool out of myself, but if
you are in doubt, then imagine a 90° sloped road. You'd need to
support the car on the trunk because there is absolutely no way the
tires would be able to hold the car in that position
In your theory, there would be a 100% load on the rear wheels and the
car could still go.
I'd be curious to learn if I am really wrong. Mathematically and
physically I mean.
>plowing understeer than the RWD, which can be made to either under or over
>steer with judicious input on the fun pedal.
I agree. But getting away from a standstill is easier with the FWD
because the RWD just slips sideways if it looses traction and you
can't steer the direction vector.
>-Fred W
>
Regards
Wolfgang
--
1999 Audi A6 Avant TDI
#45
Guest
Posts: n/a
Re: Cost of repair Audi BMW Saab...(still crossposting)
Fred W. wrote:
> "Wolfgang Pawlinetz" <w.pawlinetz@a1.net> wrote in message
> news:5qp1a0teb17een67eish24ov5r9hq33j41@4ax.com...
>> Imad Al-Ghouleh schrieb:
>>
>>> I dont know why people keep insisting that BMW is bad in winter.
>>
>> Because it is. Especially compared to a FWD saab or a quattro Audi.
>>
>>
>> BTDT.
>>
>> The rearwheel drive is fun and with all the electronic gimmicks it
>> will really do it's job. However at a certain climb angle or even
>> slipperyness of the road, the rearwheel drive gives in, then the FWD
>> and then the quattro.
>>
>
> Sorry, no. This is contrary to the laws of physics. If you assume
> equal axle weights, as the car climbs it places more weight over the
> rear axle and less over the front. So a rear wheel drive car would
> have an advantage over a FWD in climbing. Obviously, an AWD car with
> the same weight and tires would be better than either.
This is true.
> I have never found a FWD car is better than a RWD car in the snow in
> general. The reason people think that is because at the point that
> they *do* lose traction (and they all will eventually), it is easier
> for the inexperienced troglodyte driver to control the FWD's inherent
> front end plowing understeer than the RWD, which can be made to
> either under or over steer with judicious input on the fun pedal.
I think you're right. The best handling snow car I ever had or drove was my
Alfa GTV6 -- w/ RWD. I liked it even better than the original Audi Quattro --
which had gobs of traction, but wasn't particularly nimble. The only problems
the Alfa had in winter were low ground clearance, and a poor defroster.
My old 2002 never kept me from getting first tracks on a powder day, or home in
time afterward. I drove right past plenty of 4WD cars stuck in snowbanks and
ditches.
Around here we have ice storms, which are so bad it's dangerous to walk. Yet
somehow the old farmers manage to get by in their old pickup trucks, without
yuppie 4WD or highfalutin' Finnish winter tires. We're talking bargain basement
1982 Ford Rangers and Toyotas. Geez, how did people get around before Quattros
and Xi-s?
Matt O.
> "Wolfgang Pawlinetz" <w.pawlinetz@a1.net> wrote in message
> news:5qp1a0teb17een67eish24ov5r9hq33j41@4ax.com...
>> Imad Al-Ghouleh schrieb:
>>
>>> I dont know why people keep insisting that BMW is bad in winter.
>>
>> Because it is. Especially compared to a FWD saab or a quattro Audi.
>>
>>
>> BTDT.
>>
>> The rearwheel drive is fun and with all the electronic gimmicks it
>> will really do it's job. However at a certain climb angle or even
>> slipperyness of the road, the rearwheel drive gives in, then the FWD
>> and then the quattro.
>>
>
> Sorry, no. This is contrary to the laws of physics. If you assume
> equal axle weights, as the car climbs it places more weight over the
> rear axle and less over the front. So a rear wheel drive car would
> have an advantage over a FWD in climbing. Obviously, an AWD car with
> the same weight and tires would be better than either.
This is true.
> I have never found a FWD car is better than a RWD car in the snow in
> general. The reason people think that is because at the point that
> they *do* lose traction (and they all will eventually), it is easier
> for the inexperienced troglodyte driver to control the FWD's inherent
> front end plowing understeer than the RWD, which can be made to
> either under or over steer with judicious input on the fun pedal.
I think you're right. The best handling snow car I ever had or drove was my
Alfa GTV6 -- w/ RWD. I liked it even better than the original Audi Quattro --
which had gobs of traction, but wasn't particularly nimble. The only problems
the Alfa had in winter were low ground clearance, and a poor defroster.
My old 2002 never kept me from getting first tracks on a powder day, or home in
time afterward. I drove right past plenty of 4WD cars stuck in snowbanks and
ditches.
Around here we have ice storms, which are so bad it's dangerous to walk. Yet
somehow the old farmers manage to get by in their old pickup trucks, without
yuppie 4WD or highfalutin' Finnish winter tires. We're talking bargain basement
1982 Ford Rangers and Toyotas. Geez, how did people get around before Quattros
and Xi-s?
Matt O.
#46
Guest
Posts: n/a
Re: Cost of repair Audi BMW Saab...(still crossposting)
Wolfgang Pawlinetz wrote:
> The core message is that the friction force is slowly reduced but
> equally on both front and rear tires as long as you don't change the
> center of gravity.
>
> Ok, now most likely I have made a complete fool out of myself, but if
> you are in doubt, then imagine a 90° sloped road. You'd need to
> support the car on the trunk because there is absolutely no way the
> tires would be able to hold the car in that position
>
> In your theory, there would be a 100% load on the rear wheels and the
> car could still go.
>
> I'd be curious to learn if I am really wrong. Mathematically and
> physically I mean.
Not a bad try, but you're missing the key factor: Torque. Since the
center of gravity is NOT on the road, it has a torque arm to the point
of contact of the tires. The SUM of the forces on the contact area is
as you worked out, but it doesn't remain 50/50 front/rear since the rear
axle is providing a counter-clockwise (if viewed as in your drawing)
torque while the front axle can only provide a clockwise torque. To
reach rotational equilibrium more of the weight force in on the rear
axle. It's the same reason that your car will nosedive under braking
and lift the front end under acceleration.
> I agree. But getting away from a standstill is easier with the FWD
> because the RWD just slips sideways if it looses traction and you
> can't steer the direction vector.
If FWD slips you can't steer either, it's just that most FWD cars have
a front weight bias (due to having the engine, transmission, and other
such bits up front) so you have more traction all other things being equal.
Bill
> The core message is that the friction force is slowly reduced but
> equally on both front and rear tires as long as you don't change the
> center of gravity.
>
> Ok, now most likely I have made a complete fool out of myself, but if
> you are in doubt, then imagine a 90° sloped road. You'd need to
> support the car on the trunk because there is absolutely no way the
> tires would be able to hold the car in that position
>
> In your theory, there would be a 100% load on the rear wheels and the
> car could still go.
>
> I'd be curious to learn if I am really wrong. Mathematically and
> physically I mean.
Not a bad try, but you're missing the key factor: Torque. Since the
center of gravity is NOT on the road, it has a torque arm to the point
of contact of the tires. The SUM of the forces on the contact area is
as you worked out, but it doesn't remain 50/50 front/rear since the rear
axle is providing a counter-clockwise (if viewed as in your drawing)
torque while the front axle can only provide a clockwise torque. To
reach rotational equilibrium more of the weight force in on the rear
axle. It's the same reason that your car will nosedive under braking
and lift the front end under acceleration.
> I agree. But getting away from a standstill is easier with the FWD
> because the RWD just slips sideways if it looses traction and you
> can't steer the direction vector.
If FWD slips you can't steer either, it's just that most FWD cars have
a front weight bias (due to having the engine, transmission, and other
such bits up front) so you have more traction all other things being equal.
Bill
#47
Guest
Posts: n/a
Re: Cost of repair Audi BMW Saab...(still crossposting)
> [physics discussion]
Momentum, forces... one should forbid phsyics students to ever read the
internet and see the ways their science is abused for biased arguments...
In my opinion, the most important driving aspect of FWD in the snow is that
traction and steering are intimately connected, which makes the car very
intuitive to drive. You can make either concept drive relaitvely well in the
snow, and there are also examples for FWD that are undriveable in the snow.
From anecdotical experience, while I lived in Germany, when a lot of snow
fell I would never drive the BMW 320ci, it was very hard to drive, and
mpossible to drive of summer tires. We also owned a cheap FWD Fiat Uno, and
that car was a darling in the snow, you always felt what it was doing
because the steering would feel connected to your hands, the BMW would
regularly totally lose steering feel and you felt like you were just
helpless. Downright scary, and twice when surprise by snow it was a miracle
I made the journey from work to home (both in the city, 8 miles apart) in
one piece.
There is no dount in my mindthe Saab is a very soothing bad weather car.
It's my number one choice for being caught in a bad storm, and we also have
a 4x4 SUV. The more it rains, the more it feels like it steers on tramlines.
And don't be misled by the sunny California thing, we have some pretty awful
storms here every once in a while that invariably hit when you're away from
home and have no choice but heading back.
....pablo
#48
Guest
Posts: n/a
Re: Cost of repair Audi BMW Saab...(still crossposting)
On Tue, 11 May 2004 23:57:11 GMT, Bill Bradley
<senator2@NOSPAMearthlink.net> wrote:
> If FWD slips you can't steer either, it's just that most FWD cars have
>a front weight bias (due to having the engine, transmission, and other
>such bits up front) so you have more traction all other things being equal.
>
The point exactly - and the reason FWD has an advantage over RWD (in
general, you can always find exceptions). Most FWD cars have less than
optimal weight distribution with a front bias. This is a feature in
the snow (probably for acceleration too as it helps fight the FWD
front end lift issue).
Give me a RWD car for *limit* handling. Give me a FWD car for snow.
<senator2@NOSPAMearthlink.net> wrote:
> If FWD slips you can't steer either, it's just that most FWD cars have
>a front weight bias (due to having the engine, transmission, and other
>such bits up front) so you have more traction all other things being equal.
>
The point exactly - and the reason FWD has an advantage over RWD (in
general, you can always find exceptions). Most FWD cars have less than
optimal weight distribution with a front bias. This is a feature in
the snow (probably for acceleration too as it helps fight the FWD
front end lift issue).
Give me a RWD car for *limit* handling. Give me a FWD car for snow.
#49
Guest
Posts: n/a
Re: Cost of repair Audi BMW Saab...(crossposting)
On Tue, 11 May 2004 15:14:15 +0200, Peter Bozz
<fake-user@fake.email.address> wrote:
>The top selling cars in Holland in 2003 were:
> 2. Peugeot (52.412 exemplaren)
> 3. Renault (47.159 nieuwe auto's)
You mean someone outside of France buys those Frenchy cars? Wow.
<fake-user@fake.email.address> wrote:
>The top selling cars in Holland in 2003 were:
> 2. Peugeot (52.412 exemplaren)
> 3. Renault (47.159 nieuwe auto's)
You mean someone outside of France buys those Frenchy cars? Wow.
#50
Guest
Posts: n/a
Re: Cost of repair Audi BMW Saab...(still crossposting)
"-Bob-" <uctraingNOSPAM@ultranet.com> wrote in message
news:l4v2a05mn8v0viiu35ri5m805r19bd7rm9@4ax.com...
> On Tue, 11 May 2004 23:57:11 GMT, Bill Bradley
> <senator2@NOSPAMearthlink.net> wrote:
>
> > If FWD slips you can't steer either, it's just that most FWD cars have
> >a front weight bias (due to having the engine, transmission, and other
> >such bits up front) so you have more traction all other things being
equal.
> >
>
> The point exactly - and the reason FWD has an advantage over RWD (in
> general, you can always find exceptions). Most FWD cars have less than
> optimal weight distribution with a front bias. This is a feature in
> the snow (probably for acceleration too as it helps fight the FWD
> front end lift issue).
>
> Give me a RWD car for *limit* handling. Give me a FWD car for snow.
Or a viscous AWD car for both.
-Russ.
'88 iX