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Cost of repair Audi BMW Saab...(still crossposting)



 
 
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  #11  
Old May 12th 04, 04:23 PM
Michael Burman
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Bill Bradley wrote:
> That same front weight bias makes FWD more likely to spin out when
> cornering or braking. I won't call that an "exception" just a trade-off.


I'd say a RWD would spin out easier, because the amount of power you
push to backwheels when they don't have grip. Car starts going sideways.
Now that's a feature I just love with snow, ice and uphill. Our BMW
(althought Compact) won't go anywhere, it's stuck. Tyres just spin, spin
, spin and spin. Our MB with limited differential on the back, will also
make tyres spin, then lock and then.. nothing. It's stuck also.

In same situation, our Toyota & Audi go forward, because they have grip
in the snow/ice. Each of the cars have spiked wintertyres, yet they
won't make miracles if there isn't enough weight on the back.

And it's also always nice to help taxis which use MB in the winter
conditions, when it's been snowing a lot, they're stuck also. "c'mon
passengers, help me a bit, push the car".

Nothing beats AWD, but FWD is a lot better in winter conditions, you
don't get stuck. Whatever happens at the limit is usually pointless.
When the weather is bad, you drive according to it. But there's no
helping if the car won't move.

- Yak
Ads
  #12  
Old May 12th 04, 04:35 PM
C.R. Krieger
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Wolfgang Pawlinetz > wrote in message >. ..
> "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.


You should be saying "AWD", not "Quattro", as that covers *only* Audi,
and it is well-known that BMW and others *also* build AWD cars.

> >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.

>
> You almost got me there :-)


No; he *does* have you there.

> 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.


Yeah; it does.

>
> 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 /
> | |_|


What you overlooked is the *practical* 'worst case example': 45
degrees. [This assumes that the tires can generate 1.0g of tractive
force, otherwise the car slides down the slope.] Notice, at 45
degrees, where the CoG is. Depending on how high above the surface it
lies, it could come to rest directly *over* the rear axle (even
*behind it* in a tall or rear-heavy vehicle). At any rate, as long as
it *is* above the surface, it will shift *toward* the rear axle as the
angle increases. If you want a simple demonstration of this, think
about moving a refrigerator. Lying on its side, the top part could be
pretty heavy, but as you tilt it up, the upper end becomes lighter and
lighter until you have shifted the CoG past the point where the bottom
edge is on the floor. Then, the top side weight becomes *negative*
and the thing falls over the other way. Therefore, a slope *does*
influence the amount of weight (and traction) on the wheels on each
end of the car, even if it's sitting still.
--
C.R. Krieger
(Been there; dropped that)
  #13  
Old May 12th 04, 05:47 PM
Fred W.
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"Wolfgang Pawlinetz" > wrote in message
...
> "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.


<snipped a whole bunch of stuff>

No, the weight distribution (front/rear) will most certainly change as a)
the car is tilted on the longitudinal axis and b) when accelerating.

-Fred W


  #14  
Old May 12th 04, 05:59 PM
Fred W.
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"Matt O'Toole" > wrote in message
...
> Geez, how did people get around before Quattros and Xi-s?


Ummm, slowly?

Seriously. Any FWD, RWD or AWD (*including* Quattro) can be made to go
quite nicely in snow when the right tires are put on them. The rest is just
varying dgrees of confidence at incremental speeds.

Some prefer the front weight biased FWD which is sort of a point and shoot
dart approach.
Others (myself included) prefer the rear driven, power-sliding cart before
the horse.
And yet a third category wouldn't be caught dead without their full time AWD
pulling from both ends.

It's all preference and none are completely superior. As in all things in
life, it is a matter of balancing trade-offs.

-Fred W


  #15  
Old May 12th 04, 06:07 PM
Dave Hinz
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On Wed, 12 May 2004 12:59:33 -0400, Fred W. <Fred.Wills@allspam> wrote:
>
>
> Some prefer the front weight biased FWD which is sort of a point and shoot
> dart approach.
> Others (myself included) prefer the rear driven, power-sliding cart before
> the horse.
> And yet a third category wouldn't be caught dead without their full time AWD
> pulling from both ends.


Then there are the fourth category, who buy all-season tires which
suck equally in all conditions, and probably don't know _which_ of
their wheels are responsible for moving the car around. With the wrong
tires, where the drive wheels are doesn't matter.

> It's all preference and none are completely superior. As in all things in
> life, it is a matter of balancing trade-offs.


Yup. By the way, do I know you from another place, Fred?

Dave Hinz


  #16  
Old May 12th 04, 08:20 PM
Wolfgang Pawlinetz
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C.R. Krieger wrote:

>Yeah; it does.




Regards

Wolfgang

--
1999 Audi A6 Avant TDI
  #17  
Old May 12th 04, 08:20 PM
Wolfgang Pawlinetz
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"Fred W." <Fred.Wills@allspam myrealbox.com> wrote:

>No, the weight distribution (front/rear) will most certainly change as a)
>the car is tilted on the longitudinal axis and b) when accelerating.


Say folks, do you read the thread?

I already said you were right.

>-Fred W


Regards

Wolfgang

--
1999 Audi A6 Avant TDI
  #18  
Old May 12th 04, 10:36 PM
Dori A Schmetterling
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I don't, so there...

But maybe I hate formatted e-mails...

;-)
DAS
--
For direct contact replace nospam with schmetterling
---

"Somebody" > wrote in message
...

..... Honestly I hate top posts. Just scroll down to see the rest of the
converstation framed in html)
[...........]


  #19  
Old May 13th 04, 09:41 PM
E Brown
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On Tue, 11 May 2004 22:02:41 GMT, "Matt O'Toole" >
wrote:
> Geez, how did people get around before Quattros
>and Xi-s?


They bought snow tires, which shockingly few people do anymore;
they assume all-weather tires are good enough, no matter what, then
blame the car when it's the tires not gripping that's the problem.
I'm guilty of not buying snow tires in decades, but I'm in downtown
Chicago and things are plowed pretty quickly here so I can get away
with it. Also my winter beater is the 944 - easy to push out when it
gets stuck.
Emanuel
--
1983 Porsche 911
1983 Porsche 944
 




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