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

I know, it's shocking. I guess buyers are lured by the abundant "standard" gadgetry the French are so fond of, the pseudo-futuristic looks (you seen the new Megane?), and who knows, maybe they're fun to drive the 50,000 miles you can manage in them before you throw them away.

Reply to
Peter Bozz
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A short drive around where I live revealed 8 Mercs. Now, it's no Beverly Hills, just a fairly affluent neighborhood of a big Dutch city (actually, I crossed over into the affluent neighborhood from the not-so-affluent part of town I live in). There were a couple of Saabs and a few of the ubiquitous V40/V70 Volvos. I counted 6 BMWs and at least one A6, two A4s, a Jaguar XJ and a Lexus LS400. Most of the Mercs were of course C series. I didn't count the CLK Cabrio my local drug dealer drives: he's hardly representative of the general population and might skew my empirical data. I guestimate that I must have seen about

500 cars.

Most people here seem to have a, shall we say, predilection for spacious MPV type of cars, mostly uninspiring brands I coudn't even tell apart. Think Ford, Opel, Peugeot, Fiat, some Japanese and Korean brands, whatever.

I wonder, what city was it that you say you saw Mercs on every corner?

Peter

Reply to
Peter Bozz

Bill Bradley schrieb:

Yep.

Must have been the late night yesterday :-)

In fact I did the torque equilibrium but got mislead by the gemotry I'd drawn up.

You are right, the CoG shifts back and the load on the rearwheel increases. That load is then split into a component orthogonal to the road (for friction) and one parallel to the road (pulling the car back).

So the total orthogonal force on the road for friction is still less then if the car would be on a horizontal plane, but it's higher than on the front wheels.

Regards

Wolfgang

Reply to
Wolfgang Pawlinetz

Reply to
Imad Al-Ghouleh

Reply to
Imad Al-Ghouleh

Imad Al-Ghouleh schrieb:

*LOL*

Yep, would do us good. :-)

Regards

Wolfgang

Reply to
Wolfgang Pawlinetz

(please excuse the top post, but with the HTML formatted original it's just easier than trying to add the tags to make my reply look right. Honestly I hate top posts. Just scroll down to see the rest of the converstation framed in html)

Nice job of the physics. The only thing you're missing is that on an angle the center of gravity will change, placing more weight on the rearmost wheels. On a car that was perfectly flat, say, a steel plate with tiny wheels, your math is perfect. On a car that was, say, 7 stories high, you can see that a small tilt would place *all* the weight on the rear wheels and the fronts would actually come up off the ground and it would tip over. Just prior to that the front wheel would have zero weight. At smaller angles, or a shorter vehicle, the shift would be someplace in between.

In a real car, much of the weight is low (drivetrain) and some of it is higher (greenhouse). The center of gravity is somewhere between the ground (steel plate) and 7 stories up (my tower car).

So a car on a slope will have some amount of increased weight distribution on the rearmost wheels, and therefore the /4 trick won't work even if the car is 50/50 on a level slope where /4 is correct.

I can't give you math for it, but I'd be the weight transfer on a moderate to steep driveway type hill would be on the order of 5% or so. Strictly a guess, but I suspect a generous one. BMW and other makers try to lower the center of gravity all the time for handling reasons, so it's probably not immense. And the number varies by the steepness of the hill of course. But I'm not up for a calculus function to describe the relationship, especially since I don't know what the center of gravity is to plug in.

So anyway most bimmers are close to 50/50 to start with. Let's go with that. Say going up the hill, it's now 45/55.

Front drivers are probably closer to 60/40 in general. Yes I know, I'm being very inexact here. But with the same transfer, you're now at 55/45. Amazing... the same weight on the drive axel in both cases.

My numbers are made up, poke at them all you want I don't mind. The concept is there though. Play with the numbers and get small variations.

But front drive still wins, no matter how you dice it up. I submit this. Back up you driveway in the FWD car. With math above, you have 65% of weight on the drive wheels, vs RWD's best of 55%. With your math, you have 60% vs 50%.

Now, your point about the direction of the vector of the force is valid. As the angle increases, the force decreases, until it reaches zero. Your car on the wall will indeed have zero force on the rear wheels, only because the vectors are straight down. At 89%, where there is still some amount of lateral force (not enough to produce enough friction to hold the car mind you) almost all the lateral force would be on the rear wheels, but the size of that horizontal vector has become very small. So yes, nearly 100% of the force is on the rear wheels and nearly zero on the fronts, but, the amount of this force in the useful direction is so little that it doesn't help the car to stay put and it slides down the hill. Consider a car on say a 70 degree angle. Add much more and the downward component of the vector will overcome the friction of the tires and the car will slide. Let's imagine that 70 degrees is very near this point. Now walk up to that car and lift the front bumper

Reply to
Somebody

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

Reply to
Michael Burman

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.

No; he *does* have you there.

Yeah; it does.

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)

Reply to
C.R. Krieger

Not if they don't *have* them. Most BMWs don't.

-- C.R. Krieger (Been there; drove that)

Reply to
C.R. Krieger

"crippled in handling"? Apparently, Fred hasn't experienced the difference between dry road AWD neutrality and BMW's famous trailing throttle oversteer ...

-- C.R. Krieger (Been there; done that in the Kink)

Reply to
C.R. Krieger

While the BMWs you *don't* see are the 'Xi AWD cars that beat you there ...

And some of us know that twisty roads, autocrossing, and driving speed events on race tracks wears out the *front* tires a lot more than it does the rears - unless your idea of 'spirited driving' includes lots of burnouts. It's worst on FWDs.

Actually, the end of *my* BMW life will have included driving Audi Quattros (including turbos) for 14 years, lots of fun FWDs *and* lots of RWD and a few AWD BMWs - not to mention our current Jaguar X-Type AWD (a 3.0 5-speed Sport, so you can forget trotting out your tired old 'but they're slow and have bad autoboxes' line). Of the lot, I found the Audis (at least all of them after the first 4000/90Q) to be the most boring. Even my Fiat 128 was more entertaining - when it ran. ;^)

-- C.R. Krieger (Been there; done that)

Reply to
C.R. Krieger

OK; but who won? ;^)

-- C.R. Krieger (Been there; done that)

Reply to
C.R. Krieger

"C.R. Krieger" escribió en el mensaje news: snipped-for-privacy@posting.google.com...

If it's really slippery, and given the same driver and tyres and similar engines, Quattro still beats your Xi.

And some other ones of us know that if you go drifting on an M3, which is my point, and what really good drivers and real BMWs are best at, my argument still holds perfectly true.

Quite possibly true, but Audis may still probably be the safest of all of those.

Reply to
JP Roberts

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

Reply to
Fred W.

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

Reply to
Fred W.

Hmmm, trailing throttle oversteer... just another tool in the driver's toolbox, no? What better way to get that back end around the corner in a hurry? ;-)

-Fred W

Reply to
Fred W.

Oh, oh. That sure looks like flame bait posted to an audi newsgroup to me...

-Fred W

Reply to
Fred W.

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.

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

Dave Hinz

Reply to
Dave Hinz

"left foot braking", anyone? Fun technique in a Saab, is to keep on the gas, hit the brakes with your left foot, and let the back end slide to where you want it. Makes going around corners on snow/ice much more fun and exciting, and with practice you can get some great speed improvements.

Dave Hinz

Reply to
Dave Hinz

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