1. It s bad practice to put the weight on structural points of car?
2. sub frame and lower arms are he points where the car sits, so when you lifting it it like you just replacing the wheel with the axle stand (bypassing the suspension strut) and rising it up
3. so by your theory we should never park up with 2 wheels on walkway (car not in level) because it will be damaging sub-frame... said that they are still safest points to lift your car,
4. if you know others, name them (other than 4 lifting points), if not your theory got no basis.
1. No, good solid secure structural points on the car like the chassis rails are fine, or even a steel subframe is fine. Cast aluminium doesn't behave like steel and is more likely to crack, steel would bend before it cracked.
2. Yes, but you don't have the weight of half the car on 1 single point on the arm or subframe when all 4 wheels are attached and it's on the road, the load is SPREAD across the structure. A jack places ALL the stress onto an area the size of your palm.
Oh, and you say you "bypass the suspension strut"...I'm sorry, but that carry's A LOT of the cars weight through to the body when on it's wheels, so if you "bypass it", then all that weight is focused elsewhere....on a cast aluminium part.
3. I think you need to go and read what I said again. When you park on a kerb all 4 wheels are still on the ground and the load is still being SPREAD across the structure, not focused onto an area the size of a trolley jack head.
4. I'm sorry, but HOW does not naming other areas to lift by mean that it is automatically correct to lift by a cast aluminium part??? All it means is that Audi never designed anywhere with that application in mind.
As I have ALREADY said, I have used those areas before, but I don't like it and its NOT good practice. Problem is, Audi don't give any dedicated central lift points on these cars for people to lift with trolley jacks.
As far as Audi engineers are concerned, all work will be carried out on a 2-post or 4-post lift, hence the lack of jacking points.
Seriously, if you want to argue, at least read what people write and make your posts coherent.
Fact still remains, it is not good practice, even though it does work. Like I said, it's like tightening a bolt by feel instead of using a torque wrench, it works, but it's not right, and it increases the POTENTIAL for something to go wrong.