silente wrote:I would like to add my question here..
I have seen very rarely if ever a suspension going to have a positive camber change in bump (camber becaming "more positive" when wheels go closer to the chassis).
Whay nobody does it?...
Well, I'll try to expand humble sabot correct answer, for dummies like me.
Short answer: because it would give you less area under the wheel to grip the road. Check this images.
In cornering, a roll induces positive camber. So, you lose grip because you lose patch area.
Like this:
You have to
feel why, it's not enough to read about it. It's easy to watch it on an open wheeler (or watching the wonderful wheel cam clips previously posted by 747Heavy, "gracias, tío") but it's better when you feel it on your guts, specially when you take it to the limit and the butterflies in your stomach mix with the feeling of the curve being taken. However, I'm digressing here.
The conventional solution is an unequal arms suspension (or whatever the english term is for this one), like this:
The PROBLEM you have with this solution (there is no perfection, except in some female breasts) is
when you combine roll and bump (or you, heaven forbids, try to lower the suspension without knowing what you're doing, following Mr. Beckman advice to minimize weight transfer, blessed be his soul anyway, as is described in the link to "Physics of Racing" given by humble sabot) and you get this:
No wonder some rookies try to figure out why the INNER part of the tyre wears away in a lower car... but you, the karters in this thread, intuitively understand why.
Notice that the tyre tuck shown in the previous youtube posts have the very same effect... it gives you camber
because the tyre is moving under the rim (or
tucking, as I said previously) and it is changing the "angle"of the tyre more than any bump or droop,
because the point of support of the wheel is moving laterally under it.
I say it again: on the other hand, bump or droop, on
hard suspensions, as God intended for race cars to have, it's minute. It's not ply bias, friends, or so I think (well, or so I feel, to follow my own advice
).
Besides,
the slip angle gives you the same effect, even if you have no centripetal (lateral) acceleration. It's easy to think that the tuck is created only by that lateral force. It's not.
Check this video and watch the tyre moving laterally (around 12 seconds and again at 30 seconds into the clip). Slip angle it's a property of tyres,
because the car wouldn't move laterally without that slip angle or twisting of the tyre, btw. We had a very long thread on it, a couple of years ago.
[youtube]
http://www.youtube.com/watch?v=W8UiE7yvO_M[/youtube]
On a side note, this slip angle also happens when you accelerate. Again, the car wouldn't move forward if the tyre did not deform this way when accelerating (not laterally, but "around" its axis of rotation).
Notice ALSO how the HEIGHT of the axle varies when the tyre deforms. Watch the video again, and, instead of watching the tyre, concentrate on the distance between the huge silver axle and the moving surface. It changes, ain't it? Of course: when the tyre deforms, it becomes shorter! There are no bumps in this video, but you can see the end result of
tuck.
Again, this happens also when you accelerate: the tyre wraps around itself and become shorter. I don't know how to put this in better words, but you probably are understanding me by now. Anyway, check around 48 seconds into this clip (the slip angle is exaggerated in a dragster, but happens even in a Yugo):
[youtube]
http://www.youtube.com/watch?v=3Ug6w4ZjwVo[/youtube]
Those deformations are huge in a hard suspension car, compared with bump and droop.
Of course, if you're driving a Super V8, the suspension
actually moves, but those are stock cars that weight a ton (figuratively speaking).
I guess that's one of the reasons why good F1 drivers start at kart races, because the suspension of an F1 car, at 600 kilos, and with such large tyres, moves very little.
This is another fine point: when you take the bump, with almost no compression of the suspension,
the walls take the load and compress, and if you are taking a curve, you feel the walls are "harder", because of this load. This helps a little to keep tuck under control, not much, but... a tenth is a tenth (and like a car length at 150 kph). Again, is the
feeling of it what makes me say so (well, Colombia is passion, our national motto, so I might be exaggerating a tad here, isn't it? Besides, I'm Spaniard, which is a bad combination... and I'm not much of a driver, but I enjoy a lot
the understanding).
Finally, this is a forum of friends, not a class. So, besides the encouragement given to you by forty-two to ask questions, I would like to encourage you to give answers, no matter what. Hey, who cares if you're wrong? People won't respond when you ask them to help you to write something, but make a mistake and everybody will have an opinion. That's when you learn, or at least I do.
So, where was I wrong? Tell me. I'm no female breast...
