forty-two wrote:By the way, welcome to the Forum C09.
Glad to see you're asking interesting questions so soon after joining. I lurked around for some time before plucking up the courage to start asking questions!
On topic, could it be that the MP4-25 (and 24 to an extent) was suffering precisely from the inner wheel camber issue raised above, leading to both LH and JB locking up the inside wheel so frequently, or do you guys think it's as simple as McLaren running super stiff?
Thank you Forty Two. Creepy avatar. Asked Questions first day Signed up. Don't know much, willing to learn, fascinating. Anyone here know who Mordin Solus is?
"Those who dance are often thought mad by those who cannot hear the music."
"The only man who never makes a mistake is the man who never does anything."
WilliamsF1 wrote:What are those on the ends of the push rod?
in this case, they are "only" normal dampers. The car has a "simple" front suspension system without the typical rockers/bellcranks.
It´s similar in principle, to "old style" suspensions layouts, seen it the 70´s which run a coil over spring/damper unit between the wishbones. But in this case the cross-section is slightly reduced for better aero/less drag
The part infront of the damper, contains a preloaded coil spring or a bellville washers stack, to have a "Zero Droop" setup which is quite popular with some open wheel cars. ( for example Formula Fords)
It makes for good mechanical stiffness, and easy integration of the suspension, but does not allow to compensate for the "bad" motion ratio.
later Tyrells, used the interesting "HydroLink" suspension system, but where not very successful with it, and later converted back to a more conventional system.
As introduced in 1988, the 017 had a fairly conventional pull rod front suspension with dual vertically oriented shocks operating on rockers. During the season, they switched to this push rod type with externally-mounted shocks. They're not hydraulic other than having conventional innards. Springs are internal. There was a rumor at one point that these could be adjusted for ride height on the fly, but when we got the car there was a dummy line leading to the shock. Neither Palmer or Bailey can remember such a device actually working, and there's no provision for it in the cockpit. http://forums.autosport.com/lofiversion ... 74748.html
Last edited by 747heavy on Mon Jan 24, 2011 3:19 am, edited 1 time in total.
"Make the suspension adjustable and they will adjust it wrong ...... look what they can do to a carburetor in just a few moments of stupidity with a screwdriver." - Colin Chapman
“Simplicity is the ultimate sophistication.” - Leonardo da Vinci
747heavy wrote:one factor which comes to mind is suspension stiffness. Very few people actually know (IMHO) what is "true" position/angle of the tire to the ground (camber & toe) during cornering.
It´s easy to overlook things like rim deflection, wheelbearing deflection and/or buckling of toe links etc. under load. And please don´t tell me, that it´s "bad design" when thing likes this happen, you try to built a race car not a tank. And these things will happen on race and championship winning cars. The trick is, to be aware of it and to deal with it, so that it does not has a detrimental effect on performance.
@silente I think the most simplistic answer to your question is that anything that happens in bump happens to the outside in roll. For the most part, unless you have odd tyres (like Ciro's cart tyres, bias ply?) you're going to have better grip if you keep em more upright rather than lean em over particularly.
One thing that seems to get missed often is king pin inclination. It's in the same region as caster, in that it depends primarily on the alignment of the pickup points on the upright.
also: http://phors.locost7.info/contents.htm <- quite good, and probably the best primer i've read online. Fiddling with the suspension in Racer the car sim with the sim set to display the suspension points was another one of those learning tools.
the four immutable forces:
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.
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.
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):
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...
Ciro Pabón wrote: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.
More semantics than anything, but sidewall deflection or "tuck" does not result in camber change in and of itself. Camber (more properly inclination) is the orientation of the wheel (or beads of the tire), not the orientation of the sidewall. Same thing with slip angle - measure of wheel orientation rather than tire twist and wrap-up. Makes things a little easier to keep straight in your head.
To the earlier question of why people don't make their kinematics so the wheels go more positive in bump-
It could be done, if your a-arms had "reverse" inclination between them and a negative VSAL. Some people are too afraid to think outside of the box and try different things. Others... you pick your static and dynamic VSAL based on what you think is going to give you the best compromise of performance over your full range of handling. Negative VSAL probably isn't the best compromise.
Keep in mind.. infinite VSAL = no camber change in bump, at the expense of roll. Track/2 VSAL = no camber change in roll, at the expense of bump. Generally your compromise range will be between track/2 and infinity, but always a positive number. In order to get to a reverse VSAL length you effectively have to go past infinity, which I believe gives you outrageous amounts of camber change in roll (I could be wrong, would have to sim it).
Edit - Forgot I had blogged a bit about this. Put together this graphic quickly, which shows the trade-off in camber rates as a function of VSAL (which is a function of relative A-arm inclination)
Jersey Tom wrote:To the earlier question of why people don't make their kinematics so the wheels go more positive in bump
When Renault were running Michelin tyres - looking at the car head on it appeared that the front geometry would do just that (always very hard to tell just by looking, what with the very long VSAL and limited travel).
Howver, I did wonder whether they were doing the following:
Running lots of static negative camber with restricted roll would keep the tyres angled favourably for cornering. Allowing positive camber in bump could present the tyres to the road vertically when the car pitches under braking.