Mave
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| posted on 30/11/05 at 08:08 PM |
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"Some very outdated schools of thought put the wishbone pivots at an angle to the c/l laterally, to induce the desired anti's."
Ehm, in other words; we're now past the laws of physics?!?!?!? Please come with some better explanation on your thoughts Syd, as your statements
fall into the same category as saying that the earth is flat.
And that only happens when I'm drunk.
Anti-dive and anti-squat do work, and it is ALL in the orientation of the wishbones. Sure you can take a stiffer spring, but that upsets the rest of
the characteristics.
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suparuss
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| posted on 1/12/05 at 05:39 PM |
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to make anti-dive/squat geometry work only needs a couple of degrees and wouldnt be a visible change. maybe youve seen the diagram in a book some
where and didnt notice that it was exadurated for easy identification purposes.
from what the pic shows of the zonda upper wishbone it is no more than a semi trailing arm. the the upper outer mount appears to be a single ball
joint so if the bottom mount is parralel then toe wont be effected by the upper wishbone. the reason for the trailing arm setup could (as said
earlier) be simply a compromise to make use of available structure, and/or (also as said earlier) to get a longer wishbone for better geometry.
another point is that at an angle the arch the wishbone follows is skewed so that any camber change in bump or droop is slightly less, which would
make sense with short upper wishbones and is one of the problems i had when designing my rear geometry due to having to leave room for the engine.
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Stephant
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| posted on 1/12/05 at 06:00 PM |
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Ok Sid i'll try:
To make things clear ,it allways helpes to
imagine the extremes .Lets say the inner wishbone axles are mounted at an angle of 45°!!The driven wheel forces the upright to move vorward,this force
is directed at an angle of 45° to the wishbone,which means that half of the force tries to move the wishbone down and therefor the Car up.At the time
of accelerating the tyres have to take a higher load.If Newton didn't die ,he would have put that in a law,I guess.
I haven't seen any existing race car suspension like you,but I got payed for designing car suspension for several years,so I've
"heard" a few things.I didn't
say you should give the Mini anti squat,it already has it.But this is a discussion forum where people just offer opinions and these may differ some
times.
Best regards,Stephan
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Syd Bridge
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| posted on 1/12/05 at 06:19 PM |
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Good Luck Chaps.
No use arguing with all you experts.
Syd. 
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JoelP
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| posted on 1/12/05 at 07:46 PM |
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i agree with stephant. His description is accurate.
It works by the wishbone pivots pointing up above the centre of mass, so the direction of the change of momentum is below the plane of the wishbone
pivots, and aiming towards it.
sorry sid 
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Rorty
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| posted on 2/12/05 at 04:15 AM |
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Ignoring absolutely everything that charlatan said, the upper rear wishbones may be angled for anti squat, though without seeing the set-up in
its entirety, it's a bit hard to be certain.
I would imagine it's all more to do with bling and "tech-supremacy" than any real world gains or improvements.
There are rarely any truly evolutionary contributions to suspension design now. Most "developments" are re-visited or re-hashed
technologies.
These scenarios and discussions occur as frequently as bowel movements and bore me to further bowel movements – which is why this is my first post on
the matter.
Cheers, Rorty.
"Faster than a speeding Pullet".
PLEASE DON'T U2U ME IF YOU WANT A QUICK RESPONSE. TRY EMAILING ME INSTEAD!
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TheGecko
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| posted on 2/12/05 at 05:46 AM |
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quote:
Originally posted by Rorty
without seeing the set-up in its entirety, it's a bit hard to be certain.
I agree that trying to 'analyse' a suspension design from one photograph is a singularly fruitless exercise. Must say however I do love
the look of that rocker arm - wonder if it's cast or was machined from a large and expensive billet?
With reponse to Syd's remark:
quote:
Until then, have a good close look at any modern racecar. If it would be found anywhere, it surely would be there. And just plainly
Aint!!!
I would doubt that racecar practice, particularly current F1 practice, would be all that comparable with road cars. They run very wide, very sticky
rubber; they have suspension travel strictly limited for aero reasons; they corner at speeds (and attendant side forces) far above what most of us
will ever see; they have very different masses, mass distributions, and sprung/unsprung mass ratios to road cars; etc, etc, etc. Far more
inspiration/insight might be found in machinery with close ambitions to our own - small, road going cars although RWD examples are very few and far
between in the era of the hot hatch.
After pushing myself into 'analysis paralysis' with too much dealving into the intricacies of suspension design, I have gone for a very
simple strut layout at the back of middy. Re-use the FWD donors struts, converted to adjustable coil-over (cheap, easy). Simple wide based lower
wishbone. Toe rod made from the original tie-rod and a rose-joint. Job done. Will I be able to claim fractions of a degree
'improvement' in camber-gain per degree-of-roll etc compared to some other car? No, because I'll neither know nor care. If it
handles abysmally (which I doubt) I'll rework it until it doesn't.
Best regards,
Dominic
[Edited on 2/12/2005 by TheGecko]
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Alan B
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| posted on 2/12/05 at 01:11 PM |
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quote:
.......Will I be able to claim fractions of a degree 'improvement' in camber-gain per degree-of-roll etc compared to some other
car? No, because I'll neither know nor care. If it handles abysmally (which I doubt) I'll rework it until it doesn't........
Amen.
My philosophy too.
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Stephant
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| posted on 2/12/05 at 04:52 PM |
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Hi
I didn't want to say,that the pictured suspension setup was made for anti squat.
Of course it takes a lot more than one picture from above, to get an idea of what they wanted to achieve.May be it just suits the frame design and
they have only one type of suspension bracket .I just wanted to commend the "nonexistance" of anti squat.
Best regards,Stephan
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Mave
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| posted on 2/12/05 at 06:34 PM |
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Well Syd, in that test you guys seem to have left out the biggest contributing factor; there was no weight transfer due to braking, as the centre of
gravity of the vehicle was not moving. So of course the test results proved disappointing!
I can tell you from my experience in designing AND testing bike anti-dive and anti-squat suspension systems that it does work. So luckily I can still
say that Newton was right all along.
Marcel
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Stephant
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| posted on 2/12/05 at 06:42 PM |
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Syd
May be we misunderstood each other.
However,I'm not sure if tests with slicks + tyre softener give the right results in that case,but I know that playing with anti squat at 4WD
cars is done to get slightly changes at the ballance , but the top wishbone angle at the picture above surely has nothing to do with anti squat.
Best regards,Stephan
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cymtriks
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| posted on 2/12/05 at 08:22 PM |
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I partly agree with Syd....
Ok here's my take on this debate we keep hearing between Syd and others.
Point 1
Think of the car as a mass supported by a system of linkages. If this car was supported by very soft springs then it would be free to move about on
its supporting linkages and would move about the geometric roll centres in every direction.
Point 2
Think of the opposite case. Make the springs very stiff or just replace them with rose jointed links. The car's linkages still move but only by
microscopic ammounts. The important thing now is the CoG, the roll centres just drop out of the picture from a practical point of view. The car now
appears to roll about the CoG with the springs just holding it up. This is exactly what I think Syd is describing
Conclusion
In a road car the result will be some way between point 1 and point 2 so the car will tend to roll, in cornering and front to back in squat and dive,
about a point between the geometric RC and the CoG. Given the stiffness of a road spring I would expect this point to be closer to the RC for a road
car and closer to the CoG for a race car.
Comments all!
Especially Syd, is this what you've been getting at?
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Stephant
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| posted on 3/12/05 at 03:09 PM |
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Hi
Cymtriks:
The forces produced by anti squat have nothing to do with the hardness of springs,they just get added to the spring forces(under acceleration) and are
produced by suspension geometrie.
A look at the rear suspension of Nascars shows a simple example,of how that is achieved.They usually have the rear axle located by three lateral
links (two lower ones and one above in the middle)+panhard rod.There are several mounting holes(vertical) at the axle ,to set anti squat /anti
dive.
If the springs are locked,as discribed in "point two" not only the roll centre gets out of"view",the whole suspension
geometrie doesn't still exist,as there is no movement.In that case you could simply weld the uprights to the chassis,to get the same.As I hope
to understand Syd now ,he just wanted to say,that the "toe out"mounting of the upper wishbone doesn't produce anti squat,something i
would agree, too.
Best regards,Stephan
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cymtriks
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| posted on 3/12/05 at 06:13 PM |
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Stephant,
This is a long running issue which Syd keeps bringing up. I don't think that you have understood my points!
My point 1 and point 2 are the extreme cases. Point 1 is a very soft case, by which I mean "mathematically" soft, a limiting condition.
Point 2 is also meant to be a limiting case, "mathematically" hard. My reference to replacing the springs with solid links was intended to
illustrate the limiting nature of point 2, a solid link is still a spring, only a very stiff one!
Remember that a suspension theory needs to account for both "soft" and "hard" suspension cases. As Syd points out traditional
suspension theory does not do this as it assumes a "soft spring" case, as in my Point 1 case, to apply all the time.
In practice springs are somewhere in between "soft" and "hard" so the true roll centre must be somewhere between the geometric
roll centre and the CoG.
Syd, are you out there!
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Stephant
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| posted on 3/12/05 at 07:46 PM |
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cymtriks
I still don't understand what you mean by "true" rollcentre.The rollcentre doesn't change it's position with different
springs.
It's influence to the body roll and load transfer just gets lost by locking the springs(or making them hard as discribed)
Best regards,Stephan
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cymtriks
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| posted on 3/12/05 at 09:38 PM |
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Stephant,
The true roll centre is the one that the car actually rolls about.
The geometric roll centre is the one determined by the suspension geometry.
Ask youself this question. How hard do the springs have to be before the car behaves like a solid mass and rolls about the CoG? In my example, point
2, I used an extreme case of a solid bar which locks out the roll centre. But what about a very hard spring? How hard is hard? At some point the
geometric roll centre will be replaced by the CoG as the point about which the car actually moves.
For a road car the springs will have plenty of movement but they not free moving either so the true roll centre is close to the geometric one but
slightly offest towards the CoG.
Please Syd, is this what you mean?
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andygtt
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| posted on 3/12/05 at 10:00 PM |
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Is whats being disputed whether IRS can produce any antisquat or if antisquat is not actually existant.
Drag cars use antisquat but I've never seen one use an IRS system and I've read that usable antisquat is difficult to active in an IRS.
Andy
please redefine your limits.
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Peteff
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| posted on 4/12/05 at 12:43 AM |
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All this....
from the picture of a Zondas' rear wishbones and you can't even see both ends of them ? Does anti squat exist, does Santa Claus exist, do
fish fart?
This is a long topic, click here to review it.
You're not kidding.
yours, Pete
I went into the RSPCA office the other day. It was so small you could hardly swing a cat in there.
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Stephant
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| posted on 4/12/05 at 10:10 AM |
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Hi Cymtriks
Of course you can define the changes in tyre load and body roll resulting from changes in spring rate as a changed rollcentre in reality,but what has
it all to do with anti squat?
To me,this discussion startet with "anti squat is nonsens,the springs hold the car up".Antisquat is only dealing with lateral forces,which
have no influence to rollcentres etc.
However,we all think the picture above showes almost nothing to discuss about and I just wanted to say,that fishes do fart.
Best regards,Stephan
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Peteff
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| posted on 4/12/05 at 11:23 AM |
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I just wanted to say,that fishes do fart.
Thanks Stephan, at last something useful from this thread.
yours, Pete
I went into the RSPCA office the other day. It was so small you could hardly swing a cat in there.
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locost_bryan
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| posted on 7/12/05 at 03:10 AM |
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quote:
Originally posted by Stephant
A look at the rear suspension of Nascars shows a simple example,of how that is achieved.They usually have the rear axle located by three lateral
links (two lower ones and one above in the middle)+panhard rod.There are several mounting holes(vertical) at the axle ,to set anti squat /anti
dive.
By lateral links, you mean trailing links - lateral means relating to the sides of an object or to sideways movement.
Anti-squat and anti-dive of course apply to the lateral roll centre.
iirc anti-aquat in a irs is achieved by angling the wishbone pivots so that they aren't parallel (when viewed from the side of the car).
The Jag XJS had both...
Bryan Miller
Auckland NZ
Bruce McLaren - "Where's my F1 car?"
John Cooper - "In that rack of tubes, son"
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Stephant
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| posted on 7/12/05 at 07:48 PM |
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Hi
my english isn't good enough to explain properly,(learnt it 25 years ago in scool)I was talking about forces
,working parallel to the middle axle of the car and thought lateral was the right term.
Regards,Stephan
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kb58
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| posted on 7/12/05 at 08:04 PM |
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quote:
Originally posted by locost_bryan
iirc anti-aquat in a irs is achieved by angling the wishbone pivots so that they aren't parallel (when viewed from the side of the car).
Both upper and lower are angled, so a line projected through their pivots will pass through the CG of the car. That's "100%"
anti-squat. That said, most designers have little to none as it tends to bind up...
Carroll Smith has a great explanation in his books.
Mid-engine Locost - http://www.midlana.com
And the book - http://www.lulu.com/shop/kurt-bilinski/midlana/paperback/product-21330662.html
Kimini - a tube-frame, carbon shell, Honda Prelude VTEC mid-engine Mini: http://www.kimini.com
And its book -
http://www.lulu.com/shop/kurt-bilinski/kimini-how-to-design-and-build-a-mid-engine-sports-car-from-scratch/paperback/product-4858803.html
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locost_bryan
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| posted on 9/12/05 at 12:31 AM |
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quote:
Originally posted by Stephant
Hi
my english isn't good enough to explain properly,(learnt it 25 years ago in scool)I was talking about forces
,working parallel to the middle axle of the car and thought lateral was the right term.
Regards,Stephan
Sorry, Stephan, should have noticed the Berlin location 
Bryan Miller
Auckland NZ
Bruce McLaren - "Where's my F1 car?"
John Cooper - "In that rack of tubes, son"
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Stephant
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| posted on 9/12/05 at 07:35 AM |
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Hi
no problem Bryan, this forum
will be a good training.
Regards,Stephan
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