Fred W B
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| posted on 28/10/07 at 04:28 PM |
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Interesting discussion on RC height
roll centre discussion
with input from dennis
Cheers
Fred W B
[Edited on 28/10/07 by Fred W B]
You can do it quickly. You can do it cheap. You can do it right. – Pick any two.
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Syd Bridge
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| posted on 29/10/07 at 10:42 AM |
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Of course, all of that relies on you believing in 'Roll Centres' as a proven and true concept,..which they aren't. They have no
basis in maths nor physics nor practical observation.
Jay Novak comes close to the truth, without saying exactly what goes on. I only wonder if he really knows, or is quoting from other sources, just
like one or two wannabe's on here????
On the other hand, after a few bevies, leprechauns have been seen and engaged in conversation, as have fairies at the bottom of the garden. 
Cheers,
Syd. 
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Fred W B
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| posted on 29/10/07 at 11:29 AM |
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Hi Syd
So are you ever going to break down and explain to all us less bright people how it does actually work?
Even if a car does not behave as people think is does in the roll centre theory, surely it makes a convenient graphical way of comparing one
suspension to another?
Cheers
Fred W B
You can do it quickly. You can do it cheap. You can do it right. – Pick any two.
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kb58
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| posted on 29/10/07 at 01:21 PM |
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A lot of cars do just fine with imperfect chassis designs. There are many ways to do things and what's right for one person is wrong for
another. If a driver doesn't like the "perfect" chassis that was designed for him, what does that mean exactly? Either the
driver's wrong or the chassis is, or both. I'm not convinced there's One Answer, and it's nearly impossible to change only one
variable, anyway. Changing RC height to see how it changes things, without changing anything else, is nearly impossible.
[Edited on 10/29/07 by kb58]
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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Syd Bridge
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| posted on 29/10/07 at 06:09 PM |
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Read the posts by Jay Novak in that thread.
He more or less calls 'rollcentres' for the BS that it is. Also read the rest of what he says, and think hard about it. Draw pictures if
you have to.
But, a car does not roll about those mythical centres. Geez, just by moving the shock upper mount, or the pushrod mount, you change the roll
behaviour. So, that 'rollcentres' fairytale is shown as the fertiliser it is.
Cheers,
Syd.
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rpmagazine
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| posted on 30/10/07 at 08:55 AM |
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By this I assume you mean geometric RC's or do you include the force based ones in the bullshit category?
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kb58
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| posted on 30/10/07 at 07:03 PM |
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quote:
Originally posted by Syd Bridge
Read the posts by Jay Novak in that thread.
He more or less calls 'rollcentres' for the BS that it is. Also read the rest of what he says, and think hard about it. Draw pictures if
you have to.
But, a car does not roll about those mythical centres. Geez, just by moving the shock upper mount, or the pushrod mount, you change the roll
behaviour. So, that 'rollcentres' fairytale is shown as the fertiliser it is.
Cheers,
Syd.
I'm all ears. I know there have been (and are) many takes on this, and I want to hear your thoughts. If you prefer, you can PM me.
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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rpmagazine
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| posted on 30/10/07 at 08:06 PM |
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I have spoke to an OEM engineer who works with Adams software and he agrees with the view of the geometric RC's. He also said that it was
interesting that his work seemed to have a correlation with them all the same.
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Doug68
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| posted on 30/10/07 at 10:15 PM |
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This may throw some more light on the force based approach.
Doug. 1TG
Sports Car Builders WA
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TheGecko
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| posted on 31/10/07 at 10:42 AM |
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I was about to reply that those who're interested should hunt down one of Bill Mitchell's articles on Force Application Points but Doug
beat me to it. The geometric roll centre is just an abstraction - it is not a "real" point about which anything actually happens. The
Mitchell article pointed to by Doug puts it all into pretty plain English.
Dominic
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Syd Bridge
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| posted on 31/10/07 at 10:42 AM |
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I've been involved in enough of these to know that I don't want to get into it deeply again.
None of the arguments in those texts above take into account the springs, and how they act on the system as a whole.
Stiffer springs change the whole system, and hence roll behaviour and weight transfer, and those mythical and ever elusive 'centres'. They
don't exist as single entities, and are ever changing.
Changing the angle and height of the coilover or pushrod makes greater changes to the roll behaviour, than anything you do with wishbone geometry.
This a plain and simple truth derived from simple mechanics and first principles.
It's also a good reason to take a hit on weight, and use pushrod/inboard suspension on closed high performance cars. Spring specs and behaviour,
and total car dynamics can be a lot more easily controlled.
Cheers,
Syd.
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rpmagazine
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| posted on 31/10/07 at 09:09 PM |
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Mitchell's article is interesting though I would give it no more weight than some of the articles on opposing views, it is all part of the
bigger picture.
WRT push-rods, they are fine for limited suspension movement and light vehicles. It does also require an additional spend on good bearings/machining
and also very good dampers. The other aspect is that they are also a very high maintenance point on the vehicles that use them as tolerances are very
important. I had some good advice to stay away from them...for my application.
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kb58
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| posted on 31/10/07 at 09:17 PM |
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quote:
Originally posted by Doug68
This may throw some more light on the force based approach.
I read the Michell paper closely and found it very interesting. While I agree with his argument that the KRC is a consequence of the FAPs, I
don't see it as being being flat out wrong either, at least for what we do.
He mentions how important it is to have the FAP-CG moment arm unchanging in length. This fits with the current usage of the RC to do the same
thing.
He says that we should keep the FAP height (relative to the chassis) constant; this, too, is fulfilled by current usage of the RC method.
Even with the slightly inaccurate understanding of what an RC is, it seems to result in a suspension that is nearly, or exactly the same.
I wish he would have had two example suspension designs, one using the RC in the traditional method, and the other using his FAP-CG method. I'd
be very interested to see how different the final pickup points really are.
Oh, and I found his comment of how the RC should be below the CG instead of the centerline of the car very enlightening. It's a very good
point!
[Edited on 10/31/07 by kb58]
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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Syd Bridge
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| posted on 31/10/07 at 09:53 PM |
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Two things I find that get lost in all these pseudo intellectual discussions, are the most important to car handling....
Keep the total mass as low as possible, and keep every possible part of that mass as low as possible.
Put all that Rollcentre crap where it belongs, stick with basics and you won't be far out.
For all of you armchair experts, cop this,.... I've just now finished the wishbone geometry for a track car. The outer wishbone separation is
250mm vertically, and the inner pivot separation is 133mm. The upper wishbone is longer than the lower. These are long wishbones, relatively, and will
be travelling quicker than anything you lot will build in your sheds!
Cheers,
Syd.
[Edited on 31/10/07 by Syd Bridge]
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JoelP
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| posted on 31/10/07 at 11:03 PM |
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the problem with RCs as i see it is that its a gross oversimplification, you can have a 'normal' looking set up with a given RC height,
and design something thats blatently diabolical with the same RC height. Ive only thought about it with static RCs so maybe working it out at
different positions/rolls would change that, but for me, it seems a lot more constructive to just work out camber change over your own specific bump
and roll figures and take it from there.
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kb58
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| posted on 31/10/07 at 11:37 PM |
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Okay, I've snapped:
Syd, as I said, I'm all ears - I want to learn - but all I hear is how clueless everyone is. What's with this?:
-"pseudo intellectual discussions"
-"all of you armchair experts"
-"and [what I'm designing] will be travelling quicker than anything you lot will build in your sheds."
Is arrogance the price of knowledge, Syd?
Why allude to being some kind of Suspension Oracle, yet view with distain our attempts at understanding? You won't explain anything, yet insult
our attempts to do so on our own.
Why are you here? I'm disappointed that it's apparently not to educate or enlighten. Answering everything with, "Wow are you guys
wrong", is worst than useless.
Cheers.
[Edited on 10/31/07 by kb58]
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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rpmagazine
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| posted on 1/11/07 at 12:13 AM |
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SO far all I have seen from you Syd is smoke, arrogance and other peoples work and I too tire of your expressed arrogance Syd. I think it is time to
put up or shut up.
I would like to know your formal qualifications and experience before I give any weight to your opinions.
As for the comparisons of what we are building, well simply it does not reflect well on you, nor is it even the point of building your own car.
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Syd Bridge
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| posted on 1/11/07 at 04:02 PM |
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Wow, raw nerves or what??
I don't profess to be a suspension 'oracle', or any other type of expert. Suspension design is very simple and relies more on simple
geometrical constraints than anything else.
What you read as arrogance, I write as common sense and straight talking. I don't believe anything until proven.
'Roll centres' theory assumes that they exist, then all these professors write articles trying to prove how they exist. None of the
articles and book sections I've ever read, clearly defines 'roll centres' in a precise and accurate engineering manner.
I come at it from the other direction. I don't believe the theory and assumption, then look for an answer that shows me I'm wrong and that
'roll centres' are real.
If you lot can't open your minds, and think about this for yourselves, then I'm not about to write a treatise on the subject, only to find
my words repeated with someone elses name to it. Plain and simple.
I come across a few well known names in my work on occasions, and have asked about these mythical points, only to find that the people I'm
talking to come at the situation the same as me. What I have had explained to me however, makes an awful lot of sense.
What I'm trying to get you lot to do, is look at it from the same perspective as me, when it was all new to me. It didn't make good
engineering based sense, ...and still doesn't. The many variables in the system negate any mathematical model which may come close to
approximating the situation in a definitive manner.
What I find curious in all this, is that the most heated and smokey people are the ones who are writers. They seek the attention of the world. All
I'm doing is quelling their fire a bit, with a bit of doubt cast on their beliefs, which are derived from someone elses published work
anyway.
I've explained myself and my learnings to a couple of people on here. They have understood and thanked me, privately. They also won't be
seen replying to this thread either.
Cheers,
Syd.
[Is arrogance the price of knowledge, Syd? ]
If you see it as arrogance, then your problem.
The price of knowledge???Years of bloody hard graft, and I'm not about to distribute the fruits gratis! Someone wants my knowledge, they pay
for it, pure and simple!
After all, you do 'sell ' your books, don't you? Or are they now free to anyone who wants one? The same as Mr.
rpmagazines little tomes, and he doesn't give them away either.
When you fellas start giving away for free your publications, I might consider writing something which you can also distribute freely. But, I'm
not holding my breath!!
If you're going to make money off my back, then I'll have a whopping great chunk of it, .............cash,....up front.
[Edited on 1/11/07 by Syd Bridge]
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varg
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| posted on 2/11/07 at 05:16 PM |
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Syd Bridge:
In Issue no.66 of the magazine "Race Tech" there is an article named "Suspension Masterclass Part 1" written by Peter Ellray
one of the designers of the Le Mans winning Bentley that proves the existence of the geometric roll centre using the "Kennedy-Arronhold
Theorem". Is the vehicle your currently building using the "there is no roll centre theory" going to be faster than the Bentley? Now
I don't belive that the roll centre is a point that the car rolls about so roll centre is a bad name for the point were talking about but it is
an important factor in understanding the way the weight travels around on the car.
You also state that nobody takes springs into concern and that moving the coilover mount has a bigger impact on the cars roll behavior than any change
in wishbone geometry. That might very well be true but that is because it changes the motion ratio of the tire in addition to changing the roll
resitance of the axle meaning that the tire travells a different amount in regard to the change of load that it experiences from the cornering.
Changing the wishbone geometry is a way to change the roll resitance of the axle without chaning the motion ratio of the tire.
Finnaly I would like to give my personal view on the roll centre. I don't think that the placement of the roll centre is that important... Keep
it fairly low and you will probably be alright. Optimize for camber change and then fix the weight transfer distrubution with anti roll bars.
Hope that made any sense!
And Syd. No hard feelings, just want to here your take on what I written above and what Peter Elleray say. If you know something that I don't
I'm all ears, willing to admit I'm wrong and learn
[Edited on 2/11/07 by varg]
[Edited on 2/11/07 by varg]
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Syd Bridge
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| posted on 2/11/07 at 07:57 PM |
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'Nuff been said already.
If you are indeed a genuine 'newbie', then my apologies.
Cheers,
Syd.
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andygtt
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| posted on 3/11/07 at 08:41 PM |
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Syd
Why are you here. purelly to sell your expertise? or just upset those you think are less able or experienced than you.
Straight talking is not how your posts are coming across.....
'Armchair experts' are one of your quotes along with all but stating that our shed built cars are rubbish compared to yours.
These are your comments not ours and smack of a 17year old troll.
I am quite sure this is not the person you are (having seen other posts from you) and you probably have forgotten more that I will ever know about
suspension design (I certainly hope so anyway)...... but please do not patronise and belittle those that are trying to learn and build the best car
they can.
PS I paid an expert to design my geometry based on a proven race car.
Andy
please redefine your limits.
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rpmagazine
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| posted on 5/11/07 at 01:44 AM |
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Syd you are quite correct that I sell Race Magazine and it sells well.
However I have seen nothing from you in words, ideas or actions that I would pay you money for...perhaps you should show me something so that I can
take you even a little bit seriously.
I also asked you a simple enough question in that I asked for your formal qualifications and experience and you have ignored it...why?
I have no problem with the concept that geometric roll centers are not the only or best design tool, but you are simply lambasting a theory with no
proof or evidence and claiming secret knowledge...with as far as information or evidence demonstrated so far - no basis in fact or action.
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Syd Bridge
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| posted on 5/11/07 at 09:40 AM |
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Neil, I'll meet you in person one day soon, possibly. I'll be in Sydney in the New Year.
Then you might change your mind, and also apologise for your personal statements towards me.
My qualifications? Sufficient for the purpose, then some. Exactly what they are needs not be publicised. You'll find out on the day. I
don't see a need for a public 'Outing', as such.
What I want you lot to do is put aside all you've read, think about what hapens when a car Starts cornering, then goes into and through the
corner.
Where are the forces applied? What are the forces? How do those forces change and interact?How does the mechanical configuration affect, and is
affected by, those forces?
Then you go to a racetrack, and one driver wants a soft setup, and another hard, both have differing camber and associated settings, and they both do
the same times.
At that point all the theory goes out the window.
Cheers,
Syd.
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rpmagazine
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| posted on 5/11/07 at 10:36 AM |
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What personal statements Syd?
I've commented on your actions as per this thread and forum and no more.
Until I see some evidence I remain sceptical and why should I not?
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Doug68
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| posted on 5/11/07 at 12:12 PM |
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Syd,
I appreciate what you are trying to do here, you I believe are trying to get people to think about what they’re doing with their design and to
challenge the conventional wisdom.
Both are laudable ambitions IMHO
However when you opened your input to the thread you opened with…
“…I only wonder if he really knows, or is quoting from other sources, just like one or two wannabe's on here????”
Now that is not an encouraging statement is it? Essentially telling the reader they’re not up to the task, it is not going to encourage them seek out
further words of wisdom on the subject or too give any weight to the person giving that information. Additionally in conveys prior baggage in the
argument clearly this is a subject you’ve been through before and are getting tired of the “Hoary Chestnut” coming up again, except the majority of
people in the conversation I doubt have been privy to all that gone before.
Now if we look at your last post you say…
“…What I want you lot to do is put aside all you've read, think about what hapens when a car Starts cornering, then goes into and through the
corner.
Where are the forces applied? What are the forces? How do those forces change and interact? How does the mechanical configuration affect, and is
affected by, those forces? …”
Now this is a statement that most people will engage with, there are direct statements about points you feel need thought, that’s something that can
be worked with. If you had opened your participation in the thread with the last comment rather than the first I’m sure the tone of the conversation
would have been a whole lot different.
Now if you really wanted to drive the point home you might give an example of an actual vehicle that follows your given method and clearly would be
all “wrong” if looked at from the traditional roll-center point of view. For example the Williams shown on the link is clearly “odd” but given F1’s
extremely small vertical suspension movements and fixation with aerodynamics it may not be that relevant to the discussion here?
Also please stop using the phrase “you lot” it’s derisory and rubs people up the wrong way, which is fine if you want to rub people up the wrong way
but probably most of the time you don’t.
I hope you take the above in the good spirit it is intended in, I am sure you would much rather be discussing what people have discovered after
carefully thinking and doing the math on the subject rather than what’s going on now.
Doug. 1TG
Sports Car Builders WA
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