Ringius
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| posted on 8/7/08 at 09:51 PM |
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From an arm-chair amateur...
If you compensate fully for body roll, you are likely to sacrifice braking, at least if the car will dive under braking (which it will, more or
less).
The Mazda Miata uses 0.5 degs camber change per 1 deg roll, as does a number of other sportier production cars. These does probably have more
suspension travel than you will have though.
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MikeCapon
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| posted on 10/7/08 at 08:15 AM |
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This is a really good thread! Fascinating to watch as an interested observer from the comfort of my armchair. Now that the bullets seem to have
stopped flying for a moment can I stick my head out of the trench and ask a simple question.
The basis, or reason for all this debate seems to me to be the supposed difficulty in deciding which factors determine the dynamic behaviour of the
chassis in relation to the road surface and hence how best to design a chassis/suspension system to enable the tyres to best do their job. The
different schools of thought seem to be clutching onto their own theories and simply decrying the others because "You can't prove
it".
Why can't you prove it? Having worked with different datalogging systems and in particular with one very good DA engineer it seems to me that
with just a gyro, 4 suspension pots and IR ride height sensors together with the usual throttle position, brake pressure wheel speeds and steering
angle the behaviour of the chassis could be measured. From here the different theories could be proven or otherwise. The effects of spring changes,
altered pick up points etc could also be compared.
If, as seems likely, no existing theory "fits" the result at least the answer is there and all that remains is to find the equation that
gives that result?
(Pulls head quickly back into trench and prepares coat)
www.shock-factory.co.uk
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rpmagazine
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| posted on 10/7/08 at 08:52 AM |
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I gleaned this from the WWW...so you must take its absolute accuracy with a pinch of salt.
"1st generation MX5 (Miata) The front roll centre was 61mm, the rear 120mm. Camber gain was 0.91 degrees per inch at the front and 0.58 at the
rear.
The new Caterham CSR has RCs at 30mm/65mm front/rear
The Elise roll centres are 30mm/75mm front/rear. The camber gain is 0.31/0.45 degrees per inch front/rear. The effecive swing axle length is about
180inches/110inches front/rear"
Mike of course you can do all of that and more. All of the OEM's do such things...but generally few people who are going to build their own car
have the desire/skill/time/ability to analyse the results. There are simply *so* many variables e.g. slip angles of tyres, which can effectively be
ignored up to .4G but then becomes an issue etc etc. If you have data recording as per the latest Motec dash etc then you can do it...damper rates
etc require higher rates...so it all becomes quite expensive too. It is probably cheaper hiring a professional driver for a couple of days to refine
what you already have?
[Edited on 10/7/08 by rpmagazine]
www.racemagazine.com.au
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Syd Bridge
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| posted on 10/7/08 at 09:25 AM |
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 Roll centres,utter BS, you just can't let them go.
I'm not outraged, more like dismayed and disappointed, that an alternative view is put down without good reason. It was taught that the earth
was flat for years, you couldn't go faster than the speed of sound,and the smallest particles were electrons and neutrons,....
I work with DAQ every week, it's the prime development tool, that's how I know.
Cheers,
Syd.
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rpmagazine
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| posted on 10/7/08 at 09:42 AM |
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Geez syd just let it go and allow us to use the forum to share ideas.
If you have a theory start another thread, in fact I'll go and do it now and you can answer my previous question without derailing this thread.
www.racemagazine.com.au
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ravingfool
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| posted on 10/7/08 at 11:58 AM |
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Very interesting thread that I will have to read again I think to fully understand all the different ideas as I have absolutely no knowledge of
suspension geometry as such, only a basic grounding in mechanics and I'm not awake enough to deal with it!
But Syd, I would just like to point out that in known history the Earth was never thought to be flat, that is pure myth I'm afraid and as one
opposed to the proliferation of incorrect information being stated as fact, I thought you'd want to know 
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MikeCapon
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| posted on 10/7/08 at 04:43 PM |
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"It's how I think. You look at everything you've done before. You look at other people's work. You feel you can improve and
don't give any secrets away. We do still look at roll centre and geometry, but if I gave you positions or camber change details my opposition
would think I was mental - or they wouldn't believe them."
Tony Southgate
"You cannot reduce the unwanted in a design to zero - you can only hope to minimise what is not good. You can draw the position of the Roll
Centre in static geometry but the dynamic position is a different matter. The point about which a car rolls can be totally modified by altering the
springs, or the weight transfer and the consequent loading on the tyres."
Trevor Harris
I think these two, very credible designers are worth listening to.
Also posted in the other thread.
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Dom9
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| posted on 16/7/08 at 02:51 PM |
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Sorry guys, late to this thread as work has picked up recently and i haven't any spare time to work on my own project!
I am, however, reading it with interest! I have always been interested in suspension design and whilst studying at Imperial College for my
undergraduate degree I spent a lot of time doing my own background reading on suspension design, RCs, camber etc etc As I knew it would one day come
in useful.
Truth be told, I have forgotten as lot of it and was hoping to refresh my memory in the coming months before undertaking my chassis design.
I am interested in what Syd is referring to and I agree with a lot of it and have never understood how suspension could be designed around static roll
centres when the sidewalls of tyres deflect and there is a certain amount of slip etc etc. Or perhaps I should say that i could never understand how a
lot of people took roll centres to be the be all and end all when there are so many other dynamic events happening during cornering!
Anyway, my point is, and I am very sorry that I have lost the back issue (if anyone has one; please, please scan my letter), that I wrote a letter to
Race Car Engineering many, many years ago (I want to guess at about July 2001) about the Dax camber compensation suspension.
The month before they had run an article about the Dax system and had not discussed the effect on roll centres in much detail, other than to show it
moves about. Now, it appeared obvious to me that if this system worked (i.e. aided cornering forces), and it was being tested by F1 teams apparently,
then roll centre muct have nothing to do with anything - Which Syd seems to be suggesting!
My letter was not intended to rubbish the camber compensation system but I asked teh question; "we have been told that RC is important for
suspension design, but teh RC is always moving in this system... So what do we think now?" or something like that! (I have no copies and it was
7 years ago).
I never got an answer from the editorial team of the mag, anyone writing in or the designer.... 
So, it's very interesting here everyone's views on this!
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rpmagazine
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| posted on 17/7/08 at 10:15 AM |
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I might suggest that you read it again and see who defined GRC's in such a manner. Most of us do not think of them as anything but a tool.
www.racemagazine.com.au
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Dom9
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| posted on 18/7/08 at 12:34 PM |
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Sorry rpmagazine - That wasn't intended as a comment towards you or anyone else on this thread... Perhaps a re-read of my post is in order?
It was more an observation about the fact that every book I read (at least 7) about 10 years ago went on and on about roll centres but there appears
to be no updated text 10 years later, unless someone can point me towards one, reflecting this 'new' thinking...
When I was at Lotus I managed to get a copy of their suspension design and ride and handling manual, that was quite interesting I seem to remember...
I must dig it out and see what that says but I think it pretty much followed the other texts I read!
So, feel free to suggest away, where you think it is necessary! I don't think I mentioned anything about the posters on this thread worrying
about roll centres... Did I?
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rpmagazine
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| posted on 19/7/08 at 06:27 AM |
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Dom9 our issue with GRC's is that they are an accepted if flawed tool. We know that the theory has holes in it e.g. the compliance issue of tyre
flex etc that you mention.
There are other theories 'out there' perhaps much the same as Syd has so briefly alluded to. The 'problem' perhaps is that the
GRC theory gives us the starting point with an somewhat predictable outcome, so syd's shouting it down without providing an alternative is in
reality not helpful.
Milliken is a good read, if somewhat too analytical/mathematical. There is another book that is due for release and I will have a copy soon as part of
the pre-press release. I will post some details when I am allowed to.
[Edited on 19/7/08 by rpmagazine]
www.racemagazine.com.au
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Dom9
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 posted on 23/7/08 at 03:26 PM |
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Cheers rpmagazine, I look forward to hearing about it!
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rpmagazine
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| posted on 9/4/09 at 12:02 PM |
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http://hem.passagen.se/hemipanter/
www.racemagazine.com.au
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kb58
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| posted on 9/4/09 at 03:44 PM |
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quote:
Originally posted by rpmagazine
Dom9 our issue with GRC's is that they are an accepted if flawed tool. We know that the theory has holes in it e.g. the compliance issue of tyre
flex etc that you mention. [Edited on 19/7/08 by rpmagazine]
My epiphany with RCs came when I realized the GRC method completely neglects wheel load, always giving both tires equal "voting power"
regardless what the tires are doing.
Consider the case of going round a turn, where 70% vehicle weight is on one tire and 30% on the other; it seems wrong that the 30% tire still has 50%
say in where the RC is. Or, how about taking the same corner at maximum speed where it's common to have essentially zero load on the inside
tire. It can't be right that this useless tires is still dictating RC location.
That's when I started reading up on articles by Ortiz and Mitchell and now look at things very different.
[Edited on 4/10/09 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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Doug68
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| posted on 10/4/09 at 01:24 PM |
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Not being a stirrer but...
Go on say it: "SydBridge was right after all"
ROFL
Just pulling your chain 
From my point of view the more I learn, the more I realise what an amateur I really am.
[Edited on 11/4/09 by Doug68]
Doug. 1TG
Sports Car Builders WA
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cheapracer
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| posted on 11/4/09 at 02:39 PM |
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Probably the place to bring this up, this is the RCR SLR Exo car and I have been very supportive of it until I saw the first pictures of it in action
- just have a look at the lovely positive camber on the outside tyres, not to mention the painfully short upper top rear arms causing the inside
negative camber - my point is that beauty doesn't mean function. In this case the top front arms are way too long to give proper camber control,
F1 cars have long top arms and pushrod suspension etc. for aero reasons and mechanical grip is way secondry to that so copying F1 designs for road use
is just silly.
[Edited on 11/4/09 by cheapracer]
 
Rescued attachment SLR4 positive camber.jpg
It's coming....
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cheapracer
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| posted on 11/4/09 at 03:01 PM |
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..and when I ran the aprox pivot point figures through a simple RC calculator I find that gains positive camber at a rate of around 75% - can't
quite understand why this wasn't figured.
 
Rescued attachment SLR3 roll 2 degree.jpg
It's coming....
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kb58
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| posted on 11/4/09 at 04:05 PM |
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Maybe they felt that straightline traction was more important.
quote:
Originally posted by cheapracer... beauty doesn't mean function....
And something some builders never figure out. Big anti-roll bars would help hide the problem.
Is the car you're selling a market competitor with this one?
[Edited on 4/11/09 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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Doug68
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| posted on 12/4/09 at 05:13 AM |
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cheapracer, probably a better place to bring this up would be the
forum the picture came from.
RCR has a pretty good rep for building quality vehicles so I'd be surprised if there was not some method to the design. The other thing is
that, as you probably know this was the first day the car was at the track so there's a lot of sorting to do with it generally I am sure.
Doug. 1TG
Sports Car Builders WA
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TheGecko
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| posted on 13/4/09 at 03:29 AM |
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I'm not convinced that RCR aren't guilty of choosing style over substance. Here's two shots of the rear suspension of one of their
Coupe's, taken at an open day at their Australian distributor.
To me at least, the flashy, too short, billet top arm would be lighter and simpler as a steel tube construction (although it'd still be too
short). And, feeding the spring loads into the end of that tube where it acts in direct shear on the shank of what looks like a 1/2" rod-end?
Odd - very odd.
Dominic
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cheapracer
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| posted on 13/4/09 at 12:13 PM |
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Kurt, yep, 0-100-0 may have been on their minds! Roll bars will help but only mask what is basically a wrong design - it gains positive camber from 0
degrees roll on. I guess some thick ones with some static camber to start you off, not going to help you much in the wet though with no compliance and
a dancing inner rear.
FWIW - Don't see them as my competition, In fact I have actively forum supported the SLR, as I do the whole industry, as more sales of this type
of car will only help me - I think this is more a direct Atom competitor and I don't see much change from 40K US on the road for one of these
and the ilk (carbon fibre battery boxes etc.) of those who will undertake one.
I see my direct competitor as MEV actually but hope that general interest in all the mid engined trend thingies including your beast will benefit all
of us with greater spurred interest from John Smith.
Doug, I don't post in that forum, this is but 1 of 4 forums I go to and this is a modern example on offer for this suspension related topic. I
hope something of it helps one of the builders here and to me this is what forums like this are about. I didn't get the pic from that forum, I
got it from another forum - only this picture showing the cars dynamics amongsy many others was removed after another person mentioned about it - as
odd as the ultra short Aarms and the loads put onto the heim joints pictured above as mentioned by Gecko. I already knew about and mentioned those
elsewhere a while back in another forum. With all that torque and the rubber that thing wears I wouldn't want to be booting it up in a bumpy
corner.
Doug you are welcome to bag the crap out of mine soon :-)
It's coming....
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Doug68
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| posted on 13/4/09 at 12:25 PM |
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cheaperacer, I don't want to bag the crap out of anyone's work.
Generally unless I think someone's going to hurt themselves or someone else if I can't find anything nice to say then I try to STFU.
Doug. 1TG
Sports Car Builders WA
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cheapracer
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| posted on 13/4/09 at 04:18 PM |
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... can't find anything nice to say then I try to STFU.
Thats very good advice for you but umm, you just said that in a very nasty way, lol!
It's coming....
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cheapracer
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| posted on 21/4/09 at 12:27 PM |
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quote:
Originally posted by cheapracer
FWIW - Don't see them as my competition, In fact I have actively forum supported the SLR, as I do the whole industry,
Well after Fran himself wrote this today I won't be supporting the overpriced and IMO with supporting evidence, suspicious handling SLR
anymore. someone should tell him you can own a Rocket, a Sonic and an Atomic for 1 of his SLR's - oh hang on, I did!
MEV build some cool cars but you must compare apples to apples... I admire what MEV builds for the price and I am not picking on them to be
detrimental or start a flame war.....just using their cars as an example....
It's coming....
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kb58
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| posted on 21/4/09 at 01:48 PM |
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quote:
Originally posted by Doug68
Generally unless I think someone's going to hurt themselves ...then I try to STFU.
I've found saying something is often pointless even if well-intended. It often causes said dangerous person to get defensive, coming back with
an "oh yeah, I'll show you," reply, and crash their car anyway...
[Edited on 4/21/09 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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