ned
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| posted on 5/12/03 at 01:58 PM |
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Craig,
I think this is the aspect that concerns me most:
quote:
The only problem with de-dion is when you hit lots of bumps with your inside wheel mid corner as this will change the camber of the outside wheel
which has most of the load.
Most of the roads around my way are as bumpy as anything, IRS should handle these better and give a slightly better ride (not that i'm bothered
about the comfor of the ride that much!) and when i take the car on track, as the weight/cog moves when the car corners it allows the outside tyres to
maintain level, thus generating grip and the inside doesn't matter if you run over the kerbs, I think most people use the kerbs on track days,
especially in chicanes and this would surely unsettle the dedion beam so your contact patch would be compromised.
this is all IMHO of course, but ifdedion is so great why is that race cars stopped using this system years ago in favour of irs? all but the oldest of
the leman prototype style sportscars that I see when we're racing during the year have pure irs suspension with unequal length wishbones, albeit
if they do have perfectly setup geometry, cornerweights and some, anti roll bars.
Ned.
beware, I've got yellow skin
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stephen_gusterson
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| posted on 5/12/03 at 02:25 PM |
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race cars are looking for every little bit of gain.
schumacher gets wieghed before he goes to the bog as the contents of his rectum will be worth 1.2 seconds over a 90 minute race.
We, on the other hand, will be going down the A24 or whatever and having the occasional track day.
I doubt the difference between dedion and IRS are really gonna show up that much 
When I did a single seater experience at silverstone, it taught me that you will NEVER get the best out of a car on the road. I was thinking this
having recovered from a spin onto the grass. Do that on the road and they would have been scraping me up.
You can get more performance on a track due to margins allowable for error - ie grass, not a truck in the way.
but, are not racing lcosts live axle....
atb
steve
[Edited on 5/12/03 by stephen_gusterson]
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ned
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| posted on 5/12/03 at 02:28 PM |
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Steve,
I think the racing locost being live axle isn't really an issue. It's like that because it was in the book (which practically are the
regs) and it keeps the cost and ease of build down.
Ned.
beware, I've got yellow skin
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stephen_gusterson
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| posted on 5/12/03 at 03:31 PM |
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quote:
Originally posted by ned
Steve,
and it keeps the cost and ease of build down.
Ned.
right on 
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craig1410
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| posted on 5/12/03 at 08:37 PM |
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I think that's checkmate to Steve 
Sorry Ned,
Craig.
Ned,
One thing in response to some of your points. If IRS is so good for a Lotus 7 type car then why are Cateringvan using de-dion?
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stephen_gusterson
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| posted on 5/12/03 at 08:42 PM |
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Not getting at ned at all.
for each his own.
a well made irs will have very good camber control.
however, a poorly done homer attempt might have the opposite effect!
if i was building a std car (did I mention I wasnt  ) then id go live axle - simplest way.
atb
steve
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jcduroc
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| posted on 5/12/03 at 11:18 PM |
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Camber Control
quote:
Originally posted by stephen_gusterson
... a well made irs will have very good camber control ... however, a poorly done homer attempt might have the opposite effect!
Steve
How "much" is good camber control? (In your opinion, of course)
Joćo
JCM
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stephen_gusterson
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| posted on 5/12/03 at 11:56 PM |
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what a dangerous question to try and answer!
there are many books on this subject, and I am no expert!!!
However, my small knowlege is that many cars apply a little (negative?) camber at the rear to allow for the distortion of the tire in cornering.
Ideally, I suspect that should be a constant - ie the tire should have the same angle thro its entire travel.
when I did my unstd front suspension, i used a program from TOL group (yahoo) that allowed simple modelling. Its not hard to come up with a model that
accurate to less than adegree over an 80mm travel. However, translating that into metal and getting the same results insnt always that accurate.
my front suspension is accurate to approx 0.5 or so degrees over the normal travel.
I wouldnt be suprised for someone to now tell me that in some instances you do need varying camber.......
suspension appears to be a minefield - which is why I would go live axle if I was building a locost and not this frankenstien car
atb
steve
quote:
Originally posted by jcduroc
quote:
Originally posted by stephen_gusterson
... a well made irs will have very good camber control ... however, a poorly done homer attempt might have the opposite effect!
Steve
How "much" is good camber control? (In your opinion, of course)
Joćo
[Edited on 5/12/03 by stephen_gusterson]
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craig1410
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| posted on 6/12/03 at 12:04 AM |
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Guys,
Surely on an IRS car you would want to gain negative camber on the outer wheel and gain positive camber on the inside wheel to counteract body roll? I
think this is one area where the complexity of interaction on an IRS system is much greater than on a live or de-dion axle and thus more difficult for
the novice to get anywhere near correct.
Of course the problem with gaining negative camber like this is that it adversely affects the contact patch during straight line acceleration when the
car squats.
I am starting to think that IRS only really makes sense when you add anti squat anti dive geometry and anti-roll bars. Without those I don't
think you can avoid the compromise between cornering performance and straight line traction. Of course de-dion and live have other compromises too but
they have simplicity on their side.
Does that make sense?
Cheers,
Craig.
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Liam
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| posted on 6/12/03 at 12:18 AM |
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hello...
Steve - If you want no camber change you can just have parallel equal length wishbones! But you do want camber change - when the car rolls in a
corner the outside wheel effectively goes into bump and the inside wheel into droop. To keep the wheels upright and gripping you want suspension that
gives negative camber in bump and positive in droop - unequal length converging wishbones. Of course if you achieve this then you have undesirable
camber change in squat and dive.
The design of unequal length converging wishbone geometry is simply a compromise between keeping the wheels upright in roll and keeping them upright
in dive and squat. When i was waving tape measures at various sevens in my early stages i noticed that choosing this compromise is a matter of
guesswork and voodoo. And maybe experience. A book locost has a lot of camber change hence good performance in roll and poor performance in
dive/squat. A Dax has near parallel wishbones giving good performace in dive/squat. My geometry lies somewhere between but erring towards better
performance in dive/squat (i'll avoid bad camber change in roll with anti-roll bars stopping me roll so much).
A decent IRS is always potentially better than live or de-deon, but like many have said, not all that much, and drivers like us would probably never
notice (unless we're talking really bumpy roads). I do disagree, however, with some peoples opinions that the inexperienced home builder should
avoid the 'black art' of double wishbone design for fear of creating an ill-handling death trap. If your double wishbone geometry looks a
bit like what other peoples look like then it'll be fine - as i said it's just a compromise.
Enough Bishop's Finger fueled waffle..
Liam
[Edited on 6/12/03 by Liam]
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JoelP
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| posted on 6/12/03 at 12:31 AM |
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me, id do it like liam, with a very stiff anti roll bar, and closer to even length wishbones.
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dozracing
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| posted on 6/12/03 at 12:38 PM |
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Quote from Milliken and Milliken - Race Car Vehicle Dynamics published by Society of Automotive Engineers when i bought it it cost me £100 so its a
very in depth technical book.
"The advantages of the de Dion are that the unsprung mass is much lower resulting in better road holding on rough roads (like independent
suspension). It is a beam type axle so the tires (tyres!!) always remain square to the road, thus no camber compromise exists (unlike independent
suspension). This gives it supposed advantages over both the independent and the conventional beam (live) axle."
Obviously good and bad exist in both designs and it also depends what you are using the car for.
Caterham and Lotus used de Dion for the 7 and were very successful with it in racing.
F1 cars use double wishbones (irs) but i do know of at least one F1 aero dynamics guy who fancies using a live axle style rear suspension in order to
gain camber advantagtes and much improved aero dynamics around the rear suspension. His name is Frank Dernie and he is now Chief race engineer for
Williams.
For me the decision to go de Dion was mainly that everyone on here was discussing it and seemed keen, and when i thought about it i realised that it
was the genuine Lotus 7 alternative to the live axle. Not everyone thinks like me i'm sure but i like the Locost because its an affordable Lotus
7. I'm after building and driving a Lotus 7 and this is the closest i can afford to get.
Other people may not feel so nostalgic and simply want to build a kit car and see a 7 as just that, for them authentisity is not such an issue. Due to
the popularity of the MK and Luego, IRS is quite common and accepted now for the Locost.
Kind regards,
Darren
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stephen_gusterson
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| posted on 6/12/03 at 09:26 PM |
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see
I told you I was better saying nothing mr duroc
suspension for amateurs seems far too tech'y for me and that the potential of getting a worse result than IRS is far too great.
atb
steve
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