Mr Whippy
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| posted on 2/12/07 at 07:02 PM |
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Suspension nonsense
Sigh, reading through the dross on the web about suspension geometry I ask myself does anyone have a clue what their taking about. Take Roll Center,
some say it should always be below ground level, others have it almost at the tops of the tyres! Folk on here seem to generally agree that the lower
wishbones are level so that’s how high the roll centers ever going to get. There all over the place!
This sucks…
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MikeRJ
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| posted on 2/12/07 at 07:28 PM |
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Others will say that the concept of the roll center is worthless...
You could spend years agonising about suspension geometry, but I reckon that unless you are designing some novel suspension for a competition car,
then simply follow a proven design.
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britishtrident
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| posted on 2/12/07 at 07:48 PM |
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quote:
Originally posted by Mr Whippy
Sigh, reading through the dross on the web about suspension geometry I ask myself does anyone have a clue what their taking about. Take Roll Center,
some say it should always be below ground level, others have it almost at the tops of the tyres! Folk on here seem to generally agree that the lower
wishbones are level so that’s how high the roll centers ever going to get. There all over the place!
This sucks…
Roll centre is only one aspect what really matters in the roll axis inclination, and roll couple distribution. However if you get the roll centre too
high particular with a short virtual swing axle length you get jacking effects and tuck under --- well known example M151 Jeep , VW Beeetle, Triumph
Herald, Mk1 Imp.
Usual position for roll centres on a Seven class car are ground level to about 125mm.
The rear should be slightly higher than the front..
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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Werner Van Loock
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| posted on 2/12/07 at 07:54 PM |
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It's all theory, just like chassis design, wether triangulation, ladder, spaceframe, monocoque, etc...
Put something together with possibility to adjust and try it out.
That's what people call development 
http://www.clubstylus.be
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watsonpj
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| posted on 2/12/07 at 08:22 PM |
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looks like britishtrident cleared up your confusion Whippy
quote:
Roll centre is only one aspect what really matters in the roll axis inclination, and roll couple distribution. However if you get the roll centre too
high particular with a short virtual swing axle length you get jacking effects and tuck under
 certainly helped me
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Uphill Racer
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| posted on 2/12/07 at 10:31 PM |
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Personally I wouldnt have the front roll centre where it could move above and below ground.
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Chippy
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| posted on 2/12/07 at 11:03 PM |
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I have designed several cars in the past, from the ground up, and have generaly used roll centres of 3" front and 4" rear. All of the cars
have been "sports" type. The one to the left of this post,
<
<
<
is one such, because while it may look "Locost", it's actualy a one of special, based roughly on Locost/Lotus design. Cheers Ray
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Mr Whippy
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| posted on 3/12/07 at 12:09 AM |
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that was helpful, thanks 
So really all I should be looking out for is that the wheels should not tuck in when the suspension's under load on one side. I can manage
that.
Cheers
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blakep82
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| posted on 3/12/07 at 12:23 AM |
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if you build you suspension, and its not 'ideal', well, i guess you won't really know what you're missing... hope that makes
some kind of sense!
most production cars have not got perfect suspension (i forget where i read that) and they have millions of pounds spent on their suspension.
________________________
IVA manual link http://www.businesslink.gov.uk/bdotg/action/detail?type=RESOURCES&itemId=1081997083
don't write OT on a new thread title, you're creating the topic, everything you write is very much ON topic!
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Uphill Racer
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| posted on 3/12/07 at 12:30 AM |
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Suspension geometry has only one flaw, it moves. 
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Delinquent
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| posted on 3/12/07 at 11:12 AM |
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Mr Whippy - if it helps, I've spoken to no less than 4 "professional" suspension designers now about my set up (as in, they are paid
to do it for a living by race teams etc), and every one of them has conflicted somewhere. I've just decided to go with my best shot after
reading several books (again all of which conflict) and make them "very adjustable" and see what happens!!!
ETA - also look at some of the cars you can buy from showrooms and compare their setups to suggested methods - according to the theory some cars
should never make it more than 10ft from the delivery truck...
[Edited on 3/12/07 by Delinquent]
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