t.j.
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| posted on 8/9/06 at 06:38 AM |
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postive camber vs roll-centre
Last check on my suspension.
Could some-one give his opinion?
Front:
roll-centre(stat) 45 mm above ground
bump-steer zero
My q is: is it better to gain for the not "loaded" wheel a little bit positive camber (to compensate body-roll) or result in zero or
negative camber??
By replacing the inner pivots of the upper brackets i could gain other values.
But if I place the upper lower then my static roll-centre will drop dramaticly.
So:
Could some one say how much is the movement of the wheel?
5 cm up? and 5 down?
Thnx Theo
[Edited on 8/9/06 by t.j.]
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Syd Bridge
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| posted on 8/9/06 at 08:16 AM |
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You're thinking in the right direction. Forget those cursed 'roll centres', they're not one or the other, but fictional and
have no bearing how your car behaves.
Cheers,
Syd 
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MikeRJ
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| posted on 8/9/06 at 11:16 AM |
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quote:
Originally posted by Syd Bridge
You're thinking in the right direction. Forget those cursed 'roll centres', they're not one or the other, but fictional and
have no bearing how your car behaves.
Cheers,
Syd
They are no more fictional than the cars COG, and have equal bearing on the dynamcis.
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britishtrident
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| posted on 8/9/06 at 11:52 AM |
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Taking the long view the aim is to keep all 4 wheels firmly on the deck and reasonably upright at all times.
Roll centres are important but not the be all and end all -- the most important thing is that front and rear roll centres are playing in the same b
all park and sensible in relation to the cg height of the vehicle and weight distribution.
A little posative camber on the inside wheel pays dividends particularly on vehicles with soft long travel suspension but only if the roll centres
are chosen so that excessive roll stiffness from the springs and anti roll bar is not required at one end of the vehicle -- ie it dosen't
corner with only 3 wheels on the deck.
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Liam
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| posted on 8/9/06 at 03:55 PM |
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quote:
Originally posted by Syd Bridge
You're thinking in the right direction. Forget those cursed 'roll centres', they're not one or the other, but fictional and
have no bearing how your car behaves.
Cheers,
Syd
You're forever spouting this (without offering your prefered method of suspension analysis, I might add)
I think we all understand the rc is just a virtual point, but the fact remains that it is a useful tool for quickly and easily analysing car
suspensions, especially for those without access to more sophisticated means. Is it really practical/possible for the layman to start deriving a
model of vehicle dynamics from first principles? If the rc was irrelevant to how your car behaves, it's use as a design parameter (at all
levels of the industry) would have died a death long ago.
Liam
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Syd Bridge
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| posted on 8/9/06 at 05:43 PM |
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The few from this forum who I have met personally, and explained this situation to, have been converted and satisfied with my explanation.
I won't put the realities on an open forum, for the same reasons that the people who enlightened me don't.
Whenever I may meet any of you, and you wish to hear my version, then I would be pleased to take the time to explain it.
Cheers,
Syd.
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t.j.
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| posted on 8/9/06 at 06:52 PM |
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Yeah, right, now i know everything?????
Nobody has given an answer.
So i stick with me own design and see what happens when i drive it.
Superb or ......
Grzt Theo
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Fred W B
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| posted on 9/9/06 at 06:58 PM |
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quote:
I won't put the realities on an open forum, for the same reasons that the people who enlightened me don't.
Syd - If you have a better mousetrap, who do you keep mentioning it here, if you are not prepared to share?
Cheers
Fred W B
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C10CoryM
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| posted on 10/9/06 at 02:03 AM |
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TJ, what exactly are you after?
Generally you end up with some positive camber on the inside wheel when cornering. More to do with the need of a increasing (negative) camber curve
when it becomes the outside (loaded) tire than anything else. Also because you get some lift of the chassis on the inside due to body roll if your
roll centre is high (jacking effect).
I like to see 3" (7.6cm) of bump and 3" jounce for street performance or bumpy tracks. As soon as you bottom out, all your carefull
planning goes tits up and the car will try to slide off the track suddenly. If you have smooth corners you can get away with 2" or so (5cm).
Does that help?
As always my disclaimer is that my experience is with heavy cars so bear that in mind .
Syd, maybe you should explain to someone here and let them convert the masses if you are too busy to do so. I'm always up to learn new
information especially if it corrects my faulty way of thinking. You should also explain your views on anti-squat too.
Until then, there is no point gabbing about it. It's like saying you have a really hot wife but no pictures to back it up.
"Our watchword evermore shall be: The Maple Leaf Forever!"
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leto
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| posted on 10/9/06 at 07:03 AM |
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For once I'm more on Syd's line. Keep an eye the roll center but don't let it be your prime desigen criteria. Just look at what
happen at roll, roll center for one side go down while the other side go up. You are clueless to what will happen to your RC in real life. Camber
compensation, on the other hand, is something very real and use full.
“I'm gonna ride around in style
I'm gonna drive everybody wild
'Cause I'll have the only one there is a round”. (J. Cash)
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MikeRJ
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| posted on 10/9/06 at 01:02 PM |
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quote:
Originally posted by leto
Camber compensation, on the other hand, is something very real and use full.
Not at all convinced on camber compensation, at least not the Dax system. Its overly complicated and all the extra suspension joints must cause
unwanted "stiction". If it was so good wht don't dedicated track cars such the the Atom and the WLR etc use it?
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iiyama
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| posted on 10/9/06 at 01:53 PM |
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NOt sure there are that many more joints in the system. About 4 from memory and they are rose jointed. Cant see thats gonna cause a lot, (if any),
stiction.
Also seems to work well. A Dax with CC spanked all others, including 2 atoms, at the recent time attack at silverstone.....
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C10CoryM
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| posted on 10/9/06 at 03:49 PM |
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quote:
Originally posted by leto
Keep an eye the roll center but don't let it be your prime desigen criteria.
Agreed. Main thing is to keep the tires in good contact with the road in your required circumstances. I'd rather have a nice big contact
patch and traction than a RC that barely moves. Having said that, its possible to have both so why would one "Forget those cursed 'roll
centres' "?
Cheers.
"Our watchword evermore shall be: The Maple Leaf Forever!"
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roadboy
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| posted on 10/9/06 at 05:02 PM |
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The Dax system looks as if it should work fine but if so why have the combined minds of the worlds racecar designers not come up with it or copied
it.
As a point of interest the Atom is renowned for poor handling, we have a couple of customers who had them & got rid because of the handling.
Regds
Ian
Jude Performance Services
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iiyama
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| posted on 10/9/06 at 05:09 PM |
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Isnt it in effect just an anti roll bar?
If its broke, fix it. If it aint broke, take it apart and find out how it works!
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MikeRJ
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| posted on 10/9/06 at 07:14 PM |
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quote:
Originally posted by iiyama
Isnt it in effect just an anti roll bar?
No it doesn't stop the body from rolling, it just ensures that the wheels stay at the appropriate angle to the ground. Well, most of the time
anyway. Passive systems like Dax's inevitably don't work well for some suspension movements, in the Dax case a single wheel in bump or
droop will still cause camber change.
I like the idea of these systems, and logicaly it seems like a good idea, but if it gave worthwhile results I'm convinced more cars would have
it.
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