Tralfaz
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| posted on 23/5/07 at 03:11 PM |
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Roll Couple Distribution. (%)
Anyone have any thoughts,comments,suggestions, or real world data on this subject with regards to Sevens or similar cars. (Track Use)
Regards,
T
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speedyxjs
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| posted on 23/5/07 at 03:16 PM |
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At the risk of sounding a bit stupid, what is Roll Couple Distribution?
How long can i resist the temptation to drop a V8 in?
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jabs
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| posted on 23/5/07 at 03:18 PM |
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Roll Couple Distribution - is a controlling factor of understeer and oversteer. Increasing roll stiffness at one end of a car will produce a greater
tire slip angle of the outside tire.
To control a car that is oversteering you would increase the roll stiffness at the front end of the vehicle. Install a stiffer outside front spring or
stiffer anti-roll bar. The reverse is also true for an understeering car.
Roll couple is adjusted with spring and anti-roll bar rates. The stiffer end of a vehicle will lose traction first. So if a cars front suspension is
stiffer that the rear, the roll couple distribution will produce understeer because the front end is handling more weight transfer.
or see http://members.aol.com/sccacuda/cars/7SmthTa.html
[Edited on 23/5/07 by jabs]
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britishtrident
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| posted on 23/5/07 at 07:39 PM |
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How long is a piece of string ?
On seven type cars the roll centres are largely dictated by the rear suspension system used,
For track use in Clubmans Formula racing rear axle location has tended towards lower roll centres with body roll controlled by anti-roll bars.
Caterham/Lotus 7 style suspension location has a much lower roll centre than "The Book" or Westfield style panhard rod, Munford or Wobble
links will give an even lower rear rc.
Some research into the development history of the Mallock U2 might point you in the right direction.
Common practice seems to be to get the front rc 20 to 40 mm lower than the rear and tune out the resultant oversteer/understeer by
softening/stiffening the rear springs.
[Edited on 23/5/07 by britishtrident]
[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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Tralfaz
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| posted on 23/5/07 at 08:53 PM |
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My suspension is completely designed and fabrication is nearly complete. Everything was designed in Susprog3D and fully analyzed. At this point I need
to select spring and ARB rates.
What I had originally planned seems ok, but the Roll Couple Distribution has only a very slight front bias. From what I had read there was some
indication that a more signifigant front bias was desirable (58-60%). As metioned, I can easily tune by swapping out Springs/ARB's, but I was
looking for any "Free" input.
T
[Edited on 23/5/07 by Tralfaz]
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Doug68
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| posted on 23/5/07 at 09:15 PM |
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There needs to be sufficient difference in the front to rear wheel frequency so that harmonics (?) aren't set up between the 2 ends. 10 cpm
appears to be enough from what I've read.
Also I've seen vehicles end up with higher wheel frequencies at the front than the rear which seems counter intuitive but appears to work.
Ignore spring rates until you find the required wheel frequencies to give the weight transfer required.
For a load case assume the vehicle can pull a constant 1g turn, assuming the same size tires all round, you'll want a little bit more load on
the front so it's grip is exceeded first, then it'll understeer (gently hopefully) but with a prod of the right foot you'll be able
to get the back end to catch up.
I expect to go through several sets of springs and ARB's in the search to make my car do this, when the time comes.
[Edited on 23/5/07 by Doug68]
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britishtrident
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| posted on 24/5/07 at 07:32 PM |
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Driver preference pays such a big part only way is to start with by selecting the frequecies and work from there, an adustable ARB at at front is a
big help.
[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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