Delinquent
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| posted on 2/10/07 at 02:38 PM |
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Virtual Swing Arm length
My latest battle in the continual confusion that is car suspension...
Two different reading sources both mention choosing a virtual swing arm length, but neither chose to make note of any beneficial way to chose it! Is
this a case of "I know - 17.325 meters is a nice number" or is there any theory or formula's that might aid one in the choice?!
Asked this in a couple of places now, and not had a response yet so am leaning heavily toward the "stick a pin in the screen" approach
[Edited on 2/10/07 by Delinquent]
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britishtrident
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| posted on 2/10/07 at 02:51 PM |
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For a front engined rwd road car always should be greater than twice the track width through the full range of travel to avoid nasty jacking
effects.
Also avoid making too long (17 metres sounds too long for a road car) because it reduces the camber gain on roll. Longer you make the virtual swing
axle the more you will have to increase the roll resistance.
For example Morgans have a front virtual swing axle of infinite length but drive OK(ish !) because the suspension is rock hard, same goes for most
current F1 cars.
The front of rear engined RWD cars and rear of FWD cars are special cases. ie Imps worked very nicely with swing axles on the front and Minis/Metros
with plain trailing arms on the rear.
[Edited on 2/10/07 by britishtrident]
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Delinquent
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| posted on 2/10/07 at 03:03 PM |
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sorry - forgot to mention it's of the mid engined variety! Interesting point on the reduction of camber though - I was playing around and going
on the book I'm reading at the moment, I'm allowing 2-3 deg max roll, so need to allow for up to 3 deg camber change on bump - which
I'm nowhere near getting atm.
[Edited on 2/10/07 by Delinquent]
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britishtrident
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| posted on 4/10/07 at 08:08 AM |
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You can never get enough camber gain on bump if you try you just end up with the equivalent of a swing axle.
Most cars these days run with 1 degree negative camber --- radial tyres are fairly tolerant of camber compared to old Xply tyres.
Also at the front the Castor angle will give extra negative camber when the steering is turned.
[Edited on 4/10/07 by britishtrident]
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britishtrident
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| posted on 4/10/07 at 08:10 AM |
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You could do a lot worse than look at the geometry of an MGTF (the 21 Model century not the 1950s model)
[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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Delinquent
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| posted on 4/10/07 at 09:07 AM |
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quote:
Originally posted by britishtrident
You can never get enough camber gain on bump if you try you just end up with the equivalent of a swing axle.
Most cars these days run with 1 degree negative camber --- radial tyres are fairly tolerant of camber compared to old Xply tyres.
Also at the front the Castor angle will give extra negative camber when the steering is turned.
[Edited on 4/10/07 by britishtrident]
A good point - must remember to look at this more dynamically. Just realised that the measurements taken on camber were done with just the body roll
introduced, not with the wheels turned! Ooops.
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