nludkin
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| posted on 27/12/05 at 08:44 PM |
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Top wishbones
I have a question for the suspension designers out there!
If I had a chassis that had the top wishbone mounts about 2-3 centimeters nearer to the centerline of the car than they should be. Suppose that
instead of moving them outwards to where they should be, I was to make longer wishbones. Would this effect the handling of the car dramatically?
Would it result in serious understeer in cornering?
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Mark Allanson
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| posted on 27/12/05 at 09:03 PM |
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The roll anges would interfere with the brake centres thus increasing the thread length by about 120%.
To be serious, I dont have a clue, and would be very disinclined to change anything like that without some serious professional input.
If you can keep you head, whilst all others around you are losing theirs, you are not fully aware of the situation
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omega 24 v6
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| posted on 27/12/05 at 09:05 PM |
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I'm not really a suspension freak (meant in a nice way) but from what i can gather the big question would be bump steer unless tour inner
s/rack joints were in line with the upper and lower inner w/bone mounts.
I'm sure there will be more said shortly
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britishtrident
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| posted on 27/12/05 at 09:16 PM |
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It would change a few things to varying degrees --- camber change on roll and bump, have more minor effects on bump steer and roll centre position
when cornering.
Reduction of camber change on bump and under braking is good but the one that is likely to be a major problem is camber when cornering -- the book
design dosen't put enough load on the inside edges of the tyres as it is so needs quite a bit of static negative camber. If you are using Sierra
front end parts you could win some of it back by using offset mushrooms to increases the virtual king pin inclination.
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Mark Allanson
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| posted on 27/12/05 at 10:13 PM |
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KPI, virtual or otherwise, is engineered in as a direct ratio to the softness of the front suspension, if you have hard suspension, the less KPI you
need.
You could only win back the camber change, if the suspension was sufficiently soft to change the angle of the chassis to the upright with the steering
angle applied (no steering angle change, no camber change with KPI)
If you can keep you head, whilst all others around you are losing theirs, you are not fully aware of the situation
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Triton
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| posted on 27/12/05 at 10:36 PM |
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quote:
Originally posted by nludkin
I have a question for the suspension designers out there!
If I had a chassis that had the top wishbone mounts about 2-3 centimeters nearer to the centerline of the car than they should be. Suppose that
instead of moving them outwards to where they should be, I was to make longer wishbones. Would this effect the handling of the car dramatically?
Would it result in serious understeer in cornering?
How though?
My Daughter has taken over production of the damn fine Triton race seats and her contact email is emmatrs@live.co.uk.
www.tritonraceseats.com
www.hairyhedgehog.com
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nludkin
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| posted on 27/12/05 at 11:53 PM |
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Well, if the top wishbones were longer then the axis of rotation would be in a different place and the arc travelled by the wishbone would be
different?
Surely this would change the graduation of camber from "designed" spec. Would it be significant though?
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pgpsmith
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| posted on 28/12/05 at 04:46 AM |
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You could try to quantify the change by entering both the existing and the proposed geometry into the demo version of SusProg 3D (bevinyoung.com.au)
or the suspension spreadsheet found in the files section of http://groups.yahoo.com/group/Locost_North_America/ . Just remember: "garbage in,
garbage out."
This, taken with some of the previous posts (and reading some Carroll Smith and Alan Staniforth) will at least educate your guess.
Regards,
Pete
"Suspensions are peculiar things," he said, as if trying to explain away some awkward relatives.
Live and don't learn, that's us. - Calvin and Hobbes
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britishtrident
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| posted on 28/12/05 at 11:19 AM |
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quote:
Originally posted by nludkin
Well, if the top wishbones were longer then the axis of rotation would be in a different place and the arc travelled by the wishbone would be
different?
Surely this would change the graduation of camber from "designed" spec. Would it be significant though?
Problem is the book design is marginal in this respect to get the tyre working properly in turns it means loading even for street use at least -1.5
degrees of camber in the straight ahead position --- for the track some use -2.0 or even -2.5 degrees.
It would help to run at a higher ride height so that the lower wishbone slopes doward more from the chassis towards the ball joint but this of
course raises the cg height and has effects on the roll centre.
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NS Dev
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| posted on 28/12/05 at 02:40 PM |
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Don't do it.
The angle at the chassis end and the shorter top bone give the "correct" camber change in roll, changing this will dramatically affect the
dynamics of the car
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t.j.
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 posted on 13/2/06 at 07:30 PM |
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quote:
Originally posted by NS Dev
Don't do it.
The angle at the chassis end and the shorter top bone give the "correct" camber change in roll, changing this will dramatically affect the
dynamics of the car
I've did it, so my camber is changed. So??
I managed to recalculate the bumpsteer to zero. Roll-centre at 50 mm.
My camber gain is .20 deg at 1 inch bump.
If i place the inner pivots of the lower wishbones also closer to the centre-line?
Or should i lower the inner pivots of the upper wishbones and raise the RC to 60 mm?
Is there anybody who did this to?
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