liam.mccaffrey
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| posted on 25/7/04 at 04:16 PM |
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to be equal length wishbones or not to be, that is the question
which is better unequal length wishbones
OR
equal length wishbones
any advantages or disadvantages or opinions welcome
do you get undesireble camber changes in body roll with equal length wishbones, i it severe, can it be minimised with ARB?
any advice appreciated
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JoelP
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| posted on 25/7/04 at 05:17 PM |
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with equal length wishbones (assuming they are parallel too), any body roll leads to adverse camber (cant remember if out at the top is pos or neg!).
so you want to minimise body roll, either by strong springs or (preferably?) with an ARB.
with a shorter upper bone the top of the wheel is pulled in in either bump or droop, so roll is less bad.
basically the choice is determined by the main use of the car.
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Mark Allanson
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| posted on 25/7/04 at 08:11 PM |
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I will probably be told different later in the thread, but the idea of unequal length wishbones is to give a negative camber on compression to match
the roll of the car so the wheel maintains the static camber it was setup with. The trick is to match the camber change to the body roll. For this
reason all those suspension kits you can buy for saxos etc actually detract from the handling and make my life difficult trying to set them up after
an accident.
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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boost
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| posted on 25/7/04 at 08:43 PM |
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there is a good section on this subject in tuning to win.
ISBN 0-87938-071-3 this is one of the best books in my colection
it shows you how to work out role centors and the things you need to consiner when desining suspension linkage.
[Edited on 25/7/04 by boost]
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iwbunting
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| posted on 25/7/04 at 09:23 PM |
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I'm in a similar position.Equal/unequal rear toe in or not.
I bought the book by Des Hamill - Suspension and breaks for road and track ISBN 1-903706-73-4.If nothing else it explains in understandable terms all
the ins and outs of the various suspension types and mentions a lot about wishbone front and rear suspension.Hope this helps.
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liam.mccaffrey
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| posted on 25/7/04 at 09:24 PM |
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ok how much difference would there be between say a car with equal length and paralell wishbones and a well set up ARB system
and
say a book standard front suspension setup without ARB
how would they differ in various situations, eg hillclimb, circuit racing, motorway cruising that sort of thing
Basically what i am trying to say is should i have equal wishbones or not, i am building a custom chassis anyway so building to book dimensions is not
a benefit
cheers
BTW i have the des hammil book and to be honest i didn't like it i found it really easy to put down
[Edited on 25/7/04 by liam.mccaffrey]
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iwbunting
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| posted on 25/7/04 at 09:27 PM |
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Oh well so much for that suggestion.
Hope you have better luck with others.
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Mark Allanson
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| posted on 25/7/04 at 09:28 PM |
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The way I see it, the stiffer the ARB, the more equal the wishbones can be.
End result required is that the tyre contact patch is maximised at all times
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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iwbunting
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| posted on 25/7/04 at 09:30 PM |
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Just a thought ! Have a look at ........
http://www.gmecca.com/byorc/index.html
Lot of info across the board.
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boost
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| posted on 25/7/04 at 09:30 PM |
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i would have shorter top arm what slope down and have the bottom ones paralell with the floor.
to work out how much and at what angle take a bit of thinking and working out.
[Edited on 25/7/04 by boost]
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liam.mccaffrey
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| posted on 25/7/04 at 09:31 PM |
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iwbunting
i'm sorry i didn't mean for the post to sound negative in any way, the des hammil book is really good and full of useful stuff, what i
should have said was i found it dificult to read, do you know what i mean? thanks for the sugestion it was much appreciated
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iwbunting
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| posted on 25/7/04 at 09:33 PM |
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Anyone else read des hamills book ???
Conclusion ... Not worth reading ????
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iwbunting
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| posted on 25/7/04 at 09:40 PM |
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This is something that i am looking into myself.
Suggestions so far would have it that the top wishbone should ideally be 2/3rds length of bottom and sit lower at the chassis end whilst the bottom
should sit higher,although both of these factors as i see it could be made adjustable by welding multi postion brackets onto the chassis.
On a similar line should rear IRS hav toe in or not dependant on use or be adjustable.
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boost
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| posted on 25/7/04 at 10:15 PM |
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it is hard to put in to words but here we go
ok the top arm is shorter so when the car rolls the outside wheel will go in neg camber because it has a shorter arc the it will pull the top of the
wheel in so the tire will stay flat on the floor.
The top arm is angled down from the wheel to the chasie so the inside wheel will go in to posative camber when it drops because when it reches 90
degres to the chasie it is at it most exstended point comperd to the bottom wish bone.
but there is a compromise the camber changers when you go over a bump.
the longer you arms are the less differnce between the arm there is so this problem is not as bigger problem.
to work out your roll center you draw a mock suspention set up to scale and exstend a line from the top and bottom wishbone and where they meet take a
line from that point and draw a line to the middle of the tire on the other side then draw a line down the middle where these lines meet is where the
roll center is it has nothing to do with the center of gravity (a high center of gravity meens it will roll round this point more)
hope you get it?
try cuting bits of paper out to do a mock up and see what happens you can use drawing pins as pivits
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iwbunting
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| posted on 25/7/04 at 11:11 PM |
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You could also try downloading the suspension software from : -
http://locost7.info/mirror/les.php
or try :-
http://locost7.info/files/suspension/slarck.zip
Not sure if they will give the answers you are looking for but give it a try.
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iwbunting
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| posted on 25/7/04 at 11:20 PM |
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Just remembered.
A good explanation of a-arm suspension at :- http://www.rqriley.com/suspensn.html
Refer to the section "The Double A-Arm Suspension System" and figure 12 and also the last section "Suspension Guidelines for
Extremely Low Mass Vehicles".
Hope these might help you.
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pbura
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| posted on 26/7/04 at 01:24 AM |
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Really encourage you to stick to the reading, Liam. If you're designing a car you should have a handle on the various trade-offs and
compromises.
"Tune to Win" (recommended earlier) is very readable. Caroll Smith is practical and funny, and does a good job of diagrams. My only beef
is no index. Allan Staniforth is also easy to read, and humorous. I have "Race and Rally Car Source Book", but understand that all that
material, plus more, is in "Competition Car Suspension".
Don't feel bad if things don't start to make much sense until the second or third time through.
Have noticed that the rears of IRS cars have less camber gain than the fronts, no doubt because the premium is on getting the power down when the car
is going straight. As a result, some rear grip is lost in cornering, which is not too bad because it's the front tires that do most of the work
in cornering. This is a classic example of a design trade-off.
BoL,
Pete
Pete
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