nitram38
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| posted on 3/5/06 at 02:28 PM |
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Un-equal wishbones
I am currently designing my next project in solidworks.
I want the wishbones to be spot on so I have played around with different mounting points and wisbone lengths.
What do you think of 1/4 degree neg camber gain for 2" of suspension travel on each side?
Would this be a good amount?
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kb58
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| posted on 3/5/06 at 02:31 PM |
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No one can answer that because it depends on weight, CG height, track width, caster, type of tires, spring rate, anti-rollbar rate, shock valving...
and most importantly, what the car is being used for.
[Edited on 5/3/06 by kb58]
Mid-engine Locost - http://www.midlana.com
And the book - http://www.lulu.com/shop/kurt-bilinski/midlana/paperback/product-21330662.html
Kimini - a tube-frame, carbon shell, Honda Prelude VTEC mid-engine Mini: http://www.kimini.com
And its book -
http://www.lulu.com/shop/kurt-bilinski/kimini-how-to-design-and-build-a-mid-engine-sports-car-from-scratch/paperback/product-4858803.html
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nitram38
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| posted on 3/5/06 at 02:36 PM |
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This is for the front suspension on a rear engined car. The 2" travel will probably be the maximum travel.
The rear suspension will have greater camber gain of around 1/2 to 1 degree.
It will be a road/trackday car.
What have some of you guys used on your own cars?
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kb58
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| posted on 3/5/06 at 05:49 PM |
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2" suspension travel... total or +/-2"?
What's your target front roll center height?
[Edited on 5/3/06 by kb58]
Mid-engine Locost - http://www.midlana.com
And the book - http://www.lulu.com/shop/kurt-bilinski/midlana/paperback/product-21330662.html
Kimini - a tube-frame, carbon shell, Honda Prelude VTEC mid-engine Mini: http://www.kimini.com
And its book -
http://www.lulu.com/shop/kurt-bilinski/kimini-how-to-design-and-build-a-mid-engine-sports-car-from-scratch/paperback/product-4858803.html
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nitram38
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| posted on 3/5/06 at 06:55 PM |
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2" is total suspension travel.
I have not calculated the roll centre yet, although I am not expecting excessive roll as this will be a wide, low car.
All I am after is knowing whether this is a typical value or should I be increasing or decreasing it.
Increasing negative camber has got to be better in corners, but obviously going too far would not.
If I run with 1/4-1/2 a degree stationary, then adding a 1/4 degree under load must help?
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kb58
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| posted on 3/5/06 at 07:32 PM |
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But that's what you need to determin, how much the car's going to roll. If you have rock hard suspension, a wide car, and don't
pull 2Gs, it's not an issue.
You have to figure the lateral weight transfer to find how much the suspension compresses. That'll tell you how much camber compensation you
need, because with the above information you will know how much the car leans.
If you want to figure these number on your own I suggest the following book:
http://www.amazon.com/gp/product/1560915269/qid=1098139991/sr=2-1/ref=pd_ka_b_2_1/104-5668310-0335108?n=283155
I can't throw out a number because you haven't supplied all the design information. The above book will let you calculate it yourself.
[Edited on 5/3/06 by kb58]
Mid-engine Locost - http://www.midlana.com
And the book - http://www.lulu.com/shop/kurt-bilinski/midlana/paperback/product-21330662.html
Kimini - a tube-frame, carbon shell, Honda Prelude VTEC mid-engine Mini: http://www.kimini.com
And its book -
http://www.lulu.com/shop/kurt-bilinski/kimini-how-to-design-and-build-a-mid-engine-sports-car-from-scratch/paperback/product-4858803.html
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Mad Dave
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| posted on 3/5/06 at 08:15 PM |
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You need to position the roll centre first and then experiment with the locations of wishbones etc. You can make a car corner flat with soft springs
if you wanted just by setting the geometry, its not just the CofG and width that determines this. I started off with the roll centre position and
then looked at the roll centre migration. If the roll centre shifts dramatically you get inconsistent handling. The camber gain was a result of this
and was ok compared to body roll. If you concentrate on maximising the camber gain then the roll centre migration shifts massively (I tried it).
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NS Dev
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| posted on 4/5/06 at 01:36 PM |
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There are umpteen answers to this one but in practical terms I'd aim for a bit more than that.
Ultimately you're trying to present a square tyre print to the road, and regardless of roll, I would think tyre tuck-under would require 1/4
degree alone??
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
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nitram38
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| posted on 4/5/06 at 01:43 PM |
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I have played around with the bracket mount postions and I have only managed to get 0.5 degree max.
Thanks for the advice, I may have to redesign the chassis slightly.
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Marcus
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| posted on 4/5/06 at 01:51 PM |
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A book Locost has unequal length wishbones, the top being shorter by about 2" (ISTR). I remember messing around with my chassis, before it had
the engine in, and the wheels stayed pretty much square to the tarmac even at quite high roll angles. Sorry I can't put numbers to it (
I'm not a suspension guru!), but it wouldn't be a bad point to start.
Marcus
Marcus
Because kits are for girls!!
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nitram38
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| posted on 4/5/06 at 01:57 PM |
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I can make the bones not gain any camber or even gain positive (not nice). I assumed that to gain a little more negative camber under braking and
turning would be benificial to grip.
I think that I will stick to the 0.5 degree gain in negative.
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NS Dev
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| posted on 4/5/06 at 02:21 PM |
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Ok, just done a quick and very rough recalc and maybe 0.5 is enough, certainly at least 0.25 more than book, prob 0.3 more than book, so I'll
shut up!
PS negative under braking is bad, but you can't do a damn sight about it if you want it in roll!
[Edited on 4/5/06 by NS Dev]
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
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britishtrident
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| posted on 4/5/06 at 02:25 PM |
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Negative camber under braking is not good -- but it is well nigh impossible to avoid if tyres are going to be at anywhere near sensible cambers when
conering.
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nitram38
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| posted on 4/5/06 at 02:29 PM |
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Cheers gentlemen.
Suck it and see time!
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NS Dev
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| posted on 4/5/06 at 03:04 PM |
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I usually use the trial and error method!
it's amazing really, you can look at so many carefully designed cars, where a couple of years later somebody points out a glaring error in the
suspension design.
Lots to be said for trial and error as long as there has been a liberal application of common sense!
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
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nitram38
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| posted on 4/5/06 at 04:29 PM |
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I have had an interesting chat with someone who builds and races R1 rear engined cars.
He advised me that 1/4 degree is about right. He said there are other factors, but most suspension designs come out around that figure.
So a 1/4 it is!
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