rpmagazine
|
| posted on 8/8/07 at 12:57 PM |
|
|
A arm length
What real pivot to pivot swing arm lengths have people used on the rear of a middy and why?
|
|
|
|
|
kb58
|
| posted on 8/8/07 at 01:19 PM |
|
|
That's too vague of a question; it's like asking what spring rates people use. Without knowing everything else, the answers aren't
very useful.
That said, a general guideline is that the A-arms should be as long as possible, to minimize camber change with wheel movement. Your engine choice and
body shell dictate the inside and outside limits.
[Edited on 8/8/07 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
|
|
|
rpmagazine
|
| posted on 8/8/07 at 01:32 PM |
|
|
Not really too vague, I am not asking for information on suspension design, that is taken care of. Instead I have packaging constraints with the
component group I currently have and the top rear A arm is around 250mm long with the current 1570mm rear track and transverse engine. Body shell will
be made to suit chassis, so that is not a problem.
I would like to run longer arms but cannot as it stands and would like to know what other people have been able to get to work.
|
|
|
Doug68
|
| posted on 8/8/07 at 02:40 PM |
|
|
Bottom ~530mm
Top ~320
Track ~1620
But I don't have a sideway engine in the way to worry about.
As you can see from the picture there's still a bit more design work to do here, ARB design, a few brackets etc.
 
Rescued attachment rear.jpg
|
|
|
nasty-bob
|
| posted on 8/8/07 at 04:20 PM |
|
|
Bottom: 480mm
Top: 412mm
Track 1600mm
I also have the engine the right way round, but all cars like yours will have that problem. You have the advantage of a short wheelbase (potentially)
so its swing and roundabouts.
Your a bit stuck with it really...unless you make it 2 meters wide 
ATB
|
|
|
kb58
|
| posted on 8/8/07 at 04:49 PM |
|
|
It all comes down to tire control. What camber curve do you need; that's what sets the length. Also, if you have really stiff suspension, the
car's going to lean so little that it just doesn't matter in the big picture. That's why I was saying that it's hard to make
suggestions without knowing the overall design goals. What's the car for?
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
|
|
|
Alan B
|
| posted on 8/8/07 at 11:43 PM |
|
|
I have 260mm top, 318 lower and 1600 track.
Honda I-V-TEC transverse mounted.
|
|
|
Doug68
|
| posted on 9/8/07 at 12:56 AM |
|
|
KB58, you're right the numbers in themselves are fairly meaningless.
But trivia goes they're interesting enough.
Doug. 1TG
Sports Car Builders WA
|
|
|
rpmagazine
|
| posted on 9/8/07 at 03:29 AM |
|
|
KB58 I am aware of the camber curves and under steer curves etc etc. It is more of a packaging issue that I am concerned about, after all
'perfaction' WRT suspension is just a myth.
The car is for competition work and fairly large amounts of suspension travel (150mm total) will be called for.
Nasty...yes can make it wider, but then that has its disadvantages too!
Doug I've always admired your solidworks drawings...wish I had the time/skill to do the same.
Interesting to see the track widths. How many have a wider front track?
|
|
|
kb58
|
| posted on 9/8/07 at 04:07 AM |
|
|
I do, the Mini (even stock) has about a 2" wider front track.
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
|
|
|
Doug68
|
| posted on 9/8/07 at 04:18 AM |
|
|
RPMagazine, I'm using SolidEdge BTW. At the start of this project I didn't know how to use this thing at all and have learned it along
the way.
From my point of view if I didn't have access to this type of tool I'd never have got the design stage I'm at now as the iterations
would just take too long.
So I would say it is a very worthwhile exercise to go learn.
Similarly programs like Susprog3D make the iterative process of suspension design a LOT less effort.
None of these tools stop stupid design though 
Front track is 1600mm I lifted the numbers for track wheel - base from the ford GT as a starting point. Basically its as wide as practical and as
long as it needs to be. The wheel base has shrunk a bit during the design process depending upon how the weight balance looks further on I may force
that back in again though.
|
|
|
Syd Bridge
|
| posted on 9/8/07 at 09:02 AM |
|
|
All of my rear suspension drawings for the sports racecars usually end up with the top wishbone slightly longer than the lower.
Work it out for yourselves. 
Cheers,
Syd. 
|
|
|
v8kid
|
| posted on 9/8/07 at 07:45 PM |
|
|
Chaps I know I'm deviating a bit but your track widths are quite a bit more than I'm used to. A 1600mm track allowing for 10" wide
wheels at the rear will give an overall width of 1854mm. Hells Bells!! that won't even fit on a standard trailer !!
My track at the rear is 1490mm with 10" wide rims gives an overall width of 1744mm which I thought was the giddy limit but I'm feeling
inadequate now.
Is there some confusion here between track and width?
|
|
|
Alan B
|
| posted on 9/8/07 at 09:00 PM |
|
|
No confusion here...1600mm mid-tyre width to mid-tyre width..ie track
|
|
|
kb58
|
| posted on 9/8/07 at 10:55 PM |
|
|
quote:
Originally posted by Syd Bridge
All of my rear suspension drawings for the sports racecars usually end up with the top wishbone slightly longer than the lower.
Work it out for yourselves.
Cheers,
Syd.
So the upper arm pulls inward slower than the bottom, resulting in large positive camber in bump and droop?
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
|
|
|
Tralfaz
|
| posted on 9/8/07 at 11:41 PM |
|
|
Not Necessarily, if the upper is horizontal at rest and the lower angles down, in bump the upper will be pulling in and the lower pushing out.
Messy in droop though....but the car may be running Zero droop
|
|
|
Doug68
|
| posted on 9/8/07 at 11:50 PM |
|
|
The overall width of my car is a bit under 2m.
Hopefully I'll be driving it not putting it on a trailer
Some car widths:
Ford GT: 1953mm
Ferrari F430: 1905mm
Dodge Viper: 1911mm
McLaren F1: 1821mm
Lamborghini Gallardo: 1900mm
|
|
|
rpmagazine
|
| posted on 10/8/07 at 01:12 AM |
|
|
I was working on 1570 rear track, 17 x 9" wide Enkei rims (wt 7.3kg), 45mm offset plus 8mm tyre bulge and OA width of 1830-1840mm with bodywork
overhang for ADR compliance.
It will fit comfortably on the trailers available at my local garage, but as Doug said it is intended for road use.
It is telling that Porsche cars are not that wide.
WRT the engine wrong way around, the current design was chosen to meet specific project guidelines and was not made from any philosophical position! I
would prefer the inline arrangement, but do not want the additional/potential $10,000 cost, which would blow out the $40,000 budget.
Transverse does have the torque input being inline with the centreline of the car, which is an advantage for the large torque/low weight car at the
limits of adhesion...but it is a bugger to package!
[Edited on 10/8/07 by rpmagazine]
|
|
|
v8kid
|
| posted on 10/8/07 at 08:40 AM |
|
|
"Some car widths:
Ford GT: 1953mm
Ferrari F430: 1905mm
Dodge Viper: 1911mm
McLaren F1: 1821mm
Lamborghini Gallardo: 1900mm"
The respective tracks are quite a bit less a quick net search showed 1709,1616.1547,1473,1592 which is significant.
Also all these cars are luxury items and relatively heavy if we want examplars would the Juno be more appropriate at 1551 track and 550kg?
Anyhow back to the question of arm lengths top 290mm bottom 325mm and it sits well on the road under all conditiond (a bit loose under power on dirt
track roads but thats to be expected).
I know the length should be longer but it was a packaging issue to get the c of g lower I wanted to put the exhausts right where the ideal pickup
points were and weight ,as always, triumphed over geometry.
|
|
|
Doug68
|
| posted on 10/8/07 at 10:31 AM |
|
|
To be clear...
The car I'm building has a rear track of 1620mm and will be ~1950mm wide.
Weight wise it's going to be a FB at ~950kg.
|
|
|
rpmagazine
|
| posted on 11/8/07 at 12:47 AM |
|
|
quote:
Originally posted by v8kid
"Some car widths:
Ford GT: 1953mm
Ferrari F430: 1905mm
Dodge Viper: 1911mm
McLaren F1: 1821mm
Lamborghini Gallardo: 1900mm"
The respective tracks are quite a bit less a quick net search showed 1709,1616.1547,1473,1592 which is significant.
Also all these cars are luxury items and relatively heavy if we want examplars would the Juno be more appropriate at 1551 track and 550kg?
Anyhow back to the question of arm lengths top 290mm bottom 325mm and it sits well on the road under all conditiond (a bit loose under power on dirt
track roads but thats to be expected).
I know the length should be longer but it was a packaging issue to get the c of g lower I wanted to put the exhausts right where the ideal pickup
points were and weight ,as always, triumphed over geometry.
Personally I would not pick the Juno given it's suspension travel from max droop to max bump may only be 60-70mm and I plan on more than twice
that.
I have some other options to get longer arms but I am loosing a great deal of torsional stiffness in doing some of them...I will post pics
tomorrow.
I'll have a good look at a strut now...easy to package and perhaps a reasonable solution at the rear.
|
|
|
