Suspension design help

[Sid]

I had one of those slapping your forehead 'doh' moments yesterday.
I'm looking at designing the suspension for my project with a lot of trepidation because while I'm very good with engines, my knowledge of what's going on underneath a car is a bit sketchy. I've got Mr Milliken's book, but it's very hard work.

Anyway I suddenly remembered what my wife does for a living ( told you it was a 'doh' moment ) - she's a technician at an educational establishment.
Their design and technology department has all sorts of interesting software and the IT people feel that it wouldn't be stretching a point too far to get some of it loaded onto her work laptop, which she brings home. Soooo, I now have access to suspension analysis and design software. I won't say what exactly, in case it actually was stretching a point too far

This is going to be a big help. It's easier to use than I thought, and I've been playing around with it already and working through some tutorials.

But I still don't have a starting point, so I need some help.

Would someone be prepared to give me some basic dimensions from their car ? doesn't matter if it's a GT40, Lola, Porsche - anything will do.

For the front I need the length of the wishbones and the height of the upright, plus the vertical distance between the chassis pick up points.
For the rear I need the length of the bottom wishbone, the top link, the height of the upright, the vertical distance between the chassis pick up points and a length for the radius arms.

This will help me out greatly, and be assured that if there is anything I can do in return, I'll be more than happy to return the favour.

 

[Chip Smith]

I found this to be very helpfull.
3D Double A Arm Wishbone Suspension Bump Steer Software Program
First the full front and rear analizer is under $500 last I looked.
But the good news is they have a demo version to download that is good for 30 days and it has several test vehicles that you can look at and change things around then rerun to see the difference. One of the cars on the list is a C5 corvette and has all the pick up points and a-arm, ball joint and sway bar points.
I really found it easy to use and recomend it.

 

[Jim Cowden]

Sid

Others may have a different approach but you start with your wheel design first.
The offset will govern a lot of your measurements in upright,scrub radius,arm length ect ect.

It is tempting to start making stuff with out the wheel and tyre but you come unglued in the end.

Jim

 

[Sid]

I'm OK with the software I've got Chip, but those Corvette pick up points in the demo will come in very useful.
A donor C5 would be a rare thing in the UK I imagine, but my mates wife works for an engine company that does a lot of business in the USA, so I could get parts shipped here at reasonable cost.

Thanks again :thumbsup:

PS - Just checked C5 prices here - wow, they are expensive for a 10 year old car ( the equivalent of 24k US dollars ) and totally out of the question as a complete donor vehicle. But if I can get parts from the US.....

 

[Sid]

Sid

Others may have a different approach but you start with your wheel design first.
The offset will govern a lot of your measurements in upright,scrub radius,arm length ect ect.

It is tempting to start making stuff with out the wheel and tyre but you come unglued in the end.

Jim

I'll see what retro looking wheels are available for C5 hubs then and pick some sizes.

 

[Chip Smith]

I guess here in the states we get spoiled. I paid $850 for all 8 a-arms and uprights with spindles and stock brakes.
I watched Wheeler Dealers from the UK on a cable channel here and saw them trying to source some Jeep parts from the US and how hard it was.
I might help you out finding some parts and ship if you go that way. Personal Message me if you want.

Chip

 

[Jac Mac]

Do you get any Supra stuff in the breakers yards in the UK, this Toyota stuff has the rack out front, vented rotors etc & uses the Ford 5 on 4.5" pcd stud pattern, both top & bottom w/bones are reasonably compatible with the basic GT40 floorpan /layout & the bottom w/bone uses the coilover suspension as load carrier. Top W/bone is forged alloy, lower is steel... can be either forged or welded pressed steel.
Rear hub carrier brg & axle could be mounted on a fabricated upright @ rear.

 

[David Sturch]

Sid,
Here's mine for the front. Upper lenght 8" (205mm) width 16"(405mm).
Lower lenght 12" (305mm) width 16"(405mm)
Upright hight 8.5' (215mm) Wheel -13"X6" x4.5" backspace.
Let me know how it work's out.
Dave

 

[Bill R.]

Sid

Others may have a different approach but you start with your wheel design first.
The offset will govern a lot of your measurements in upright,scrub radius,arm length ect ect.

It is tempting to start making stuff with out the wheel and tyre but you come unglued in the end.

Jim

I agree with the idea of having the wheels sorted out before the suspension is designed.

What effect does wheel design have on the rear suspension? I understand offset has an effect on the scrub radius of the front. Since the rear wheels don't pivot about the king pin, what affect would offset have on the rear? Im planning on using the factory offset for a C5 Corvette suspension based car in the front and using a deepdish style wheel with corvette c5 suspension in the back. Also the car will be mid engined.

 

[Sid]

Do you get any Supra stuff in the breakers yards in the UK

We do Jac. They have increased in price recently though because of the drifting craze starting to catch on. For every serious drift car though I'd guess there are 10 or 20 that are just styled that way. I checked prices quickly online and I'm looking at the equivalent of 800 US dollars for a complete set of wishbones. Complete car maybe 2k for a really beaten up example.

Dave :- Can you give me a vertical distance between the chassis pick up points for the wishbones ? How much castor do you have at the front ?

I'll start setting it up in the suspension analysis software and maybe it'll give some results you can use.

 

[Sid]

I might help you out finding some parts and ship if you go that way. Personal Message me if you want.

Chip

That's really good of you Chip. It's some months away because my budget is coming from the sale of my current project, which I still have to finish.

 

[Jim Cowden]

I agree with the idea of having the wheels sorted out before the suspension is designed.

What effect does wheel design have on the rear suspension? I understand offset has an effect on the scrub radius of the front. Since the rear wheels don't pivot about the king pin, what affect would offset have on the rear? Im planning on using the factory offset for a C5 Corvette suspension based car in the front and using a deepdish style wheel with corvette c5 suspension in the back. Also the car will be mid engined.

Bill they say that if the rear wheel has a large offset the wheel bearings can have higher loadings due to mechanical leverage, a wheel with a 50-50 split will have less loading if you get my drift.
You may have to monitor the bearing wear on the rear.

Jim

 

[David Sturch]

Sid,
Lower distance 18" and upper 24". Distance between the two is 9.5 inches and hight on the bottom 2.5". The front secttion is 28" OD wide and space your mounting points accordingly if you need the roll center. As for the camber angle I would base it on 3" of travel. The wheel diameter would be 21.9" for the front. Just remember this is all top secret. The front section was based on the Triumph Herald if i'm not mistaken.
Dave

 

[Bill R.]

Bill they say that if the rear wheel has a large offset the wheel bearings can have higher loadings due to mechanical leverage, a wheel with a 50-50 split will have less loading if you get my drift.
You may have to monitor the bearing wear on the rear.

Jim

Thanks Jim
Never thought of that but makes good intuitive sense. So with a deepdish wheel, the arm working on the bearing is longer and therefore greater force is applied to that bearing. Gotcha. And that's good news too. That design element shouldn't be a problem then!

 

[Mick Ridley]

hi
here are 2 good books , both are very informative, and are easy to read, both books are at least 20yrs old, but they do explain, all parts of suspension geometry, and how to design your own

competition car SUSPENSION design construction tuning by Allan Staniforth

this is the more modern book, and is written by an english person (I Think )

HOW TO MAKE YOUR CAR HANDLE by Fred Phun

this book is easyer to read, but it is an american book, with reference to american cars

 

[Sid]

I've got the 'How to make your car handle' Mick, the book by Allan Staniforth I keep hearing about, and how good it is. Handy that I have a birthday coming up

What I want to do with this project is to try and recreate some of the experience of driving a 60's GT racer. Both the good bits and the bad bits, so I'd rather have suspension which is 'authentic' than modern cutting edge.
20 year old books are fine.