Looks like im going to have to design my own wishbones.....

[darkcat]

Well, im at a point now where im going to have to design and build my own wishbones, i have a pair of MX5 front hubs, but the generic wishbones arent going to fit my build.
Does anyone have any experience doing this? i know its a BIG step, and i hope to god that my welding is up to scratch (will over-engineer!)

Does anyone have any tips on suspension design? or any good websites for this sort of thing?

Im going to follow quite closely my TVR Chimaera design.....

---

www.miniv8.co.uk ----

Edited by darkcat on Friday 20th August 14:48

[Liquid Knight]

Have a look at how Mark and Jamie at Wisbech Engineering did it.

[Dr Derek Doctors]

Meh, wishbone design is fairly straightforward.

If you already have set suspension mounts on the chassis and pick up points on the uprights it's just a case of conecting the dots and using some common sense.

Do you have any 3D CAD software? If you do it'll be a stroll in the park.

[GTRCLIVE]

You need to do a little drawing 2D cad or even pen and paper. But remember you have to be close to the original inboard pickup points other wise your end up with bad Bump Steer.

Are you keepin the original inboard mini Pick points ??



This is the Std Mini front end....

[GTRCLIVE]

Add that 100mm to the vertical dims to get the normal ride height position.

[darkcat]

GTRCLIVE said:

Are you keepin the original inboard mini Pick points ??

not at all no, im building a custom chassis...

so a questions to throw out there:
- equal or unequal length?

[singlecoil]

darkcat said:

GTRCLIVE said:

Are you keepin the original inboard mini Pick points ??

not at all no, im building a custom chassis...

so a questions to throw out there:
- equal or unequal length?

Please don't think I am being rude, and I am certainly not trying to be discouraging, but are you sure you are tackling this project in the best possible way, and from the right position (in terms of knowledge and experience)?

[Sam_68]

darkcat said:

Does anyone have any tips on suspension design?

I'm gonna be a bit more blunt than Singlecoil: based on what you've said so far, the best tip I can give you on suspension design is to make sure your life insurance is paid up...

...or find someone who knows what they are doing to design it for you.

The actual, physical design of the wishbones is easy; as Dr DD says, it's just a matter of joining the dots with a bit of common sense.

Getting the geometry right in a car with the extreme short wheelbase and weight distribution issues of a V8 engined Mini (I assume this is the project you're asking in connection with?) is something very few experienced suspension experts (myself inluded) would be willing to tackle. Not only do you need to work out inboard pick-up positions that give acceptable steering and camber curves with the MX5 uprights, but you need to consider the roll centre location, roll axis inclination and front & rear roll stiffness (which means designing the front and rear suspension to work with each other).

Given the fact that the weight distribution and wheelbase will have an overbearing influence on the way the car handles, I'd be looking to design the uprights to suit the geometry, not the other way round.

Good luck.

You'll need it...

[darkcat]

singlecoil / Sam
- yes i understand the issues, I have a very good understanding of suspension geometry / handling effects etc, but i really dont want to just jump in to creating new suspension parts, hence the questions.
I must say however, that this is NOT being designed as a track car, so perfect handling and stability are not my major concern, though it would be nice if it doesnt spin out on every roundabout.
the reason im looking at going about it this way is that i have not yet found a suitable donor setup.
Im going to be setting it up reasonably hard, and with quite large ARB's, to minimise roll etc.

Edited by darkcat on Saturday 21st August 12:53

[Sam_68]

darkcat said:

I have a very good understanding of suspension geometry / handling effects etc.

OK, just so long as you know what you're up against.

Out of interest, where is the engine? front or middle?

And what are you doing about the roll centres? I note from one of your other posts that you seem to be suggesting that you will graft an MX5's rear suspension onto the back, too, so are intending to replicate MX5 geometry front and rear?

If so, how do you intend to overcome the very different static and dynamic weight distribution?

Ackerman, with the shorter wheelbase?

Don't forget to invite us to the funeral.

[darkcat]

Sam_68 said:

darkcat said:

I have a very good understanding of suspension geometry / handling effects etc.

OK, just so long as you know what you're up against.

Out of interest, where is the engine? front or middle?

And what are you doing about the roll centres? I note from one of your other posts that you seem to be suggesting that you will graft an MX5's rear suspension onto the back, too, so are intending to replicate MX5 geometry front and rear?

If so, how do you intend to overcome the very different static and dynamic weight distribution?

Ackerman, with the shorter wheelbase?

Don't forget to invite us to the funeral.

Front engined (well.. pretty much mid..)

Im not going to be using the original rear sub frame at all, so can play about with the correct mounting positions etc to get the geometry close enough. As i said it will be set up VERY firm, so wil have a smaller window of deflection to worry about (for the dymanic weight dist)

Ackerman... i'll be using standard MX5 hubs and rack so should be ok, cal always tweek if required

[Sam_68]

darkcat said:

As i said it will be set up VERY firm, so wil have a smaller window of deflection to worry about (for the dymanic weight dist)

Good idea, provided you only intend running on very smooth tarmac. Don't forget to ring your local Highways Department to ask them to start filling in the potholes now, so that they'll be ready by the time you've got the car finished.

I've said it before on these forums, but stiff ARB's are the work of the Devil and a crutch for the incompetent suspension designer.

darkcat said:

Ackerman... i'll be using standard MX5 hubs and rack so should be ok

Despite the different wheelbase and weight distribution?

Don't forget that 100% Ackerman is acheived when lines projected along the steering arms meet in the centre of the rear axle... move the rear axle relative to the front, and you change the Ackerman effect. And, of course, the amount of Ackerman you actually want will depend on how the front end loads up in a corner (ie. diagonal weight transfer, which is dependent on roll axis inclination and front:rear roll stiffness).

You seem to be trusting to pot luck and lack of suspension movement?

Edited by Sam_68 on Saturday 21st August 14:02

[Dr Derek Doctors]

Man you are taking on a big job, starting from scratch needs some very specific knowledge, CAD, and most of all experienced people... just knowing the theory isn't really enough.

There are a lot of pitfalls that you can easily trip into and things that you can miss.

As I have said 3D CAD is a godsend, allowing you to visulise the workings and store the geometry as you go.

This was the sort of thing we used back in our student days:


Also as said ARB's are often used as crutch to cover up poor suspension design.

If I can say one more thing decide on as much stuff as possible before you start, uprights, shocks, rod ends, adjustment points etc etc do all of that and then start doing the geometry. Otherwise you'll just go around in a never ending circle.

[Sam_68]

Dr Derek Doctors said:

...3D CAD is a godsend, allowing you to visualise the workings and store the geometry as you go.

Especially the more recent versions that allow you to apply 'constraints' to objects, so that you can create 'virtual' ball joints and so on, allowing you to see and accurately measure what happens when you move the suspension through its working range. I can now do in a couple of hours what would have taken weeks of iterative drawings on a drawing board back in the old days, and I can visualise 3D geometry that would quite simply have turned my brain to marmalade.

But unless you've got access to some very fancy software (which I haven't, unfortunately ), you'll also need to do a bit of spreadsheet programming to figure out the basics of what's likely to happen when you apply real forces (via the unsprung CoG) to real springs (tip: cars don't roll around their roll axis in a corner, as many of the textbooks imply). And (further tip) you'll find the calculations vastly easier and more accurate if your roll centres don't move around dynamically.

Edited by Sam_68 on Saturday 21st August 19:48

[FlossyThePig]

What have you read about chassis design? It may be a simplistic view but the principles were defined a long time ago.

Allan Staniforth adopted a very empirical approach in his first book "High Speed Low Cost" (first published in 1969). I have read some comments knocking his string computer but it is a very quick way of showing what happens to wheel angles during at various stages of suspension travel.

The Costin and Phipps "Racing and Sports Car Chassis Design" was published in 1961 and still gets mentioned in more recent publications.

[Sam_68]

FlossyThePig said:

It may be a simplistic view but the principles were defined a long time ago.

That may well be the biggest problem; Costin and Phipps dates back to the days when 4.5" wide crossplies were considered suitable attire for high performance cars, and when Formula 1 cars had the sort of torsional stiffness, spring rates and even power:weight ratios that would be considered a little limp on some modern lightweight road-going sports cars.

At best, most of the 'amateur' textbooks treat dynamic weight transfer and damping as bolt-ons, whereas there is a good argument to say that they are now at least as important as geometry (if not more so)... especially if you're planning to bolt a couple of hundred kilos of torquey V8 into the middle of an 80" wheelbase!

I'd agree that Staniforth's 'Competition Car Suspension' remains the best primer, possibly followed up by Carroll Smith's books once you have grasped the basics (then Milliken & Milliken as a reference text if you get serious - it's not the sort of book you'd read cover to cover!).

[Dr Derek Doctors]

Sam_68 said:

(then Milliken & Milliken as a reference text if you get serious - it's not the sort of book you'd read cover to cover!).

Our university Bible

[Paul Drawmer]

I subscribe to racecar engineering, and there's a lot that goes straight over my head! Sounds as if I need to post some of the bits I don't understand up on here.

Still think the subject of this thread looks like a large hill to be climbed. Sort of like the Irish directions: "If was going there, I wouldn't start from here"

[Dr Derek Doctors]

Paul Drawmer said:

I subscribe to racecar engineering, and there's a lot that goes straight over my head! Sounds as if I need to post some of the bits I don't understand up on here.

Still think the subject of this thread looks like a large hill to be climbed. Sort of like the Irish directions: "If was going there, I wouldn't start from here"

Dont do that, you'll just get loads of contradictory mis-information from forum no-it-alls.

Read, understand and learn from proper books.

[mickrick]

Hello, sorry to butt in here, but I've been looking into buying the Milliken & Milliken book.
I wonder if some of you knowlagable guys could point me in the right direction, so I can make my mind up where to go?
There are three options on Amazon, a spiral bound,"Illustrated", and two hard covers. One published by SAE international, and the other, by The Society of Automotive Engineers Inc, "Workbook Edition" which is twice the price of the other two.
What's the difference? and why is one twice the price of the other two?
I've read a couple of Staniforth's books by the way, and also "Chassis Engineersing" by Herb Adams, so I'm ready to get my teeth into something else.

Another question also...I am of the age where "Technical Drawing" was done on a board with a pencil! I have an engineering background, and I must say, I enjoyed "TD", but I have been left behind when it comes to the computer age we live in today. But I think I could get into CAD, so muh so, if I was living in U.K. I would have signed up for evening classes long ago.
Can you recomend a CAD program I could buy, and try to teach myself at home?
Or, am I naive thinking I could tech myself?

Cheers in advance
And appologies to the O/P for going off topic. (I do think you are biting off more than you can chew though. From what you've written, your comments about a stiff road car, and ARB's tells me you don't have as much an understanding of chassis & suspension design as you think. Sorry, no offence intended.)

Edited by mickrick on Sunday 22 August 14:46