i am having a nightmare trying to sort out my irs for my 442 i have used the avon dimentions and as the rear suspension rises the top of the wheels move outwards i think this is possative camber and it should be the oposite
before i loose my temper and scrap the lot can anyone recomend a good book on suspension design or should i give up on irs and get a dedion tube from gts
does this tube fit a +4 chassis
cheers a very pissed off dave

How to build & modify Sportscar & Kit car Suspension & Brakes; Des Hammill

Simple easy to understand diagrams & description, needs to be read a few times I think to fully understand though.

I have it as well, bloody good book, cheap on Amazon

as you have both got the book which way did you decide to go with your back suspension irs live axel or dedion
cheers dave

Live axle, Cortina, in a Luego locost chassis.

Live axle, capri in a book chassis

I will start modifying after the SVA, particularly trailing arm lengths and angles

Do you have any way to move your upper chassis pivots down? If you can, that would be the way to get a more satisfactory camber curve.

Here's a free suspension program that will allow you to see what it takes to get camber behavior similar to your front. If you can achieve that, and a roll center that's (1) slightly higher than the front RC, and (2) stays fixed laterally in roll, you're home free.

Suspen

You might also need either longer upper wishbones (or shorter lowers) if you change these pivot locations.

Got a picture of your rear chassis?

Pete

quote:

---

Originally posted by dblissett
i am having a nightmare trying to sort out my irs for my 442 i have used the avon dimentions and as the rear suspension rises the top of the wheels move outwards i think this is possative camber and it should be the oposite ...

---

Hi All,

I'v had a go at making my own IRS.
My top wishbone is about two thirds the length of the bottom wishbone. They start off horizontal, and as they rise the top effectively shortens more than the bottom one thus creating negative camber on compression.

I haven't driven it yet, but it looks right.

Paul G

Try these:

Top wishbone
Chassis mounting from CL: 305 mm
-----"---------"------ from ground: 300 mm
Length: 295.5

Bottom wishbone
Chassis mounting from CL: 178 mm
-----"---------"------ from ground: 140 mm
Length: 407

Upright
CL height from ground: 269.3 (tyre rolling radius)
Top mounting from chassis CL: 585 mm
-----"---------"------ from ground: 594.3mm

Bottom mounting from chassis CL: 585mm
-----"---------"------ from ground: 144.3mm

Track is 1470 mm
Starting camber is 0ŗ (later to change to -0.5ŗ/-1ŗ according to tyres)
Roll center height: 108 mm (4 in. 1/4).

Pls, feed back the results and your opinion.

Cheers
Joćo

I don't know the avon suspension but if the top wishbone is about 2/3 the length of the lower one it is i the right ball park.
The inner pivots for the top and bottom rear wishbones need moved -- most likely the lower one will need to be raised so the lower pivot 0.5" higher at the inner end than the outer and the upper lowered by perhaps 1".

My fvourite suspension book is "How To make Your Car
Handle" author Fred Phun Publisher HP Books ISBN 0-912656-46-8

[Edited on 22/4/04 by britishtrident]

To get camber control right, your swing axle length (where lines through wishbone pivots converge) needs to be on the "car" side of the wheel - i.e. the vertical separation of the chassis pivots should be less than the vertical separation of the upright pivots.
All the above applies - try to get an old dos program called "suspen.exe" to locate your roll centre properly if you can be bothered. U2U me if you want it posting to you.
cheers
Bob C

quote:

---

Originally posted by jcduroc
Try these:
[snip]
Upright
CL height from ground: 269.3 (tyre rolling radius)
Top mounting from chassis CL: 585 mm
-----"---------"------ from ground: 594.3mm
[snip]
Pls, feed back the results and your opinion.

---

quote:

---

Originally posted by pbura

quote:

---

Originally posted by jcduroc
Try these:
[snip]
Upright
CL height from ground: 269.3 (tyre rolling radius)
Top mounting from chassis CL: 585 mm
-----"---------"------ from ground: 594.3mm
[snip]

---

Was taking a peek, but outboard top pivot height of 594.3mm appears to be incorrect (taller than the wheel). What's the right measurement?

Your chassis appears to be quite low! Is it for racing?

Pete

---

For everybody's info, below is the kind of data you get from Suspen.exe; I added some sub-captions to explain the movements.


Joćo,

Here's your data in Suspen. Sorry about the units of measure, but it was the only way. Camber change looks excessive, but if you raise the upper inboard pivot along the same tube (if possible), you will fix this, and retain the very fine RC behavior, as you've found the Magic Angle

Please feel free to U2U or e-mail if you'd like to talk about alternatives.

ATB,

Pete
Rescued attachment JCMIRS.jpg

Pete

I just converted the inches to mm.
Before going into a deep analysis of the figures pls tell me:
* between lower A-arm & chassis p/u's (pivot mountings?) 14.02 (356.11 mm); where does it come from?
* between upper A-arm & chassis p/u's (pivot mountings?) 24.02 (610.11 mm); where does it come from?

Cheers
Joćo

quote:

---

Originally posted by jcduroc
Pete

I just converted the inches to mm.
Before going into a deep analysis of the figures pls tell me:
* between lower A-arm & chassis p/u's (pivot mountings?) 14.02 (356.11 mm); where does it come from?
* between upper A-arm & chassis p/u's (pivot mountings?) 24.02 (610.11 mm); where does it come from?

Cheers
Joćo

---

Hi I know I am bit late to this thread, but I am in the stage of designing my IRS at the moment.

I'll give you a bit of background to what I have been doing.

I felt that I needed to understand a bit more about suspension geometry and the like (I want to race the car and want it handle as well as is possible having no previous experience apart from F#~+][g it up when I was a kid by lowering cars and changing wheels without thinking about the handling implications). Anyway I digress so I have tried to read as much as I can about it and then write my own software to give me an idea about what is going on.

So if you are interested I am just finishing (by the end of the weekend) the first verified (by me) draft. It is a windows program that I have developed that I hope is easy to use. The dimensions it requires to simulate camber changes are the upright dimensions, wheel tyre dimensions, track and the points in space of wishbone pickups.

The output gives you
Camber change in:
Bump or droop
Roll (roll center is calculated iteratively across the roll not just taken as the initial roll center of the car)
Bump and droop at the point of roll
Bump and droop during roll.

The output is currently to a csv file that can be read in note pad or excel (animations soon).

If you would like a copy u2u me and I will send one out.

Chaps, I just looked back over this thread & realise my comments about suspen.exe could be construed as my thinking it was not much good. That's not what I meant - it just came out wrong - the program itself is simple to use and enables you to nail your roll centres exactly where you want 'em. And as Pbura said in an email to me, it's got to be a major factor in having a car feel nice to drive - what else is there? (rhetorical question......). Previously I was just going to use the simple rules outlined by others - I'm glad I took the trouble (with a lot of help from Pete) to do it properly. My initial rear suspension roll centre moved 3" sideways with 3 degrees of roll! Now it stays put. Cheers Pete!
Bob C

here is a very rough sketch of my rear whisbones and moutings it looks like my top wish bones are to short being only 230mm long or should i add 35mm to get their true length
thanks for everybodys help as i am calming down i wont be scraping the locost just yet
cheers dave
Rescued attachment whisbonesrear.jpg

Bob it is also my understanding that it is important to try and fix the roll center.

But I do believe (pure speculation as I have not done the calcs to see if it is achievable yet) that it would be advantageous to move the roll center to the outer wheel in a corner in terms of handling, but I don't know how this would make the car feel.

So a few questions for the experts out there

So does anyone have experience of this to share?

Is it really possible to fix the roll center when different bumps and droops are added into the equation for different wheels?

p.s. my program also outputs the roll center position during roll.

quote:

---

Originally posted by Digger Barnes
Bob it is also my understanding that it is important to try and fix the roll center.

But I do believe (pure speculation as I have not done the calcs to see if it is achievable yet) that it would be advantageous to move the roll center to the outer wheel in a corner in terms of handling, but I don't know how this would make the car feel.

So a few questions for the experts out there

So does anyone have experience of this to share?

Is it really possible to fix the roll center when different bumps and droops are added into the equation for different wheels?

p.s. my program also outputs the roll center position during roll.

---

Bob C, thanks for the good report! I think that whenever anyone gets way off the book (and IRS certainly qualifies), they'd do well to understand their suspension geometry. Like you guys, I've been reading up because I don't want to screw the pooch.

Another free suspension design tool that I like is the Wishbone program from Race Tech magazine, available on their downloads page. You need to register to get it, and you'll also need Microsoft QuickBasic to run it:

https://www.racetechmag.com

What I like about Wishbone is that you can set the chassis in a particular attitude, like 2" bump or 2 degrees roll or some combination, then twiddle suspension pivots until you get results that look good to you. You can then alter the chassis position and tweak some more. I flip back and forth between 2" bump and 2 degrees roll to try to strike an effective compromise. I'll also test at 1" bump, 2 degrees roll (favored by Staniforth for his string computer) because it's a very representative condition in cornering.

After doing the design in Wishbone, you can enter the settings into Suspen and move the suspension through its paces, to get a better sense of what's happening in a dynamic sense. Suspen can do the whole job, but IMO it's a bit awkward for watching your camber change while you're tweaking a pivot height, for example.

The only thing I DON'T like about Wishbone is that you're forced to deal with bump steer, which is a PITA during this design stage, though it's a nice tool to have eventually.

I'm looking forward to checking out Digger Barnes' proggie, too.

Another thing I've done in the way of suspension design is to solve it graphically. The method I used was based on the classical "three position analysis" method for solving four-bar mechanical linkages. I have a page on my website about this. Sorry it's a bit hard to follow, but the CAD program I used was not amenable to creating images for the web, or editing text. What I like about the graphical method is the degree of control it gives you over the process, more like shooting fish in a barrel rather than jus' fishin'

Re: Fixed Roll Centers

Two writers I admire, Carroll Smith and Allan Staniforth, go on and on about the desirability of the fixed roll center. It appears to be a handling, or 'feel' issue, rather than being essential to a car's actual ability to go around corners. The book Locost has a well-fixed front roll center (and rear, with the solid axle), and I wonder if this isn't a big reason that people find the Locost's handling to be so incredible, like it's riding on rails. Again, I think the off-book builder would do well to emulate the book geometry as closely as possible, unless he really knows his stuff about suspension design (I don't). The book Locost RC moves a couple of inches towards the unloaded side in roll, BTW.

Re: IRS Considerations

I've been fooling around with jcduroc's suspension coordinates, and so far I've learned that if you want a highish RC with IRS, the layout will more closely resemble that described by type 907 and britishtrident, than what I stated in my first post on this thread. The top bone will be close to parallel, and the bottom will point upwards somewhat from wheel to chassis. I may be wrong, but with this arrangement it seems difficult to get really good camber curves in both bump and roll when the RC is much higher than about 3-4". One advantage of a solid axle or de Dion car is the higher rear RC, which limits weight transfer in roll and maximizes the rear tires ability to provide traction for accelerating, IMO. The conclusion I'm drawing is that a rear anti-roll bar is practically necessary with IRS.


Sorry about the long post!

Pete


Below is my interpretation of the book Locost front suspension in Wishbone:
Rescued attachment Wishbone.jpg

Here's the related diagram:
Rescued attachment locost2.jpg

i have to hold my hands up and say most of what is being said is way above my knowledge of suspension
with that in mind i think it might be better to admit my limitations and buy a dedion tube from gts
the last thing i want is to spend two years building a car that wont drive properly and i wont be happy with
it seemed like a good idea at the time
thanks every body dave

[Edited on 24/4/04 by dblissett]

The de Dion's awfully nice, and frankly that's how I'd go if I weren't doing inboard shocks. IRS is good, too, especially if you've got your chassis built already and all you need is to sort the wishbones.

How far along are you?

Pete

quote:

---

Originally posted by dblissett
i have to hold my hands up and say most of what is being said is way above my knowledge of suspension
with that in mind i think it might be better to admit my limitations and buy a dedion tube from gts
the last thing i want is to spend two years building a car that wont drive properly and i wont be happy with
it seemed like a good idea at the time
thanks every body dave

[Edited on 24/4/04 by dblissett]

---

The late Arthur Mallocks comment on roll centre movement in relation to chassis movement allways brings a smile to my face, he said, when describing the nine different systems they had used up to that point, " if you use a chassis mounted Watts linkage it can't move because it's got a bolt through it"

Love the quote from Mallock!
The problem with IRS isn't the suspension geometry - the fact is all the wheel loads feed to places that just aren't there on the tried & tested book design. A problem neatly side-stepped by the dedion solution!
Cheers
Bob C

It's going to be interesting to experience the difference, I have a book version finished which is a great drive and a new car under way which has inboard front suspension and IRS rear, the front also features zero scrub radius I'm treating it as an R&D exercise, I enjoy the build as much as the driving, the new car is very adjustable, front and rear

with the kind help from pbura i am going to try and sort my irs out
i will keep you all posted as to if i win or loose
only rons book said it was easy
cheers dave

[Edited on 26/4/04 by dblissett]

Dave,

Is your IRS an exact copy of the Avon? Does this mean the Avon is shite aswell?
I'd be very interested to hear how you solve it. Guess thats another Winter upgrade to add to the list

Cheers

hello northy
no its not all the same the bottom wishbones dimentions are the same
the supports for top and bottom wishbones are in the same place but my top wishbones are shorter than the avon ones they conect in almost the same place as the shocks there was a thread on the standard avon irs that thought the camber went posative as the suspension rose
search for a guy from portugal i think his name is juao or jcdoc he posted the comments on it but i have come to the conclusion that it must be a lot better than any standard production box that we all drive day to day.
cheers dave

Cheers Dave,

I'll have a look, seem to remember seeing it now.

Has anyone modeled the std Avon rear suspension in one of these packages? Don't think I'll be able to manage it

Cheers

when i have learnt how to put mine through i will put the standard avon through
this might take me a couple of months to learn though
cheers dave

Cheers Dave,

I'm not changing it now, perhaps next winter........

Cheers

It's really not hard to do; I'll post the results for everybody to see, so you can try it on your own. Probably won't be until Wednesday morning, though, because I have some rush work to do.

I'd be glad to play around with the Tiger setup, too, front and rear. The dimensions needed are the locations of ball joints and chassis pivots, plus tire diameter (rolling) and track. Steering data is optional. You can see the data screen on page 3 of this thread.

Pete

Cheers,

Wonder if my book will fall on the scanner tommorrow........

quote:

---

Originally posted by dblissett
there was a thread on the standard avon irs that thought the camber went positive as the suspension rose
search for a guy from portugal i think his name is juao or jcdoc he posted the comments on it but i have come to the conclusion that it must be a lot better than any standard production box that we all drive day to day.
cheers dave

---

quote:

---

Originally posted by dblissett
hello northy
no its not all the same the bottom wishbones dimentions are the same
the supports for top and bottom wishbones are in the same place but my top wishbones are shorter than the avon ones they conect in almost the same place as the shocks ...

---

quote:

---

Originally posted by dblissett
... but i have come to the conclusion that it must be a lot better than any standard production box that we all drive day to day.
cheers dave

---

From study of photos in mags of the Avon front end I doubts about the position of the steering rack also --- it seems quite a a lot a head of the trackrod ends and so must give a lot of toe-in in corners.

hello joao
i was trying not to slag off the avon as some people have bought one as a built chassis and i dont want to make them unhappy with there choice
hello pete
i will email you the tiger dimensions
i have started to play with the program should all the dimentions be imperial
and i now have even less time due to the birth of my second daughter last night.
eve weighing in at 9lb 12 oz ouch
thanks dave

quote:

---

Originally posted by dblissett
hello joao
i was trying not to slag off the avon as some people have bought one as a built chassis and i dont want to make them unhappy with there choice

---

quote:

---

Originally posted by dblissett
... now have even less time due to the birth of my second daughter last night.
eve weighing in at 9lb 12 oz ouch
thanks dave

---

Dave,

Sent you an e-mail to confirm some measurements. When I hear back from you, then I'll post the originals and a suggested alternative, and everybody can take some potshots

It would also help to know what your front end looks like. I know you have a +442, but would like to know also if you have book wishbones in book locations, and what your front ride height will be. The reason I ask is that it's best to have your rear RC somewhat higher than the front, for better turn-in. Also, I'd like to try matching the front and rear camber curves as best I can.

If the other thread about the Tiger wishbones pointing up toward the chassis is correct, probably the reason Tiger did it is to raise the RC so they wouldn't have to have an anti-roll bar in back, IMO.

Congratulations on Eve's safe arrival, and may all of you have a happy life together

Pete


P.S. to Joćo: I'm a widower, too, and raised four children on my own for 7 years until remarrying almost two years ago now. I'm very sorry for your loss.

quote:

---

Originally posted by pbura

P.S. to Joćo: I'm a widower, too, and raised four children on my own for 7 years until remarrying almost two years ago now. I'm very sorry for your loss.

---

Pete,

Have you got the dimensions for the std Avon rear suspension?

Would you be willing to do the front also at some point? No rush though

Well, I took a shot at Dave's suspension geometry, had a lot of fun, and got more behind with earning my daily bread

Here's the old data in Suspen:
Rescued attachment DLBIRS.jpg

And the proposal, which was formulated to minimize extra work for him. Bottom wishbones are the same with a higher mounting, and the upper are longer and mount further inboard, but at the same chassis tube height:
Rescued attachment DLBIRSREV.jpg

The change in the ride height from 4.75" to 5.5" helped raise the RC and to put the upper wishbone in a better position for bump and roll. For a lower ride height, I'd go with a shorter tire/wheel combination (this one is 185/65-14).

The most serious change was raising the lower chassis pivot 1.5" in the same lateral location, and I hope this is possible just by making a Big-Ass Bracket without any other modifications. Comments are welcome on this, and on anything else.

Pete

quote:

---

Originally posted by Northy
Pete,

Have you got the dimensions for the std Avon rear suspension?

Would you be willing to do the front also at some point? No rush though

---

quote:

---

Originally posted by pbura

No, I don't have them, but I'd be glad to help anyone that wants to analyze them.

By the way, I'm not representing myself as any kind of expert in these matters. One reason I've posted the screens from these programs is to show people how they work, and to encourage them to do the same themselves.

Generally speaking, The R/C car guys have got us Locosters buried with regard to vehicle dynamics

Pete

---

quote:

---

Originally posted by Northy Which program should I start off with as a beginner? Do you just plug numbers in?

I'm an RC guy

---

quote:

---

Originally posted by pbura

I use both Wishbone and Suspen. Wishbone is easier to set up the problem and to adjust pivot locations to try to improve camber or whatever in a given chassis position. It sort of bites for dynamic modeling, though, which is where the Suspen comes in. In Suspen, you just punch arrow buttons and the chassis bumps and rolls as you please.

This routine works well for adjusting an existing design, but for a from-scratch design I'd rather draw it (like the example on my website).

A hybrid technique, like sketching the chassis to set the uprights, track, ride height, roll center height, swing axle length, and inboard lower pivot location, then 'fishing' with Wishbone for the upper pivot, would work pretty well, too.

Digger Barnes has been working on a spreadsheet, too, and he says he'll be done with it soon. That'll be interesting to see.

These methods I'm using are low-rent, by the way. There's a program called SusProg3D that will determine pivot locations by reiterative testing, probably the way to go for most people.


Pete

P.S. You RC guys are outrageous; best automotive tech info on the web!

---

quote:

---

Originally posted by pbura
Digger Barnes has been working on a spreadsheet, too, and he says he'll be done with it soon. That'll be interesting to see.

---

That whole area of springing and weight transfer is very interesting. I haven't learned much about it yet because it doesn't come into play until way down the pike for me, but I have found this page and site to be very provocative:

http://www.smithees-racetech.com.au/wttransworksheet.html

Pete

jcduroc and pbura check your email it is finaly ready to play with.

quote:

---

Originally posted by pbura
Well, I took a shot at Dave's suspension geometry, had a lot of fun, and got more behind with earning my daily bread

---

quote:

---

Originally posted by Digger Barnes
P.S. dont you want to calculate the rear suspension with 1" of droop rather than 1" of bump as the car will dive into a corner when on the brakes lifting the rear?

---

quote:

---

Originally posted by Digger Barnes
jcduroc and pbura check your email it is finaly ready to play with.

---

No light at the end of the tunnel yet.

Just f*****g Viagra advertisements...

Joćo

quote:

---

Originally posted by Digger Barnes
No light at the end of the tunnel yet.

Just f*****g Viagra advertisements...

Joćo

---

quote:

---

Originally posted by jcduroc

BTW, where does ET41 come from? I thought Sierra normal wheels were ET38.

---

Digger,

Could I have a copy please?

Cheers

I would love a copy Please Sir.....


[Edited on 1/5/04 by F1 Mini]

Sure thing Graham and F1 just U2U an address and I'll send a copy out.

Cheers

P.S. Pete that Milliken & Millikin book will be winging its way to me very soon, I simply must have it.

quote:

---

Originally posted by Digger Barnes
P.S. Pete that Milliken & Millikin book will be winging its way to me very soon, I simply must have it.

---

Thanks Joao (sorry I don't know how to do the a properly in your name)

I should have the book on Tuesday or Wednesday. As it is a bank holiday over here I shall be relaxing for a day or two (very little on the car or the misses will kill me) so thanks but i should be ok.

But I am sure you have a book or two I would not mind a few pages from so I might email on the scrounge later on in the build (Aerodynamics anyone).

Cheers

Gareth

quote:

---

Originally posted by Digger Barnes
Thanks Joao (sorry I don't know how to do the a properly in your name)

Gareth

---

hello pete i now have the avon dimentions for you
the bottom wishbones,brackets and upright pivot points realative to the road are all the same although ride height is 4 1/2 to 5 inches
the top wishbones are longer but mounted higher at their brackets
ps i am half way through your changes as my new daughter is slowing things down
could you compare this with changes i am doing as northy and other are interested
cheers dave
Rescued attachment avon.JPG

Pete, Have reviewed this topic several times - excellent stuff. When you refer to book suspension, is your analysis for the Cortina or the Sierra uprights? Do folks generally use the same (per book) or different inboard pickups to accommodate the wider Sierra configuration or when going ++ etc? Can you get a "non-migrating" front RC down to say 2" with the Sierra upright on book chassis swivel points
Alf

quote:

---

Originally posted by SilverFox
Pete, Have reviewed this topic several times - excellent stuff. When you refer to book suspension, is your analysis for the Cortina or the Sierra uprights? Do folks generally use the same (per book) or different inboard pickups to accommodate the wider Sierra configuration or when going ++ etc? Can you get a "non-migrating" front RC down to say 2" with the Sierra upright on book chassis swivel points
Alf

---

I am building a mcsorley +442 with rear irs.I have also read the bibles and have based my wishbones on book calculations and ......... I have built in some adjustments,firstly the top wishbone is approximately 2/3rds of bottom and is fitted with a rose/ball joint at the upright end giving about 25mm adjustment in length.Secondly and foremost on the chassis side i have welding in sets of brackets with varying hole positions in the vertical plane,by doing this it has given me the ability to infinately adjust camber,height and roll centres by merely raising or lowering the inner pivot points.

Hope this might be of help.

Many thx for the clarification Pete. I will do a search for key dimensions of the Merkur/Sierra upright and get back to you
(probably e-mail) with a first cut.
unfortunately don't have MS quickbasic or any of the other tools as yet - a winter project possibly.
Have to tried Digger Barnes' software?
Dave. the only adjustability I am thinking of at present is raising the mushroom insert. My arm lengths are 17 3/4" and 12 1/2" attached to the book swivel points.
Alf

Sorry, correction 17 1/2" and 12 3/4"

quote:

---

Originally posted by SilverFox
Have to tried Digger Barnes' software?

---

Rescued attachment Sierra1.jpg

2nd pic:
Rescued attachment Sierra2.jpg

Many thanks Pete for the upright dimensions. You are a fountain of information. I am out of Town for a week and will then formaulate an option on which,
I would appreciate you analysis and assessment. Great stuff.

just a big thanks to pete bura
i have just finished your changes pete as you can see its only tack welded and the studing was to keep the brackets in line
but the main thing is it all seems to work now
its taken a lot longer than i thought but its been worth it i have been trying to sort out this backend for so long the rest of the chassis has gone rusty
cheers pete i ow you one
Rescued attachment 04a2002_0524_074843.JPG

Hey, Dave, you'll have to post another pic at ride height when you get there. Glad you're ready to move ahead.

I just reviewed my recommendations to you again (details on page 5 of this thread) and was relieved to see that they still look pretty decent from the perspective of a few more months. If I were to do a scratch design, I'd try for a bit less camber change in bump, but it's not a big deal (about 1/3 degree per inch difference).

Crossing my fingers and hoping for a good result. Wish I could drive it!

All the best,

Pete