Hi all,
Can anyone give me a hand here.
I am trying to make sense of all the terminology used but I just need clarification of the different rear ends (IRS, live, De dion etc) and what the benefits of each are.
Has anyone got some simple picture that can help an old duffer out.
Cheers
Mark

The way I've understood it so far mate is

IRS - Wishbones top and bottom (same setup as standard front end) and there is obviously the drive train is then fitted - diff and drive shafts.

DeDion is where the wheels are connected by a strong bar so they work together as one. The diff is attached solidly to the car chassis - shock for each wheel and a Panhard rod (haven't read up on this yet)

Live axle is a solid axle, diff etc which again works as one unit but doesn't need a panhard rod and is likely to be heavier than the DeDion as the diff isn't supported.

Remember I am new to all this but this is how I understand things.

live axle = truck axle. In the old fords these were held against sideways, acceleration/braking and twisting forces by cart springs. In the "book" locost parallelogram trailing arms and a panhard rod locate the axle much better.

Problem with this is unsprung wieght - so with a dedion setup the differential is taken out of the axle and bolted to the chassis, everything else is (in principle)the same.

IRS stands for independent rear suspension, and wishbones are one way of achieving this, the other popular system is semi-trailing arms used by sierras and BMWs. There are lots of other systems though.

Generally IRS gives lowest unsprung weight, live axle highest. However it's easier to get IRS wrong than dedion, so dedion is looking like the more popular option at present.
cheers
Bob

quote:

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Originally posted by chunkielad




Live axle is a solid axle, diff etc which again works as one unit but doesn't need a panhard rod and is likely to be heavier than the DeDion as the diff isn't supported.

Remember I am new to all this but this is how I understand things.

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I think I understand what is being described but any chance of some basic drawings??
Cheers
Mark

The unsprung weight isn't much diferent between the IRS and the de Dion -- the deDion gives better control of wheel camber and is considered to give the best traction on smooth surfaces.
On rougher surfaces the IRS has the advantage in that a single wheel bump has less effect on the other wheel that it does in the de Dion.

quote:

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Originally posted by Cita

quote:

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Originally posted by chunkielad

Live axle needs a Panhard rod as well...as far as i know

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Not quite - the original 7's had what's called a satchel link. Basically this was a triangular frame linking the diff centre housing with the bottom corners of the chassis (sort of where the bottom trailing arms are fitted).
But I wouldn't try this because apparently Lotus had problems with them chewing bushes.

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TheGecko - 13/1/05 at 02:55 AM

Mark,

I would start the classification of suspension types by splitting them into two categories: dependant & independant. Both are defined by the behaviour of a left & right pair of wheels (ie the front pair or the back pair).

Dependant suspensions are those in which the movement of one wheel in the pair affects the other - basically beam axles of some sort or other. Independant are everything else

For dependant axles most of the categorisation then comes down to how the axle beam is located. Common types are:

Hotchkiss axle: the axle is located by a pair of leaf springs (commonly called a cart axle as well)
Trailing arms -
4-arms: Locost style - 4 parallel trailing arms (a pair each side) locate the axle front to rear. Seperate linkage controls its location left to right (see below).
4-arms: Satchell link - the arms are not parallel. One pair (top or bottom) is angled in towards the vehicle centreline so the provide sideways location as well.
3-arms: usually one lower central arm and two top ones at the sides. rarely seen and needs a transverse location link of some sort too.
A-arm: effectively a variant of the Satchell link. The angled pair of arms form an A-frame from the chassis to a central (or other) point on the axle. Used in many of the old Lotus 7's.

Transverse location link types:
Panhard rod: a simple rod connects crossways with one end on the chassis and one on the axle. Book Locost uses this.
Watts linkage: see this page for a picture - easier than explaining in words
WOBlink: a geometrical variant of the Watts linkage that allows a lower roll centre. Fairly rare.
Mumford linkage: an even more complicated variation that allows lots of control over axle location.

A deDion is a variant of the live axle that attempts to combine some of the advantages of both independant and dependant rear ends. It has the wheels joined by a rigid tube or beam but the differential is mounted to the chassis and connected to the wheels by half shafts. It has the advantage of maintaining the wheels in a fixed geometry to each other without the unsprung weight of the differential bouncing around to upset the dynamics so much. It was popular on Formula and high performance road cars in the 50's and still sees occasional use (the recent Honda HR-V uses one) but has mostly been supplanted by independant systems of one sort or another.

Which leads us to - independant systems:

I'll do that in a second message - after lunch

Hope this helps for a start,

Dominic


[Edited on 13/1/2005 by TheGecko]

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TheGecko - 13/1/05 at 06:51 AM

OK, part 2 - independant systems. Basic categories could be:
- single arm (swing, trailing, & semi-trailing types)
- double arm (wishbone variants)
- multi-link (none of the above )
- strut

Single arm types - a single suspension member (or equivalent) attaches the wheel to the chassis. Examples are:
swing axle: original Beetle rear end is the canonical example. The wheel is fixed to the end of the axle which pivots at the diff. So - longitudinal pivot axis. Mercedes used to do a variant with a seperate swing arm that sat below the axle and had the pivot point below the diff - it was an improvement but only barely.
trailing arm: Beetle front suspension or old Mini rear. A single (or pair of on the Beetle) arm holds the wheel and is pivoted much like the wing arm on a motorbike. My 1965 Honda S600 Coupe used this style of rear suspension with individual chain drives to each rear wheel! Otherwise pretty rare for driven wheels Transverse pivot axis.
semi-trailing arm: half way house between the above. The suspension arm is pivoted at some angle between completely transverse and longitudinal, usually close to transverse. Incredibly popular when manufacturers starting using IRS as a marketing tool because it's (relatively) cheap and cheerful. Sierra rear is an example but there are thousands of others.

Double arm or wishbone types - these could fill a book on their own! Plus I'm running out of time right now. I'll write some more when I get home tonight.

Dominic

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Lotusmark2 - 13/1/05 at 08:32 AM

great so far Dominic, thanks a lot!!
I have grasped dependant but independant is still a bit unclear, any pics around that you can point me at?
Cheers
Mark
(sorry to be dim)

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TheGecko - 13/1/05 at 11:15 AM

G'day Mark,

You're not being dim

I've done a little breach of copyright and scanned two pages from my "Bosch Automotive Handbook" (4th Ed ISBN: 0-8376-0333-1).

There is a two pages spread with little thumbnails of the various major suspension types and some potted summaries. I'll write a little more later - I've only just got home and it's 21:00 here

Here's the pic - sorry it's so big but too much detail lost otherwise


Bosch_susp

Best regards,

Dominic

[Edited on 13/1/2005 by TheGecko]

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Lotusmark2 - 14/1/05 at 05:10 PM

Cheers Dominic,
Any chance you could email that expanation diagram to me so I can down size it and keep it for referance.
Mark
lotusmark2@aol.com

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TheGecko - 15/1/05 at 04:55 AM

Mark,

You should be able to just right-click on the image and save it - alternatively, it's in my Photo Archive and you could grab it from there.

Haven'y had a chance to write any more spiel - family committments Let me know if there's anything that needs more explanation.

Dominic

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krlthms - 15/1/05 at 07:59 AM

Is an independent suspension with anti roll bars still independent?
KT

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TheGecko - 15/1/05 at 10:11 AM

quote:

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Is an independent suspension with anti roll bars still independent?

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Good question

Answer - not really. The anti-roll bar links the two sides somewhat. Ani-roll bars are regarded by some designers as a quick & dirty solution to a poorly designed suspension. Gordon Murray was quite vocal about the McLaren F1 not having them and not needing them.

D

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britishtrident - 15/1/05 at 10:41 AM

Very true but still loads of reasons for using an anti roll bar (ARB) as long as the stiffness isn't too great. --- lets not go into this too deeply or this will end up a very long thread.

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krlthms - 18/1/05 at 12:40 AM

Spoilsport

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