.
...and this is a photo of an IRS system, again using a Sierra Diff and half shafts, courtesy of Ned's Locost Build Pages.
[Edited on 9/1/05 by Chris_R]
what is the difference between a sierra de dion and IRS in practice?
Which sierra donors have de-dion and which IRS?
Can the rear uprights from a de dion car be used to make an IRS setup for a chasis that has rear wishbones without modification?
The Sierra has semi-trailing IRS (I think thats what it's called). The diff, driveshafts and hubs can be used in a De dion or IRS setup
though.
Adam
To expand on phelpsa answer a bit, semi trailing arms are not an ideal form of IRS -- they can be made to work OK(ish) with a lot of effort but the
real stopper with using the complete Sierra rear semi trailing arms setup is the shear size and weight of it.
To make an IRS or de Dion you strip down the Sierrra rear and use bits of it to make a de dion or double wishbone IRS.
The handling arguments between de Dion and irs aren't that much and depend a lot on the quality of the roads you will be driving on but the de
Dion has the advantage of being less dificult to get right first time.
[Edited on 9/1/05 by britishtrident]
This is a photo of a De Dion axel, using a Sierra Diff and half shafts, courtesy of GTS Tuning
.
...and this is a photo of an IRS system, again using a Sierra Diff and half shafts, courtesy of
Ned's Locost Build Pages.
[Edited on 9/1/05 by Chris_R]
right, I understand now. I thought that the standard sierra had a de dion axle and that you could pay extra to convert it to IRS.
now that I understand that you have to convert the sierra trailing arms to either de dion or wishbone IRS can you tell me:
which one is better?
what are the advantages / disadvantages of each?
from the sierra you take the dif, driveshafts, hubs/brakes/relevant carriers. the rest is purchased or fabricated ie wishbones and extra chassis
members or dedion axle and suitable mods to chassis. there have been *shed loads* of discussions about which is better/various pro's/cons. A
quick search will give you all the answers I suspect you're looking for so you can make an informed decision.
Ned.
I'm using a DeDion although if I was doing it again I'd use a live axle.
The live axle / DeDion will break away slightly sooner but a lot more progressivly than IRS. This makes the car a lot safer to drive and arguably more
fun.
I drive an MGF as my day car that has dual wishbone IRS at the rear and it's very scary in the wet. You go from being fine to pointing the other
way in a very short space of time.
With IRS the wheels are kept vertical at all times so there is maximum tire contact with the road. It only breakes away when your tires can no longer
grip the road any more so it goes very suddenly. In contrast, with a DeDion or live axle the wheels lean as the car rolls, this causes it to break
away earlier but is much more progressive and controllable.
You get better traction under acceleration with a DeDion or live axle as the wheels stay vertical as the back squats down.
If you're building a race car that needs the absolute best handling use IRS. If you want a fun sports car for road use go with a live axle and
save your self a load of work.
The slight benifits you get from using the DeDion aren't worth the effort.
No doubt there will be some that disagree with what I have said but this is my opinion and I'll accept it may be wrong.
Having said that, if I was starting from scratch again I'd probably just by an MK IRS chassis.
just for info I'm contemplating shimming the dedion ears on my dedion axle to give a small amount of tow in and negative camber to help with
cornering/roll and oversteer..
Ned.
Andy,
As a de-dion builder myself I would agree with most of what you said above but not that the benefits of de-dion aren't worth the extra work.
To my mind, one of the biggest benefits of the de-dion axle is that you can source one much EASIER than you can source a "good" live axle.
You also have the benefits of lower unsprung weight and a wider choice of diffs and shafts etc. Fitting a de-dion axle is not much different to
fitting a live axle either, especially if you use a prefabricated axle like the one which GTS offer very cheaply.
My opinion (for what it's worth) is that unless you want to go for a full IRS setup then de-dion is the obvious choice and live axles, while
perfectly fine, are becoming rarer by the day and not worth bothering with unless you are competing in a racing class which specifically requires
them. IRS should be best providing you can engineer as much weight out of it as possible and have a very sound understanding of the principles of it
AND the facilities to set it up correctly. Even then it won't be significantly better than an "out of the box" de-dion or live axle
setup.
Cheers,
Craig.
I would dismiss using a GTS DeDion because 1) (I'm told) it won't fit a book chassis and 2) I wouldn't buy anything from GTS due to a
past bad experience.
So that leaves building a DeDion from a kit of parts supplied by Martin Keenan for £80. Getting the thing welded up in line is a complete arse and I
have concerns about it's strength. We'll see if I manage to fold it up when the cars on the road.
Using the above method a DeDion is a huge amount more work than using a live axle. It's easier to find a live axle than a DeDion kit - Donor
Spares to start with, Capris, Cortinas, P100s...... Then the panhard ros is in the way of the petrol tank. I had to modify the design to make it fit a
book chassis. I could go on and on.
I'm not trying to knock what people have done but I get the impression the questions is someone trying to decide what to use before they start
the build. My advice would be to make life as easier as possible and use a live axle.
i'm using gts's dedion tube and have modified the chassis (very little) to fit the axle, i did then have to have a custom sized tank made up
as the one darren supplied didn't actually fit a book locost with his dedion axle which I found quite amusing.
you could always deal with Mark at Triton who might be able to sort you out with an axle without having to deal with darren?
Ned.
Youve also got some common probs associated with live axles/de dion - hit a grate , if one wheel moves the other has to , roll centre is placed at hub
height with a panhard rod , or wherever you choose to mount it - a woblink maybe a better solution . a watts linkage is the best tho since it
guarantees perfect up and down movement especially good with small wheel movements and light cars .
For IRS, its more difficult to setup , but gives you control over everything , and a better ride due to a wider spring base (same roll rsistance for a
given spring rate) , but cant combine what the de dion does best , keeping the the wheel vertical (or at set camber) at all times
quote:
So that leaves building a DeDion from a kit of parts supplied by Martin Keenan for £80
quote:
...and a better ride due to a wider spring base (same roll rsistance for a given spring rate)
Andy,
That is interesting as I have successfully assembled the "kit of parts from MK" and I didn't find it to be a big deal at all. (See my
website for details)
Yes you need to be careful with alignment but the same is true with the chassis. It was no more difficult than setting the position of the front
suspension mounts.
You clearly have a bone to pick with GTS which is your business but having spent nearly £1000 with GTS myself I have found them to be very good for
the most part. As Stu16v says, there are more suppliers of de-dion bits than just GTS although they are in my experience the best value.
Anyway, I'm not trying to supress the opinion which you are entitled to but it seems clear that you are giving out a quite polarised opinion due
to a couple of bad experiences.
On the IRS debate, I'd say again that a bad IRS will be much worse than a bad de-dion axle and a good IRS will only be marginally better than a
good de-dion system. I freely acknowledge that I don't have the experience and especially the equipment to set up and IRS suspension system from
scratch which is one of the reasons I went for de-dion. I wonder how much time and money was spent setting up the production Lotus Elise suspension
from scratch?
Cheers,
Craig.
Chaps,
I don't pretend to know much about de Dion, but looking at those pics, I can't see much benefit over a live axle - it doesn't look like
a proper de Dion.
IIRC the tube connecting the "uprights" should have a bearing in the middle to allow each rear wheel to go up and down vertically. With the
"uprights" solidly connected with that tube, the uprights will twist as if mounted on the ends of a live axle, with the same twisting loads
on trailing arm bushes.
Comments/corrections please
ATB
Simon
The only advantage is the weight of the diff is taken out of the equation as far as I can see. Put the weight of the hub carriers back in there and there's not that much difference really. Live axles are getting rarer so it's a viable alternative despite needing more work.
Take into account the (lack of) weight of a percentage of the propshaft. Plus mounting the diff to the chassis means the propshaft also doesn't
move up and down anymore.
That said, I'm going the live axle route because it's probably easier in my neck of the woods.
a de dion axle can be treated to all the suspension links that a live axle can , preferably a watts linkage - the de dion is supposed to be good at giving a better ride and handling due to less unsprung weight - over a live axle ( re wider spring base) , what you dont get is control over camber during roll that you can design in and RC position , thats dictated by panhard rod etc . What you dont get with IRS is the mechanical leverage that a trailing arm can provide for traction
quote:
Originally posted by Simon
Chaps,
I don't pretend to know much about de Dion, but looking at those pics, I can't see much benefit over a live axle - it doesn't look like a proper de Dion.
IIRC the tube connecting the "uprights" should have a bearing in the middle to allow each rear wheel to go up and down vertically. With the "uprights" solidly connected with that tube, the uprights will twist as if mounted on the ends of a live axle, with the same twisting loads on trailing arm bushes.
Comments/corrections please
ATB
Simon
quote:
Originally posted by Volvorsport
a de dion axle can be treated to all the suspension links that a live axle can , preferably a watts linkage - the de dion is supposed to be good at giving a better ride and handling due to less unsprung weight - over a live axle ( re wider spring base) , what you dont get is control over camber during roll that you can design in and RC position , thats dictated by panhard rod etc . What you dont get with IRS is the mechanical leverage that a trailing arm can provide for traction
Ditto what British Trident just said, it is the P6 which is "slightly odd".
De-dion is not some sort of radical new piece of technology, it is just a slightly different design from the live axle. This is in fact why it is very
relevant for Locost use if the benefits it brings over a live axle are of particular value to you - as they were to me!
The benefits as I see it are:
1. Easier availability in combination with Sierra running gear
2. Allows the use of Sierra running gear at the back which opens up a range of LSD diffs and other goodies. The Escort Mk2 is less and less common,
certainly in my neck of the woods and the parts often cost more.
3. Lower unsprung weight (mainly the diff and half the driveshafts) which should permit a better balance between ride quality and handling.
4. Good camber control in squat which yields better start line traction than IRS and no torque reaction so gives better traction than Live axle as
well unless you take remedial steps which I won't go into here.
5. The propshaft doesn't move up and down on a de-dion axle as the diff is fixed which can simplify things and allow a smaller trannie tunnel to
be used.
6. Can be fitted to a book chassis with the most minimal of modifications
7. Can be adapted easily to wider or narrower chassis'
8. De-dion is "prettier" IMHO...
The only advantage that a Live axle has over a de-dion axle (comparing Escort Mk2 live with Sierra based de-dion) is the overall weight of the Live
axle is lower. De-dion in turn is lighter than a "typical" sierra based IRS system as determined on another thread a while back.
Let me make it clear that there is nothing at all "wrong" with a Live Axle, or IRS for that matter. However, for my purposes de-dion is
simply a no-brainer as I can get all the benefits above for very little cost and with no detriment to my build time or complexity.
Cheers,
Craig.
The IRS v Live axle debate has went of for years but if you look at the history of the Clubmans class particularly the cornering performance of
various marks of Mallock in the A & B classes the less powerful live axle B class cars cornered very well indeed but a live axle will always
suffer from torque reactions and can never put a lot power down the way an IRS or De Dion suspension can.
If you have a lot of power -- de dion or IRS is a good idea.
The main reason de Dion isn't used more on production cars is mainly to do with interior/boot space, the reason it isn't used on formula
race cars is mainly aerodynamics.
I wanna tel u a story time ----
Back in the mid 1970s F1 designers were at the end of the road with suspension development Chapman built the ultra adjustable Lotus 77 in a vain
search for any new advantage while at Ferrari Lauda tested a car with a carbon fibre de Dion rear axle and a beam front axle in the late 70s it
worked every bit as well as the well developed conventional car except that it screwed up the aerodynamics.
most of those mallocks had a WOBLINK !
i thought the mallocks used a watts linkage, is this the same as woblink?
Ned.
its a little different , has a really low roll centre - i believe it can be found in the staniforth book
I remember a nice story about one of the racing heroes of yesteryear talking about a watts linkage "I know where the roll centre is because
there's a bolt through it"
Also early lotus 6 or 7 were trying to work out how to attach the lower A arm on the back axle, found the diff drain plug was in JUST the right
place.......
I'm sure someone will add correct details (or refute) these tales
Bob C