Chris Green
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| posted on 4/9/04 at 10:06 AM |
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Stupid Question Alert! - De Dion
ok, I'm a bit of a novice to all this stuff, so bear with me!
What is a De Dion? I hear the name popping up all the time, but can't find info on them anywhere?
The search engines just direct me to dax if I search for De Dion?
Thanks a lot!
Chris.
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chrisg
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| posted on 4/9/04 at 10:20 AM |
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It's a cross between a live axle and an independant set-up.
You have the trailing arms as in the book connected to a tube axle and hubs.
The differential is attached to the chassis and the drive shafts do not run inside the tube.
The axle is usually kinked backwards to avoid the diff.
I'll try to find a picture.
Cheers
Chris
Note to all: I really don't know when to leave well alone. I tried to get clever with the mods, then when they gave me a lifeline to see the
error of my ways, I tried to incite more trouble via u2u. So now I'm banned, never to return again. They should have done it years ago!
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Mikey G
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| posted on 4/9/04 at 02:15 PM |
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It combines the advantages of Liveaxle setup with IRS unsprung weight as the diff is in a fixed position.
A live axle can be bouncy and skittish over rough surfaces as it is a very heavy item, it wants to do its own thing then! but the DeDion setup puts
less load on springs and dampers to keep your rear driving wheels on the ground and in contact with the black stuff
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Mikey G
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| posted on 4/9/04 at 02:17 PM |
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Found a piccy 
Mike
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carcentric
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| posted on 4/9/04 at 05:26 PM |
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Isn't there usually a sleeve in the crosstube somewhere that allows changes in rear track width as one or both wheels move up and down?
Some folks have said the rear suspension on my hardtail CX500 trike project is deDion, but it's different in these ways:
- it starts with a swing axle rather than IRS,
- the differential, as well as hub uprights, is bolted to crosstube,
- wheels are no longer allowed to move up and down independently (it works just like a live axle), and
- it doesn't sound or smell French.
http://www.carcentric.com/CX500trike.htm
M D "Doc" Nugent
http://www.carcentric.com
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Mikey G
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| posted on 5/9/04 at 11:09 AM |
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quote:
Originally posted by carcentric
Isn't there usually a sleeve in the crosstube somewhere that allows changes in rear track width as one or both wheels move up and down?
Dedion is a fixed track width just like a live axle, the angle change of the driveshafts during suspension movement means that something has to move
in and out, sliding joints are built into the inner joints of the sierra driveshafts
Mike
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craig1410
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| posted on 5/9/04 at 11:13 AM |
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Hi,
I have a section on my website describing the de-dion axle including a set of plans to allow you to build your own. You will also find many references
to it in my build diary.
My webste is here
Cheers,
Craig.
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Chris Green
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| posted on 5/9/04 at 07:16 PM |
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quote:
Originally posted by Mikey G
It combines the advantages of Liveaxle setup with IRS unsprung weight as the diff is in a fixed position.
A live axle can be bouncy and skittish over rough surfaces as it is a very heavy item, it wants to do its own thing then! but the DeDion setup puts
less load on springs and dampers to keep your rear driving wheels on the ground and in contact with the black stuff
thank you for the replies everyone.
Mikey, what are the advantages of a live axle?
also, does "de dion" actually mean anything, is it an abreviation? where did it originate?
Cheers,
Chris.
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Mikey G
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| posted on 5/9/04 at 07:42 PM |
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quote:
Originally posted by Chris Green
thank you for the replies everyone.
Mikey, what are the advantages of a live axle?
also, does "de dion" actually mean anything, is it an abreviation? where did it originate?
Cheers,
Chris.
Dont know what Dedion means 
the only advantage a live axle really has is simplicity. you have no complicated geometry to work out compared to an IRS setup. someone mentioned a
Live axle is also lighter than the others but i cant see that.
Mike
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carcentric
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| posted on 5/9/04 at 08:40 PM |
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Advantage of being live
In a trike, a live axle has the advantage of resisting outward lean that would be enhanced by IRS rear suspensions.
For trikes based on bikes, at least, it's bad enough not being able to lean into corners anymore, but an IRS actually makes you lean out!
Jules-Félix-Philippe-Albert de Dion de Malfiance was a French inventor in the mid-1850's. (BTW: Wouldn't Malfiance translate roughly
into "unacceptable girlfriend?"
[Edited on 5/9/04 by carcentric]
M D "Doc" Nugent
http://www.carcentric.com
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skinny
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| posted on 6/9/04 at 03:00 PM |
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the main advantage is simply unsprung weight reduction (as was said a little earlier i think) - with a live axle, the whole diff and axle casing etc
are all sprung, but with de dion, the diff is solidly mounted to the chassis and so not included in the sprung weight. this essentially means that the
suspension has less intertia and can react more quickly to bumps etc.
also, i think it offers advantages in keeping constant camber and track width
if you don't fail, you aren't trying hard enough.
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craig1410
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| posted on 6/9/04 at 06:34 PM |
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quote:
Originally posted by skinny
with a live axle, the whole diff and axle casing etc are all sprung
I think you meant "unsprung" here didn't you?
Cheers,
Craig.
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Mikey G
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| posted on 6/9/04 at 08:13 PM |
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quote:
Originally posted by craig1410
quote:
Originally posted by skinny
with a live axle, the whole diff and axle casing etc are all sprung
I think you meant "unsprung" here didn't you?
Cheers,
Craig.
I think he means 'sprung' as in the whole unit is sprung to the car whereas the Dedion setup only the tube and carriers are sprung and the
diff is rigid i.e 'unsprung'
Mike
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craig1410
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| posted on 6/9/04 at 08:22 PM |
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Mikey,
I don't think so.
"Unsprung mass" is that mass which is not on the chassis side of the springs. We always aim to reduce unsprung mass by reducing the mass
of things like wheels, tyres, hubs, axle, driveshafts, brakes etc. I think he knew what he meant but his fingers typed the wrong word. I just wanted
to clarify the point to avoid confusion - looks like I did a great job too!! 
Cheers,
Craig.
[Edited on 6/9/2004 by craig1410]
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Mikey G
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| posted on 6/9/04 at 09:03 PM |
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lol, now youve confused me
I did mention earlier that a dedion setup was a way of reducing 'unsprung weight' so i knew what i was on about "but i was just
trying to clarify/confuse the situation further"
I'll leave now
Mike
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MikeRJ
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| posted on 6/9/04 at 09:04 PM |
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quote:
Originally posted by Mikey G
quote:
Originally posted by carcentric
Isn't there usually a sleeve in the crosstube somewhere that allows changes in rear track width as one or both wheels move up and down?
Dedion is a fixed track width just like a live axle, the angle change of the driveshafts during suspension movement means that something has to move
in and out, sliding joints are built into the inner joints of the sierra driveshafts
Mike
Unless it's a Rover P6 where the axle uses fixed length driveshafts and the De-dion tube itself has a sliding joint! Barking mad idea.
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stressy
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| posted on 6/9/04 at 09:23 PM |
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Live axle IS the lightest
Hi Chris
Ive sai dit before and i will say it again. A live axle set up will normally result in the lightest car by some margin, however it is all mass
bouncing around unsprung and so on a buimpy road traction is (if done correctly) improved by going fully independant. A de dion is the half way house,
the constant relationship of hte back wheelswill allow you to get the gar in the groove easily and confidently but the reduced unsprung mass can
better handling on the bumps.
dedion can offer better traction in terms of torque distribution to both rear wheels, however on th flip side a live axle can be made with clever
adjustable links to produce some superb traction.
Cheers,
Chris
p.s youll find some weight on one of my previous posts. home builder will find it hard to match the dedion weight ive qouted tho.
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stressy
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| posted on 6/9/04 at 09:26 PM |
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Here you go
repeating a previous post......
live axle vs dedion vs irs
Having considered this in the past i came up with the following which you may find helpful. The numbers are from my own measurements and calculations
plus other peoples supplied info, so accuracy is not 100%.
live axle
axle casing inc brackets, standard diff, trailing and lateral links, coilovers, prop, brakes.
unsprung 56kg / sprung 7kg / total 63kg
dedion
std diff, trailing links, coilovers,lateral linkage, disc brakes and calipers,driveshafts and joints (narrow), propshaft, dedion tube an alloy ears
unsprung 37kg / sprung 37kg / total total 74kg
IRS
std diff, driveshafts, hubs/uprights(alloy), wisbones (std bushes), brakes, coilovers, propshaft, additional chassis work
unsprung 37kg / spung 46kg / total 83kg
Hopefully this is of some help.
The hanging masses such as shox etc are assumed 50% sprung and unsprung.
It will be worth noting that the live axle has drums not discs so could be deemed as not like for like but i didnt have the opportunity to get data
for drums from a seirra for comparison.
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Marcus
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| posted on 6/9/04 at 09:55 PM |
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De Dion - the name comes from a French bloke who made cars in the early 1900s, the De Dion Bouton being one of them, so it's not exactly a new
idea!
Marcus
Marcus
Because kits are for girls!!
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skinny
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| posted on 7/9/04 at 08:52 AM |
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quote:
Originally posted by Mikey G
quote:
Originally posted by craig1410
quote:
Originally posted by skinny
with a live axle, the whole diff and axle casing etc are all sprung
I think you meant "unsprung" here didn't you?
Cheers,
Craig.
I think he means 'sprung' as in the whole unit is sprung to the car whereas the Dedion setup only the tube and carriers are sprung and the
diff is rigid i.e 'unsprung'
Mike
whoops , yes i meant that de-dion reduces unsprung weight - the bits that dangle off the car are lighter 
if you don't fail, you aren't trying hard enough.
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MikeRJ
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| posted on 11/9/04 at 05:51 PM |
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quote:
Originally posted by carcentric
In a trike, a live axle has the advantage of resisting outward lean that would be enhanced by IRS rear suspensions.
That's not strictly true, body roll is not automaticaly greater on an IRS design compared to a live axle. The points that determine this are
the relative locations of the center of gravity and the roll center. If you could move the center of gravity well below the roll center you could
have a trike that leans into corners like a bike.
The only real advantage of a live axle, besides simplicity/cost is that it has perfect camber control during body roll, the relative angles of the
wheels to each other remains constant. The De-dion shares this property, and betters the live axle for unsprung weight. Apart from that, the De-dion
inherits all the negative aspects of the live axle.
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