garethn
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| posted on 2/3/06 at 10:08 AM |
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Which rear end
I am currently looking into building my own chassis. What are your opinions on each rear end ie Live, IRS or De-dion. ?
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oliwb
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| posted on 2/3/06 at 10:14 AM |
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Think I'm right in saying:
- IRS generally the best eg more grip etc and good ride quality and handling but heavy unless you can make your own double wishbone arrangement
- Live lighter? Obviously less grip and not as good in the bends due to camber changes etc etc
- De-dion good compromise between the two...easier to put together than fully irs but not quite as good etc etc
If I were building myself a locost I would design an IRS rear end something like the Tiger Avon perhaps....think in the long run you'll probably
appreciate putting in the extra effort.....Oli.
If your not living life on the edge you're taking up too much room!
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garethn
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| posted on 2/3/06 at 10:26 AM |
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this what I thought IRS is generally the best -does anyone know where I can get my hands on some drawings I really want to have a go at doing it
myself and not buying on off the shelf solution
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smart51
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| posted on 2/3/06 at 10:30 AM |
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de dion has the same fixed geometry as a live axle but has less unsprung weight as the diff is fixed to the chassis. They are very good on smooth
tracks and have the advantage of zero camber change in roll. They do suffer in bump, though, and can get lively on lumpy B roads.
IRS has better control of camber in bump and controled change of camber in roll. They are more tricky to adjust simply due to the fact that they can
be adjusted. For the road, they are probably a bit better.
I wouldn't change my car from one to the other as none of them are bad but I would choose IRS for a new build. It is hardly any extra effort.
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jon_boy
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| posted on 2/3/06 at 10:57 AM |
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Im doing my own IRS. Unless you are very good with the principles involved and fabricating stuff it amy be easier to use a companies off the shelf de
dion set up or something (dont think any do irs conversions as it were) as personnaly im finding it very challenging. Although hopefully rewarding.
Good luck, U2U me if you want any details etc.
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David Jenkins
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| posted on 2/3/06 at 11:27 AM |
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Here's my take on it... purely personal opinions:
Live axle: simple to install, no setup, as good as any others on smooth roads, 'lively' on bumpy stuff (I speak from personal experience!
)
IRS: complex to install & set up, good on most road surfaces. Total weight may be heavier than live axle, but unsprung weight is much lower.
DeDion: Halfway house between the two - simpler to install, performs well, but heavier unspruung weight than IRS.
DJ
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timf
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| posted on 2/3/06 at 11:46 AM |
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drawings
dedion
http://www.locostbuilders.co.uk/viewthread.php?tid=33136
irs
http://www.locostbuilders.co.uk/viewthread.php?tid=33498
both by rorty in this site
A prisoner of war is a man who tries to kill you and fails, and then asks you not to kill him."
- Sir Winston S. Churchill, 1952
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NS Dev
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| posted on 2/3/06 at 12:01 PM |
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If I were doing a scratch build I would go for De-dion.
As has been said, it's a good compromise, but that doesn't really do it justice.
A PROPERLY ENGINEERED De-Dion setup will handle extremely well.
Live axle 7's handle extremely well but the weight of the diff bouncing about the place makes rear damping difficult to sort on such a light
car, that really is the only major downside of the live axle.
De-Dion gets rid of that problem, making the dampers' lives much easier, and still retains the advantages of the live axle in camber control
etc.
A really well engineered de-dion setup should be possible to make lighter than either the live axle or wishbone IRS, in fact I would say in terms of
SPRUNG weight, wishbone IRS will be the heaviest, and done well, a de-dion setup could be made very similar to wishbone irs in terms of unsprung
weight too. You have to remember that the de-dion setup uses the same chassis mounts as a live axle car apart from the diff mount brackets, whereas a
wishbone IRS car needs considerable extra chassis tubing to mount everything off, much of which feeds loads into an area really not designed as such
on a 7 chassis!
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
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flak monkey
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| posted on 2/3/06 at 12:17 PM |
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The de dion and irs plans rorty drew up are on my site.
David
Sera
http://www.motosera.com
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britishtrident
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| posted on 2/3/06 at 12:54 PM |
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De Dion isn't a compromise --- only reason it isn't used much on production cars is the boot space it takes up -- much more than a live
axle or wishbone irs.
A De Dion setup gets rid of all the engine torque reactions a live axle suffers from ---- hence no axle tramp and much better traction, which goes a
long way to preventing the car going into the snap oversteer which has bitten more than a few Locost & Seven drivers.
In the Lauda era Ferrari built a F1 test mule with De dion rear end using carbon composite for the axle structure , according to Lauda it handled as
well as the existing F1 car straight out of the box BUT the aerodynamics wouldn't work on a single seater.
NSDev comments about the chassis loads on IRS Locosts are spot on.
Also if you do decide to build a wishbone IRS I would advise seeking advice and looking hard at the wishbone setups used by MK, MNR and GTS first
before copying the setup in the Avon book.
[Edited on 2/3/06 by britishtrident]
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craig1410
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| posted on 2/3/06 at 01:07 PM |
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De-dion would be my recommendation as it is simple to build and you avoid the hassle of finding a "good" serviceable live axle and can use
the more easily available Sierra drivetrain.
IRS may have a very small edge in ultimate performance but for the typical locost builder I would expect de-dion to outperform IRS due to the easier
setup.
There are some nice de-dion kits available now too.
Cheers,
Craig.
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procomp
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| posted on 2/3/06 at 02:07 PM |
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Hi any think that can be done to an irs setup can be done to a live axle eg toe in and camber same for the dedion with better unsprung weight. The
major disadvantage with irs is that you cant get any real useable antisquat maybe 20% at the most we run our live axle setups with anything up to 120%
the only desision is how far you can go before you get wheel hop under braking. The engine torque can be eliminated with varying the antisquat side to
side. Rear steer can also easily be reduced to virtualy zero although somtime used as a controlable benefit. Irs is better for bumpy road use but
have any of the locost manufactures done one that is of any use.
matt
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NS Dev
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| posted on 2/3/06 at 05:23 PM |
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Hmmmm, some interesting points there!
Never thought about dialling out the torque reaction with antisquat like that!
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
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Cazzy R
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| posted on 5/3/06 at 11:27 PM |
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Antisquat ??
Can someone translate and offer some sort of physical reason for it being harder to achieve with IRS?
Ta.
Cazzy R
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garethn
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| posted on 6/3/06 at 11:20 AM |
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well it looks like a de dion tube for me then.... does the geometry come mainly from the uprights ie how do I adjust camber
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smart51
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| posted on 6/3/06 at 11:31 AM |
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You don't. Thats the thing with dedion. You cannot adjust the toe or camber angles. You have to weld the tube rght.
By cannot adjust, you could employ a big hammer, or perhaps some shims.
dedion is only easier to set up because you cannot set up toe or camber.
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DIY Si
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| posted on 6/3/06 at 11:51 AM |
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In which case, anyone know of a good way of jigging etc the pieces together to get it right? Be buggered if I want to build the entire lot twice!
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craig1410
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| posted on 6/3/06 at 01:33 PM |
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I don't think it is fair to say that you can't adjust camber or toe on a de-dion setup because I for one managed to set my home-made axle
up for a little bit of tow and a little bit of negative camber which is what I was aiming for. I can't remember the exact figures now but it was
whatever figure I found in a book to be a good starting point.
Also, I believe it to be quite common for people to use shims to adjust whatever settings were designed in to the axle. This is pretty easy to do
although not quite as easy as turning a camber adjuster.
However, having said all that, one of the main advantages of de-dion is that you don't need much in the way of camber because the tyre contact
patch stays parallel to the road naturally, regardless of body roll. (Yes I know that bumps can affect this but generally speaking, on a smooth track
the axle will stay parallel to the road)
On an IRS system you need to build in dynamic camber to compensate for body roll and while this helps to keep the outside tyre contact patch parallel
to the road, it will also give dynamic camber on squat which is bad for traction. This is why de-dion axles are generally better for start line
traction (unless of course you have an IRS system with anti-squat geometry which is easier said than done for the DIY'er.)
As for toe on the de-dion axle, I just built in a little bit to aid stability and to compensate for any flex in my axle under braking loads which
would naturally induce toe out. If necessary I will adjust this with shims later.
By the way, when I assembled my axle I used two pieces if straight steel section as "railway lines" onto which I places the two halves of
my axle (ie. the bits which bolt to my hubs). I then used shims (hacksaw blades actually) to pack the inboard edges of the axle halves to create the
required geometry before tack-welding and re-checking. I checked and re-checked numerous times before (and after) fully welding. Once I got the car on
its wheels I checked again that it had the desired effect and was amazed that it had!!
HTH,
Craig.
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NS Dev
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| posted on 6/3/06 at 01:37 PM |
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Yep, piece of p*55
Get a large lump of RSJ from a scrappy near you for a couple of quid, check it's straight and flat, get two spare hub mount flanges, weld and
true them in line, at 90 deg and the right dist apart on the rsj, with gussets to stop em moving, and you have a jig, job done.
This will get you EASILY close enough, and final tweaking is easily done with shims.
I am building a wishbone IRS car but I would rather have done a full self-build de-dion.
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
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garethn
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| posted on 6/3/06 at 04:30 PM |
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has anyone built up the Rorty plans.... if so are they ok?
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