oliwb
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| posted on 6/2/07 at 01:13 PM |
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IRS or De-dion
Going to do some changes to the 7 whilst is Sorn'd.....removing the sierra back end and trying to make it lighter. But can't decide
between IRS and de-dion. I basically want something - simple, cheap, light and that handles well....I know de-dion is probably the better way to go
for these things but I'm not quite convinced and reckon I might be better to spend a bit more time and money trying to make a double wishbone
IRS arrangement. What do you all think?? Please give reasons to votes as well, if you can be bothered.....Thanks. Oli.
If your not living life on the edge you're taking up too much room!
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craig1410
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| posted on 6/2/07 at 01:16 PM |
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Hi,
I went with de-dion because it gives me 99% of the benefits of IRS with 99% of the simplicity of live axle. I made this choice several years ago when
de-dion kits were scarce but now you can buy a de-dion beam from several suppliers for not much money.
In my mind the choice has never been clearer!
Cheers,
Craig.
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Peteff
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| posted on 6/2/07 at 01:18 PM |
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If I didn't have a live axle I would go de dion as it means less alteration to the basic chassis. The kit to make them is reasonably priced from
most suppliers as well.
yours, Pete
I went into the RSPCA office the other day. It was so small you could hardly swing a cat in there.
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oliwb
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| posted on 6/2/07 at 01:24 PM |
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Planning on making it all from scratch so not too woried about buying the bits from suppliers. Also chassis is a tiger cat so different from
locost.....Figured I'd almost be grafting on the rear end of an avon.....Oli.
If your not living life on the edge you're taking up too much room!
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ch1ll1
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| posted on 6/2/07 at 01:31 PM |
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de-dion for me,
just u2u jrobert on here
he sells them and the very good
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mark chandler
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| posted on 6/2/07 at 01:34 PM |
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Being that you need to trash the suspension behind the rear bulkhead I would be inclined to make a subframe to fit around the diff and IRS it,
especially as you have no mountings for a live axle so this all needs making and bracketing on the main tub.
Strange so much attention to the front suspension then they stick on the whole rear from a sierra....
Regards Mark
[Edited on 6/2/07 by mark chandler]
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ecosse
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| posted on 6/2/07 at 01:42 PM |
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Dedion, same reasons as given i.e. nearly as good as IRS, easier to do, cheaper, and much easier to setup 
Cheers
Alex
PS
And as Paul says John (Jroberts) will supply the bits at a nice price 
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3GEComponents
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| posted on 6/2/07 at 01:43 PM |
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De-dion
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andyps
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| posted on 6/2/07 at 01:53 PM |
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I voted IRS because ultimately it is probably the better system, and can be purer in design, plus I am going for it myself. Having said that, if I had
a live axle car and wanted to change I would go de-dion as it would be much easier and probably nearly as good to most drivers.
Andy
An expert is someone who knows more and more about less and less
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britishtrident
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| posted on 6/2/07 at 01:57 PM |
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A de Dion axle has much better wheel geometry than irs, it wins on smooth surfaces, but because it is not indpendant on surfaces with single wheel
bumps irs has the advantage.
As with a live axle in a Locost de Dion is hampered by the length of the trailling links, make these as long as possible to reduce roll steer.
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MikeRJ
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| posted on 6/2/07 at 02:02 PM |
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De-dion. IRS may have the edge on rough ground, but only if properly designed and it's much easier to make a crap IRS than a good one. Ask
Tiger.
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MikeR
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| posted on 6/2/07 at 02:15 PM |
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quote:
Originally posted by jroberts
De-dion
Strangely enough i've gone de-dion. Can't think why, perhaps it was all the nagging i got off someone!!!!!
:p
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3GEComponents
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| posted on 6/2/07 at 02:35 PM |
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Mike,
Name and shame, i say
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omega 24 v6
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| posted on 6/2/07 at 03:15 PM |
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De dion for my choice as well. Unless you still want it sorned this time next year while your still trying to set up the rear suspension
Seriously it'd be quicker and for the price of a manufactured de dion you might be better buying one than spending time making one. However as
Mark will tell you I'm not one for being frivolous with the wallet.
If it looks wrong it probably is wrong.
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kb58
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| posted on 6/2/07 at 04:14 PM |
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I find it amusing how often rear suspension design is debated, specifically, how it's, "Easy to make a bad IRS." In other words, if
it's hard to do, don't do it. However, I never hear this arguement used in the other place that independent suspension is used - at the
front of the car. If the same logic is used there, it means we should use a straight front axle.
No one seems to shy away from building front independent suspension, and everyone agrees about the many benefits: wheel control, low upsprung weight,
smooth ride, etc. And yet, these same people completely change face when it comes to the back of the car. Suddenly, there's nothing wrong with
an sprung-to-unsprung weight ratio of 3:1?
While we all pretend to be race car drivers, the truth is that the vast majority of our cars will never see the track. Real-world streets are very
bumpy, so ride quality, much more so that wheel control, is the overriding factor. For real-world streets, nothing beats IRS for a smooth ride.
Is it harder to do? Yes. Do you need to know what you are doing? Yes. Can it be done badly? Yes - just like at the front of the car.
[Edited on 2/6/07 by kb58]
Mid-engine Locost - http://www.midlana.com
And the book - http://www.lulu.com/shop/kurt-bilinski/midlana/paperback/product-21330662.html
Kimini - a tube-frame, carbon shell, Honda Prelude VTEC mid-engine Mini: http://www.kimini.com
And its book -
http://www.lulu.com/shop/kurt-bilinski/kimini-how-to-design-and-build-a-mid-engine-sports-car-from-scratch/paperback/product-4858803.html
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Bob C
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| posted on 6/2/07 at 04:33 PM |
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I agree - do de-dion if you want it easy, but IRS is better. And it's really not that hard to engineer
When I completed my back end & weighed the unsprung weight with bathroom scales I asked on here if any de-dion (or live axle)users could do the
same - only got a reply from another IRS user (who's unsprung weight was the same as mine at 31kg/corner) Incidentally front & back are the
same.
Bob
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caber
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| posted on 6/2/07 at 05:47 PM |
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Oli good move to junk all that scrap! I vote De-Dion with a Panhard rod, funny that both ideas from French in the early 20th Century! I think the easy
to make and set up wins out over the theoretical advantages of independent I think the design for rear independent suspension for locosts is not
sorted yet so each set up needs way too much tinkering.
If you really want it simple I still have a spare Capri axle . . . . .
Caber
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MikeRJ
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| posted on 6/2/07 at 06:27 PM |
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quote:
Originally posted by kb58
I find it amusing how often rear suspension design is debated, specifically, how it's, "Easy to make a bad IRS." In other words, if
it's hard to do, don't do it. However, I never hear this arguement used in the other place that independent suspension is used - at the
front of the car.
The front of the book Locost already has independent suspension, the quality of the design is open to debate, but it's working well enough on
the front of thousands of Locosts.
On the rear the book chassis (and the Westfield pre-lit it was based on and the Caterham before it) were all designed with a live rear axle, so to add
IRS you either start from scratch with a pen and paper, or copy one of the existing designs. The fact that a couple of the kit manufacturers have
already managed to design IRS's that are somewhat lacking is probably enough to put a lot of builders off.
A De-dion axle requires much less in the way of chassis mods to fit, it gives similar advantages to IRS in unsprung weight over a traditional live
axle and it's proven to work very well on road and track.
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oliwb
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| posted on 6/2/07 at 06:30 PM |
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Lol - thanks, but no thanks Caber! You've all made me more confused than ever! My heart says IRS and make the effort etc to make it good. My
brain tells me I'll end up with a much better De-dion setup that I'll be able to use during the summer! I just can't decide though!
How bad is de-dion on bumpy roads - we have a lot around here and I don't really plan on going on track so want the best road setup possible!
Funny how the 3 ppl who know me and would theoretically be involved in it all say de-dion! hmmm...some more thinking to do I think....Oli.
If your not living life on the edge you're taking up too much room!
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Mansfield
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| posted on 6/2/07 at 06:47 PM |
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I am hoping the new book will offer the answer to the IRS design question.
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kb58
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| posted on 6/2/07 at 06:58 PM |
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It's all subjective; there'll never be consensus. If you put Schumacher in a straight-axle Seven, he'll blow away a IRS setup driven
by "normal" people. But put him in the IRS car, and it'll be faster than the straight-axle car, by "some amount."
I think that the lap-time advantage of the IRS is real, but the skills (as both driver and builder) or lack thereof, are a much bigger slice of the
pie.
[Edited on 2/6/07 by kb58]
Mid-engine Locost - http://www.midlana.com
And the book - http://www.lulu.com/shop/kurt-bilinski/midlana/paperback/product-21330662.html
Kimini - a tube-frame, carbon shell, Honda Prelude VTEC mid-engine Mini: http://www.kimini.com
And its book -
http://www.lulu.com/shop/kurt-bilinski/kimini-how-to-design-and-build-a-mid-engine-sports-car-from-scratch/paperback/product-4858803.html
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MikeR
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| posted on 6/2/07 at 07:04 PM |
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perhaps one difference is this......
the front end design exists, the rear end design doesn't for IRS. Its easy to copy the book and make the front end.
As for name and shame, Mr JRoberts, would i do that? I mean, who would I name Mr JRoberts? Can you think of anyone? apart from NS Dev obviously
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Syd Bridge
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| posted on 6/2/07 at 07:12 PM |
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This is all more than a little amusing.
Let me ask this;
How many (modern, since 1960) racecars do you see with DeDion backends?
Now, how many racecars do you see with IRS?
What is the back end in a BMW? Why?
What is the back end in a Merc? Why?
Still, you are building a 1950's heritage car, so keep the faith with '50s technology!
Cheers,
Syd. 
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britishtrident
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| posted on 6/2/07 at 07:55 PM |
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In the mid 70s Ferrari built a test car with a de Dion axle, Lauda spent a lot of time playing with it, they came to the conclusion it was as least
as good as the the irs BUT the existing irs set up was a known quantity for them so the de Dion got ditched.
Fitting a de Dion into in an F1 car and getting the beam stiff enough for use with slick tyres was always going to be awkward to package but then
along came the Lotus 78 & 79 to rewrite the book of F1 aerodynamics using a de dion on a venturi car is just not possible.
Astom Martin use de Dion, while Jaguar use IRS on the same platform.
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kb58
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| posted on 6/2/07 at 07:57 PM |
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Very true, Syd. Considering how much heavier these cars are ,makes the IRS solution that much more important. No matter how much work it takes, or how
much it costs, getting the unsprung weight down WILL make a big difference in ride quality. And, as said before, most cars will be driven on real
world, bumpy streets, where the sprung-to-unsprung weight ratio is a big deal.
Mid-engine Locost - http://www.midlana.com
And the book - http://www.lulu.com/shop/kurt-bilinski/midlana/paperback/product-21330662.html
Kimini - a tube-frame, carbon shell, Honda Prelude VTEC mid-engine Mini: http://www.kimini.com
And its book -
http://www.lulu.com/shop/kurt-bilinski/kimini-how-to-design-and-build-a-mid-engine-sports-car-from-scratch/paperback/product-4858803.html
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