craig1410
|
| posted on 7/2/07 at 01:34 PM |
|
|
Sorry if we have confused you....
Okay, simple answer:
The extra expense and hassle of IRS is NOT worth it compared to an off the shelf de-dion axle.
Good luck,
Craig.
|
|
|
|
|
Bob C
|
| posted on 7/2/07 at 01:48 PM |
|
|
"go with live axle as this is the lightest option by far. The so called problems of unsprung weight is only a problem if you dont sort out the
dampers to match"
Fraid I don't buy this. The way I see it you have a choice of spring rates. The one you choose determines the bounce frequency of the car then
the dampers are set to damp these oscillations. The bounce frequency is sometimes quoted in cpm (cycles per minute). Unsprung mass doesn't come
into that at all. The problem with unsprung weight is that it has to be accelerated downwards to stay in contact with the road, after a bump, when the
surface is rough, and the force available to do the accelerating is the corner weight (sprung) of the car. Stiff dampers make this WORSE as the job of
a damper is to resist movement, ie force proportional to velocity.
Another point I'd love to discover is what unsprung weight is achieved with different solutions. Easy to measure - release the spring, jack up
the chassis & put bathroom scales under the wheel. My mx5 based IRS, including disc brakes wheel tyre & driveshafts is 31kg/corner (same front
as back). Can anyone tell us what they get with say a GTS dedion or an escort axle? It would be nice to know for sure what (if any) unsprung weight
penalty different designs exact.
I have 125lb/inch springs on the back. It's actually a bit too soft (grounds sometimes with a passenger) so I'll probably settle at 150.
This still gives quite a high bounce frequency (calculated at 108cpm from memory)
Bob
|
|
|
flak monkey
|
| posted on 7/2/07 at 02:24 PM |
|
|
All I can say is the GTS de dion is very light indeed. Definately lighter than an bare escort axle. So this would lead me to the guestimate that the
de dion has considerably lower unsprung weight than the live axle by the time the diff etc is added to the live axle...
IRS gives you the lowest unsprung weight, but in total mass terms it is heavier than the de dion. I believe the de dion is the lightest overall
solution (depending on the diff weights) with some penalty on unsprung weight.
David
Sera
http://www.motosera.com
|
|
|
procomp
|
| posted on 7/2/07 at 02:51 PM |
|
|
Hi very sad that yet again people can not have a discusion whith different opinions whithout turning it into a personel slanging match  .
At the end of the day for a locost that is not exactly going to get pushed hard it really dosent matter what system is used as there is already one
appalling irs setup in use with many people saying how well it handels on the road.
However if it is for track use there is no one diffinitive best but a case of choosing what gives the best advantage over all for all circuits
used.
cheers matt
|
|
|
Minicooper
|
| posted on 7/2/07 at 03:25 PM |
|
|
For me it has to be the de dion, I have used it in the past and it works very well, easy to setup, a touch of toe in, a little negative camber,
adjusted by shims under the bolted hubs, I use 24" long links and a watts linkage across the back.
A few years back I was interested in the caterham which was de dion at the time and maybe some of them still are I don't know, I went out for a
spin and it was great, at that time they were just introducing the IRS version, I asked why they had changed the rear suspension design he told me it
was more to do with fashion than any short comings of the de dion
Cheers
David
|
|
|
Bob C
|
| posted on 7/2/07 at 03:41 PM |
|
|
Hi David,
yes I'm sure it is very light, particularly compared with a truck axle - I was hoping someone could quantify with a physical measurement.
Matt, I hope I didnt cause you grief - I quoted your text 'cos it suggested that unsprung weight didn't matter & you could fix it by
damper changes - I was saying I think that's wrong. I'd never "slag anyone off"
cheers
Bob
|
|
|
Minicooper
|
| posted on 7/2/07 at 03:53 PM |
|
|
BobC,
I wasn't answering any questions just saying that I like the de dion and a conversation that I had with a caterham chap.
My de dion tube bare is 6kgs, I haven't bothered weighing other stuff
David
|
|
|
oliwb
|
| posted on 7/2/07 at 05:47 PM |
|
|
quote:
Originally posted by craig1410
Sorry if we have confused you....
Okay, simple answer:
The extra expense and hassle of IRS is NOT worth it compared to an off the shelf de-dion axle.
Good luck,
Craig.
But I'm not going to be using an off the shelf de-dion setup. The whole thing is going to be bespoke. So if I'm going to that effort
would it not make sense to go the full hog and use one of the existing IRS designs to base mine on??
Matt - (I don't really understand anything about damper, spring rates etc etc so can't comment on your suggestions) but could you clarify
which IRS design is and isn't good? (Feel free to u2u or e-mail if you don't want it "out there"! I'd be very grateful
though if you could give some proffessional advice and help me steer clear of an inherently bad design.
Whats the best length of trailing arms to have on a de-dion? I'm going to measure my existing bodywork and see if it will accomodate a de-dion
easily. Thanks Oli.
If your not living life on the edge you're taking up too much room!
|
|
|
MikeRJ
|
| posted on 7/2/07 at 09:47 PM |
|
|
quote:
Originally posted by oliwbSo if I'm going to that effort would it not make sense to go the full hog and use one of the existing
IRS designs to base mine on??
Just be careful whose design you choose. As I said before even the kit manufacturers have managed to make some fairly poor IRS implementations.
Craig,
I was agreeing with you, sorry if that wasn't clear!
|
|
|
MikeRJ
|
| posted on 7/2/07 at 10:06 PM |
|
|
Right, I thought I remembered a previous post on rear suspension weights and an agonisingly slow search turned this up:
http://www.locostbuilders.co.uk/viewthread.php?tid=17111
Might be worth repeating the info to make it easier to find next time! These are the numbers that Stressy measured for himself:
--------------------------------------------------------
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
--------------------------------------------------------
This confirms that the overall lightest solution is the good old live axle (english I suspect), followed by the de-dion and IRS coming in last. The
sprung weights are the more important issue though, and the IRS and De-Dion tie for first place, both significantly better than the Live axle.
Of course this is only representative of the designs that stressy looked at, but most IRS and De-Dion solutions for the locost are very simmilar.
|
|
|
JoelP
|
| posted on 7/2/07 at 10:09 PM |
|
|
most locosts with IRS have a very poor inefficient lay out. You could save loads of weight if you actually designed it into the chassis rather than
welding a big box on as an afterthought.
|
|
|
britishtrident
|
| posted on 7/2/07 at 10:31 PM |
|
|
The point that is missed about double wishbone IRS is that the camber axle are only correct when the car is in steady state straight ahead conditions,
if you set up to give enough negative camber for cornering the camber angles under braking and acceleration are all wrong.
This camber problem is worse on an IRS than IFS, because at the front the castor angle can be engineered to give some negative camber gain when
cornering.
De Dion dosen't have this problem BUT (nb a big but) single wheel bumps upset things badly the camber on both rear wheels gets disturbed.
Live axles also share this problem of course but on live axle the unsprung mass to sprung mass ratio becomes silly on a very light car, not so big a
problem if you are building a Range Rover. High unsprung mass really becomes a problem on two wheel bumps, I remember from my MG TF days that a two
wheel bump mid corner could make the rear end of the car jump a couple of feet accross the road.
De Dion was the rear suspension of choice in sports car racing and GP up to the cars went mid engined, it was used by Connaught, Aston Martin, Lotus,
Maserati, Ferrari Bristol. When cars went rear engined the gearbox section of the transaxle was located behind the final drive. In fact most of the
rear engined racing car of this era were used the Colotti gearbox which was base on the Citroën DS unit which had an enormous rear over hang making a
de Dion a non starter.
In the 1970s when Ferrari built a 312 mule with a de Dion rear end the had to design a transverse gearbox to make it possible. The transverse box was
adopted the de Dion wasn't.
Another reason that de Dion went out of main stream thinking was one of the few mass production examples of the de Dion and the one most commonly used
to illustrate it in books was that used in the Rover 2000 of the early 1960s. The Rover layout was not a typical de Dion layout, to save the cost of
using plunge accepting cv joints fixed length drive shafts were used with telescopic de dion tube. This comprimise although it didn't affect
the road holding made the handling feel just a bit odd until the driver got used to it.
[Edited on 8/2/07 by britishtrident]
|
|
|
craig1410
|
| posted on 8/2/07 at 12:43 AM |
|
|
quote:
Originally posted by oliwb
quote:
Originally posted by craig1410
Sorry if we have confused you....
Okay, simple answer:
The extra expense and hassle of IRS is NOT worth it compared to an off the shelf de-dion axle.
Good luck,
Craig.
But I'm not going to be using an off the shelf de-dion setup. The whole thing is going to be bespoke. So if I'm going to that effort
would it not make sense to go the full hog and use one of the existing IRS designs to base mine on??
Matt - (I don't really understand anything about damper, spring rates etc etc so can't comment on your suggestions) but could you clarify
which IRS design is and isn't good? (Feel free to u2u or e-mail if you don't want it "out there"! I'd be very grateful
though if you could give some proffessional advice and help me steer clear of an inherently bad design.
Whats the best length of trailing arms to have on a de-dion? I'm going to measure my existing bodywork and see if it will accomodate a de-dion
easily. Thanks Oli.
Oli,
I didn't use an off the shelf de-dion axle either, I built it myself from some old MK Engineering plans. I can give you these plans if you like
but to be honest these have been surpassed by other plans from the likes of GTS Tuning. Also, I think you'd be better just buying an axle
although you might need to wait a while if you buy it from GTS as their order process is less than slick. I think there was someone else on the forum
building de-dion axles so you might be able to source one there.
Having built my own axle I'd say it was fairly straightforward and I didn't need to worry too much about geometry because on a de-dion
axle this takes care of itself.
You asked about trailing arm lengths. As far as I am aware they should be as long as possible or practical and should be exactly equal length. Mine
use rod-ends to allow me to adjust the lengths as does my panhard rod which allows me to centre the axle.
Forgive me for saying it but your comments suggest that you want to arrive at the conclusion that IRS is the way to go and you seem surprised at the
overwhelming support for de-dion. You know what my opinion is but if YOU want to do IRS then just do it and make sure you don't regret your
choices later. If you build IRS then you might end up with a slightly slower car (IMHO) but if you build a de-dion you might end up with a regrets
that you didn't build it with IRS. I think the latter is a worse outcome because it is YOUR car.
I think you will understand by now the pro's and con's of each so just make the right decision for yourself.
Cheers,
Craig.
[Edited on 8/2/2007 by craig1410]
|
|
|
Angel Acevedo
|
| posted on 8/2/07 at 01:14 AM |
|
|
Seeing the bull-fight from the barriers,
It is all a matter of weighted compromise...
What do you want?
- (I think cost is Nr 1) Cost.
- Ease of Build
- Ease of set up.
- Comfort.
Assign percentage to each desirable characteristic
Then assign grade to each setup on every characteristic.
Multiply both values and add up.
Best setup for you will be the one with the highest total.
IMHO
PS: I have a choice of 2 donors, Live axle and IRS, Planning on a Live axle as first build and IF funds, will and self confidence still alive, IRS for
the second.
Beware of what you wish.. for it may come true....
|
|
|
locostv8
|
| posted on 8/2/07 at 01:43 AM |
|
|
I had originaly intended to use a solid axle for simplicity but with further investigation will do an IRS.
http://locost7.info/files/suspension/RortyLocostIRSAssembly.pdf
http://wrangler.rutgers.edu/gallery2/v/7slotgrille/hssss/
|
|
|
RK
|
| posted on 8/2/07 at 02:06 AM |
|
|
Does anyone know how the IRS from the Sierra from England compares with that of an 80's Toyota Celica GTS (not the frame maker)? I want IRS
cause our roads are all very bumpy, unlike most of yours. Also, you can't get any solid axles here in this part of Canada, unless they come from
a Ford Ranger or Mazda B2000 pickup truck.
Seems to me that DeDion is easier for you though. This can all get too complicated, and is beginning to put me off the whole project. As soon as you
go non-standard, you introduce a whole bunch of variables that confuse mere mortals like me, who haven't changed oil in a car for over 20 years.
There I said it.
|
|
|
WIMMERA
|
| posted on 8/2/07 at 06:18 AM |
|
|
I'm with Mansfield, have a look at Haynes new book, PPC have driven the car and give it a glowing report, if that means anything.
Wimmera
|
|
|
MikeRJ
|
| posted on 8/2/07 at 08:12 AM |
|
|
quote:
Originally posted by RK
Does anyone know how the IRS from the Sierra from England compares with that of an 80's Toyota Celica GTS
I don't know what system the Celica uses, probably McPherson strut?
The Sierra uses a semi-trailing arm rear suspension (simmilar to the old E30 BMW) that is not a very high performance design and not very suitable for
a Locost due to size and weight. People have fitted them though, and the Robin Hood 2B uses this system.
|
|
|
omega 24 v6
|
| posted on 8/2/07 at 10:16 AM |
|
|
Well OLI have you made your mind up??
Seems to have become very confusing and argumentative all of a sudden.
Perhaps what this forum needs is a technical area, where all the well informed and hi tech members can post their findings, and high spec drawings,
for us all to wonder at, and perhaps benefit from.
I for one am amazed at the very different (and personally definative) views that have appeared on this thread and find them interesting. However some
of them IMHO are too in depth (for me and probably many others) and must be making it more difficult for you to make your mind up.
I see it simply as the following
1 ease and speed of getting you on the road.
2 innovatative design with little or no pointers to a proven system that'll fit your car. Or a proven system that there are plans/pointers
for available (for free)
3 It's your car and if you want IRS then go for it regardless of the time/money required to get it right. It'll make for much kudos at
any meeting when you're asked who designed/built it.
Good luck see you on Saturday.
[Edited on 8/2/07 by omega 24 v6]
If it looks wrong it probably is wrong.
|
|
|
Doug68
|
| posted on 8/2/07 at 01:20 PM |
|
|
The answer becomes absolutely clear then.
which ever one a person likes best is the best one.
And unless you've got a race to win that is, then lap times tell the complete story.
You might as well argue whats a better colour blue or red (obviously red is but that won't stop some silly bugger arguing the point)?
|
|
|
andyps
|
| posted on 8/2/07 at 01:44 PM |
|
|
quote:
Originally posted by oliwb
But I'm not going to be using an off the shelf de-dion setup. The whole thing is going to be bespoke. So if I'm going to that effort
would it not make sense to go the full hog and use one of the existing IRS designs to base mine on??
Matt - (I don't really understand anything about damper, spring rates etc etc so can't comment on your suggestions) but could you clarify
which IRS design is and isn't good? (Feel free to u2u or e-mail if you don't want it "out there"! I'd be very grateful
though if you could give some proffessional advice and help me steer clear of an inherently bad design.
Whats the best length of trailing arms to have on a de-dion? I'm going to measure my existing bodywork and see if it will accomodate a de-dion
easily. Thanks Oli.
I am sure there are people who have contributed to this thread who will design you a bespoke de-dion set up - after all, there have been expectations
that others will do so for an IRS version so maybe someone will put their own time where their mouths are....
I would say that if it is a choice between a bespoke de-dion you design yourself and an existing IRS set up you should go for the IRS set up - that
sounds easier to me.
[Edited on 8/2/07 by andyps]
Andy
An expert is someone who knows more and more about less and less
|
|
|
MikeRJ
|
| posted on 8/2/07 at 03:32 PM |
|
|
quote:
Originally posted by andyps
I am sure there are people who have contributed to this thread who will design you a bespoke de-dion set up - after all, there have been expectations
that others will do so for an IRS version so maybe someone will put their own time where their mouths are....
What can you make bespoke with a De-Dion though? The whole point is that it's simple to make as there are no tricky kinematics to sort out
(apart from trailing arms, but you are pretty much stuck with the book ones on a book chassis). Even if you want to fabricate one from some exotic
material, it will be fundamentaly the same as one you can buy wrt geometry.
With a double wishbone IRS you have lots of design decisions to make regarding the length and angles of wishbones, dimensions of uprights, significant
chassis mods etc.
|
|
|
andyps
|
| posted on 8/2/07 at 03:49 PM |
|
|
quote:
Originally posted by MikeRJ
quote:
Originally posted by andyps
I am sure there are people who have contributed to this thread who will design you a bespoke de-dion set up - after all, there have been expectations
that others will do so for an IRS version so maybe someone will put their own time where their mouths are....
What can you make bespoke with a De-Dion though? The whole point is that it's simple to make as there are no tricky kinematics to sort out
(apart from trailing arms, but you are pretty much stuck with the book ones on a book chassis). Even if you want to fabricate one from some exotic
material, it will be fundamentaly the same as one you can buy wrt geometry.
With a double wishbone IRS you have lots of design decisions to make regarding the length and angles of wishbones, dimensions of uprights, significant
chassis mods etc.
I think the original request relates to a car which doesn't have a book chassis so may need to be bespoke in terms of width and mounting points
- that is what i was trying to say.
Seems to me that this thread has become a bit of a slanging match which is not necessary, but if people challenge someone to give something for
nothing using skills gained over a long time they should be prepared/capable of doing the same themselves. Otherwise I don't want to enter into
an arguement.
Andy
An expert is someone who knows more and more about less and less
|
|
|
Bob C
|
| posted on 8/2/07 at 04:46 PM |
|
|
Rorty's IRS AND dedion designs and drawings are freely available for download from "flakmonkey"'s website. Alternatively my
IRS design using mx5 uprights can be downloaded FOC from my website (used by 1 or 2 others as well as myself). This is not a comprehensive set of
drawings like rorty's but there are some drawings, dimensions, photos and solid models - enough to do the job.
You can also buy the Avon book or the GTS plans; though the Avon geometry may be considered less than ideal plenty of folk find it just fine (which
sort of underlines the point that maybe us mere mortals will never appreciate the fractional differences between IRS and dedion.....)
cheers
Bob
|
|
|
MikeRJ
|
| posted on 8/2/07 at 05:36 PM |
|
|
quote:
Originally posted by andyps
I think the original request relates to a car which doesn't have a book chassis so may need to be bespoke in terms of width and mounting points
- that is what i was trying to say.
Ahh, ok I must have missed that.
quote:
Seems to me that this thread has become a bit of a slanging match
Sorry if my post sounded argumentative, it was not intended.
|
|
|
