craig1410
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 posted on 9/3/03 at 11:07 AM |
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Need advice - IRS or Live Axle (Oh no, not that again...)
Hi All,
Sorry to drag up what must be a question that's been asked many times (I have searched the Forum but can't find the answer)
I have built a good portion of my chassis along the lines of the McS 7+4 and had originally decided to go down the IRS route using Sierra 4x4 back end
with IRS.
However, I was originally under the impression that this had been done before but now I can't seem to find a decent set of plans for the IRS
back-end.
I'm now wondering whether the IRS is too much hassle for what will be a pretty big challenge even without it. However, since I want to use a Rover V8
I need the extra width and therefore I don't know if there are any live axles of the appropriate width that I could use to fit the 7+4 chassis.
Basically I need some good "practical" advice on whether to pursue IRS or not. I am a graduate engineer (electronic) and have a decent mechanical
knowledge having worked on Mini's since the age of twelve. However, I am aware of my limitations when it comes to suspension design and can't help
but conclude that a simple live axle has to be better than a badly designed IRS system. I also want to complete my car within 12 months if at all
possible.
What difference to handling characteristics will IRS give me on the road and the occasional track day?
Is there such a thing as a tried and tested (as in modelled and/or dynamically tested) IRS design for the Locost or should I look at Live Axle
instead?
Also, does anyone know of a suitable live axle donor car that could handle V8 torque and is the correct width?
Finally, what width of axle do I actually need for a +4 inch chassis so I can go and look around the scrap yard for a quitable donor?
Thanks guys,
Craig.
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Jon Ison
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| posted on 9/3/03 at 08:43 PM |
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Cortina axle would do fine, bit wider than escort and in a light chassis is man enough for the job, its personal choice, live or IRS, i have no probs
with the live axle set up, just back from a run in the peak district cornering at suicidal speeds, overtaking at will and knowing exactly what the car
will do when push'd hard, i prefare live, others won't, your choice.
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david walker
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| posted on 9/3/03 at 09:12 PM |
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You can't really get a live axle installation wrong. Theoretically a well set up independant back end is going to be better, but it will be marginal.
A poorly set up one will be much worse.
I think you know the answer to your own question live axles work excellently and are much quicker/easier to build.
I suspect that many builders have not actually driven or ridden in a se7en. If not I can tell you that if you find a live axle installation wanting
the you are some nutter!
To accomodate the extra width and power of your V8 it would be worth considering an Atlas axle from a 2.8 Capri.
Dave Walker, Race Engine Services - 07957 454659 or 01636 671277
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craig1410
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| posted on 9/3/03 at 09:33 PM |
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Jon/David,
Thanks for your words of wisdom 
Okay, lets say I wanted to go for a live axle from a Cortina or Capri. Aren't these getting a bit rare these days? Do you know (or know where I can
find) the actual width of these and whether there are any complications such as 5 stub hubs etc.
Part of the reason I was shying away from the live axle was due to availability of spare parts as well as the issues of unsprung weight and ride
quality etc. However, as I think you picked up on David, I do want to get my car on the road at some point hence IRS may be a bit much to take
on...
Does anyone know how wide the track on a Rover SD1 is? Could it be a realistic donor for the axle? A bit too wide I would think but worth checking
since it would simplify the donor situation a bit. I think from memory it uses a Watt Linkage, do you think this will be a problem compared with a
panhard rod?
Okay, live axle it is for now, let's see if anyone from the IRS camp can persuade me to defect!
Cheers,
Craig.
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Jon Ison
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| posted on 9/3/03 at 09:44 PM |
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have you completed your front susspension yet ??? thats one reason i suggested Cortina, if you still need cortina uprights then a doner cortina will
provide all you need, ???? just a thought, David as a point re capri axle but the chassis n car is so light they are up to it, the hardest problem is
getting the power down.......but the handling on mine is very predictable with no suprises, the ride is very smooth n comfy too,
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craig1410
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| posted on 9/3/03 at 10:14 PM |
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Jon,
Yes it makes sense to get everything from one car if possible although I'm not sure if my Wife will be very happy with an old Cortina sitting beside
the house while I take it to bits... I think I'm going to have to negotiate something with my local scrapyard so that I can "store" my vehicle at
the yard for a few weeks while I strip it for a fixed price and then leave them the wreck. That way I can flip it upside down and use large hammers
and chisels etc to effect the salvage 
I would like an LSD to help control the V8 torque, is the Atlas on the Capri an LSD or just a beefier non-LSD?
I just came across a website that explains a lot about what's involved in a wider chassis and it recommends the Cortina too. No I don't yet have any
of the donor bits, I just waded straight in to welding bits of steel together...Doh! As you can see from my Avatar, I am not too far down any
particular road just yet. I stopped building because I need to start making decisions about engine bay, trannie tunnel and rear suspension before I
can do any more chassis construction. It was fun while it lasted though
Thanks again for the advice, I think some research into Cortina's and Capri's is in order now.
Craig.
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theconrodkid
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| posted on 9/3/03 at 10:20 PM |
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how bout the volve 740 series axles,they are everywhere and never break.
who cares who wins
pass the pork pies
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david walker
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| posted on 9/3/03 at 10:21 PM |
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An LSD would be good for a V8 powered 7. As Jon has said, getting the power down can be a problem, even with a modest 1700 X'Flow the inside wheel
spins in the wet.
For a common donor the Cortina makes good sense but I'm not sure about where youll find an LSD. Some of the Capri 2.8's had LSDs' as std but not
all. I'm sure someone on here will tell us which! Capri axles are same width as Cortina and same stud pattern.
If you go independent route then the XR4x4 Sierra had a LSD as std.
Dave Walker, Race Engine Services - 07957 454659 or 01636 671277
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craig1410
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| posted on 9/3/03 at 10:31 PM |
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Hi again,
Any idea how wide a 740 Volvo is? These don't have the gearbox at the back on the diff like the 340 series do they?
Yes David, I'm worried about not being able to powerslide properly without an LSD
I've just been reading about Atlas v English etc on another post and it seems that Atlas is the axle type as opposed to English (which seems to be
better in that it's easier to get the diff out) Am I correct in thinking that either the Atlas or English axle could be fitted with an LSD diff? What
I am getting at is, could I just build the car with, say, a Capri 2.0 axle and then fit the LSD diff from a 2.8i later? Same goes for the Cortina, is
there a souped up version of it with an LSD?
Another option I found suggested was to use the Opel Manta axle which seems to be 1320mm track the same as the Capri. There have got to be motorsport
bits for the Manta, surely!
Cheers,
Craig.
ps. I'd rather use a tried and tested combination so maybe the Cortina isn't so bad, especially if I can fit an LSD diff.
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david walker
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| posted on 9/3/03 at 10:44 PM |
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Craig,
The Atlas and English parts are not interchangeable. English LSD's are available but reckon on about £350 s/hand for a good one.
For heavy competition, certainly with an heavier car you'll shear driveshafts with an English or Cortina axle. That said Quaiffe do super strong
floating shafts for English axles but the conversion costs about £700. A std Capri axle with the LSD is probably the cheapest/strongest route with
the Ford gear. As Jon said in an earlier post though, strength is unlikely to need consideration in such a lightweight car.
Not sure about Mantas and Volvos, something may be available, worth the research - let the rest of us know.
Dave Walker, Race Engine Services - 07957 454659 or 01636 671277
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Stu16v
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| posted on 9/3/03 at 10:53 PM |
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Craig, there is another option....Dedion rear axle.
I got mine from Dax minus their suspension brackets (slightly different setup and would of needed too many mods to the already built frame I had
waiting...) which I five linked a-la live axle. I went this route because
a) Less unsprung weight=better handling
b) The axle utilises standard Sierra components, no mods required and loads of easy to find spares compared to Cortina/Crapi/Escort live axles,
c) Also able to use Sierra LSD-to drop on one for any live axle variant is rare and usually expensive,
d) No set up probs, just get in and drive!
HTH Stu.
Dont just build it.....make it!
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Mark Allanson
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| posted on 9/3/03 at 11:01 PM |
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I have fitted a Capri axle, pdf on its way to you on how I did it
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craig1410
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| posted on 10/3/03 at 12:20 AM |
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Mark,
Thanks for the PDF of the Capri fitment, I'll have a study of this later. It looks at first glance to be very detailed and useful.
Stu,
I'm intrigued at your dedion setup and I think I finally understand what a de-dion setup actually is! It's basically a live axle without the drive
shafts and diff which are now "sprung" leaving only the tube itself as unsprung weight (correct?)
One thing I'm not clear on is how the ends of the tube fit to the uprights. Are the uprights Sierra items?
Also, can you tell me how much it would cost me to get the bits from Dax that I'd need?
Finally, what sort of chassis did you build, with respect to the book chassis (mods etc). Mine is currently McSorley 7+4. Would this be compatible do
you think?
You may well have offered the compromise that I am looking for. This setup would solve my main problem which I see with the Live axle - That of parts
availability for Cortina's and Capri's up here in Scotland (I can't remember the last time I saw one!)
Thanks again,
Craig.
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craig1410
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| posted on 10/3/03 at 12:42 AM |
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Stu,
I've just been onto the Dax website looking at the de-dion stuff. Can you confirm what you actually needed from them and whether you had any trouble
getting the bits you needed considering it was for a Locost...
I've got their pricelist but it doesn't have the de-dion tube on it as a separate item and there are an abundance of brackets and fixings which I
don't know if I need.
This whole idea is growing on me by the minute! Anyone else out there using de-dion?
Cheers,
Craig.
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Simon
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| posted on 10/3/03 at 09:51 AM |
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Craig,
Nobody has mentioned it in this thread, but what people are doing (if you want to go the IRS route), is to buy a couple a Jim Dudley's Tiger Avon
book, and graft the IRS design onto RC's chassis.
It's what I've done, and I've put a piccy in the photo archive.
You may also be interested to see the pics of my (unfinished) exhaust system. I'm quite pround of it!!
ATB
Simon
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craig1410
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| posted on 10/3/03 at 08:30 PM |
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Hi Simon,
Yes, I've heard of people doing that in other threads but I've also heard a lot of criticism about the quality of the drawings in the Avon book
(sounds like a cosmetic book my Wife has) which worries me. As I said in my original post, I'm not sufficiently skilled at suspension design to
"join the dots" as it were, and so would prefer a potted solution that I can build upon later once I gain experience and confidence. I really like
the idea of the De-Dion setup if the de-dion beam can be sourced cheaply enough (or manufactured for that matter). I especially like the fact that it
uses Sierra running gear but sticks to the book chassis (more or less) since this is nice and simple (or at least it sounds simple...)
I've heard lots of talk of 2 - 5 year build times from those who seek perfection and I know that I do not have enough patience to last much more than
1 year which is why it's crucial that I keep making steady progress along tried and tested lines towards a known goal (as opposed to an own goal!)
I would in fact be using a live axle right now if it was not for the shortage of suitable donor cars up here in bonnie Scotland. Also, Sierra's can
be had for peanuts whereas Cortina's and Capri's are either shot to s**t or a proudly restored collectors item.
I'm not ruling out the full IRS as you suggest but I must fully understand the pro's and con's of each choice. As I understand it now(rightly or
wrongly) the full IRS is the best for comfort, the live axle is best for grip on a smooth track with the de-dion best for a typical road where it
strikes a balance between grip and roadholding whilst maintaining decent comfort due in large part to low unsprung weight.
Does anyone "fundamentally" disagree with this statement, individual tastes excepted?
Thanks to all once again,
Craig.
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Viper
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| posted on 10/3/03 at 10:15 PM |
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Simon, Just had a look at your pics..is the angle of your rear shocks as acute as they appear? I would have thought that they could do with being a
bit more vertical..Don't get me wrong , i am not critisising your work, have you tried removing the spring from the damper and then seeing how the
shock changes plane when you compress the damper? Take a look at my photo's to see how i have differed from tigers design and to see what i am
getting at...
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Simon
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| posted on 11/3/03 at 09:34 AM |
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Viper,
You're correct - shock angle is rather excessive - so's the compression.
When I ordered them, I was told of their fully open and closed lengths and took a mid point for their "resting" length. Made some steel tube "coil
overs" to use in the mean time and to set top mounting position.
I'm going to go for stiffer strings to start with - the angle will reduce their effective poundage. If that doesn't work - I'll cut the little
blighters out and start again.
Might do it first!! After all it'll only take a couple of hours (including dismantling car and turning chassis over).
ATB
Simon
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Viper
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| posted on 11/3/03 at 10:46 PM |
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Craig.
the rear end debate will probably go on forever, the real advantage i can see to using an irs rather than a live axle is adjustability and less
unsprung weight... to me that is more beneficial..
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craig1410
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| posted on 12/3/03 at 12:13 AM |
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Viper,
You're right, that's why I was reluctant in some ways to bring this thread up in the first place. However, I think my choice will be de-dion if I
can get a suitable beam from Dax. I contacted their sales department but they won't talk to me and have referred me to the technical department.
If I did go down the IRS route, do you think the MK indy rear wishbones would be a good starting point?
What I mean is, I could buy the wishbones (planning to do that anyway since my welding isn't tidy enough) and then build the extra chassis members to
suit the required mountings. Ideally I'd like to get some plans for the mounting locations on the MK chassis but I don't suppose those are available
are they?
Has anyone reverse engineered the Mk Indy chassis IRS setup yet? I'd have more faith in it than in the Tiger Avon rear end. All I really need is
rough measurements of the centerlines and spacings. I could figure out most of the rest of it from the photographs I think (albeit crudely.) Let's
just hope for my sake that Dax will sell me a De-Dion beam axle...
Cheers,
Craig.
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Noodle
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| posted on 12/3/03 at 06:46 AM |
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Craig,
Have you tried MK for a de-dion tube? Before they went full IRS (and for a while in tandem) they were supplying de-dion setups.
I remember them saying that the drag racers preferred them.
Neil.
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craig1410
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| posted on 12/3/03 at 12:38 PM |
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Neil,
Now you mention it I think I've heard about that elsewhere too. I'll drop them an email and ask if they can supply it still.
Will let you know.
Cheers,
Craig.
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auzziejim
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| posted on 12/3/03 at 01:50 PM |
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dont bother e-mailing as they dont seem to have the time to reply they are really busy! you will be better off ringing them.
James
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Stu16v
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| posted on 14/3/03 at 06:48 PM |
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Sorry Craig, havent been about recently (working on car....).
Dax were more than helpful with the order, the only downfall was that when I ordered they were extremely busy so it did take a long time to arrive
(but they were totally honest and did warn me). IIRC it was 120 GBP with p+p.
It uses standard Sierra bearing carriers discs, driveshafts and diff.
HTH Stu.
Dont just build it.....make it!
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Stu16v
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| posted on 14/3/03 at 06:53 PM |
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Oh yeah, my chassis is all my own work, using the RC book for inspiration rather than plans. It is 4" wider, and 3" shorter in the cab area (Likkle
legs ). The Dax tube was ordered minus their suspension brackets, basically just the tube with the flanges to locate hub carriers, so i could fit my
own.
Cheers, Stu.
Dont just build it.....make it!
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