renrut
|
 posted on 27/6/11 at 02:16 PM |
|
|
Unusual Suspension Design
Wasn't sure where to put this as its entirely suspension and not really Middy but its definitely not typical locost either and thought I'd
get a better response here. Mods feel free to move as you see fit.
Anyway the question is for suspension gurus.
I've got a serious lack of space in the back of my little middy and having already built one suspension setup (mac strut) but I don't have
sufficient space and clearance for the track control rods. So I'm considering doing away with the lower ball joint and making new uprights and
lower wishbones so that the lower connection between upright and wishbone can only rotate in one plane for bump and droop. I would keep the upper
strut in place and not be fitting an upper wishbone but that seems to work fine for normal macpherson strut systems.
This all seems to make sense to me and should be lighter than the current setup albeit with less adjustability. But I'm starting to get worried
that I can't find an example of where this system has been used anywhere else. Is there some fundamental problem with it that I can't see?
Why are all the fun things in life expensive!
|
|
|
|
|
Dick Axtell
|
| posted on 27/6/11 at 02:31 PM |
|
|
quote:
Originally posted by renrut
So I'm considering doing away with the lower ball joint and making new uprights and lower wishbones so that the lower connection between upright
and wishbone can only rotate in one plane for bump and droop. I would keep the upper strut in place and not be fitting an upper wishbone but that
seems to work fine for normal macpherson strut systems.
Sounds, to me, very like a Chapman strut arrangement. Will scuffle thru old paperwork for a pic.
Pic I had in mind shows upper wishbone, therefor not fitting your description. However, thinking a little more about your proposal, you seem to imply
that there will have to be fixed length drive shafts, which will then fill the function of the absent upper wishbone.
Is that correct? Or have I pictured wrongly?
[Edited on 27/6/11 by Dick Axtell]
Work-in-Progress: Changed to Zetec + T9. Still trying!!
|
|
|
ashg
|
| posted on 27/6/11 at 02:32 PM |
|
|
this is a case of.... a picture speaks a thousand words.
Anything With Tits or Wheels Will cost you MONEY!!
Haynes Roadster (Finished)
Exocet (Finished & Sold)
New Project (Started)
|
|
|
renrut
|
| posted on 27/6/11 at 02:33 PM |
|
|
That's what I initially thought but on looking most chapman struts appear to still have a track control rod. Or are they just misnamed
macpherson struts?
ETA found some pics of an old lotus (elan possibly) chassis and that appears to not have the track control arms. If this is the case then I may be
worrying about nothing. 
[Edited on 27/6/11 by renrut]
Why are all the fun things in life expensive!
|
|
|
Dick Axtell
|
| posted on 27/6/11 at 02:46 PM |
|
|
Looking at pics of some replacement suspension parts for Lotus Elan/Europa, I note that the lower wishbone has a markedly wider spread of the
attachment points. This could allow you to avoid track control arms. Maybe.
[Edited on 27/6/11 by Dick Axtell]
Work-in-Progress: Changed to Zetec + T9. Still trying!!
|
|
|
renrut
|
| posted on 27/6/11 at 02:52 PM |
|
|
quote:
Originally posted by ashg
this is a case of.... a picture speaks a thousand words.
A picture of the elan mk1 rear suspension which appears to be exactly what I was on about without realising it.
[img]http://lotuselan.files.wordpress.com/2010/03/lotusrearsuspension017.jpg?w=1024&h=722[/img]
quote:
Originally posted by Dick Axtell
Looking at pics of some replacement suspension parts for Lotus Elan/Europa, I note that the lower wishbone has a markedly wider spread of the
attachment points. This could allow you to avoid track control arms. Maybe.
It does look to have quite wide spacing between the mounting points on the hub side and that would make it less susceptible to twisting which I
can't see the strut helping with much at all.
I should phone my bro, he has an 1970 Elan+2 in bits in his garage and could have a look and take some dimensions for me.
Why are all the fun things in life expensive!
|
|
|
MikeRJ
|
| posted on 27/6/11 at 02:56 PM |
|
|
I think what you are proposing is to replace the lower balljoint with a simple bushed pivot? If so this this method is widely used on Locost IRS
designs. By using a rectangular "wishbone" (suitably triangulated!) you can attach the bottom of the upright via two rod ends to give you
some toe adjustment.
This scheme doesn't allow you to add/remove toe-in on bump as a separate track control arm would, but some may regard this as an advantage,
since getting this correct can be tricky and getting it wrong will make a very ill handling car.
[Edited on 27/6/11 by MikeRJ]
|
|
|
renrut
|
| posted on 27/6/11 at 03:25 PM |
|
|
I had a look over a lot of locost IRS designs but they all still seem to have a top wishbone which this wouldn't but yes thats pretty much
it.
It's amazing how many ways other people can say the same thing simpler than myself!
Why are all the fun things in life expensive!
|
|
|
MikeRJ
|
| posted on 27/6/11 at 04:24 PM |
|
|
I don't foresee any major issues translating this to a simple McPherson strut design. I'm certain this scheme has been used on some
production cars though I don't know which ones off hand.
I guess this shows the basic design (though probably not with drums and universal jointed driveshafts):
|
|
|
ashg
|
| posted on 27/6/11 at 05:48 PM |
|
|
Anything With Tits or Wheels Will cost you MONEY!!
Haynes Roadster (Finished)
Exocet (Finished & Sold)
New Project (Started)
|
|
|
Volvorsport
|
| posted on 27/6/11 at 05:57 PM |
|
|
is the gearbox in the way of a de dion setup ?
lotuses have non plunging driveshafts as part of wheel control .
www.dbsmotorsport.co.uk
getting dirty under a bus
|
|
|
renrut
|
| posted on 27/6/11 at 06:51 PM |
|
|
quote:
Originally posted by Volvorsport
is the gearbox in the way of a de dion setup ?
lotuses have non plunging driveshafts as part of wheel control .
Not the gearbox but the chain differential. Going up means I hit the exhaust, going down I hit the ground and going backwards puts me outside the
car.
I do have plunging driveshafts. Is that likely to make a big difference as surely it will need some sort of wheel to diff movement with the axle
swing?
|
|
|
MikeRJ
|
| posted on 27/6/11 at 07:20 PM |
|
|
quote:
Originally posted by Volvorsport
is the gearbox in the way of a de dion setup ?
lotuses have non plunging driveshafts as part of wheel control .
So do Jaguars, at least the older ones.
quote:
Originally posted by renrut
I do have plunging driveshafts. Is that likely to make a big difference as surely it will need some sort of wheel to diff movement with the axle
swing?
You will need plunging driveshafts with the scheme you have outlined, it will bind up if you don't.
[Edited on 27/6/11 by MikeRJ]
|
|
|
Doug68
|
| posted on 28/6/11 at 06:27 AM |
|
|
I don't know of any 1/2 shafts that don't plunge in some way unless they're being used as part of the swing axle for example.
Most I believe achieve it by plunge in the CV joint itself.
Back to your original question, it sounds to me like you've designed yourself into a corner. Either:
a. You compromise and do what you've describe above.
b. Layout the suspension you really want and rework the rest of the design until it fits.
It may seem like a lot of work to do now, but in a few years when you are driving the thing and its too late to change will it bother you or not?
Doug. 1TG
Sports Car Builders WA
|
|
|
renrut
|
| posted on 29/6/11 at 12:16 PM |
|
|
Well mine plunge as part of the inner CV joint so thats that.
I'm well aware I've designed myself into a corner, mostly through making too many assumptions at the starting point (I'd have used a
shorter engine for a start!) and trying to retain too much of the original car to save effort which has backfired. Laying out the suspension I should
really use (double wishbone) is basically rip it all up and start again type of problem as the whole rear chassis will need remaking.
Having internet investigated the 60s Elan and Elan+2 which is the only example of this suspension style being used on a production car it works well
but it doesn't handle high suspension loads very well (e.g. powerful engines and sticky track tyres) and tends to lose its rigidity as a result.
Lotus stopped using it after the Elan and went to double wishbone and there are a lot of kits out there to convert Elans to double wishbone which
suggests it was an experiment that didn't quite work.
Having said that I don't intend to put sticky track rubber on (its a weekend toy and occasional track car rather than dedicated) and the Elan
suspension was some of the best in the day anyway so its hardly like I'm moving over to cart springs and wooden wheels.
I think this is the way to go. If it doesn't work I'll still need to rebuild the whole back of the car anyway. If it works then I've
got a nice simple lightweight suspension setup.
If I make the lower joint between upright and wishbone out of rose joints rather than using a bush setup this would hopefully improve its location as
well. I'll still have the bushes at the wishbone to chassis joint so should still maintain some compliance.
Why are all the fun things in life expensive!
|
|
|
renrut
|
| posted on 4/7/11 at 11:20 AM |
|
|
Now I'm going down this route I'm looking for some advice and experience from the knowledgeable chaps on here.
It looks like I'm going to have to fabricate my own uprights unless I can weld to the existing ones. I believe the existing ones are steel so
should be doable but is there a big IVA/MOT no no about doing so or is it ok as long as the welds are good? This would obviously save me a lot of
hassle as the only bit I really want to change is the lower wishbone link.
Secondly what sort of size rose joints should I be looking for to attach the lower wishbone to the upright? It'll be 2 so I can nicely adjust
the static toe to how I want it. I figure I need something at least as strong as the existing lower ball which is attached to the upright by a typical
taper into the upright which ends with a M10 thread so probably average about 12mm diameter.
Would 2x M12 rose joints (one either side of the upright) be sufficient or should I be looking for something beefier like M14? I'm struggling to
find proper strength information on rose joints.
Why are all the fun things in life expensive!
|
|
|
Neville Jones
|
| posted on 4/7/11 at 07:22 PM |
|
|
What uprights are you contemplating welding to?
If they are Ford, they may well be cast SG iron. Non weldable.
Check them with a file first.
Cheers,
Nev.
|
|
|
renrut
|
| posted on 4/7/11 at 08:46 PM |
|
|
quote:
Originally posted by Neville Jones
What uprights are you contemplating welding to?
If they are Ford, they may well be cast SG iron. Non weldable.
Check them with a file first.
Cheers,
Nev.
They're fiat items. How does a file check them? What should I be looking for?
Also I've heard rumours that welding to suspension parts can be an MOT failure, which we all know is a bit silly but is there any truth to this
rumour as obviously its a lot easier to tell if someone has done aftermarket welding to an OEM cast upright than say a fabricated locost one.
[Edited on 4/7/11 by renrut]
Why are all the fun things in life expensive!
|
|
|
renrut
|
| posted on 5/7/11 at 08:52 PM |
|
|
Done some test welds on a spare upright. Looks to have taken, repeated bashing with a large hammer doesn't seem to have done anything other than
round the edges a little.
Yes I know they're not pretty, its to test if it works or not. Any wise thoughts?
Next I guess would be making up the brackets to go on the bottom.
Why are all the fun things in life expensive!
|
|
|
