JC
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| posted on 7/5/06 at 08:17 PM |
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Midi rear suspension
I saw the Z cars stand at Stoneleigh last week and was very impressed! Got me thinking. At the moment I am using donor struts with a bespoke lower
arm, with track control arms to control the toe angle. Having seen the Z cars trailing arm arrangement I have come up with the following. Rotate the
hubs forward 90 degrees (and swap sides so the caliper is on top) so that the strut would face forward. Replace the strut with a tube that goes
forwards then meets a bar at right angles which is hinged onto a transverse chassis member (suitably triangulated), to form a trailing arm. This
would need no track control arm and could use a conventional coil-over. There would be no camber gain on bump, but no awkward bump-steer type effects.
Would it work? Would the hub be strong enough? Opinions please. i will try to get some pics!
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britishtrident
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| posted on 7/5/06 at 08:35 PM |
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Great if you want to make a spinning top.
Not only zero camber gain but ground level roll centre .
Plain trailling arms are OK on small fwd drive car where they were used because they counteract the natural understeer of a an extremely nose heavy
car such as a Mini or Metro but on a Midi they would only increase the over steer.
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jimmyjoebob
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| posted on 7/5/06 at 08:39 PM |
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This sounds very much like the suspension used by GTM on their Libra model. They must have a web site. Your car should be light enough to require only
lightweight tubing to be used!
If at first you don't succeed, hide all evidence you ever tried!
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jimmyjoebob
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| posted on 7/5/06 at 09:03 PM |
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This is alink to the GTM libra suspension web page - not exactly like yours but similar!
http://www.gtmcars.com/libra_suspension.php
If at first you don't succeed, hide all evidence you ever tried!
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JC
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| posted on 7/5/06 at 09:17 PM |
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The Libra uses Twin trailing arms cleverly angled to give camber gain. The Z cars stuff uses just one. This is the best link i could
find:http://www.zcars.org.uk/mini/selfbuild2.htm
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jimmyjoebob
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| posted on 7/5/06 at 09:45 PM |
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I will try and find the kit car article that featured a blue car (blonde identification I know!) - the twin wishbone libra design wasn't the one
I was thinking of even though that was the link I found.
If at first you don't succeed, hide all evidence you ever tried!
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russbost
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| posted on 7/5/06 at 10:12 PM |
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My concern would be that when used the ordinary way the casting around the strut is supporting (largely) forces along its length as it is additionaly
supported by the lower arm, when turned forward there would be a moment about the strut casting which would increase in leverage the further the strut
mount is from the centre of the hub spindle - it may well be strong enough, but then again it may not & I can think of only one easy way to find
out! It's an interesting idea tho & nice to see someone thinking outside the box.
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NOTE:This user is registered as a LocostBuilders trader and may offer commercial services to other users
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nitram38
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| posted on 7/5/06 at 11:15 PM |
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Just look at F1 suspension. They still use unequal wishbones and shocks in the same plane as the normal locost (yes I know they are inboard).
Something to be said for keeping it simple.
Someone also mentioned camber gain?
Get your A arms the correct length and you can build this into car anyway.
What will really fry your brain is not having the rear arms pivoting parrallel to the centreline of your car. This helps 'steer' the rear
wheels into bends under camber/load changes.
Just don't ask me to work it out for you!
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TheGecko
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| posted on 8/5/06 at 01:03 AM |
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The real question is, what is the problem you see with the struts that makes you want to change?
I've just been through a similar analysis exercise as I'm building (albeit incredibly slowly) a midi and using struts at the back. A
chance conversation with a local Locost builder about his de Dion rear had me thinking again about rear suspension options. I spent a number of hours
with a hub assembly on the bench while I measured up and drew various options for a de Dion adapter. At the end of the day, I decided that the camber
and toe control advantages gained weren't justified by the amount of fabrication work needed to make the de Dion. Plus, I'd need 4
trailing arms and either a Panhard rod or Watts link as opposed to two wishbones and two toe links.
From your original message, it appears that your concerns are either with toe control (bump steer) or perhaps spring/damper options. Here's how
I'm addressing those issues:
- toe control is with a single link on each side to the original steering arm. The link is made from the donor tie rod - I may even re-use the inner
pivot as it's already threaded to bolt to a bracket, just needing a small boot to keep the grease in. Minimising bump steer will be done the
same as at the front end - some careful planning and then measure and adjust before finalising the inner pivot position and toe link length.
- spring/damper. I'm converting the factory (Corolla) strut tubes to adjustable coil-over with some simple spring sleeve kits. These are
cheap - ie about $40 AUD per side (that's about 16 quid) - and allow the use of common 2.5" springs. Dampers are open choice as the
struts are fully rebuildable. I'll probably go with Koni Sport Yellow cartridges but there's a wide range of adjustable inserts
available.
The biggest problem I have had with the struts is the height of the top mount and the structural problem of making it stiff enough in all planes.
I've dealt with that the same way you appear to have, with the use (where appropriate) of larger than 25x25 tube, although all still in 1.6
wall. The height I handled by allowing the strut to 'poke up' through the surrounding bodywork by 100mm and the disguising that with roll
bar braces and engine cover.
Anyway, all said, I agree with some of the other comments. Simple single trailing arms aren't going to any better than the struts (and will
probably be worse) and good double trailing arms (like the Libra) are a complex design/fabrication exercise.
Best regards,
Dominic
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JC
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| posted on 8/5/06 at 12:28 PM |
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Thanks for all the input. The reason I was considering this setup was that it removes a lot of variables that, as nitram says, are frying my brain!
Gecko, I too have seen the coilover sleeves available over here but I don't think I can re-build the shocks on my struts. How do I find out?
Finally, if the potential is to make a spinning top, why have Z cars used it, even on their bespoke car?(Although the Civic engined version appears to
use a slightly semi-trailing arm, which according to my Staniforth book, will raise the roll centre). Thanks again from confused of Lincolnshire !
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TheGecko
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| posted on 8/5/06 at 11:52 PM |
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quote:
Originally posted by JC I don't think I can re-build the shocks on my struts. How do I find out?
JC, I can't see
enough detail in any of the photos on your blog, but the pointer to a rebuildable strut is a removable top flange. The Corolla ones have a big hex
nut arrangement (about 55mm or so! - I used a Stilson wrench ) but I've seen some that are pin-drive i.e. a pair of diametrically opposed
holes in the flange face. Even if the ones that came off your donor aren't rebuildable, it may well be that there are interchangeable parts
from another model that are.
Job one - pull up that corrugated dust boot and have a good look at the top of the strut tube where the shaft comes out. If it looks removable, then
the strut is probably rebuildable. The other option is to look up the catalogues of suspension suppliers and see whether they offer inserts
(catridges) or replacement strut assemblies for the model in question.
There's some photos of the same sleeves I'm using on a friends web site
(clicky) although those are on his RWD Corolla tarmac rally car. Same
principle though. Pic 13 shows the top end of the strut tube with a pin-drive cap (included with the Koni Yellow insert from memory).
On the subject of removing variables, be careful you aren't replacing problems you can see with ones you can't! Also, one man's
problematic variable is another man's useful adjustment
Anyway, good luck with whatever you do.
Dominic
[Edited on 8/5/2006 by TheGecko]
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