aerosam
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| posted on 4/3/08 at 04:59 PM |
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Wishbone Questions
Hi guys, couple of quick questions:
First, why are the front wishbones made from round tubing instead of square, is this functional or purely asthetic?
Second, I'm planning on using a BMW 3 or 5 series as my donor so I'll be building an IRS back end, is there any reason why I
couldn't use the original trailing arms from the beemer, rather than having to build a complicated double wishbone setup?
Thanks!
Sam
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Mr Whippy
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| posted on 4/3/08 at 05:02 PM |
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if you have some square tube you could use it but oval looks best.
How can you do a IRS rear end and still use trailing arms, that would require a rigid axle surely?
Fame is when your old car is plastered all over the internet
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Miks15
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| posted on 4/3/08 at 05:19 PM |
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hey sam,
i am using a bmw 3 series as my donor car aswell.
The trailing arm on the hub carrir comes out to the full width of the body.
Therefore to be able to use this you chassis would also need to have structure right out to the widht of the wheels.
The locost chassis is just over a meter wide so unless you want to extend the chassis out further to the full width it would not be easy to use.
For this reason i wll be cutting up my hub carriers and fabricating new bits on so that i can use a double wishbone setup.
Hope this helps.
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aerosam
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| posted on 4/3/08 at 06:56 PM |
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quote:
Originally posted by Mr Whippy
if you have some square tube you could use it but oval looks best.
How can you do a IRS rear end and still use trailing arms, that would require a rigid axle surely?
Hopefully this will work, my first go at posting a pic on this site.
Here's a drawing of the e30 rear suspension, hopefully this will shed some more light on the subject.
[img]/upload/e30_rear_susp_diagram.jpg[/img]
 
Rescued attachment e30_rear_susp_diagram.jpg
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aerosam
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| posted on 4/3/08 at 07:03 PM |
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quote:
Originally posted by Miks15
hey sam,
i am using a bmw 3 series as my donor car aswell.
The trailing arm on the hub carrir comes out to the full width of the body.
Therefore to be able to use this you chassis would also need to have structure right out to the widht of the wheels.
The locost chassis is just over a meter wide so unless you want to extend the chassis out further to the full width it would not be easy to use.
For this reason i wll be cutting up my hub carriers and fabricating new bits on so that i can use a double wishbone setup.
Hope this helps.
HI there Miks, are you using the book chassis? I waqs planning on making either the Mcsorley +4" chassis or even the bigger Viento. Cos this is
what I want to fit in it:
An all aluminium 3.0 (218bhp) or even a 4.0 (286bhp) 30v V8!
 
Rescued attachment bmw v8.jpg
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blueshift
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| posted on 4/3/08 at 07:23 PM |
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You may well find that the original suspension weighs an effing ton compared with a locost alternative.
Though with 280BHP to push you around you may not care 
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Mr Whippy
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| posted on 4/3/08 at 08:08 PM |
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Oh I see it's like a sierra, Robin Hood used a similar method
Fame is when your old car is plastered all over the internet
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Miks15
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| posted on 4/3/08 at 08:37 PM |
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ahh ive got ya sam!
im using an E36 which is where its slightly different!
plus only a puny 1.6 102hp
ive uve got any tips to do with using your bmw parts please let me know as i dont think there are many using it!
thanks
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hemibum
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| posted on 4/3/08 at 09:33 PM |
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quote:
Originally posted by aerosam
quote:
Originally posted by Mr Whippy
if you have some square tube you could use it but oval looks best.
How can you do a IRS rear end and still use trailing arms, that would require a rigid axle surely?
Hopefully this will work, my first go at posting a pic on this site.
Here's a drawing of the e30 rear suspension, hopefully this will shed some more light on the subject.
[img]/upload/e30_rear_susp_diagram.jpg[/img]
Jeez, but that's a heavy looking mother of an assembly. Diff, shafts and hubs, maybe fine, but surely everything else has to be binned and
replaced with fabbed stuff.
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hemibum
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 posted on 4/3/08 at 09:45 PM |
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quote:
Originally posted by aerosam
quote:
Originally posted by Miks15
hey sam,
i am using a bmw 3 series as my donor car aswell.
The trailing arm on the hub carrir comes out to the full width of the body.
Therefore to be able to use this you chassis would also need to have structure right out to the widht of the wheels.
The locost chassis is just over a meter wide so unless you want to extend the chassis out further to the full width it would not be easy to use.
For this reason i wll be cutting up my hub carriers and fabricating new bits on so that i can use a double wishbone setup.
Hope this helps.
HI there Miks, are you using the book chassis? I waqs planning on making either the Mcsorley +4" chassis or even the bigger Viento. Cos this is
what I want to fit in it:
An all aluminium 3.0 (218bhp) or even a 4.0 (286bhp) 30v V8!
Ouch! Looks like you'll be missing a couple of valves then! Seriously though, wish you the best with that project, keep us updated please.
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aerosam
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| posted on 5/3/08 at 10:14 AM |
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OOps, 8x4=32! doh!
yeah I will be binning the axle carrier (in fact the one on the E34 5 series I am after is even bigger!) and just using the hubs, diff, shafts and
probably the trailing arms. WIll start a build diary as soon as I have a donor to strip.
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MikeRJ
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| posted on 5/3/08 at 07:02 PM |
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Semi-trailing rear suspension gives nasty geometry changes (toe and camber) as the suspension moves that are generally not desirable in something
designed to handle well. That BMW don't use it any more should be evidence of this.
I would consider using the diff, driveshafts and hubs in a De-dion or double wishbone IRS.
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aerosam
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| posted on 6/3/08 at 09:56 AM |
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That's a good point about the geometry Mike, but as it's my first build I'm trying to keep it simple.
A De-dion axle is a bar linkint the 2 hubs together isn't it? Doesn't this just convert IRS back to live axle (thus defeating the point of
IRS) whilst adding a shed load of weight?
Double wishbone is probably the way to go but looks scary complicated
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MikeRJ
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| posted on 6/3/08 at 11:42 AM |
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quote:
Originally posted by aerosam
A De-dion axle is a bar linkint the 2 hubs together isn't it? Doesn't this just convert IRS back to live axle (thus defeating the point of
IRS) whilst adding a shed load of weight?
Not quite. It gives you the advantages of a live axle (e.g. perfect camber control in roll), but because the diff and one half of the driveshafts are
fixed to the chassis you don't pay the unsprung weight penalty of a real live axle. You do still have the disadvantage of a non-IRS system,
i.e. bump on one side gives camber change on the other), but even so they tend to work very well (as Caterham found).
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