adrianreeve
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| posted on 9/5/19 at 01:20 PM |
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Has anyone made their wishbones from ERW?
Hello, just wondering if anyone has made their wishbones from ERW instead of seamless tubing? Looking at the mechanical properties of each, it would
seem that either would be suitable? If so, 1.5 or 2mm wall thickness? Would be nice to hear from people with cars on the road to see if there have
been any issues.
Thanks very much
Adrian
[Edited on 9/5/19 by adrianreeve]
[Edited on 9/5/19 by adrianreeve]
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rusty nuts
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| posted on 9/5/19 at 01:55 PM |
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There was a spate of wishbone failure several years ago , worth doing a search. There was also issues with the wishbone crush tubes being too short on
at least one manufacturer’s items which I think may have been a contributing factor to at least some failures. Personally I would prefer to make them
stronger rather than have them fail.
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907
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| posted on 9/5/19 at 02:03 PM |
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Like the old song... Ya knee bones connected to ya thigh bone....
Or.. A ten tonne hook on a five tonne chain...
If for instance you were to use CDS; that is material that gains strength by cold working (work hardening), and then you weld it,
thus changing its crystal structure back to a semi annealed state you have lost most of the gains. (around the weld area)
To carry that a little further into the chassis then your W/B's are attached to an ERW square box frame. (maybe)
Personally I feel that unless weight is of critical importance then better to use a bigger diameter tube or/and increased wall.
My own are 22.2mm (7/8" with a 2mm wall, but still seamed tube.
Paul G
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Sam_68
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| posted on 9/5/19 at 02:31 PM |
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If you design them correctly (and yes, I know that involves quite a big 'if', then the individual tubes in a wishbone should be in
pretty much pure tension or compression, so ERW or CDS should make too much difference, in theory.
In practice, I'd need a damned good reason not to use CDS, though.
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AdamR20
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| posted on 9/5/19 at 02:50 PM |
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Cost?
ERW here, as on all the 7 (quantity, not type) kit cars I've owned, and I'm still alive with all my limbs intact.
7/8" bottom and 3/4" top, 14G all round. Way overbuilt but still much lighter than off the shelf offerings due to sensible design - no
huge 4mm plates holding things together and not a transit van ball joint in sight!
[Edited on 9/5/19 by AdamR20]
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Slimy38
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| posted on 9/5/19 at 03:08 PM |
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quote:
Originally posted by AdamR20
Cost?
Same here, it was all cost related. The one thing I did read about (and made sure I adhered to) was to make sure the weld seam was inside the joins.
Once I'd finished, there was only a small portion of ERW seam left visible.
Of course, I don't actually know whether welding on a weld is a good idea, the joys of reading random stuff on the internet I guess!!
I've just had a look at what I used, it was 19mm x 1.5mm and 25mm x 1.5mm. The bush outers were made from a length of 33.7mm x 2.6mm. With
shipping and VAT that was £50, an equivalent CDS was four times more if I remember correctly.
[Edited on 9/5/19 by Slimy38]
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Mr Whippy
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| posted on 9/5/19 at 09:58 PM |
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Tbh when you see what modern production cars use these days those on a 7 look beefy
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steve m
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| posted on 10/5/19 at 06:53 AM |
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Mine are ERW and not CDS as at the time I couldn't find any CDS, or not at a price that i liked!
however, i did buy thicker walled ERW, than the book said for the whishbones
never had an issue
steve
Thats was probably spelt wrong, or had some grammer, that the "grammer police have to have a moan at
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adrianreeve
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| posted on 10/5/19 at 06:55 AM |
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Thanks, what wall thickness did you go for? Was thinking 2mm.
Cheers
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MikeRJ
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| posted on 10/5/19 at 12:15 PM |
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As Sam says the design of the wishbone is of more importance than the exact type of tube in this case. The spate of failures we saw on here years
back was mainly caused by a terrible design to turned the wishbone from a triangle (with pure tensile/compression stress) to a parallelogram with
significant bending forces around a big stress raiser.
Horrible
 
Description
Better
 
Start of the front suspension.
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steve m
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| posted on 10/5/19 at 07:16 PM |
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I don't remember what thickness, I bought,
But do remember why, a Friend used to make fairground rides, and he said they only used ERW, as it was cheap, and some of those fairground rides
weighed several tons, and lots of kids!
My car doesn't, but does have one big kid inside!
steve
Thats was probably spelt wrong, or had some grammer, that the "grammer police have to have a moan at
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mark chandler
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| posted on 11/5/19 at 06:55 AM |
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Pop down your local independent landrover dealer, they will have a pile of steering drag links with fused track rod ends being thrown out from
90's, they buy complete replacements from Bearmach so it's not worth the effort freeing up.
My car has the shock pointing at the lower all joint using this steel and just 1/2" ERW for the top..
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myke pocock
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| posted on 11/5/19 at 05:30 PM |
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For what its worth and putting my six penny worth in, considering the overall cost of the car to completion I cannot see a reason why you wouldnt get
seamless for the job. Peace of mind to me!
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bozla
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| posted on 11/5/19 at 08:59 PM |
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You'd probably be alright with erw, just shot blast after welding - will add strength in the surface. 750 formula book states that cds is only
required for roll over bar and anti-roll bars.
18 awg (1mm), I'd probably go for 1.6mm.
[Edited on 11/5/19 by bozla]
[Edited on 11/5/19 by bozla]
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coyoteboy
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| posted on 12/5/19 at 08:35 AM |
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quote:
Originally posted by Mr Whippy
Tbh when you see what modern production cars use these days those on a 7 look beefy
Really?
https://images.app.goo.gl/K4hxgax6rDJ2rBUx8
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perksy
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| posted on 12/5/19 at 05:05 PM |
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I was behind a lad in a Formula 27 once on a club run
He had a front wishbone fail just as we pulled up to a junction 
If it had happened two minutes earlier gowd knows what would of happened as we weren't hanging about 
Wishbones need 'over engineering' if anything
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AdamR20
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| posted on 12/5/19 at 06:39 PM |
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A tenner says they would have failed anyway even if made in CDS It's much more about design than material IMO.
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