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]

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.

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

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.

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]

quote:

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Originally posted by AdamR20
Cost?

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Tbh when you see what modern production cars use these days those on a 7 look beefy

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

Thanks, what wall thickness did you go for? Was thinking 2mm.

Cheers

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.

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

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..

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!

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]

quote:

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Originally posted by Mr Whippy
Tbh when you see what modern production cars use these days those on a 7 look beefy

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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

A tenner says they would have failed anyway even if made in CDS It's much more about design than material IMO.