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Oval Wishbone Tube

scootz - 25/10/11 at 04:24 PM

Can anyone explain the advantages / disadvantages of using oval tube for front wishbones please!

Ta muchly!

steve m - 25/10/11 at 04:36 PM

Areodynamic ?

dave r - 25/10/11 at 04:37 PM

bling

Bare - 25/10/11 at 05:12 PM

Welll Dohhh! it's to make oneself more attractive to Wimmin. Everybody Knows that!

eddie99 - 25/10/11 at 05:31 PM

Advantages are because the load in the wishbones are front to back under braking etc... Oval tube is stronger horizontally....
Oval is more aero

Disadvantages - Cost, Harder to fabricate with.

Talon Motorsport - 25/10/11 at 05:42 PM

Oval or flat oval tube stood vertical is strong but in used as wishbone material it is used horizontal which makes it weaker than round tube. So in short use flat oval and have weaker wishbones by design.

[Edited on 25/10/11 by Talon Motorsport]

britishtrident - 25/10/11 at 05:49 PM

quote:
Originally posted by eddie99
Advantages are because the load in the wishbones are front to back under braking etc... Oval tube is stronger horizontally....
Oval is more aero

Disadvantages - Cost, Harder to fabricate with.

Not really from the design point of view i(ignoring the spring loads) under braking front part of wishbone is loaded in tension, rear part in compression.

Superimposed on this the wishbone has a substantial bending moment from the spring load but this acts on the weakest axis of the oval tube.

Really it boils down to a looks/aero thing and a bigger diameter would just look clumsy.

[Edited on 25/10/11 by britishtrident]

britishtrident - 25/10/11 at 05:58 PM

Oval tube is not weaker than round, it is actually stiffer & stronger than round tube of the same cross-section height it is however less structurally efficient .
That is a round tube with equivalent bending stiffness would be lighter.

eddie99 - 25/10/11 at 06:01 PM

Hi Phil,
Without wishing to be rude, race car designers that choose to use oval tube come from highly educated backgrounds with masses of experience.
Its quite easy to prove that the principle loads in a wishbone will be in the horizontal plane.
If you take the example of a top wishbone there is no vertical load because there is nothing to restrain it from moving vertically.
On a lower wishbone you have the damper load trying to bend the tube that is true, but on say an F1 car that load will be fed so far outboard as to avoid any significant bending load in the wishbone, yet they still will use and always have an oval tube, because what you get is the load caused by the braking forces.
The braking load will be many times higher than the damper load. The damper load is the weight of the wheel, upright etc multiplied by hitting the kerb etc. So this is a fairly lightweight assembly. With braking you have a much larger mass (corner weight of the whole car) being restrained by the wishbone legs.
Cars have had strain gauges used to determine the actual loads. You'll find the above is true, its datalogged values.

It is unusual to find a common design principle used so commonly without it being for a reason. It comes from the fact that the real engineers who first concieved it do know a thing or two.

[Edited on 25/10/11 by eddie99]

mark chandler - 25/10/11 at 06:13 PM

quote:
Originally posted by eddie99
Hi Phil,
Without wishing to be rude, race car designers that choose to use oval tube come from highly educated backgrounds with masses of experience.
Its quite easy to prove that the principle loads in a wishbone will be in the horizontal plane.
If you take the example of a top wishbone there is no vertical load because there is nothing to restrain it from moving vertically.
On a lower wishbone you have the damper load trying to bend the tube that is true, but on say an F1 car that load will be fed so far outboard as to avoid any significant bending load in the wishbone, yet they still will use and always have an oval tube, because what you get is the load caused by the braking forces.
The braking load will be many times higher than the damper load. The damper load is the weight of the wheel, upright etc multiplied by hitting the kerb etc. So this is a fairly lightweight assembly. With braking you have a much larger mass (corner weight of the whole car) being restrained by the wishbone legs.
Cars have had strain gauges used to determine the actual loads. You'll find the above is true, its datalogged values.

It is unusual to find a common design principle used so commonly without it being for a reason. It comes from the fact that the real engineers who first concieved it do know a thing or two.

[Edited on 25/10/11 by eddie99]

I agree with you, however in the locost design you have a 2:1 weight ratio because of the leverage of the spring/shock on the front bone, this load is in the wrong direction, racing cars have the pushrod acting upon the upright/ball joint/rose joint so this load is not applied to the wishbone that then makes oval a good choice.

So we end up adding a big spreader plate extending half way down the lower bone, this induces a stress point where the plate ends and its well known for inferior designs to bend here when braking and catching a curb. The spreader plate kind of defeats the object !

[Edited on 25/10/11 by mark chandler]

procomp - 25/10/11 at 06:14 PM

Hi

I think the trouble here is that " Talon motorsport " use a wishbone design where the damper sits so far inboard from the upright that its ridiculous. So in his circumstances he would need a much stronger design to cope with the loads.

Cheers Matt

caber - 25/10/11 at 06:27 PM

I just thought it was very cheap from Tesco's on the bottom of shopping trolleys

Caber

Talon Motorsport - 25/10/11 at 06:44 PM

quote:
Originally posted by procomp
Hi

I think the trouble here is that " Talon motorsport " use a wishbone design where the damper sits so far inboard from the upright that its ridiculous. So in his circumstances he would need a much stronger design to cope with the loads.

Cheers Matt

I did'nt design it I just supply the demand for it.

Neville Jones - 26/10/11 at 11:57 AM

That tube in the pics should not be anywhere near a Locost or any other cars wishbones.

It is NOT what is used in racecars, at least not at the level I see. Proper racecar Oval Tube is rolled from round, and is true oval/ellipse, and seamless. Only available in CrMo as far as I'm aware, which causes problems of its own to the unaware and home fabricator.

That Flat Sided Oval, as it is sold by stockists, is seamed and fairly soft rubbish, and meant for furniture or supermarket trolleys. Dangerous to be halfway polite. But, use the thicker wall stuff and you will probably get away with it, albeit with wishbones that would do justice to a NASCAR dirt tracker.( And even they use Seamless or DOM mechanical.) You won't need springs, just attach them solid and watch them bend!

Cheers,
Nev.

And BT, you've been asked too many times to stop giving the impression you are an engineer! Stop talking a load of , er...ah... bovine animal derived organic fertiliser!

[Edited on 26/10/11 by Neville Jones]

britishtrident - 26/10/11 at 01:05 PM

Captain Insecure is at it again, funny thing but has anybody else noticed that Neville Jones rarely contributes anything constructive to a discussion?
Did I post anything that that was incorrect ? as anybody who actually understands framed structures and the properties of structural sections will confirm I didn't.
I also stayed on topic didn't divert the thread into smoke screen discussion on the weld-ability of chrome alloy steels.

In future remember about 40% of posters on this forum probably have some sort of engineering related qualification, perhaps as many as 20% might have HNC/HND or higher perhaps 10% have a 2.1 or higher Honours Degree in an engineering related subject and a few might have a Phd. Out of that lot we have a lot of specialised knowledge.

scootz - 26/10/11 at 02:09 PM

Thanks for the input guys... Just thought I'd ask as I saw it advertised by ADR Engineering for what I thought was reasonable money....

Linky

nick205 - 26/10/11 at 03:11 PM

Personally I don't like the look of it for wishbones at all. Not from a technical perspective, purely aesthetic, a well fabricated round tube construction just looks better to me.

phelpsa - 26/10/11 at 06:56 PM

quote:
Originally posted by eddie99
Hi Phil,
Without wishing to be rude, race car designers that choose to use oval tube come from highly educated backgrounds with masses of experience.
Its quite easy to prove that the principle loads in a wishbone will be in the horizontal plane.
If you take the example of a top wishbone there is no vertical load because there is nothing to restrain it from moving vertically.
On a lower wishbone you have the damper load trying to bend the tube that is true, but on say an F1 car that load will be fed so far outboard as to avoid any significant bending load in the wishbone, yet they still will use and always have an oval tube, because what you get is the load caused by the braking forces.
The braking load will be many times higher than the damper load. The damper load is the weight of the wheel, upright etc multiplied by hitting the kerb etc. So this is a fairly lightweight assembly. With braking you have a much larger mass (corner weight of the whole car) being restrained by the wishbone legs.
Cars have had strain gauges used to determine the actual loads. You'll find the above is true, its datalogged values.

It is unusual to find a common design principle used so commonly without it being for a reason. It comes from the fact that the real engineers who first concieved it do know a thing or two.

[Edited on 25/10/11 by eddie99]

This is only if you're putting the wishbones into bending which ideally they wouldn't be. You certainly wont find any oval section in F1.... You also are unlikely to find any spring/damper loads going into the wishbones in F1 (although I haven't fully looked into that).

I have seen oval used to create a 'sacrificial' wishbone, ie a buckling weakness to save the chassis.

SPYDER - 27/10/11 at 10:53 AM

According to this guy on Pistonheads there's another advantage that we seem to have overlooked...

Quote-" One of the details I love about the CGT is that the lower rear wishbones are aerodynamically shaped to aid downforce. "

phelpsa - 27/10/11 at 06:13 PM

Downforce... dubious (nice idea though). Drag reduction, maybe with aero section, not really with oval.

Badger_McLetcher - 27/10/11 at 06:19 PM

quote:
Quote-" One of the details I love about the CGT is that the lower rear wishbones are aerodynamically shaped to aid downforce. "

TBH that's incorrect. If the profile is symmetrical and is horizontal in the airstream, no downforce would be created. On top of this even if the wishbones were shaped to create downforce, the aerodynamics on a 7 style car are such a mess it would be lost in the turbulence.

I would NOT use these for Locost design lower wishbones- they look to be far too weak on the vertical axis, especially when you consider some people have had the wishbone design fail due to the damper induced bending loads with the normal tube used.
They would probably be ok for the upper wishbones however, but you'd basically be doing it for the look of the thing rather than any other benefit.

[Edited on 27/10/11 by Badger_McLetcher]

procomp - 27/10/11 at 07:30 PM

Hi

Having used this tubing for the last 15 years for lower wishbones ( correctly designed ) it has proved to be very useful to enable the braking forces to be controlled whilst still giving the weak link to save chassis damage during accident damage. Although the sizes listed above are too weak for the application. The 32 x 16 x 2mm wall is more suited to the application.

Where it has gained a bad reputation is from where manufacturers such as MNR MK Mac#1 and now the Haynes chassis have indeed placed there damper mounting in a rather silly position quite some distance inboard from the ball joint rather than a more suitable position far closer to the ball joint. I have yet too see a properly engineered wishbone using this material have any problem what so ever. For the top wishbones the tubing was available in 25 x 15 x 2mm but this was found to be to strong and led to the chassis taking too much load during accidents so was dropped in favour of a round 19 x 1.6mm. However when required for bling i just get friends at SPA to make either the true oval as mentioned above or the teardrop ( aero ) as supplied a lot of the race part manufacturers.

If anyone has concerns about it's use on their kit just stick a straight edge under the wishbone legs on a regular basis and check for a bend. Possibly worth while on kits from the manufacturers listed above.

Cheers Matt

Neville Jones - 28/10/11 at 09:33 AM

quote:
Originally posted by procomp
The 32 x 16 x 2mm wall is more suited to the application.

Cheers Matt

More suited to a tractor more likely! A little over twice the weight of a suitably designed item. But very safe.

It'll certainly do the job, but a 'properly engineered' wishbone need not be quite so heavy.

Cheers,
Nev.

Bare - 28/10/11 at 05:18 PM

quote:
Originally posted by SPYDER
According to this guy on Pistonheads there's another advantage that we seem to have overlooked...

Quote-" One of the details I love about the CGT is that the lower rear wishbones are aerodynamically shaped to aid downforce. "

[img]http://i156.photobucket.com/albums/t39/stefaneinz/CGT%20detail]

Seductive Words... But I claim "'bullshit'
Lotsa Aero info available on these cars... read and learn ..OR... be subject to whatever brochure babble comes along.

[Edited on 28/10/11 by Bare]