Rear lower wish bone

[Piero]

Hi guys

I am looking to make a rear lower wish bone for a Triumph GT6

here,s one I like the BASIC look off, next to the original cast iron one,

I was wondering what size and thicknes tube you would recomend, maybe even the flavour of steel ????

I am also trying to find out what adjusting bush was used, but its a long shot to find that

The original wishbone is in the middle in photo No 1

 

[PhillipM]

Be careful loading joints across a thread in shear like that, bad design from a stress point of view, even worse when you consider stress-corrosion cracking will start right at the thread root where stress is concentrated already.

 

[Rocketman]

Unless you can run design cals on the design you intend to use compared to the original I wouldn't bother.

 

[Piero]

I am ALWAYS open to listening

but a quick google search shows its not uncommen

http://www.elephantracing.com/suspension/controlarm/991-control-arms.htm

 

[PhillipM]

I know it's not uncommon, and it's also not uncommon for some very big names who should know better to have issues with them snapping.

You'll note they've actually put the lower joint there in line so it's in tension rather than shear, which is the right way to load it.

 

[Piero]

so how is that any differant from the ones I posted pics off ??????

you can see the lower wishbone is in line with the drive shafts ???

Am I missing it ???

 

[PhillipM]

Because it's in line with the loading, whereas the other design has them in shear, and it has them in shear with a foot long lever at that.

 

[Rocketman]

I am ALWAYS open to listening

but a quick google search shows its not uncommen

http://www.elephantracing.com/suspension/controlarm/991-control-arms.htm

They have ran design cals on this or tested it to the loads in other ways. How do you propose to test your suspension parts?

 

[Piero]

if we look at the 3rd photo I posted, the lower wishbone is a triangle.

the front most rose joint that is attached to the front arm of the wishbone is acting in much the same way as the radious arm in the GT6 (see pic 1 and two)

the other leg of the lower wish bone in photo 3 is at right angles to the car, much the same as the GT6

yes ??? No ????

 

[711jrp]

While I agree fully with what Philip is saying, you do see rose joints in shear, Piero the third photo is actually quite interesting and proves your point but not in the way you think. both the bottom joints are in tension separately and shear as a pair along the lines of what Phil said but the top joint at the king pin is a single joint in shear like what you want to do.

 

[PhillipM]

They're not in shear as a pair as such, as the lateral joint can rotate around the pivot, it's not constrained as the other end is a balljoint at the hub,
so the majority of loading will go through the joint that's at 45*

 

[711jrp]

Yes I do see what you are saying and do agree, but as the links cannot rotate independently from each other they have to remain as a triangle there is a shear force applied to the joints but not enough to worry about. In this example the front arm is bolted to the rear to allow caster adjustment but in a lot of cases these will be one part.

 

[Piero]

I fully understand shear and being under tension.

If we look souly at the gt6 and more so the wish bone I would like to make.

Please explain how the adjusting bolt can give way???

I am not arguing I am simply failing to see how it's possible.

The vertical link has a radius arm.
This provents the vertical link from moving forward and backward of the wheel arch .

What little play that does take place is taken up by the bush at the inside were the adjustable bush is.

The Rose joints on the other hand have no bush at all.

in the case of the rose joint Set up. The forces are aplied to the suspension set up.

 

[pedrobedro]

If the bush is free to move there is no load on the thread. The joint looks like a piece of tube with a PU bush fitted welded to the top of a bolt.

 

[rikrobson]

I'd look at what the GRP4 Boys do with the escort front control arms. These use rose joints on the inner joint. What is the benefit from the adjustment on the rear suspension apart from changing the camber?

 

[PhillipM]

There's definately load on the thread, your brake torque is reacted through it.

 

[SmartWerks]

Isn't this the sort of job that if you have to ask you shouldn't be doing it?

 

[normspanners]

Be careful loading joints across a thread in shear like that

But it isnt in shear it is in line !
There is NO issue using joint like that I have made several, different motor sport suspension components speak with Bill Mcgill at http://www.mcgillmotorsport.com/ motor sport he can supply joints threaded fittings etc all ready for welding
There is no spring bearing on the wishbone
t45 tube for wishbones

What is the benefit from the adjustment on the rear suspension apart from changing the camber?

For one, less unsprung weight

 

[Piero]

How come your seeing it's not in shear and everyone one else can't see it.

it's got me baffled

 

[normspanners]

The tie rod removes most of the shear force
and the combination of coilover position and top link removes a lot of the braking force IMO
I presume you are getting rid of the leaf spring ?

What is the benefit from the adjustment on the rear suspension apart from changing the camber?

no need to alter anything they handle well

Just what you want a leaf spring as a top arm