TCA dimension

[greenamex2]

Probably a bit of a 'how longs a piece of skin question but I'll try anyway.

What would be the minimum diameter and thickness tube you would use for a track control arm in a macpherson strut setup.

The front of the car weighs about 450Kg and it runs on track day tyres.

Taking my existing TCA (which has never bent) and turning into a tube you get the equivelent material of a 31.5mm diameter by 3.25mm wall thickness tube.

Does this sound about right?

Thanks

[TEAM78]

How do you benefit from this if there is no mass reduction to be had??
sounds robust to me but it also depends on your mechanical trail and other suspension parameters assuming the lateral forces the tyre can generate at various vertical loads are known, but im guessing your after a reasonable FOS here as well. your not refering to the LCA maybe??

[greenamex2]

I have in my possession the last ever new TCA for a Toyota Corolla GT. Every other one is suffering from 25 years of rust and general abuse.

They are also really wobbly. In group A they initially had to weld another bit of plate to the bottom, after this Toyota homologated various custom built options.

Mine need something doing to them as the lower ball joint are now spinning in the 'housing'. My Dad has spot welded the ball joint in place but I consider this a temporary solution.

What does LCA stand for?

[Highside]

Hi Denis,

Have you got a photo or a drawing of the original part?

Cheers

Rob

[phoenix]

As the car is pretty light I would think that the dimension you mentioned are plenty strong enough - in fact probably overkill.

If there are no other attachments to the tca along its length (e.g. a compression strut or an anti toll bar pickup) which would add bending loads and if the tca has ball joints at both ends (i.e. a rodend or similar on the inner end as well as the ball joint at the outer end) I think you would be safe to go considerably lighter as the tca will be acting simply in compression and tension.

A 1" or 25mm dia 14 gauge tube (2mm wall) would be fine. If you look at single seater and clubmans chassis they would prbably be using 3/4" or 19mm tube of 16 gauge or thinner wall.

But use cold drawn seamless tube, not erw.

[greenamex2]

See attached, I hope.

http://www.rscc.co.uk/dscn0446.jpg

http://www.rscc.co.uk/dscn0447.jpg

[edited pics to clickable links - they were HUGE!]

[greenamex2]

Originally Posted by phoenix

As the car is pretty light I would think that the dimension you mentioned are plenty strong enough - in fact probably overkill.

If there are no other attachments to the tca along its length (e.g. a compression strut or an anti toll bar pickup) which would add bending loads and if the tca has ball joints at both ends (i.e. a rodend or similar on the inner end as well as the ball joint at the outer end) I think you would be safe to go considerably lighter as the tca will be acting simply in compression and tension.

A 1" or 25mm dia 14 gauge tube (2mm wall) would be fine. If you look at single seater and clubmans chassis they would prbably be using 3/4" or 19mm tube of 16 gauge or thinner wall.

But use cold drawn seamless tube, not erw.

There is an anti roll bar and the castor control arm to worry about.

However I think you are right. The standard arm is so cheaply/poorly designed that I could go a bit lighter and still end up with something significantly stiffer.

[phoenix]

Looking at the pictures, I would say that the size of the arm was controlled to a great extent by the size of the lower ball joint and the inner bush housing.

If you replace the outer ball joint with a rod end and a bolt or stud through the bottom of the strut and use a rodend at the inner end too, then the dimensions of the tca can be reduced accordingly.

The tube will need reinforcement around the pickup points of the antil roll bar (on our car the anti roll bar picks up on top of the tca, so a simple U bracket wrapped round the tube provides the pickup point and the reinforcement) and more reinforcement where the castor control arm attaches to spread the load. You might want to consider using 12 gauge tube for the tca to be extra sure. I am sure it will still be lighter and stronger than the original item.

Best not to drill holes in the tube to make attachments as these will cause stress points. Better to add brackets to provide the mounting points if you can - just as we have done with our A/R bar pickups.

[Highside]

Originally Posted by phoenix

Looking at the pictures, I would say that the size of the arm was controlled to a great extent by the size of the lower ball joint and the inner bush housing.....

<Snip: lots of sensible stuff from Phoenix>

....... Better to add brackets to provide the mounting points if you can - just as we have done with our A/R bar pickups.

Yep - I think Pheonix has it covered. Interesting that Toyota chose to make your TCA's out or recycled boat anchors - how much do they weigh?

[greenamex2]

Cheers for that, pretty much confirmed what I thought.

They aren't as heavy as they probably look as they are pretty short.

Does look like I have some more weight savings to add to my list though, and it's 50% unsprung!

If you think the TCA's are overweight, you should see the castor arm, rear lower links and panhard rod.

The castor arms are solid 18mm steel!

The rear lower links and are all 1 inch diameter (at least) 8 guage or worse.

The rear upper links were made out of McDonalds straws!

[phoenix]

A mate of mine fabricates (mainly) Escorts for rallying and rallycross - has done for years - and 12 gauge 1" is more than adequate for four links and panhard rods to control a heavy axle when stage rallying - so some weight to be saved there. I would also think that 12 gauge tube could be used for the castor links - but you may have to go up on OD to get the strength. After all a larger OD tube is harder to bend than a smaller solid rod, isn't it? Best not to do a 'Colin Chapman' and make things too close to the limit though!