Upper Strut Bars. Which is the best material? Steel vs Aluminium.

[ByronRichesMk1]

I posted this in the Wheels & Suspension forum but I haven't had much feedback so I figured i'd post in here to see if anyone else has a bit of an idea.
So which would be better? A steel 1piece upper strut brace, or an aluminium one? I realise aluminium would be a lot lighter, but wouldn't it flex more? Thus negating the purpose of a strut bar?
Cheers for any input

[kaanage]

Steel for sure, especially if it can be an alloy steel like 4130, though you'd need to heat treat it after fabrication.

Some of the aluminum ones are a joke and only good for pose value - you can bend them by hand to get them to fit the strut mounts!!

[Tim]

it depends on the grades of steel or aluminium used.

[kaanage]

I have pretty much zero confidence in the aluminum strut braces having seen a few. Either the grade of aluminum is non-structural (ie unalloyed) or the braces have not been heat treated after being welded together which gives you an expensive stiff brace with brittle welds and soft alloy around them.

A mild steel brace may well be heavier but is guaranteed to be stiff and strong if the weld look even remotely passable and the gauge if the steel is enough that you can't deform it by squeezing with your hand. High strength alloyed steel needs proper heat treatment as just as alloyed aluminum does.

[Tim]

I cant say that ive ever seen even a cheap chinese one fail except from overtightening an adjustable one.
You talk as though the cars have zero structural integrity as standard and that the load on the bars is huge. Your car is not made of cheese. The strength of the bar its self is not always proportionate to the strength of the structure it creates

[kaanage]

But that's the whole point of the exercise. The body is quite rigid, especially with the firewall welded just behind the strut mounts so any deflection is going to be quite small - it's the distance to the LCA that acts as a multiplier for effect on the suspension geomtry

Now force will be proportional to deflection and rigidity so if the brace isn't very rigid, then it won't apply much force back against the deflection caused by the relative strut movement. The resultant movement will attempt to compress the brace which is going to be pretty good no matter what the material EXCEPT that the length of the brace means that it will bow and a floppy length of aluminum isn't going to resist the bowing to any great degree over the sort of movements we are discussing.

For an underbrace, where the deflection results in a net tension, a cable would work as long as it was very stiff in tension.

[Tim]

It is a common misonception that an upper strut brace is under compression during cornering. They are actually under tension. This being the case your above argument is actually not valid.

Its mostly above my head but this article may explain it for you a little better.
Isn't a strut tower bar under compression?

[mikinoz]

My personal experience from MK1's are with steel. I don't think that the weight saving is worth messing about with alloy for in this application.

[ByronRichesMk1]

Cheers for all the points guys!
I'll have to have a read through that article you posted as well Tim. It's gotten me interested!
Looks like steel is the go for me then!

[Tim]

If you havent done the lower bar then that is the one that makes a nice difference on a mk1 I think especially given they have no traditional subframe. If its steel youre after then TPR Engineering sell them

[kaanage]

It is a common misonception that an upper strut brace is under compression during cornering. They are actually under tension. This being the case your above argument is actually not valid.

Its mostly above my head but this article may explain it for you a little better.
Isn't a strut tower bar under compression?

Interesting - my perspective of the effect of strut bars when used in competition has mainly been with rally cars where side loadings aren't quite so high and bump loadings are far worse. Still, the fact that most strut braces don't connect in a straight line from tower to tower (they usually need a couple of bends to clear engine components) makes me dubious of most alloy strut braces.

Thanks though - always good to have something pointed out.

[ByronRichesMk1]

If you havent done the lower bar then that is the one that makes a nice difference on a mk1 I think especially given they have no traditional subframe. If its steel youre after then TPR Engineering sell them

Okay thanks!
I'll go and have a look.. The one I was looking at was a Weichers one off VWHeritage because I need to put an order in.. Figured i'd throw it in the cart too.. I'll go look though!

[SMOK3Y]

the older & the more worn the car is the more itll bennefit. on my old VN commodore cheap strut brace made a stunning difference (they had shocking movement in their towers)

[gldgti]

in terms of the original question, I think the most accurate answer is this:

If you plot density against material stiffness, you will find that you can almost always make a more efficient structure out of steel than from aluminium. However, the nature of the component has a large part to play in the design compromises that always need to be made.

Nonetheless, for an essentially basic component like a strut brace, you will have far more success with little effort with steel than you could with aluminium. Sure, you could make a good one out of aluminium, but not without an aweful lot more work.

[hiho]

Yank physics.