Strut Bracing Fixed Or Useless ?

[The Bogan]

I was talking to a engineer today about cars and shiny things and his professional opinion was that if a strut brace was not a solid item it is useless.

He was looking in the engine bays of my MX5 which has a one piece strut brace and a 180 with a (insert brand name here) strut brace with a hinge thingie at the tower which connects the mounting brackets to the brace.

Thoughts....

[GTSBoy]

Well, if you look at it critically......the whole point of a strut brace is to stop the tops of the suspension towers moving relative to each other. So in that case, you can have pin joints at each end of the brace and so long as the brace is sufficiently stiff that it won't deform itself under load, then it will hold the tops of the towers at the same distance relative to each other all the time. At least it will along the line of the brace. It can't do anything about motions out of that plane (ie fore-aft movement of the towers).

On that basis a brace will almost certainly improve the "stiffness" of the chassis. What it really means is that when you have really big loads being put into one tower (ie the outside wheel in a corner) then the brace will transfer some of that load into the opposite side of the car and the total deformation of the chassis will be less. Depending on how flexible the chassis is, you may or may not notice a benefit.

But, pin joints allow the rectangle that consists of the crossmember, the two towers and the brace itself to freely deform. If you take the assumption that those 4 elements are all at right angles to each other (they're not, but it helps to understand what I mean if you do), then putting a big load into the top of one of the towers in the direction that the brace runs will cause the top of the rectangle to want to move to one side. This will deform the rectangle into a parallelogram. Pin joints allow this to happen freely. If the brace has no pin joints at the ends, then the connection of the brace to the top of the tower now allows it to resist moments (torque) as well as simple sideways load, and will add additional "stiffness" into the structure. What it does mean though is that if you do not have pin joints then the actual brace itself needs to be much thicker/heavier/able to withstand bending load because the act of resisting the moment load input at the tower/brace joint will put a bending load into the brace itself. If you have a skinny little tubular brace without pin joints, then it will deflect upwards in the middle during heavy loading from one end, and will not do much to stiffen the chassis as a result.

Edited May 21, 2014 by GTSBoy

[The Bogan]

That's along the lines of what he was saying. I've seen some hard core looking strut braces on some of the boys cars, I may look into a big arse solid bar to replace my standard solid one.

Awesome reply BTW.

[omnigear]

Wouldn't it be better if it was triangulate. from struts and the firewall.

[GTSBoy]

It would. That's really the only sort of strut brace that makes any practical sense. In the rear they tie them down to the boot floor between the towers and that would have to help as well.

Ideally in the front, you'd want triangulation in the vertical plane as well (or instead) of the horizontal plane. But there's an engine in the way which kind of ruins that! Horizontal triangulation at least stops the towers being able to move fore-aft relative to the rest of the car. That's actually probably not too much of a problem on quite a few cars anyway because the inner guards will be quite strong in that direction, but some cars would no doubt see a big benefit.

Of course, on Skylines, the question is a bit moot anyway, seeing as they don't have struts.

[colourclassic]

Of course, on Skylines, the question is a bit moot anyway, seeing as they don't have struts.

So is that to say multi-link suspension doesn't suffer from load deflection?

[GTSBoy]

They do a little bit, but it is nowhere near as bad as on, say, an S14. The upper suspension arm mounting points on the Skyline are still attached to the "strut towers" so are subject to whatever deflection turns up in those structures. But if you have a look at them, they are a long way down compared to the tops of struts, in fairly strongly built structures. The amount of deflection that gets into that part of the car won't be heaps.

Anecdotally, plenty of people report that putting a strut brace onto an R chassis car makes it feel better. It's probably less about stopping the upper suspension mounting points moving around than it is about simply tieing the front of the car together a little better. Overall chassis stiffness improves, and so then does suspension performance.

[ichi-go]

Thanks for the detailed explaination

Now to convince myself on shelling out for that one piece $$$ strut brace

[mistermeena]

Mine is off the car at the moment and I don't feel any difference at all. Personally don't think it does much/anything - most of them are a fashion item

[hardsteppa]

Thos will be falling on to alot if deaf ears i think, but i recently fitted a b-pillar brace which made a noticable difference to reducing chassis flex (rear inside wheel lifts more in corner, less felx/droop), whereas i couldn't feel any difference with front strut tower brace.

[89CAL]

I think the front strut brace in mine made a little bit of a difference. Not huge but it did feel a little more solid in the front. But I basically got mine for free so wasnt really hanging on it making a difference at all

[omnigear]

that might be just the feeling, if there was actual numbers or a test done to see the difference. The thing is that human sensation can hinder the actual result even if it was a blind test, maybe a race car driver can tell. IDK.

Thos will be falling on to alot if deaf ears i think, but i recently fitted a b-pillar brace which made a noticable difference to reducing chassis flex (rear inside wheel lifts more in corner, less felx/droop), whereas i couldn't feel any difference with front strut tower brace.

[hardsteppa]

that might be just the feeling, if there was actual numbers or a test done to see the difference. The thing is that human sensation can hinder the actual result even if it was a blind test, maybe a race car driver can tell. IDK.

yeah no shit it was just the feeling, how many ppl do you know outside of car companies that have rigs to test chassis flex....If you drive it and it feels better to you, then it's a good result. i actually didn't think it would do anything, was just curious, so not like I had convinced myself it would feel better with it fitted.

[Blackkers]

After I fitted and tightened the f**k out of the rear strut brace the inside rear wheel lifts off the ground driving into a mates driveway. Having never done that before it makes me think there must be a difference. It is a standard R33 GTR rear brace and I think its the same as the gts-25t S2 factory brace

[GTSBoy]

All the suspension is bolted to the subframe.

[simpletool]

I have a typical just hap strut brace and it makes a subtle but entirely noticeable and repeatable difference.

R34 had one stock and I'd be confident it's for a reason. The R34 chassis was much more rigid than R33.

[The Bogan]

My assumption (and assumptions are like arse holes, everyone has one) is if it has a hinge at the tower it will pivot under load and thus not lock in the suspension geometry (the only thing trying to lock it in a the friction from the ?M8? bolt trying to restrain a lever of around 1.5 meters, not likely).

It may keep the towers at the same distance from each other on the X axis but the Y axis will move around.

Every stock brace I've seen is solid, every good quality (big dollar shiny race car type) brace I've seen is solid.

Are the hinged braces like the old exposed pod filters, i.e. looks good but does not perform (apart from the seat of the pants dyno results).