Rear Strute Brace Preload?

[Torques]

R33GTST ->

I'm wondering if and in what direction a pre-load should/can be applied

to a rear strut brace? The brace must be adjustable for a reason.

I'm not talking about inches but just put the brace under minimal tension so there is no 'slack'

Thanks ..

[Duncan]

Not all braces are adjustable...as far as I know preload is not required in any direction. It just allows for a little more variance in mounting width than the bolt holes do.

[GTSBoy]

As above. Pre-load not required or desirable.

[Torques]

Thanks,

That clarifies it ..

[_x_FiReStOrM_x_]

Preload 'may' also damage strut top stud threads.

[Dose Pipe Sutututu]

I always like a little bit of outter preload, if there is 0 preload (this is all knocked up in my head, no proof) the rear strut towers will flex until it is loaded up on the bar, i.e. this being they move towards each other under heavy suspension load.

Like I said, there's no proof for that, but that's how I see it in my head

[GTSBoy]

Define "pre-load". The way I see it, unless the bar will deflect, and unless the joints at either end have slop, the bar can be considered to be incompressible. On that basis, if it is set up so that there is no slop in it at all, but no actual force being applied outwards, then there should be no initial "loading up on the bar" phase. As soon as force is applied to the bar at one end by the strut tower, then the bar will transfer that load to the other strut tower.

If the bar will deflect up/down, then it isn't strong enough and won't do much. If there is slop in the joints at either end, then the maximum movement that the strut tower can make before loading the bar and hence the opposite tower is the amount of slop. So if there is an adjuster on the bar, you just wind the slop out of it.

Of course, "winding the slop out of it" assumes that the towers are only ever forced towards each other by suspension forces. If the suspension forces can in fact spread the towers apart, then the slop will still be there, and the correct solution is to make sure that there is no slop at all. And if these spreading forces do exist, then preload would be a bad thing.

[sadr33]

Everything has a dead zone, strut bars are no different. Even metal compresses and flexes in varying ammounts depending on load, especially the bolts.

Close to that dead zone, when load is applied in either direction that load initally meets less resistance with the frist few minute movements comapred to past these minute movements. So if you pre load the bar you are moving away from this dead zone and any load will meet a higher initial resistance in one direction but not the other.

Somebody will have a tougher time beinding a stick of bamoo if its already being held beint in one direction that another. The downside is they will have a much easier time going in the other direction.

Now whether you want the strut bar to strech or pull I dont know. Maybe this is why its best not to preload the bar. You dont know which direction is beneficial. pesonally I would pull it together SLIGHTLY, i.e shotern in a littltle.

Not much is needed as the dead zone is small by the way.

[KiwiRS4T]

What we need is a volunter to sit in the back of (my Stagea would be easier than) a Skyline with a dial gauge attached to the end of a strut bar which is only bolted at the other end and observe the range and direction of movement relative to the opposite strut tower!

[GTSBoy]

Stagea possibly not a good representative for a Skyline seeing as any wagon should have lots more body flex. A big square cavity is always going to be more flexy than a smaller space that is crossed by a rear deck and seat back steelwork. But a valid idea nonetheless.

In reality, what you actually want instead of a dial gauge though, is a strain gauge pressed in between the end of a (strut) bar and the tower, so you can measure how much force is involved.

[Torques]

Well,

I tightened the braces rear and front to eliminate the dead zone.

By tightening I mean not insane amounts of force but merely about an eights to a quarter turn.

When you 'stretch' as opposed to tighten the braces slightly flex, that's why I tightened them.

[BLK34-GTT]

I have a b-pillar 'lock bar' that sits between the two b-pillars and pushes outwards creating chassis rigidness, when I put this in I tightened the sh1t out of it, and found that this made quite a noticeable difference to the handling.

For my front strut brace, I jacked the front of my car up (to take the weight off the suspension struts), and then tightened the strut brace quite a bit (not a stupid amount, but enough to apply a decent amount of pressure on the struts). I found that this seemed to make the handling feel more 'stiffer' and responsive.

Wasn't sure if the above would do anything positive but gave it a go and it seemed to help!

[Torques]

I'm trying to figure out if one has to jack up the car when installing these braces.

So when you jack the car up I think the chassis flexes downwards (?) unless you jack it up on both sides and support it evenly.

From factory I could imagine that the geometry of the car is set with the car standing on its own feet, and that would seem like the natural

position to fit the braces (?)

But I am just theorizing ,,,,

Any thoughts on this ..?

I have a b-pillar 'lock bar' that sits between the two b-pillars and pushes outwards creating chassis rigidness, when I put this in I tightened the sh1t out of it, and found that this made quite a noticeable difference to the handling.

For my front strut brace, I jacked the front of my car up (to take the weight off the suspension struts), and then tightened the strut brace quite a bit (not a stupid amount, but enough to apply a decent amount of pressure on the struts). I found that this seemed to make the handling feel more 'stiffer' and responsive.

Wasn't sure if the above would do anything positive but gave it a go and it seemed to help!

[BLK34-GTT]

I'm trying to figure out if one has to jack up the car when installing these braces.

So when you jack the car up I think the chassis flexes downwards (?) unless you jack it up on both sides and support it evenly.

From factory I could imagine that the geometry of the car is set with the car standing on its own feet, and that would seem like the natural

position to fit the braces (?)

But I am just theorizing ,,,,

Any thoughts on this ..?

That sounds right, so when jacking up the car the suspension struts should widen slightly as the weight of the car is not being placed on them, which in turn should allow the strut brace to be expanded outwards more. Whether or not this should be done or is necessary, I'm not sure, but I did it anyway (about a year and a half ago), and it certainly doesn't seem to have done any damage.

[Torques]

Hi!

So you jacked the car up and did not support it evenly?

Then you installed the (rear?) brace?

Right?

[BLK34-GTT]

I jacked the car up by the centre point just back from the centre of your front bumper, this was for the front strut brace. I believe it would work the same if you jack the car up by the diff, which is what I jack it up by when changing rear suspension, but I don't have a rear strut brace.

Let me know if the rear strut makes much difference!

[GTSBoy]

I jacked the car up by the centre point just back from the centre of your front bumper,

Please tell me you did this under the front subframe and not under the radiator support panel.

[BLK34-GTT]

Please tell me you did this under the front subframe and not under the radiator support panel.

The bar was very thick and connected to the chassis, definitely no bending happening

[MrStabby]

Its probably worth mentioning that rear strut braces OFFER NO BENEFIT AT ALL on Skylines. The upper and lower control arms connect to the rear subframe, not the body of the car. The arms provide all the lateral control. The upper mount of the shock doesn't have any lateral force on it, and a strut bar only provides resistance to lateral force.

Front suspension is different because the mount for the upper arm is connected to the body of the car. Not right at the shock tower, but close. So it reduces the flex of the body and therefore of the upper arm mount.

[Torques]

Hi,

I am not that familiar with the suspension and will have to think about what you wrote.

However (and I am not imagining this) ->

After In had the rear brace installed the car is now very willingly going into a controlled oversteer/drift.

This was not the case before.

Also the rear feels less wobbly.

(I am still on the standard suspension)

Its probably worth mentioning that rear strut braces OFFER NO BENEFIT AT ALL on Skylines. The upper and lower control arms connect to the rear subframe, not the body of the car. The arms provide all the lateral control. The upper mount of the shock doesn't have any lateral force on it, and a strut bar only provides resistance to lateral force.

Front suspension is different because the mount for the upper arm is connected to the body of the car. Not right at the shock tower, but close. So it reduces the flex of the body and therefore of the upper arm mount.

Edited November 9, 2012 by Torques