Rear Strut tower bar tension?

[MrMazda92]

So, today I got around to installing my rear STB in the '92(Thanks Mark!!)

Anyways, I loosened the bar until both mounts were bolted in tightly, and jacked the rear up from the center. I tensioned the bar until it was difficult to turn, and backed it off a single turn. This seemed a balanced setting, and during my test drive afterwards it definitely felt more solid in the back(I like to carve corners in curvy roads), and when the TTLs turned the body roll was noticeably diminished.

I'm just curious how tight others set theirs, during install. Did you have any issues with overtightening, or undertightening? I doubt there would be an issue with undertightening, beyond the bar not being as effective...

I also noticed an increase in vibration over bumps, which I expected and consider to be a fair tradeoff.

[jeffs93toy]

I made my strut tower bars for all my cars and although the mx3 doesnt have a rear one (dont relish the idea of cutting panels again) Id have to say that every install ive done has been just about the same as yours.

I normally tighten the bolts down and then about a half turn back again. Not sure if its just me planning on having to take them off at some point or what, but i did definately notice a major difference when i started putting the strut tower bars on.

[Mooneggs]

Some rear strut bars do not have the option to tighten and "pull" the strut bar towards the middle (mazdaspeed and beefy CS versions). From my n00b perspective it seems that it won't matter until you are actually in the turn that the bar starts to "work" and the physics kick in. Instead of the car flexing like normal it meets the bar and has to stop. so I don't know if those fractions of tightening or pre loading will make a difference? Engineers? Ryan? what say thee?

[jeffs93toy]

My understanding as to how these bars help your corning ability is when one strut expands the the other contracts due to the Gs of a turn the chasis will flex, and all these bars are designed to do is reduce the amount of flex.

If im incorrect about this or im off please someone tell me. It might help me in a new design for my strut tower bars.

[MrMazda92]

Okay, so after driving with the bar "pre-loaded", both pulling and pushing(in and out in other words), and just bolted on with the car resting on the ground, I can say without a doubt the feel is WAY better if you do NOT pre-load the bar.

Mark is dead on, and MS had it right as well, go figure. =)

[Ryan]

I don't know enough about vehicle dynamics to know if the vertcial load or the lever action moment has more of an effect on our mcpherson setup. All I know is mcpherson was never designed for race cars, its just cheap and easy, so this is moot if you're serious about racing. Get a double wishbone setup.

It could be pre-loading in tension or compression, depending on what movement has the greatest effect. On intuition I'd guess preload in compression, to keep the towers apart. When you corner it pushes up into the tower, which I'd imagine pushes the tower to the inside, but the loaded tire also pivoting around the TTL's and pushing out at the top.

The most important thing will be having a bar with tight tolerances. If it can wiggle in and out half a mm, you're probably losing most of its effect. Everything deforms a teeny bit when you load it, and gets harder as you load it, so pre-loading it is a good idea, if you knew which way to load it. Doing it the wrong way will be a detriment.

I unno. Ask Google, and see if you can follow some one elses reasoning.

One way to tell would be to hang a light string between the towers that is tight as you can get it before breaking it, and then go corner and see if it snaps or if it sags. The other way would be with a strain gauge, but none of you have those hanging around.

[MrMazda92]

I don't know enough about vehicle dynamics to know if the vertcial load or the lever action moment has more of an effect on our mcpherson setup. All I know is mcpherson was never designed for race cars, its just cheap and easy, so this is moot if you're serious about racing. Get a double wishbone setup.

It could be pre-loading in tension or compression, depending on what movement has the greatest effect. On intuition I'd guess preload in compression, to keep the towers apart. When you corner it pushes up into the tower, which I'd imagine pushes the tower to the inside, but the loaded tire also pivoting around the TTL's and pushing out at the top.

The most important thing will be having a bar with tight tolerances. If it can wiggle in and out half a mm, you're probably losing most of its effect. Everything deforms a teeny bit when you load it, and gets harder as you load it, so pre-loading it is a good idea, if you knew which way to load it. Doing it the wrong way will be a detriment.

I unno. Ask Google, and see if you can follow some one elses reasoning.

One way to tell would be to hang a light string between the towers that is tight as you can get it before breaking it, and then go corner and see if it snaps or if it sags. The other way would be with a strain gauge, but none of you have those hanging around.

Compression showed a discernible improvement over tension, by my testing.(granted, this was just feel, and noise level)

Still, I wasn't too happy with the feel while cornering until I set the bar while on the ground. I'm fairly positive that the noise coming from the rear was more related to the trunk trim than the strut towers, and I trimmed a slightly larger hole while resetting the bar, so It's hard to say which resolved the noise.

[Josh]

Well the Uni-body is designed to bend and flex at the strut towers to make the ride more comfortable. so they are designed to move in and out, and its not just during cornering. By putting the brace in you are stopping that movement causing it to be more rigid. and if you have the GS rear tie bar that just completes the setup. It forces the suspension to work a little harder. It will stiffen your ride some.

I have a little story about feeling the effects of bar vs no bar.
with my Koni Reds and Eibach springs I had front and rear strut tower braces (always put in place with the car on the ground never preloading the bar). Before my AWD swap I had to drive down to Tacoma Washington which the I5 down there is horrible and paved in concrete horizontally across the freeway in like 10-15 foot strips, extremely bumpy and uncomfortable, really like 2 miles of rocking horse type movement. Well I went down there with my brace installed and then picked up the rear end for my AWD swap, in the MX3 (I dont have a truck). So I took the brace out so I could lay the heavy a-- rear end in the mx3 length wise from the rear to center console. I am unsure the exact weight of the rear end itself but i would guess 250 to 300 pounds. I neglected to reinstall the bar for my long journey back north. when I did hit that bad spot in the freeway it was hell. with the unforgiving suspension I had and the lack of the bar there was only one place the car could use to absorb the constant bouncing at 60 mph. it was the first time while driving that I could actually feel the strut towers moving, and recognized then how much influence and additional support the strut tower bars give. It took me from 90% believer to a 110% if i were to rate it and they were just cheep Reactive bars that I had installed at the time.

Thought I would share

Definitely a must for anyone who wants to get more out of their suspension. BUT I wouldn't tension the bars, snug maybe. if you install them with the car on the ground and the suspension under load, then snug it up. That is going to be a more realistic setting for your suspension than preloading your bar with the car jacked in the air under no load. I think if we were to measure how much the strut towers move from no load to loaded we would be surprised.

It could be so much of a difference that you could be effecting your camber, and that would be giving it negative camber (just a though, would have to measure the effects to confirm). It wouldn't be much but it would be enough to measure.

[MrMazda92]

Thanks for that Josh, good point about the Camber too! I'd been a little worried about this when I looked at my car from the rear... Tensioning the bar(pulling the towers together) had an undesired effect on camber, I forgot to mention that.

Anyways, that's definitely worth reading guys!

[Nd4SpdSe]

I used to preload the rear strut bar (inwards) for autocrossing. It was recommended by someone to help the rear rotate and encourage the rear wheel to lift on corners. I didn't know if I got any lift, don't think so, but i found it did help.

[MrMazda92]

I used to preload the rear strut bar (inwards) for autocrossing. It was recommended by someone to help the rear rotate and encourage the rear wheel to lift on corners. I didn't know if I got any lift, don't think so, but i found it did help.

It definitely affects the amount of surface area your tire sees...