Stress bar at CABs

[xLibelle]

Arguably, we have stress bars that solidify the tops of our strut mounts. What about the span between the control arm bushings?

I imagine its less likely as the strut-top points to alter width, but i could see it changing the geometry of the front suspension to an extent. Is this a considerable place to add support? Any thoughts?






This came up because i was aligning a door and had the jack under the cab. put the car down and the door was nolonger aligned. I was not surprised but at the same time, just a little.
Its said the point of the strut-top stress bar is to keep the width from expanding. I imagine that while hard braking or in a turn, the caster is effected by a decrease in cab to cab distance.

oh, also, Flyin'Miata has the butterfly support to solidify the two hemispheres together too. Something to consider.

[emi325i]

haha.. i had a jetta III once.. the doors wouldn't open when the car was jacked up.

[JGood]

Connecting the frame rails at that point won't really limit vertical movement, which is what you are looking at with door alignment. The front subframe ties the frame rails together just a few inches ahead of the CAB's, which will limit the horizontal movement of the individual rails. The movement of strut towers is horizontal, and only because of the leverage - the forces are being applied down low, and there's not as much support at the very top of the tower. I doubt there would be any change at all if you tied the frame rails together right behind the front subframe, except the car would be heavier.



Just my uneducated, inexperienced, virtually useless 2 cents.

[BrandC]

My question is: why are so many people concerned with chassis rigidity? 98% of this population do not even race/track their vehicles.

Also, a bit of chassis flex is a good thing on a street vehicle. Otherwise, lots of suspension parts would break prematurely.

[Jordan]

I installed a e36 Xbrace on my old e30 back in the day. It made a noticeable difference, but nothing alarmingly huge.

[mattdk318i]

Sort of like a butt strut for a cabrio. Which is actually a good mod

http://www.strong-strut.com/Butt-Strut.htm

[xLibelle]

Let me first say, i laugh at street driven cars with a strut tower brace. Its rice! RICE I say!! This discussion should be considered HPDEs, race, and possibly auto-x only.

jgood, please keep those two cents, you might need them. what you misunderstood me say, was when i jacked up the car at this location, i realized that the frame's rigidity is not all what its cracked up to be and a vertical movement would indicate an ability in other directions as well.

to bring it back down to the level of the lay, picture a 2x6 board. Place it flat hanging out unsuported and walk to the end - it bends. turn it upright and it has a little more gout to hold your weight. Thats the same premise with the extention of the strut tower from the core framework. That being said, that doesnt mean vertical movement doesnt happen but it is more likely for the tower to twist and move laterally... and then vertically.

So here is the force, youre in a hard turn and weight is transfered to the front outside wheel in what be a considerable lateral force. Think of the strut tower as a lever. Forces from bottom of tire towards inside of car, then the most solid point of pivot being the control arm's pivot point, and the weakest link is the highest point, the strut tower top. That force would be away from center of car thus expanding the strut tower distance twisting the frame. This in turn provides a poor change in camber... but this is so minuscule.

The other motion i'm interested in is one i hear less discussed (which is probably because its not actually an issue, i only thought to bring it up because of the frame flex i witnessed the other day.) If you were to hit the brakes, lets say pre turn 8a at road atlanta, you have some serious weight on those front wheels which translates directly to the control arm bushing points moving closer together. This would induce a poor change in caster and slight change in camber as well. Which funny enough, could be a good thing in a need to get your speed down before turn 8a. But what i'm investigating is the suspension geometry change due to a frame flex during a turn.

Here is the combined scenerio w/o suspension reinforcements. Hard turn will induce a force both laterally towards the inside of the car and longitudinally towards the rear. The inward motion decreases camber corrected by a strut tower brace. The rearward motion would decrease caster, hurting turn-in. Is it enough for the addition of a "butt-strut" for the front of the car???

IDK guys, maybe the answer is with the fact that Groupe-A teams didnt do it because it wasnt an issue. Maybe the tranny support bar is the solidifying component that negates this issue.
i'm still interested in other thoughts......

[nando]

full on race cars have roll cages welded directly to important parts of the chassis such as the strut towers. of course they aren't going to use a strut brace or other such devices.. it's built into the cage itself.

[gearheadE30]

On our cars I bet it doesn't make much of a difference. Take a civic or something, however, and I bet it would do quite a bit. My friend bent the fender on his civic when he jacked 1 side up and left it overnight.

[xLibelle]

full on race cars have roll cages welded directly to important parts of the chassis such as the strut towers. of course they aren't going to use a strut brace or other such devices.. it's built into the cage itself.

ok, duh, i didnt mean in a situation with full cage. BUT this is the kind of thing the builders have to consider

[BrandC]

Sort of like a butt strut for a cabrio. Which is actually a good mod

http://www.strong-strut.com/Butt-Strut.htm

This thing looks pretty interesting, but for $340 I'm going to pass on something with "questionable" benefits.

[tjts1]

I can hear my e30 flex while cornering on public roads as the door moves around in the frame. Its not the most reassuring feeling. The e36 was a huge step forward in body rigidity from the e30. Just look at the thickness of the fully boxed rocker panels for example. Before getting stiffer springs I would consider increasing body rigidity first. A stiffer chassis with a the same springs will make the suspension feel more solid. My neighbor across the street has a fully caged civic daily driver (madman). Even with the stock springs it rides like a truck.

[mattdk318i]

This thing looks pretty interesting, but for $340 I'm going to pass on something with "questionable" benefits.

I thought the same, I was thinking if i could find some 3/8 steel flat bar, Take it to a shop to have it bent according to the subframe bolts on my car.
Probably spend 100$ tops

[asubimmer]

Let me first say, i laugh at street driven cars with a strut tower brace. Its rice! RICE I say!!

hey turd, learn what rice means. Too many ppl don't use the term rice correctly. So genius, please explain to us how susp mods are rice? Is running H&R/IE3 and bilstein/koni's rice too?

The boat paint job e30 on here is rice...
strut bars aren't

[HST]

Unless you came up with some bitchin' custom fabed shit, I'd think that the x brace is your best bet to stiffen up the frame up front.