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Craigorypeck
Craigorypeck New Reader
2/18/18 12:13 p.m.

On a Mcphearson strut equipped car is it more beneficial to have a solid strut brace. I'm getting told a straight rose jointed bar between the tops will suffice. But my thouhts are it should be solid to avoid a parallelogram skewed springing on cornering. Even the ones that are bolt hinged don't make much sense either. The bay may skew on hard cornering and the tightened bolts may retain that skew till cornering the other way when the force is great enough to force the bolts.. Anyway, anyone even care to comment? 

malibuguy
malibuguy GRM+ Memberand Reader
2/18/18 12:47 p.m.

Im for the rigid kind...and then tie in the firewall.

I made this for my tercel and it was very alarming how much of a difference it made.

spandak
spandak Reader
2/18/18 12:52 p.m.

It makes sense that the solid bar would be better. I put the cheapest aluminum hinged ebay bar on my E36 and it still made a difference. 

Craigorypeck
Craigorypeck New Reader
2/18/18 1:27 p.m.
malibuguy said:

Im for the rigid kind...and then tie in the firewall.

 

That's what I was aiming for too.

 

Nearly all aftermarket seem to be hinged. Maybe it just don't matter that much if your just looking for a bitta bling and an arm rest for a hot motor. 

 

Ransom
Ransom GRM+ Memberand PowerDork
2/18/18 1:42 p.m.

Even speaking only to rigidity between points, there are formulae indicating the difference between a rigid and pivoting location of a column end. Solid is more rigid, substantially. I'll see if I can find a link...

(I was disappointed to learn this after I made a strut tower brace for my 2002 out of a surplus helicopter control rod, which naturally mounted with heim joints. In single shear. I have learned things since then.)

Knurled.
Knurled. MegaDork
2/18/18 1:44 p.m.

I wouldn't bother with one if the strut towers are tied into the firewall like in that first pic.  You already have a really great "brace" there, and it adds no weight to the car.

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
2/18/18 2:00 p.m.

No pivots. Most aftermarket units are good for towel racks, nothing more. Solid is harder to do and better. 

markwemple
markwemple UberDork
2/18/18 2:08 p.m.

Make sure your class allows it. My Spec7 only allows 1 bar and it doesn't tie into the firewall. Otherwise, build a solid one. I think the majority are hinged to allow ease of fitment. Solid bars don't allow for variations in builds or previous shunts.

bentwrench
bentwrench SuperDork
2/18/18 2:09 p.m.

I my opinion a cross bar without a tie in to the firewall is kind of useless.

Many cars have the towers close to the firewall and therefore don't benefit as much from a brace.

pilotbraden
pilotbraden UltraDork
2/18/18 2:34 p.m.

The Neuspeed bars on my A2GTIs worked great. They did not have a hinge nor did they connect to the firewall.

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
2/18/18 3:16 p.m.
bentwrench said:

I my opinion a cross bar without a tie in to the firewall is kind of useless.

Many cars have the towers close to the firewall and therefore don't benefit as much from a brace.

Depends on the firewall. On a car I do a lot with, you’re basically bolting to tissue paper at the firewall. All the structure is down further where you can’t reach it. But a solid brace makes a difference you can feel at the wheel. 

ChasH
ChasH New Reader
2/18/18 3:28 p.m.

Even with race tires, the horizontal forces at the top of a strut are not large. The large force is vertical and is handled poorly by a horizontal element.

Most strut braces, especially for a car on street tires, are a waste of money and not worth the extra weight.

edizzle89
edizzle89 Dork
2/19/18 8:51 a.m.

I got a Cusco hinged bar to try to help compensate for the 'radiator support' i cut out (doesnt actually support the radiator). It gives me a little piece of mind and it probably doesn't make it any worse

 

GameboyRMH
GameboyRMH GRM+ Memberand MegaDork
2/19/18 8:57 a.m.

+1 for solid and connected to the firewall.

Tyler H
Tyler H GRM+ Memberand UltraDork
2/19/18 9:04 a.m.

What's the point of putting a bar in, if it has hinges?  I went with the Rouge Engineering race brace for my E46 because it was the only fabricated one that doesn't have a hinge, other than the BMW upgrade part...but the BMW bar is made out of cast metal and breaks.

Primary purpose on the E46 is to strengthen the strut tower sheet metal.

Nick Comstock
Nick Comstock MegaDork
2/19/18 9:16 a.m.

I like how it ranges from people saying the effect is very noticeable to others saying it's worthless and not worth the weight. 

I think we've cleared this one up pretty pretty well cool

Pete Gossett
Pete Gossett GRM+ Memberand MegaDork
2/19/18 9:25 a.m.
Nick Comstock said:

I like how it ranges from people saying the effect is very noticeable to others saying it's worthless and not worth the weight. 

I think we've cleared this one up pretty pretty well cool

And probably 100% accurate without knowing each specific chassis.

Craigorypeck
Craigorypeck New Reader
2/19/18 9:58 a.m.

They all stop the strut tops from pushing and pulling apart.

But the solid variety may also help more with keeping the bay stable.

It may also transfer/increase torsional force in another area of the shell.

Does this matter. IDK.

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
2/19/18 10:10 a.m.
edizzle89 said:

I got a Cusco hinged bar to try to help compensate for the 'radiator support' i cut out (doesnt actually support the radiator). It gives me a little piece of mind and it probably doesn't make it any worse

 

That radiator "support" probably had a pretty significant contribution to the front rigidity. Depending on the design of the car, it may be the only thing connecting both sides of the front structure together. It's also likely that there's something behind the bumper.

On a Miata - which is a double wishbone and not a strut - you can measure the shock mounts moving apart when you put the car on a lift. If your shock tower brace is adjustable and you adjust it with the car on the ground, it will no longer fit when the wheels are unloaded. So they pretty clearly do something.

Now, when a car is cornering you have a big vertical load on one side and very little on the other. This will cause the shock tops to move laterally and the whole structure to parallelogram. If you have a pivot point in your shock bar, it'll let this happen. If you don't, it won't. Cars with struts also put some side load through the top of the strut tower under these circumstances.

 

For those who want to bolt it to the firewall - on a Miata, you can see the firewall flex when you're bleeding the brakes. Not dealing with massive brake pressures as you try to stop for turn 1 in a high power/weight car, but simply pushing fluid around. And the section of firewall that's accessible for shock tower braces is even less solid, it's basically just a water shield. Tying in to that is basically useless.

Knurled.
Knurled. MegaDork
2/19/18 11:53 a.m.

In reply to Keith Tanner :

The firewall may flex under brake pressure but that isn't the force we are concerned with, it is chassis twist.

 

On RX-7s, the front sway bar contributes heavily to chassis twist, since it mounts way out front.  Some racers run stiff springs and no bar to compensate...

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
2/19/18 12:28 p.m.

I know it's not what we're concerned with, but it does illustrate the fact that it's not very strong. I could probably grab the part at the top and fold it down with my hand. You can triangulate to it, but you're only adding road-hugging weight.

edizzle89
edizzle89 Dork
2/19/18 12:38 p.m.
Keith Tanner said:
edizzle89 said:

I got a Cusco hinged bar to try to help compensate for the 'radiator support' i cut out (doesnt actually support the radiator). It gives me a little piece of mind and it probably doesn't make it any worse

 

That radiator "support" probably had a pretty significant contribution to the front rigidity. Depending on the design of the car, it may be the only thing connecting both sides of the front structure together. It's also likely that there's something behind the bumper.

i did some research before cutting it out and the general consensus from the Z31 community was that it does help rigidity some but isnt crucial. several suggested doing the 'power brace' mod similar to what's available for the 240sx's to help gain back some of the support. I plan on doing it once the Z is on the road again.

the brace being the bar welded between the tension rod brackets

ChasH
ChasH New Reader
2/19/18 12:48 p.m.
Tyler H said:

What's the point of putting a bar in, if it has hinges?  I went with the Rouge Engineering race brace for my E46 because it was the only fabricated one that doesn't have a hinge, other than the BMW upgrade part...but the BMW bar is made out of cast metal and breaks.

Primary purpose on the E46 is to strengthen the strut tower sheet metal.

Hinges don't really matter. A horizontal bar is a poor choice to brace against a vertical force. Most braces are a waste of money, especially on street tires.

The BMW CSL race car had no strut brace.

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
2/19/18 12:49 p.m.

Ever put a car on a lift and measured how much that vertical force results in a lateral displacement? It happens.

It's possible that some things have changed since the CSL was state of the art, of course.

I was going to make a comment about knowing who you're talking to, but I changed my mind.

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