I am not sure if everyone knows this, and I understand some people want the look, but for those who dont know and are looking for performance advantages spend your money on quality suspension parts.

Strut braces are almost useless on a street suspended FB, several reason for this include:

1. the suspension location of our cars is very close to the firewall which acts as a stiffening member.
2. street suspension has rubber/polyurethene mounts which flexs much more than your metal body. Eliminating all the rubber/poly in the suspension makes for a very harsh and loud ride, but eliminates all this flex. This is the perpetual trade-off between comfort and mechanical grip.
3. you are going to need full race rubber and suspension to create enough lateral grip to ever make your strut top move in any direction.
4. A full race car cage has the strut brace built into the cage, it is welded into the entire cage which makes the actual body strength irrelevant as the cage takes all the stresses.

Thoughts invited?

 

Interesting. I agree with every word of this too. The RX-7's chassis is suprisingly stiff. If you look at where the suspension components are mounted, they are generally very close to some of the stiffest parts of the car, like the firewall. I'm no expert on suspension geometry, and this is actually one subject that I don't know a whole lot about, but this is the main reason I have never really even thought about getting a strut tower brace.

Edit: I just remembered what the chassis torsional regidity is. Its somewhere around the 6700 ft lb mark, which is a lot.

 

lier say it isn't so. i put liek 5 strut braces on my honda civic and i was taking 35 mph turns at like 45. they work really good. JK what your saying makes sense for the first gens. some car it will help. have you tried a rear bar in your first gen. I would think it would help more than a front bar.
Lates Matt

 

I can see why a strut bar would help on a civic. Just watch one going around a track sometime. Their chassis aren't very stiff as far as "sports" cars go. They always lift up the inside rear wheel it seems. They are econo boxes after all.

 

Let's look at it this way, if the strut towers were moving around to any significant amount, the paint around the edges of the hood would be all chipped up from all the times the fender and hood rubbed against each other.

On the other hand, I run my race car on the track and the body is noticably more flexible after a few years even with a full roll cage. When I first took the car to the track it was easy to open the door when one wheel was jacked off the ground, now it's not so easy.

I don't believe a strut bar would make significant handling differences but it would definately help the chasis absorb vibration on the track. Hopefully it would help stop the body from turning into a wet noodle after being pounded around the track for a few yaers.

ed

 

ed,

You are right, hard track use will increase the flexibility of the chassis.

Matt,

Sounds like you're just taking the corners better, its unlikely your strut bar has improved your lateral grip, however have you upgraded your tires, because they are the most obvious and easy way to increase grip, upgrading your bushings and then shocks (dampers) and springs.

Note when I spoke of roll cages I meant the full style not just in cabin 4 or 6 point.

 

While I agree that overall the 1st gen is faily stiff, 20+ years of use tends to soften things up.
I mean c'mon, these cars are WAY past their original designed lifespan.

I do use a Tri-bar in my car. I felt it made a noticeble difference under even moderate driving, in terms of "feel".

My wife even noticed the difference in the car BEFORE I told her that the bar was installed.

That said, I don't know what kind of quantifiable results they provide.

 

I can't say it has or hasn't made a difference on my first gen, as I upgraded eveything at the same time. I does make a great place to put my hand and support myself, when I am leaning over the bay, working on the car.

I did notice a difference in the one I put on the 2nd gen.

 

1. The strut towers close to the firewall? Hardly! They're flappin' out there in the breeze!

The difference between no brace, and the installation of this:



was incredible. I wasn't expecting to feel a difference, but the car feels more "solid", especially noticeable in one wheel bumps and situations that call for some articulation like turning into/out of an angled drive.

2. Everything flexes to a degree. Unfortunately it's not "the bushing moves therefore the metal doesn't," it's all cumulative. There is a surprising amount of flex in a non seam welded chassis.

3. Bumps. It's not about steady state stuff, it's about the irregularities that make you need a suspension in the first place. If roads (or even racetracks) were dead smooth you could get away with welding the axles right to the shell.

4. Most/all racing classes (here, anyway) that an RX-7 is eligible for where a cage is required forbid going through the firewall to the struts. (Only counterexample I can think of is certain classes of drag racing...)