Hello fellow forum members! I'm interested in developing my own chassis struts/reinforcement for streetcar applications. The common answer when seeking stiffness is to put a roll cage in the car but this compromises functionality and sometimes safety (very little headroom to ride without a helmet and roll).

For these reasons, I am interested in making some prototypes that are more focused on stiffening the chassis from the outside. I would be open to investigating roll bars as well if they could be applied without completely hacking the stock interior and compromising the use of storage bins. Below are some existing products that are on the market. Tell me why (or why not) you believe they are successful and how you would potentially improve them.





Here is what the chassis looks like when all stripped down, just for reference


I'm not going to BS you and tell you I have any kind of experience racing or developing cars seriously, but I'm young and driven; and eager to hear what you guys have to say on the topic. Keeping with that, flame me if you think this is all a load of ****!

I'm really just looking to spark a conversation and get some good info from you crazy rx7 owners who are by far the most driven and passionate car enthusiasts when it comes to building things themselves

 

I don't understand developing racing solutions for streetcars.
If it's for a streetcar, just about any combination of tubing and bracketry can be bolted on pretty much at random and as long as it's powdercoated a bright neon color, you have a product.
Street vehicles do not get pushed hard enough under repeatable conditions to quantify the benefits of such a product.

 

so the flex in the chassis is negligible at best for street applications?
feel free to call me on my bullshit, I'm open to all opinions

 

Perhaps we need to define "street applications".

For example, I daily my FC and today I drove about 40 miles, part on an interstate at @75, the rest on surface streets. At no time in any situation was I using even 50% of the car's capability.
Like most street cars, mine would probably benefit most from a new set of tires, not a geegaw to bolt on the chassis somewhere.

This usually works differently...you'd identify a problem with your car, develop a "fix" of some kind and then offer it as advice or a product for sale.
You are bravely searching for a problem on which to apply your admittedly meagre "racing and development" skills...you can see the problem?

 

In 26 years of driving on the street with my RX-7, not once was any "chassis stiffening" needed when driving to work, driving to school, or even when driving to the store to pick up groceries.

How about making something more practical like a reinforcement for the center console, 20B-friendly sway bar, power window relay kit, composite sunroof panel, or rebuilt wiper switch?

 

Good points being made here. My reasoning for looking into chassis stiffness is to sharpen handling and improve response. You can feel the capabilities of a well handling car at almost any speed and the almost effortless cornering ability makes it exciting to drive. A car which has 4xx horsepower is much more exciting, but much more likely to get you in trouble with the law.
I was looking at ways to improve the driving experience of our sports car in a way you can feel on the street.

The composite sun roof idea is a good one. I guess my roof isnt the only one rusting out

 

If you toss Melanie in the passenger seat..Topless.. and go through a couple quick turns..and Bumps..

That'll "stiffen yer Chassis"..!!!

Unless you plan on tracking that car,or adding 600hp to it,all that stuff is just "there"..No real reason for it to "be there"

 

 

That would require that you identify the root cause of deficiencies you imagine.
In other words, why doesn't the FC handle as sharply as you'd like?
What other "fixes" have you tried (like tire pressure or alignment specs) before deciding a bolt on brace was the way to go?

Even if you did produce an actual part, how could you demonstrate/quantify it's efficacy?

 

The best and easiest way to stiffen up a body is to do some seam welding ie between every factory spot weld you do a small spot weld about 5 to 10 mm long weld mainly around the front rails top and bottom. Along the sills and tunnel and all around the rear suspension pick up points. also the front and rear k frames .This will stiffen up the body around 50+ %

 

I have heard of people spraying polystyrene foam into the frame rails.

Would i do it? No. I have been daily driving my vert for 5 years and chassis flex is still minimal. Since the vert doesn't have a proper roof, it tends to flex slightly just behind the doors, but this flexing rarely happens. The only time I can even notice this "slight" flexing is when i back out of my parents driveway which has a funky grade to it at the end. Other than that, the chassis is pretty stiff.

If we where talking about a fox body convertible mustang, it would be a different story.

 

So the general consensus seems to be that stiffening the chassis isn`t all to applicable to a streetcar.

perhaps the question i should ask instead is what do you guys see as the biggest area of possible improvement in the FC platform? What do you guys thing would make the car more exciting to drive on the street? Am I trying to reinvent the wheel instead of leaving well enough alone here?

 

i think you actually WANT some chassis flex in a street driven car.
having no flex at all, will make it a harsh ride.

going up a curb or driveway with no flex and an open diff will result in getting stuck right there on the spot

 

Mazda did some research with the FD, and they found that the front strut bar adds 3% to the rigidity of the front end, the windshield adds 5%...

actually the biggest structural problem with the FC is the front sway bar, its basically a lever to bend the chassis, -12% rigidity...

with a fast street car, the name of the game is to make a bunch of little improvements, without compromising comfort/noise/etc. if you stack a bunch of small things together, it adds up to be pretty big.

so, what mean? it means add the strut bar, by itself you won't notice, but coupled with a more performance oriented alignment, shocks, springs, etc you will end up with a car that is quite good, with no downsides.

 

Most FC owners are too cheap and are way behind on their to do list (even in terms of maintenance, let alone things not working) to worry about chassis stiffening.

And if it doesn't pimp the ride (like bright coilover kits or wheels), most won't put it on their **** condition FC.

Don't mean to insult anyone...but even those pics show fancy parts on dirty cars with oil seal leaks. Fix and maintain if first, then modify, IMHO.

 

i am with you on having a stiffer chassis, it makes the car more fun to drive and i think it just feels better even if it is only a street car. i race mine, also race a supra and a z24 (v6 caviler)
first get front and rear strut braces and a front lower subframe brace and swaybars. then look into the bars you have pictured. other bars to think about is a floor brace, harness bar.
but the more bracing you add the heaver the car gets so you need to find ways to loose weight also

 

Driving the stock car faster would sure make it more exciting, lmao.

For instance, the car in the videos is on stock blown struts with Tein lowering springs, no other modifications, and it even has intact DTSS!
https://www.rx7club.com/2nd-generati.../#post11712375

Pretty exciting, lol!

 

a stiffer chassis makes everything respond nicer.

Do you "need" it, no.... but you also don't "need" more than 20 hp.

people already make all the things you've posted...

if you want to make something make something that doesn't already exist for our cars like this:
https://www.flyinmiata.com/index.php...umber=13-69010
https://www.flyinmiata.com/index.php...0%20%201990-97

I'm also tired of people saying "FC owners don't buy anything, we're cheap", that's a great way to get nothing new made... good job?

 

Sweet lord above those miata braces are cool!
I posted the existing products to see if you guys would point out any obvious flaws in the way they are mounted to the chassis. I was thinking of making a structure which would stretch the length of the car connecting the front and rear sub frames to the framerail. Somewhat similar to that miata brace posted but im not sure if the exhaust allows for that kind of structure to be built under the FC.

Not everybody thinks chassis reinforcement is needed but a few of you think its a nice touch for a more aggressively driven car. I might start generating some ideas in May once my finals are done if there's still interest then

 

From a vehicle dynamics standpoint, the point of chassis stiffening is to amplify the effects of an adjustable suspension.

A chassis, like any structure, can flex and bend. It has a torsional rigidity and bending stiffness. In karts, these numbers are low, allowing the chassis to flex. In this case, the chassis *is* the suspension.

So when a designer steps up to the complications that independently-sprung suspensions bring, (s)he must analyze the system including the chassis as a sprung element of a system. Practically, however, this analysis often does little good, as the springing characteristics of the chassis are far harder to modify and tune that the spring perches and dampers in the suspensions.

As such, in modern practice, one tries to stiffen the chassis as much as possible to make tuning the suspension more direct. You're essentially removing a variable from a rather complex system dynamics equation.

However, if you aren't looking at the easier variables first (e.g. tuning the spring rates, damping, roll centers, Anti-roll bar setup) then going after chassis stiffness is practically worthless.

tl;dr
Chassis stiffening is sham unless you're looking for the last 10% of performance. Your chassis (if not falling apart with rust) is far stiff enough from the factory. Buy some adjustable springs/dampers/arb's and get a good set of tires. That will pay off far more than any braces will.

Want to really get the biggest bang for your buck? Get this textbook:
Milliken Research Associates, Inc. -- "Race Car Vehicle Dynamics"
That's what'll teach you to get the most out of your chassis. But be warned, it's a college textbook, and requires time, patience, and work to turn a heap of pages into practicable knowledge.

Edit:
Just read you are looking at "developing prototypes." Definitely suggest getting the book above then. And quantitative measurements of chassis stiffening measures (e.g. torsional testing of the chassis before/after mods, that'd be really cool to know, instead of rando's saying "well, i put the strut brace on, and it just *feels* 'tighter'", whatever that means...) would be awesome.