making a strut brace

[mys38u]

ive got a s3 rx7 and wanna make a strut brace, any recommendations for type of material and dimensions?? or tips on how to make one?? thanx guys :)

[Matty]

doing it properly would involve doing what none of the aftermarket people do, and having it as a single structural piece. By this I mean NO HEIM JOINTS! They all do it, and it's stupid. just have bolted together joints. Or even weld it together (less easy to remove)

Make sure the towers are well attached too, no point being able to flex them around.

Minimise the amount of bends in the bar. Make it as straight as possible between the two towers.

for example: a bad design:
http://www.rspeed.net/images/product/316-105.jpg

a good design: (except for the aforementioned Heim joints)
http://www.miataparts.com/images/miatastrutbar04.jpg

[mys38u]

thanx matty, any idea about material??

[karl_2ltGC]

my folks 1980 264 volvo has factory strut braces!

They go from strut to firewall....you should mosey on down to the wreckers and check them out...they might be adaptable to the rx7

But i would think steel would be best material.....
Are the struts higher than the engine...if so it would be very easy to make...

[Group3JDatsun]

Material will depend on design. I've got a car in my garage atm (not mine) which has a horizont strut brace (ie no bends) which has the brackets welded to the chassis. It's made of 30mm x 30mm Aluminium RHS. It's in a rally car and has done a sensational job - to the point where the car has been run without it and the strut towers have moved by ~5mm (new brace needed making). Having been run for the last 3 or 4 years, it appears to have no banana to it.
However, if it's got bends, it's likely to need something stronger. 4130 chrome moly would be the go (strong and light), but I'm unsure if it's available in a small enough diameter and with a suitable wall thickness.


Karl,

Why do you say no spherical bearings? I'm not a fan of them in the majority of applications, but I'm interested in your reasoning.

[Matty]

actually it was me that said no spherical joints. I said that as a mechanical engineer - they represent another degree of freedom, and their removal will make the whole system significantly stiffer, which is what you want from a strut brace.

By way of example, those braces shown above are for the Mazda MX-5. The latest MX-5's have a brace from the factory, and it is BOLTED together at each end... and I suspect the Mazda engineers know a thing or two about chassis design. (sorry, couldn't find a picture of it)

material - Steel is much stiffer than aluminium, but also heavier, I think either (used proportianately) would be fine. In a limited space application as engine bays tend to be, the steel is the winner.

[bahaimus]

I made one for a car I used to have. It was made from stainless steel. It used a box section that I had no choice but to make bends in. The bends were made by making a cut through three sides of the box to create a gap, bend as needed and then tigged back together again. There were no discernible creases in the metal to indictae weakness.

The strut top plates were made from stainless plate and brackets tig welded on to attach the cross bar to.

The cross bar was bolted to the brackets, but used two smaller bolts instead of one larger to prevent the cross bar being able to turn within the bracket.

I'm no mechanical engineer (not completed anyway) but I considered it to be a much better and effective design than those that were commercially available.

I wish I had a picture of it......

[sssgtr]

Also use a solid cross section material, not a hollow section.
Just from browsing some sites, 6061 T6 seems to be good.

[mys38u]

how do u go a about making/cutting the hats? or is it better to attach straight to the tower?

[rodhog]

Matty I have no time to build one even though I have been (moved on) a Aircraft maintenance engineer and can get and build carbon fiber bits. But I just want to buy one
Can you like show me what you mean for bolted. My Mx-6 4WS has one on the back it's 3 piece and has 2 bolts.

[Matty]

Originally posted by rodhog
Matty I have no time to build one even though I have been (moved on) a Aircraft maintenance engineer and can get and build carbon fiber bits. But I just want to buy one
Can you like show me what you mean for bolted. My Mx-6 4WS has one on the back it's 3 piece and has 2 bolts.

here you go:
http://a15.g.akamai.net/7/15/5509/1023065079/autospeed.com/site/autospeed//images/1409_2hi.jpg

of course, the need for no hinge points is fairly obvious in a car like the MX5 where the shock towers are well below the engine (that the bar has to span). In a car with struts and very tall towers, the uprights of the brace are not so tall, and there is much less lever arm to create a torque about, so flexible joints may be acceptable.

[rodhog]

Thanks Matty
My shock towers are level with the top of the engine
and the back on works well I can tell the back is so still with almost slicks and wet road it can slide about quite a bit. even with really soft springs in corners the back feels strong but the front feels crap. I found a couple all bolted and one from K-mac they showed me has bolts only in the middle for size.
What do you think?