Stiffening the convertible chassis

[OrganicMechanic]

impressed--

I thinks I am going to invest in the X-brace.

I think my rear is solid with the poly sub-frame bushings.

[gazellebeigem3]

Kind of hard to get anything in across there, a real honest to god engineering nightmare.

im sure you could suss out something

[Liam]

Why not just have it follow the subframe instead of dropping down so much? Why not have it go over the exhaust instead?

Kind of hard to get anything in across there, a real honest to god engineering nightmare.

[CorvallisBMW]

Why not just have it follow the subframe instead of dropping down so much? Why not have it go over the exhaust instead?

There is very, very little room up there. I doubt it could be made to fit, and believe me I tried.

[PiercedE30]

Why not just have it follow the subframe instead of dropping down so much? Why not have it go over the exhaust instead?

[Liam]

The convertibles really get the biggest bang out of the Zen/Mason X brace, they never should have left the factory without one.

[CorvallisBMW]

Ever since I installed the stiff suspension on my car (Billy's+H&R's, Vorschlag camber/castor plates, IE 25/22mm sways, 17" tires, etc), the inherent flexibility of the e30 convertible chassis has become very apparent. Every bump I hit was felt as a wave quivering it's way through the chassis, shaking the whole thing. So earlier this month I decided to finally do something about it. I invested in a Mason Engineering from X-brace, and fabricated a custom rear brace to tie together the rear subframe studs. As several people have pointed out to me already, the subframe studs are already tied together...by the subframe! This is true, but those big rubber bushings mean that there is so much absorbtion of motion that any chassis flex is absorbed by them instead of being stymied by the subframe. It therefor does not do anything to actually prevent chassis flex.

First, this Mason brace is a work of art. It's beautiful, TIG welded by hand and made out of very stiff, very clean oval tubing. This means extra ground clearance, and it even clears my massive 25mm front sway bar:



The rear bar I made myself out of 1"x"0.058 4130 chromolly tubing. It's similar in concept to the 'butt-strut' that is so popular among Z3 roadster owners who are trying to get rid of their chassis flex as well. This was just a prototype really, there are a lot of improvements that can be made (such as the way the tubes join around the notch for the exhaust). When installed, the bottom of the brace sits 1.5" below the exhaust, so I lost that much ground clearance in the back. But I still have just over 4", so I think I'll be ok. We'll see.








The first drive after installing these was, simply, AMAZING.

FUCK. ME. AMAZING.

I might as well be driving a coupe! It killed 75% of any noticeable chassis shake and flex and even helped to reduce cowl shake. The whole car felt more planted and solid. Now when I hit a bump, I don't feel the whole car trembling and quivering around me. It's really incredible, I never thought a convertible could feel like this. I always assumed that I would be forced to live with this inherent downside of having no roof. But I'm happy to say, the condition is curable! I would highly, HIGHLY recommend the x-brace and butt-strutt to convertible owners who are looking for more performance, comfort or simply enjoyment out of their cars. And of course, less flex in the chassis means less chance for chassis fatigue and less rattles inside the cabin, two nice added bonuses :)


Enough posting, time to go out for another drive!! :)