Slow Car Fast
January 18, 2011 - Since I had the welder out and the front wheels off, the obvious thing to do is to add a front sway bar.
The car needs more roll stiffness, and I've been looking at how to add a front bar for a while. Of course, I'm trying to use a Miata part because I have a huge collection of them.
I built a couple of plates with studs in them and welded that to the bottom of the frame rail. I considered simply installing some rivnuts, but the sway bar mounts see quite a bit of load and I can see myself ripping them out of the frame. So I have a nice solid mount instead.
The geometry would have worked better if the bar was on top of the frame rail instead of underneath, but the packaging would simply not allow that. Even if I could cut a big enough hole in the panel above the rail, there isn't enough room for the bar to go between the engine and radiator. We'll see how it works. On a short drive, the car did feel more settled. Too much traffic to try out the handling balance. I'm still dialing in the spring rates so I'm not sure exactly what the sway bar sizes will be yet. This one's off a 2004 Mazdaspeed turbo Miata. Why? Because that's what I had on hand! If I want a softer bar, I can use a non-turbo version. If I want an adjustable bar, I can use one of the Flyin' Miata ones.
And yes, I have an idea for a rear bar. We'll see if it will package.
entry 536 - tags: sway bar, handling
January 18, 2011 - The sway bar has an upward angle to it due to the bar placement.
The stock end link - the black one - made this as bad as it could be. So I decided to go with a shorter unit. I have boxes full of old Miata suspension pieces, of course, and the heim-jointed end link in the middle is from the "end link" box. Seriously, I have a box for Miata end links. I also have a box for bumpstops, a wall full of springs, a cord of sway bars, random steering column parts, etc. And at least three boxes of wires. But I digress.
The unmodified heim-jointed link was still too long. So I cut it down, as you can see on the right. There's still a lot of thread engagement so strength is not a problem, but I've made the angle of the bar much better.
It's not the only suspension work I did today. When I was first doing the suspension work on the car, I didn't pay too much attention to the control arms and suspension uprights I used. All the important dimensions are the same. But in my fevered excitement to assemble the car for the First Drive, I left those parts on the car. And that was a problem.
Mazda tweaked the Miata's suspension in 1999. The control arms got beefed up a bit, although the dimensions were basically unchanged. The one change was on the taper of the upper ball joint. The steering knuckle/upright was also very similar, with the steering arm moved up by 7mm and the appropriate taper on the seat for the upper ball joint.
Well, when I looked at what was on the car, I realized that I had the new design upper control arm on one side, but the older steering knuckle. On the other, I had the older parts. This is less than ideal, so I swapped everything out for the newer designs. It was actually a pretty quick job, the guy who built this car was careful to leave enough room to do things like remove suspension bolts. Whew!
entry 537 - tags: suspension, sway bar, end links