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DIY 2001 braces
The 2001 Miata has some new chassis bracing, though only the "LS" and "sport package" trim levels have them. The 2001 indeed has a very noticeably stiffer chassis, so much so that the ride improvement is apparent.
The Japanese text above reads "truss member".
Hans Mattes, a fellow Miatapile, emailed me about his DIY braces:
>I noticed your posting on the Miata Forum regarding chassis braces for
>the M2 Miata. I have a '99 10AE that I autocross so I too was
>interested in that issue. I've added 4 chassis braces to my car and
>they have had a significant effect on stiffening the car -- which was
>already quite stiff since the 10AE has a factory front tower brace and I
>had previously installed a Hard Dog Sport bar with dual diagonals. The
>four additional braces that I added were homebrew, requiring a hacksaw,
>a drill (to drill the braces, not the car) and miscellaneous wrenches,
>tape measure, cardboard & tape (for templates), marking pens, etc. The
>braces were constructed out of 1" square aluminum and steel tubing from
>Home Depot.
>
>The braces are all under the car and were installed with the car on jack
>stands. They were intended to mimic the bracing that the factory has
>put on the '01 model.
>
>One brace connects the left and right mounting bolts at the rear of the
>front suspension, where the front cradle is bolted to the body/chassis
>right at the front of the two square channels that run under the car.
>My brace is just a straight piece of 1" square tubing with bolt holes at
>both ends. (Actually, it's necessary to cut away three of the four
>walls of the square tubing for about 1 1/2" and drill a bolt hole in the
>remaining tab.)
>
>The second and third braces do a similar job at the back of the car,
>connecting the left and right sides of the factory bracing -- the second
>brace between the fronts of the left and right lower A-arm mounts and
>the third brace between the left and right fronts of the longitudinal
>factory bracing where it connects to the body pan near those square
>channels as they bend to rise above the rear suspension (just at the
>back of the seat wells). Both of these braces are straight pieces of
>square tubing, but the "tops" of the tubing had to be cut in appropriate
>
>curves to clear the exhaust pipe and the Power Plant Frame.
>
>The fourth brace is physically simple but a bit harder to describe --
>but I feel that it does a lot of good. It's a four foot long piece of
>thinwall square steel tubing (the others are 1/8" wall aluminum, but I
>couldn't find a four foot long piece of aluminum) with bolt holes
>drilled at either end. At one end, the hole is 15/16" (as are all the
>holes in all the other braces to give clearance Mazda's 17 mm bolts).
>That hole is used to attach the 4 foot brace to the bolt at the driver's
>
>end of brace number one. The hole at the other end is only 5/16"
>diameter and it provides clearance for a 2 1/2", 5/16" diameter bolt
>that attaches the 4 foot bar to the passenger's side of brace number
>three. (It's actually not bolted all the way over on the passenger's
>side, but as far over as is possible while still clearing the cat.) The
>
>four foot piece then acts like a triangulation brace and prevents
>chassis flex.
>
>The only downside of all this is about 3/4" of reduced ground clearance
>and about 8 to 10 pounds. The cost was about $25. The car seems much
>more solid. I'm pleased. (And I'm not, generally, easy to please.
>I've built, installed, and then discarded about half a dozen braces up
>to this point.)
>
>I hope all this is useful to you.
>
>Hans Mattes
>
Hans emailed me again, and included pictures:
>Jason:
>
>I've finished building, modifying, adjusting, "improving," and otherwise
>screwing around with homemade chassis braces for my '99 Miata. They are
>intended to mimic the braces that the factory put on the '01 model. I
>think
>they do that well.
>
>I've included some pictures.
>
>The file "Miata brace.gif" is a drawing of the additional factory bracing
>added to the '01 model.
<Note: this is the picture at the top>
>
>I've added three braces which are intended to simulate the same effect. I
>call them a rear brace, a diagonal brace, and a front brace. That's fairly
>descriptive: the rear and front braces are transverse braces, across the
>driveshaft tunnel, and exert an effect only in direct tension or
>compression; they have no resistance to twisting. The diagonal brace also
>includes a transverse brace across the driveshaft tunnel, but it has other
>elements to resist chassis twisting.
>
>The file "Miata Rear, Diag, & Front Braces.jpg" shows all three braces, but
>it is particularly intended to show the rear brace. The rear brace is cut
>with a jigsaw from 1"x1" square aluminum tubing with a 1/8" wall thickness.
>As with all the materials used in my braces, the aluminum was purchased at
>the local Yardbirds (similar to a Home Depot). The brace is notched to
>clear the exhaust pipe and the PowerPlantFrame (PPF). It is attached using
>the factory bolts that secure the lateral factory bracing at the front set
>of rear A-arm bushings. The '99 already had a transverse brace from the
>factory which was attached by the bolts that secure the lateral factory
>bracing at the rear set of rear A-arm bushings.) You can also see the
>diagonal brace in this picture. It is attached using the factory bolts
>that
>secure the front of the lateral factory bracing at the rear of the floor
>pan.
>
>The file "Miata Diag Brace - Welded and Painted.jpg" shows the diagonal
>brace while the paint is drying.
>It is built from 1"x1" square steel
>tubing
>with 1/16" wall thickness. I had bends made by a local muffler shop and
>welded it myself (Santa brought me a welder!). The ends of the brace where
>they bolt to the car (3 places) are reinforced with 1"x1" angle iron which
>is welded to the bolt tab and across the cut end of the 1" tubing. It
>seems
>quite strong. All bolt holes are 15/32" diameter. That makes alignment
>critical because there's no slop in the fitment, but I wanted the bracing
>to
>be really rigid and not depend on the tightness of the bolts for its
>strength. I torqued all bolts to 85 ft-lbs.
>
>The file "Miata Diag Brace - from rear.jpg" shows the diagonal brace
>installed in the car. The brace attaches both at the front of the rear
>lateral factory bracing (both sides) and at the drivers side of the
>rearmost
>bolt attaching the front suspension to the Miata floor pan. By crossing
>the
>drive tunnel at an angle (which is chosen to clear the cat), the diagonal
>brace is intended to prevent chassis twist. This picture also shows the
>front brace, which is a piece of electrical conduit, flattened at the ends
>and located by both of the rearmost bolts attaching the front suspension to
>the Miata floor pan.
>
>The file "Miata Front & Diag Brace.jpg" shows a side view of the area where
>the diagonal brace and the front brace are bolted to the floor pan.
>
>In total, these braces have a noticeable and positive effect. The car is
>very solid. All three braces weigh less that 15 pounds (about the same a 2
>gallons of gas, but located lower in the car.)
>
>If you'd like to share any of this with others, that's OK with me. I hope
>you find it interesting.
>
>Hans
>