Suspension and Shocks

By Miq Millman

Suspension / shocks / upgrades:

Shocks:

   Shocks control the cars bouncing.  In the extreme cases they can also
   effect how much the car moves in turns as well as in relation to how the
   road travels.  Generally it is not expected to have a shock so stiff that
   it doubles in function as an anti-sway bar.  The shock should be stiff
   enough to keep the vehicle from oscillating after hitting a bump.

What is Jounce?

   Jounce is when the shock is un-compressed (the secondand further time
   after the initial compression).  Many shocks out there (the stock Miata
   shocks for example) do _not_ compensate for this, or even adjust it.

What is rebound?

   This is the subsequent compression of the shock absorber and the only 
   movement that most simple shocks are capabile of controlling.  It is an
   easier mechanism to control, infact usually just putting a stiffer medium
   in the compression chamber will suffice.

When are my shocks bad?

   When your Miata's back end starts to bounce like a pogo-stick after going
   over a speed bump or one side of the car starts to make a clanking noise
   as the suspension travels through its range until it hits the bump stops.
   This is generally a good time to replace the shocks.

   If you decide that some racing application venue is your cup of tea, then
   no matter the condition of the stock setup, you will want to replace them.

   Adjustable shocks allow you to change the stiffness of the shock to suit
   various needs.  If you don't care that the dime you just drove over is
   heads or tails, let alone the make up of the dropped pocket change in the
   street, than likely you can get away with some racer's old stock setup.
   Likely you will find slightly used stock components with less than 1000
   miles on them.  However, taking a Miata to 8/10's or more of its
   mechanical capabilities it not the place where you test out the structural
   regidity and constitution of the door panels as they scrape on the ground
   in that tight sweeper turn.

GAB vs. Koni vs. Tokiko

   These are the tree major suppliers of shocks for the Miata.  They all have
   their benefits and limitaions.

   GAB is the only manufacturer to make a shock that adjusts for both rebound
   and jounce.  As well, their 8 way adjustables have a range that is just a
   tad stiffer than stock to making you wonder if the shocks are actually
   moving at all and aren't just red chucks of aluminum stuffed into the
   cavity.  The adjustment can be done while the car is sitting in a parking 
   lot with no tools at all, the knobs are just infront of the lower pickup 
   points.  The major limitations of GAB are two fold, their price (close to
   $600+ retail) and the lack of availability.  (only available though a
   company called Wingz in the Bay Area (510) California)

   Koni is the widest accecpted choice for the serious auto crosser, they
   have the benefit of having adjustable spring perches, which in a
   non-competitive modus are a boon since you can change the ride height.
   Unfortunantly in the Solo II world, the perches are just a tad off so you
   end up with a car that rides about 1/3 to 3/4" higher than before.
   Adjustment isn't as easily done as the GAB, the shocks have to accessed
   from the top, which is a bit of a reach for the rears.

   Tokiko is gaining popularity, probably because they weren't available the
   first three years of Miata production.  They price similar to the Koni's
   at about $440 for a set, and are also adjustable from the tops of the
   shock.  There have been models of Tokiko in the past that had the
   adjustment wrench break off.  Likely this is no longer a real concern.
   The 5 way adjustments are all stiffer than the stock setting.  As an added
   bonus, the Tokiko setup seems to drop the ride height about 1/4".

"R" package Bilsteins

   These are non adjustable, stiffer than stock, and seem to be just ok as a
   performance shock.  Hot shoes are replacing them with Koni's in the Solo
   II autocross world.

Suspension bracing:

Or What's missing from my Miata?

   In 1992 Mazda added a "track bar" that tied in the inner points of the
   rear suspension.  This can easily be retrofitted to the earlier cars.
   Supposedly it reduces a shimmey effect felt at 65 mph.  Putting this item
   will slightly reduce the options your Miata might have for cat-back
   exhaust systems.

   With the 1994 model change, a number of chassis braces were added to
   stiffen up the beloved ragtop.  It was rumored that most if not all of
   these items were originally taken off the earlier cars to cut costs.  The
   side brace between the seatbelt mounts is the least noticed change that
   was made.  It was added to improve side impact resistance and not make the
   vehicle feel tauter.

   The other suspension braces in 1994+ models tied the outer points of the
   lower suspension and are duplicated buy a couple of manufacturers.
   Notable in their infamy, Wiz Performance braces require a new four wheel
   alignment becuase they tie into the bolts used for alignment; Racing Beat,
   makers of the best braces are difficult to reach at times and
   occaisionally are out of stock.

What extras can I add?

   Shock tower braces are open to debate for being useful.  It is my
   humble opionion that the stiffer your suspension is, the more you will
   see gained from this brace.  Oh, and it does look nifty spaning across
   the engine compartment.

A plug for rollbars

   If you can handle the limited use of the rear window and the horrors of
   taking a dremel to the sheet metal in your Miata, a four point rollbar
   will do wonders to the stiffness and responsiveness.  As well the piece
   of mind offereed by knowing that should bad things happen, you are
   better prepared.

Springs:
   To cut or not to cut, that is the question.

   Cutting the springs is an old trick.  It changes the geometry of the
   spring stiffening up the constant K, and at the same time shortens the
   overall length.  There is no tried and true rhyme or reason to the
   correlation between how much you lop off and the results.  Thus it's
   generally considered lucky if you get a good result.  (i.e. try it if you
   must, but if you mess up the springs, I don't know you, I never told you
   to do this, don't come after me for the price of new stock springs)

Stiffer does not == lower.

   The best performance spring would have a "progressive" stiffness.  That
   means that as the spring gets further compressed, the constant K (amount
   of springiness) gets higher.  Thus you can very easily get a stiffer, more
   responsive spring on your Miata and not lower the car.

   As well, you can get a spring that lowers the car and is very mushy and
   unresponsive.

   From the performance aspect, you want to lower the car as much as feasible
   because lowering the entire body lowers the center of mass, which in turn
   lets the car take turns much better, and much faster.  Bear in mind that
   the Miata is already a low clearance vehicle, so you probably don't want
   to go much farther than 1" or so.

   For what its worth, my car is lowered 1 1/4" in the rear, 3/4" in the front.
   It makes the car sit very level, canceling out the tail high look that
   stock Miata's sometimes have.

Sway bars:

SoloII CS recommendations

   Just about everyone that does well in Solo II CS has the large (15/16")
   front bar from Rod Millen or its resellers.

When is too much too much?  (adjustable endlinks)

   Stiffening up the front too much can cause the outside rear end to lift.
   Since the Miata has the power going to the rear wheels, this makes for
   nifty wheelspin.  Wheelspin may look cool at the stop light drags, but it
   makes for a slow transition.  In addition to wheelspin, too much front bar
   will make the car understeer (as you take that turn too fast the front end
   smacks into the outside barrier first, as opposed to oversteer where the
   rear end smacks into the outside barrier first).

   The counter for too much front bar is to add a rear bar as well to get it
   really really stiff.  (Oversteer plus understeer equals neutral handling??)

Bushing materials

   Bushing material is pretty simple.  You have stock mushy rubber.  You have
   slightly harder squeeky urethane.  You have custom made super stiff
   bushings made out of Delrin or aluminum.

   The stiffer the bushing, the better the job your suspension bars will be
   able to do.  The stiffer the bushing the more harder the job your
   suspension bars will be able to do.  No I didn't just repeat myself.  If
   the bars do a better job that's great.  If they work harder, then that
   means more wear and tear on the the car.  That's no so great.

   As is most things in life, your car's suspension is a series of trade
   offs.  Decide what you want to do, then make the choices offered.

The total suspension package.

   My suggestions to make a not necessarily CS legal, well handling Miata:

   GAB shocks (the adjustability and Jouce control give these a long life)
   Eibach springs (lowers car 1") not legal for CS Solo II
   Urethane bushings
   Racing Beat Adjustable anti-sway bars (set to middle hole in rear, front
       hole in front) (rear not legal for CS Solo II)
   Racing Beat lower suspension braces (not legal in CS Solo II)
   A good agressive alignment (see Tip #3)
   Sticky rubber on stock rims (Dunlop SP8000 in 195/55/14 is current fave)

   Do all the above, you can easily see 1.1 lateral G's on a skip pad.



-- 
Miq Millman   mmillman@ptdcs2.intel.com	  503 642 6139   (Aloha site)
AL4-55  Intel, 5200 NE Elam Young Parkway, Hillsboro, OR 97124-6497
See also miq@teleport.com