Just got a 90 miata - Miata Forumz - Mazda Miata Chat Forums
Miata Forumz - Mazda Miata Chat Forums
Miata Forumz - Mazda Miata Chat Forums



NA (1989-1997) NA Miata discussion within. The MX5's first generation, the NA, sold over 400,000 units from 1989 to 1997.

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Old 03-25-2014, 02:43 AM   #1
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Default Just got a 90 miata

First of all, I'd like to say I couldn't be happier with my decision on joining the miata family. I've always loved miatas, it was only a matter of time before I got my hands on one. It's a 1990 mariner blue 1.6L w/ 89K One thing I've noticed, is that she has the "infamous 65 mph shimmy", what would be the best way to get rid of it? Replace the shocks? Get more bars? Any advice would be greatly appreciated!

Also, in the near future when I decide to start upgrading the suspension/safety of the car, is it best to get every bar I can get for the car? Or is that pointless to do and should I just go with a few certain bars? If so, which bars? I'm thinking of starting out with a hard dog roll bar, a 3 point strut tower brace, rear strut tower braces, and front/rear chassis braces. Please let me know what you guys think! Thanks again for the help! I never knew it could feel so good to own a Miata
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Old 03-28-2014, 03:56 PM   #2
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Imbalance resonance at 65 mph is often caused by the locking lug nuts weighing more than the regular ones. Either get all four nuts the same or swap the locks to one side and place them across from each other in the bolt pattern.

If not the nuts, then rebalance the tires. The stock tire circumference lends itself to a resonance at ~65mph.

If you ever want to track the car, a Hard Dog M2 Sport Rollbar with either single or double diagonals will be a necessary investment. The door bars from Hard Dog are very streetable and will do more than any other bracing to tighten up the car. They tie in to the base of the rollbar and triangulate the structure.

The 3 point shock tower brace should theoretically be helpful but few people use them. The braces that fit behind the fenders and tie in to the door hinges are more popular. I have the stainless frame rails and they helped, but that was before I added the door bars. If I did the door bars first I don't know if there would have been so dramatic a change with the rails.

Get the Hard Dog padding if you get the roll bar. It is special high density padding with adhesive backing and a really nicely stitched fitted cover with velcro closure. If you are rear ended at low speed without high density padding it will crack your skull wide open. Stock seats are designed to bend backward in a rear collision and the first thing solid you will hit is the bar.

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Old 03-28-2014, 06:17 PM   #3
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Is it true that the hard top helps in such a dramatic way? I have been wondering about frame stiffness as well.
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Old 03-31-2014, 08:00 AM   #4
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The hard top will not do much for it. The hard top is plastic (FRP) so it will crack if you put it on a flimsy chassis. Mine is cracked in a few spots from the previous owner's exploits.
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Old 03-31-2014, 09:51 AM   #5
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So to stay on the OP's topic, what do you consider essential for chassis stiffening if the intention is to track the car? no intent to thread jack
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Old 03-31-2014, 09:32 PM   #6
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I'm just talking about stuff such as sway bars, anti roll bars, strut tower braces, chassis braces, etc.
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Old 04-01-2014, 08:32 AM   #7
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Quote:
Originally Posted by BoomBoom View Post
So to stay on the OP's topic, what do you consider essential for chassis stiffening if the intention is to track the car? no intent to thread jack
Quote:
Originally Posted by MiataAffair View Post
I'm just talking about stuff such as sway bars, anti roll bars, strut tower braces, chassis braces, etc.
Nothing is essential except a rollbar to be "legal" to get onto the track. Sway bars and stronger springs are advisable. Adding stronger springs and sway bars keeps the car from rolling over onto the bumpstops when cornering and allows the suspension to remain active mid-corner instead of binding up when bottomed out. Stronger spring rates necessitate better shock valving or your car will bounce like a basketball in an uncontrollable manner. That's where the downward spending spiral begins. Street tires require less spring because they don't grip as much in turns and therefore generate less body roll.

Better than stock compound brake pads are highly advisable for fade resistance. Cobalt XR4 compound pads are a great dual duty pad that require no complex bedding-in procedure.

Always add fresh fluid and bleed out the old brake fluid before every track day. Regular DOT 3 & 4 Valvoline brake fluid works fine (white bottle blue label). Do this every time or you'll have a bad day.

My '96 had some factory subframe bracing that was not present in some of the earlier cars. If your car doesn't have a tubular brace running from the left to right rear lower control arm mounting points below and behind the differential, then your car is not equipped with a whole list of other factory braces.

Stainless steel frame rail braces make a noticeable difference and are non-intrusive. Door bars from Bethania Garage were a nice addition for rigidity and were not a hindrance to ingress and egress as I had expected.

Flyin' Miata makes a "butterfly brace" that I would not consider because it interferes with serviceability.

Again, none of these but the rollbar are actually required for a trackday and you can always add them as you feel it necessary. The first couple of trackdays are always about learning the track and learning the car. People ask all the time if they should put sticky tires on their car before their first trackday and the answer is "never". Learn to drive it on older street rubber and you will always learn more. The car will break away more gently and be easier to save. Street tires will give you plenty of warning by starting to sing and then squeal at their limit. An R-compound tire or similar will break away more suddenly and at higher G forces thereby throwing you into the deep end of the pool very quickly. They are also more difficult to recover.

Any thoughts or questions?
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Old 04-01-2014, 09:45 AM   #8
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Very thorough response. Thank you for that. It looks like my best course of action would be to install the "required" track pieces and the rest will fall into place as I get more comfortable in a track type situation. The closest Ive ever done to racing was a Mk1 Mr2 hornet car on an empty dirt track. That was more "dive in, power out". Much to learn but thankfully you are an active member and an experienced driver when it comes to road courses. Holy cow MiataAffair, I just jacked the snot out of your thread. I am sorry for that. Hopefully this information is useful to you as well.
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