Wheel and Suspension Facts And Figures

[Okibi]

I thought i'd start a sticky with Chris's advice regarding suspension modification.

Perhaps we can add some OEM wheel specs etc. and make this a great starting point to answer the regular questions.

Suspension heights are are calculated via a vertical measurement from the wheel centre to wheel arch.

These measurements are specified by the vehicle manufacturer at the time Aust Compliance is granted. A new vehicle data sheet (NVD1) is issued to the various State/Territory rego authorities. The NA6 NVD1 is known as MAZDA 26 and states the following -

A NA standard is 350 mm front and 370 mm rear. Minimum allowed is 320 mm front and 335 mm rear.

The 100 mm rule is minimum ground clearance for any item (except wheel/tyre).

A lot of aftermarket suspension kits drop the cars lower than minimum spec. .......

Road Vehicle Descriptor (RVD1) sheets replaced NVD1 sheets in 1999. They gave additional information including measurements at full bump and minimum ground clearance (101mm). The last one issued for the NB8B series was RVD1MC-152 issued 20/11/2003.

NB8B

FRONT 352 SE 345
REAR 371 SE 364

MINIMUM

FRONT 351 SE 344
REAR 370 SE 363

MINIMUM AT FULL BUMP

FRONT 265 SE SAME
REAR 271 SE SAME

Basically any lowering of a NB8B is outside the RVD1 specs and can be defected. The only way around this is to have an engineer inspect the car and issue a certificate. Just another way for the bureaucrats to **** us off……

NB8A

FRONT 352
REAR 371

MINIMUM

FRONT 322
REAR 338

[Okibi]

Miata.Net Wheel Weights

Keith's Miata Wheel Machine

Miata.Net Tire Size Calculator

[JBT]

Wheel and tyre bible

[Okibi]

More great links from MX5Racing

The Australian Design Rules

NC MX-5 Road Vehicle Descriptor (RVD1)

[sliq]

viewtopic.php?f=76&t=15398

here are some alignment specs posted up by Charlie Brown

[MINX]

NB8B

FRONT 352 SE 345
REAR 371 SE 364

Just measured my SE heights. Iassume it is Std SE suspension, done 45k.
Front 320
Rear 345

Seems even all round.

[philz]

needs more low, you should be under 300mm on all corners

[ebola]

I'm in the process of officially getting an engineers cert for my Rims (16x7) and a few other bits and pieces. My Engineer showed me this doc, which unfortunately applies to us all in NSW possibly other states too:

http://www.rta.nsw.gov.au/registration/downloads/vsi/vsi09_rev4.pdf

Key points are:
1) For Vehicle weight between 801 - 1200kg the rim width increase above the widest optional wheel available for the axle assembly used is 39mm (1.5 inches)
2) A 25mm increase in wheel track limit also applies


This means on My NA6 cooming with 5.5 inch standard my max width is 7 inches.
I wanted 9inch 6ULs

[philz]

engineers certificate for wheels??

Just go 15x9

[ebola]

engineers certificate for wheels??

Yeah well I have just passed my BD roll bar, Autotechnica seat and a few defects. Part of the engineering checklist is the wheel track, wheel sizes and checking tire ratings etc. So by default it gets done.

Aparently one of the most common fails is having lower load/speed rated tires than standard. If you ever see a Hummer with 22inch 35profile tires, chances are they are under speed/load ratings. My NA has a tire rating of 82. The Falken Azenis RT215s I am running have a rating of 87, so its all good!

On the other side, I couldn't get my Harness passed because it does not carry the ADR approval tag on it. If anyone knows of an ADR approved harness please let me know.

OK, enough of the beige pants.

[Sean]

I'm interested to hear the wording (and actual situation) with the rollbar.

The rules around proximity to vehicle occupants and padding are pretty strict and I would have thought they ruled out classification and certification as a roll bar. My understandinging (could be wrong) is that it could only be passed as a style accessory, as a style accessory it's likely it could be self certified.

I guess it all comes down to the individual engineer

[Matty]

They can call it a fish tank as far as I'm concerned, as long as they sign the piece of paper.

[ebola]

I'm interested to hear the wording (and actual situation) with the rollbar.

The rules around proximity to vehicle occupants and padding are pretty strict and I would have thought they ruled out classification and certification as a roll bar. My understandinging (could be wrong) is that it could only be passed as a style accessory, as a style accessory it's likely it could be self certified.

I guess it all comes down to the individual engineer

I was nervous while he was inspecting and measuring everything. He had a massive protractor and list of things to check. It was actually an asset to have the Autotechnica seat in the car because is doesn't recline. Another snagging point is that the roll bar is mounted to a seatbelt mount. Which the standard advises against but the engineer deemed to be acceptable. The third was that I was asked by the engineer to cover the roll bar in foam. It actually looks pretty tough like that however I cannot close the roof. I'm finding a solution for that today.

[Sean]

Cool,

The padding must satisfy his wants, like I said, engineer to engineer it can vary a fair bit. At the end of the day most of them are covering thier own butt as much as caring for the actual rules.

[Adam_NAclubman]

I'm planning on getting the foam for my bar and strapping it down at certain points with cable ties because I want to slice a bit off the top so the hardtop fits over it