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I have been noticing that the rear suspension is hitting the bump stops more frequently with time, even with small bumps and at low speeds. Also, the measurement from the wheel centre to top of wheel arch opening is 10 mm (left) and 12 mm (right) shorter than what they are supposed to be. For reference, at the front I am measuring 372 mm, which is only 3 mm lower. The suspension hasn't been modified from what I can see. The car does not bounce over those sharp speed bumps that you normally see at supermarket parkings.
My uneducated diagnosis is that I may need new springs? If so, should I also replace the shocks at the same time.
The car has 90,000 km and is 12 years old.

Your car is far too young to be having such problems.
Springs never fail, if anything it might be the shocks or something else. Take it to a suspension specialist or Mazda to check.

Check the big forum in case similar issues have been encountered there:
https://forum.miata.net/vb/
&
https://forum.miata.net/vb/forumdisplay.php?f=79

bruce wrote:Your car is far too young to be having such problems.
Springs never fail, if anything it might be the shocks or something else. Take it to a suspension specialist or Mazda to check.

Thanks bruce. Any suspension specialist to recommend around Melbourne? The only one that I know is Pedders but I haven't read very strong recommendations about them here in forum.

The ability of my original NC3 std suspenders to soak up the lumps and bumps of country roads was better than any of the family chariots, however it used to regularly land on the bump stops with bigger dips in the road once the odo was 40,000km and the car was definitely sitting lower on the RHS, without the driver.

So I recently fitted Koni's and Progress Springs, although I raised the car with spring spacers as I need the clearance to get over speed humps and into driveways more than the a car lowered 30+mm.

I have a complete set of OE NC3 springs and shocks, but there were changes after the NC1 that will mean these shocks and springs may not suit.
The rears I think are similar, but the OE NC3 fronts will possibly lower your NC1 too much.

kishigae,

Have you had the suspension problem sorted?
Greg.

Maybe it's just the bumpstops failing, so you notice it hitting them because they're failed?

I don't know. One suspension mechanic told me that the shock absorbers needed to be replaced. So I had new KYBs OEM apec replacements installed, but it has barely changed. Another suspension specialist is now telling me that they don't see anything wrong with it, and is suggesting to put coil overs with slightly harder springs.
Maybe it's the car normal behaviour and I am driving too fast over bumps.

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Seems the Op has a split personality!!

Not being a barge owner, I can't comment on the peculiarities of the species. However crashing over road humps is almost certainly down to shock absorber (aka damper) deterioration, and/or failure of the bump stops. I'd be amazed if the bump stops weren't replaced with the new shocks, but if they looked ok maybe not. Sadly looking ok isn't the same as working ok. Another possibility is shot suspension bushes, but again the car doesn't seem old enough for that to be the problem. Has the car been accident damaged, if it has been rear-ended there may be residual damage/misalignment causing noise. Similarly, the exhaust hitting the body structure.

I suggest that chasing around suspension places is not a good strategy. You need to identify a decent place (not necessarily the cheapest) and work with them in a systematic way to track down and isolate the problem. I'll let people here from Melbourne suggest good places, or speak to the Victorian track crowd who should know the shops that know these cars and are competent in working on them.

Good luck, keep us posted on progress!

Try Nathan at Advantage Suspension in Moorabin.

Straight shooter (sometimes too straight!) knows his stuff and doesn't try to sell you anything you don't need

Thank you greenMachine and AndyT. Both mechanics were recommended. The first one was Trutrack in North Melbourne and the second one was Centreline in Thomastown. I may visit these folk in Moorabbin to see what they say.

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