NA wheel wobbles

[91mx5]

Hi Guys,

I recently changed the original "daisy" wheels on my 91 NA to Rodney Jane Quest 14". The originals were a bit dull and I was looking for a bit of sparkle. As my Yokohama C Drive tyres are almost new, I decided to stay with 14"wheels. I'll go bigger when the tyres are worn out. The new wheels have about 7mm more offset (42mm) and required hub rings to reduce the size of the hole in the centre of the wheel. Since fitting, the car has the shakes at 100kph. The wheels have been rebalanced with only one needing a 10gram reduction, but the car still shakes at 100. Bob Jane swapped the plastic hub rings to aluminium type. I'm almost ready to put the original wheels back on and abandon the new ones. I haven't had a wheel alignment, but the car tracks dead straight if you let go of the steering wheel. Assuming the wheels are ok as they were brand new and not hit any potholes etc, do you have any ideas on this? Could the extra offset have upset things? Are Chinese alloys crap? All was well before changing the wheels.

If I go back to the original wheels, I'd like to get them powder coated before refitting. Does anyone know where I can get this done in Brisbane, preferably on north side.

Allan

[RawSouth]

Have you checked that the wheels arent warped? It is also possible that the tyres are not perfectly round.

I dont think offset would have that kind of effect

[Charlie Brown]

Sounds like the typical 100kph shimmy that NA's get in the front wheels.

Do a search either here or on Miata.net for the answers. There's been a million posts on the subject.

[Hammer]

Sounds like the typical 100kph shimmy that NA's get in the front wheels.

Do a search either here or on Miata.net for the answers. There's been a million posts on the subject.

If this is the case, Mazda fixed this by fitting extra under body bracing.

If the wheels aren't warped, have you checked your wheel bearings? They might need replacing.

[Steampunk]

are the hub rings exactly flush and centre the wheel perfectly? My guess is they still have a very small gap. Even if its a 1/4 of a mm, it will cause the shaking at speed.

[NMX516]

Cheap wheels are rubbish, which is extenuated on an MX5, especially on an early NA with limited under car bracing...

Go back to the standard wheels or upgrade to something like the NB8A wheels which do look great on an NA, but they are 15 inch, so will require new tyres. No idea what you paid for the wheels, but you'd get NB8A rims for a few hundred a set. Tyres - Option 1 Garage at Hamilton has been selling Kumho KU31's in 205/50/15 to suit for ~$100 each in the recent past. With your C-Drives being fairly new you should be able to get a good trade-in deal on them. You could even sell the std wheels if you really wanted to. I would expect powder coating to cost $100 per wheel, if not more.

So, worst case, $400 for NB8A wheels, $450 for tyres, total $850. Refund on the new 14inch wheels - $500?? Trade in, or just sell the C-Drives, $50 each, total $700 back. Total cost then of upgrade to decent 15 inch wheels made for the MX5, and new tyres, $150 which is cheaper than getting the MX5 14's powder coated. Problem solved

[Locutus]

despite your balancing and rebalancing, i still think it is a wheel balance issue. i had the same problem on my NA, but gave up and just lived with it.

mine was an NA8, so had some underbody bracing, and wheels were rays so no quality issues there. but of course YMMV.

imo the best way to tackle the shimmy is to have the tyres removed, balance the bare wheels, refit tyres and balance again. make it clear you don't want them balanced 'within tolerance' - you want them as close to perfect as possible.

[Tezzax5]

What did they use to balance wheels with?
You might want to consider an on car wheel balance or a static balance.
I used to drive around in a 71 super beetle and most of them also suffer the dreaded shimmy with after market wheels as well.

[Red Dragon]

I put 15" R.Jane wheels on my NA and they have been good.
But years ago I had a set of R.O.H wheels on another car from new straight out of the showrooom,and they could never be balanced properly after changing the tyres.
My local tyre shop after a lot of testing decided they were out of round and even though I hadn't purchased them from him he arranged for R.O.H. to inspect the wheels.
Result: FREE New set of wheels even after a couple of years use, it seems the original set of tyres somehow overcame the problem but the new tyres couldn't.
HAVE YOUR WHEELS CHECKED FOR THIS PROBLEM BY YOUR DEALER

[91mx5]

Thanks for all of your comments. Sounds like these low budget wheels are more trouble than they are worth. I didn't know the NA had an issue with shimmy as mine was fine on the original wheels. Richard from MX5-Plus told me a while ago that the original wheel/tire combo was pretty good and that the daisy wheels are very light. Maybe the new ones have added a bit of unsprung weight to the equation. Seems like Richard is right, but they look a bit ordinary. I think I'll get them painted or powder coated and put them back on.

Allan

[manga_blue]

You can check straightness and roundness by jacking up each wheel and hand spinning it with an object like a screwdriver fixed very close to the rim. (or borrow a dial gauge if you need definitive measures for a refund discussion with the supplier)

Most shimmy comes from problems with front wheels and suspension. Have you tried finding the straightest pair and putting them on the front?

Just as a left field suggestion ... have you considered that your old wheels might be bent or out of round and that the tyres were worn back to round while they were on them. Moving them onto round wheels could make them wonky again. Maybe you could also try the straightness test on the shoulders of the tyres?