Question regarding wheel weights and vibration

[speed freak]

Hey there

So I have a 2001 NB8B and ever since I bought the car it has had a shimmy/vibration in the rear end (Im 100% sure its in the rear)

When I got it the car had odd tyres so I went and bought some RE002's got them balanced and a wheel alignment and it still does it.

I recently got coilovers fitted and it seemed to disappear all together for maybe 3 or 4 days then it returned (thought it could have been worn shocks) and since then Iv also had a new wheel alignment done by a proper alignment place and its still there.

Iv had MX5 Plus check over it and they couldn't really see anything wrong and Iv been told the bushes/steering components are in good condition.

Now on to wheel weights. I seriously think it could be down to poor balancing it really feels the same as if the front wheels need a balance and the steering wheel shakes it feels exactly like that but in the rear end, not so much through the steering wheel. In saying that it does shake/shimmy the car, the seats vibrate because of it etc. Im certain (not ruling it out though) its not a buckled wheel as it doesn't do it 100% of the time or sometimes its there but some days its very bad and other days not so bad and kinda tolerable.

I noticed the other day that the wheels apart from one (which Iv heard is normal) has the normal wheel weights on the inside flat part of the wheel. I noticed on the rear wheels though along with the normal ones they also have a weight over the inner(side of the wheel closest to diff etc) edge of the wheel, it looks as though it clips over the edge of the wheel.

Is that normal? Iv never seen wheel weights there before especially not since it has the 'normal' weights on the inside of the wheel. Could this be causing the rear wheels to be poorly balanced and cause the vibration/shake? Main reason I don't think its a buckled wheel is it also disappears and gets less noticeable with less psi in the tires, the more pressure the worse it is. Some days it will be very bad others not so much.

It doesn't make me love my NB any less but it is frustrating especially because its my daily driver, I don't like to be shaken on my way to work lol. It gets worse on rough country roads too.

Thanks in advance for any help!

Its a 2001 NB8B with 102000 km

[JBT]

I had a drive of a bog stock NB8B a couple of weeks ago and it was doing pretty much what you describe. It had about 70,000 km on it and was a one owner car. It also had a clip on weight on at least two of the wheels as I recall, but I doubt they would have much effect. Coincidentally, it was also fitted with RE002 tyres but they were about 4 years old if memory serves correctly. The vibes were a bit random but could be felt anywhere from 40-100 km/hr. To me, it felt like extremely high tyre pressure or flat spotted tyres. It wasn't really shaking the steering wheel but the whole car.

We checked the wheels for buckling and tyre run out but all seemed good. Tyre pressures were at 32 psi cold - a touch high I reckon but the owner had tried various settings from 28-35 with little effect on the vibes.

All I could find that was a bit suss was all the tyres were very slightly out of round. We checked that by jacking each wheel and placing a straight block of wood behind the tyre. Then we spun the wheel slowly and found a 1-2mm gap would appear at one point during the turn. The owner was going to see about borrowing a set of wheels/tyres that were known to be good (no vibes) and try them to see if the vibes disappeared. I haven't heard back so don't know what happened.

[NitroDann]

The weights often fall off. Could have flat spots.

Could be the 100kph shimmy if it happens on the highway.

Could be a bent wheel or hub.

Start with balance, get them balanced and have them remove all the weights and use the stick on type not the ones that get pinched on. Note what weights are where, if it fixes it, and returns check which weighs fell off.

Dann

[project.r.racing]

The weights often fall off. Could have flat spots.

Could be the 100kph shimmy if it happens on the highway.

Could be a bent wheel or hub.

Start with balance, get them balanced and have them remove all the weights and use the stick on type not the ones that get pinched on. Note what weights are where, if it fixes it, and returns check which weighs fell off.

Dann

This is my thoughts too. I will add that while getting the wheel balanced, ask them to check if it is bent. Many will just balance (as requested) and return it back to you. You'll see if its bent while on the balancing machine.

but you can check if it is bent at home by spinning the wheel and watching both lips.

[speed freak]

Cheers guys Ill jack up each corner and test the roundness of the wheels on my weekend. Just to clarify it does shake the whole car, not the steering wheel, in particular the back of the car. I originally thought it could have been the crappy tyres, they looked new just sh*t brand and odd tyres on the rear with one very worn RE001. But new tyres didn't fix it. Shouldn't have a flat spot, never locked up a wheel or pulled the handbrake.

Iv played with tyre pressures and Im currently running 36 psi cold front and rear as MX5 Plus recommended. Iv tried anything from 26 psi up to 36 psi. The less psi in the tyres the less noticeable it is but its still there. Its still got the factory 16" wheels.

All wheels bar one have the stick on wheel weights, I rang the shop that fitted the new tyres the day after as I noticed one wheel had no weights and he said that's how its meant to be. Then I noticed that the 2 rear wheels also have a clip on type as well even on the wheel with no stick on wheel weights.

Iv read about the 100 km/h shimmy but I don't think that is it. Or it could be? It happens anywhere from about 40 km/h up to around 100 or 110 km/h. I might just take it to a reputable shop get all the wheel weights taken off even the clip on ones if they can, get them to check the wheels and tyres for roundness and get them to balance them properly.

[manga_blue]

I'd just rotate the wheels and see whether or not the problem seems to travel around with a wheel or two first.

[JBT]

....Im currently running 36 psi cold front and rear....It happens anywhere from about 40 km/h up to around 100 or 110 km/h.

Then it's unlikely to be balance as that won't have an affect at low speed. 36 psi is way too high IMO.
The things in common with your car and the one I drove are the model and the tyres......hmmm.

[speed freak]

Hmm its got me stumped. Ill rotate the tyres around see if it makes a difference otherwise Ill take them to a tyre shop and get them to check for buckles and check the tyres. I thought it could be the Bridgestones but it done the exact same thing with the "old" tyres that I took off the car.

What PSI should I run in these wheels/tyres? MX5 Plus said they use 36 psi, on the door mazda say use 26 psi. On any other car with 16" or 17" or higher that run low profile tyres you would run anything from 36 psi up to 42 psi.

Must not be to do with balancing then, could it be a bent driveshaft or something? Or even the tailshaft from the gearbox? Do these ever need tightening or greasing or anything? Its so frustrating but Ill swap some wheels around on the car and go from there.

Or any chance someone on the Gold Coast or Brisbane reading this have a spare set of wheels I could borrow to test?

[Magpie]

I have some 15" wheels at home, however I'm not back till early November.

I would suggest use the tyre placard for on the road and 36 for track.

[JBT]

....could it be a bent driveshaft or something? Or even the tailshaft from the gearbox? Do these ever need tightening or greasing or anything?

Never need tightening or greasing, just replacement if the boots split or the joints fail - you'll know all about it if that happens. They would have to be way out of balance to cause vibration and it would always be there at all speeds and just get worse as speed increases. There are plenty of MX-5s out there with 200,000km + on their original drive shafts without problems. Besides, MX-5+ couldn't see anything there, so count that out.

[NitroDann]

Im inclined to dissagree, PhilM, previous Newcastle Chapter Leader (title..?) just had a tailshaft fixed whos joints were stuffed and caused this issue, took him ages to find it.

Tried everything.

Dann

[speed freak]

I have some 15" wheels at home, however I'm not back till early November.

I would suggest use the tyre placard for on the road and 36 for track.

Ok well Ill have another play around with tyre pressures and also get the wheels/tyres checked out for any abnormalities and possibly get a balance done too. If I cant find a solution in the next few weeks I might test those 15s if you don't mind Mark as long as they fit over the nb8b brakes. Not sure about running 26 psi in 16" wheels though seems too low to me.

....could it be a bent driveshaft or something? Or even the tailshaft from the gearbox? Do these ever need tightening or greasing or anything?

Never need tightening or greasing, just replacement if the boots split or the joints fail - you'll know all about it if that happens. They would have to be way out of balance to cause vibration and it would always be there at all speeds and just get worse as speed increases. There are plenty of MX-5s out there with 200,000km + on their original drive shafts without problems. Besides, MX-5+ couldn't see anything there, so count that out.

That's what I thought too, it was just another possible cause I thought of. If it was the tailshaft Im sure it would vibrate the car much worse even compared to a bad day with whatever is causing the vibration in my mx. Although MX5 Plus didn't/wouldn't have checked the tailshaft I don't think, when I got the coilovers fitted I just asked how the bushes were and I got told they were good and the steering components were good. I didn't ask them to check driveshafts or taishaft.

Im inclined to dissagree, PhilM, previous Newcastle Chapter Leader (title..?) just had a tailshaft fixed whos joints were stuffed and caused this issue, took him ages to find it.

Tried everything.

Dann

This is interesting, do you know what type of mx he has and rough km on it? Its a possible cause I guess but mine only has 102 000 km could the tailshaft possibly be worn a little at this many km? Is there anyway I can test at home to see if its loose/bent?

[NitroDann]

That diff/axle combo had changed hands a few times.

You just remove it, there is 4 bolts, and feel the joints are smooth and not crunchy when you flex them.

Dann

[JBT]

That car I drove with the same symptoms as yours had the drive shafts replaced and tail shaft universals replaced. Problem was still there.
I suspect the tyres being slightly out of round or that brand/model having some compatibility issue with the car.

[NitroDann]

Could be 20 things, start with the cheapest and move on to the easiest.

Dann