Rear End Roaring Noise / Vibration with New Tires?
 

2009 RX-8 Sport with 14.5k on the odometer.

The stock tires were starting to make a roaring noise due to cupping, and they also were picking up a vibration from the rear with a *thump thump thump thump* type noise at highway speeds.

So here is what I did...

1. Bought new General UHP Exclaim's from discount tire
a. Hated the tires - the car was no longer fun to drive.
b. Noise was still prevalent, but most of the roaring had gone
2. Took it back and got Yokohama 520's put on.
a. Really like the handling
b. Noise is still prevalent. Vibration above 50mph
3. Took it into the dealer.
a. They said they couldn't find a noise... which I find hard to believe since my wife can even notice it
b. They performed an alignment, it was slightly off but within factory specs

Today I STILL have the *thump thump thump thump* noise coming from what sounds like the left rear. There is also a slight vibration at highway speeds. This car used to be smooth as butter on the highway!

What could cause this?? Bad rotor? Something in the suspension? Help me help the dealer please!

Thanks in advance!

They did a 4 wheel alignment?
Do you have the numbers?

Did they perform a good dynamic or road force balance on the wheels? Your wheels may also be bent but you'd think they'd mention that...

Visual inspection... Look over the back end. Anything look wrong?
Do you have a torque wrench? check your lug nuts.

Also do an advanced search for similar cases.

I do have the numbers, but not with me at the moment. They did a 4 wheel alignment. Lugs are tight.

I'm unaware of the type of balancing that they did on the wheels. Discount Tire is the one who did the wheel balancing. Is there a possibility that they could not be balanced correctly?

Nothing visible from the rear. And I haven't hit anything hard enough to bend a wheel.

Have a look between the wheel and the hub... is the wheel seated firmly against the hub?
Maybe it's show and tell time... Pictures?

could be a warped rotor, wheel bearing, or the tires.

rotors dont warp.... you put uneven deposits on them from improper bedding, or abuse outside of that pad compounds heat range

They can warp, from lug nuts not being tightened in the proper sequence.

Could be worth undoing the lug nuts and tightening them the right way.

It could also be a bad tire. Since the problem is in the left rear, swap that wheel with another and see if the problem moves with it.

Ken

dunno Ken, havent read that one... i just recall Eric Meyer and countless other non-amatuer track guys with loads of experience all saying basically the same thing, what i posted above.

heres your problem, they balanced the tires right after they mounted them. When you mount tires you put a grease on them that takes two weeks to seat. If you wait two weeks to balance them the balance will be correct. If you balance them new the tire can still shift on the wheel taking out the balance. You should actually drive with no balance on the wheel and shoot past the 50-60mph mark which is where the most imbalance vibration will exist. Never get a tire balanced immediatly always wait for the grease to settle they used while mounting the tire.

yea, I've been thinking about that for a long time. so its true?

Yes its very true. Its best to wait for two weeks before you balance your tires. This is comming from my dad and not me. He works as a front end master specialist for hendricks motor sports. He knows a little bit about the subject:P

I always have the impression that you supposed to have the tires mounted, take the car for a spin to seat in the tires then have them balanced.

If you are saying "roaring" I am going with wheel bearing. Thump thump thump and I am thinking, rim, rotor, tire.

I've also seen the "brake rotors don't warp" passage from Carroll Smith's book. I think in that context - a car worked on by people who know what they're doing - it's absolutely true. But that world is not populated by clueless grease monkeys. I've had rotors warped by incorrect tightening. Surprised me when it happened, but it has a couple of times. Loosening and re-torquing fixed it.

Of course, DoctorWho's problem can't be brake rotors - he's complaining of a vibration at speed, not pulsing of the brake pedal. But it could be a warped wheel from uneven tightening.

Rejoining the main conversation, I never heard the "balance after two weeks" philosophy, but given the nature of tires it makes sense that they might need rebalancing after two weeks. I've also been told to get an alignment a couple of hundred miles after new tires, not immediately.

I still think it's worth swapping a couple of wheels to see if it's just a bad tire.

Ken

Hum computer balance machine is designed to do it right after mount. But it does sound like these need to be rebalanced.

Have them also inspect hub bearing play. Make mazda use instruments lol.... make em earn that warranty. :)