Paul330

Hi,

I have an '09 Z06 that has a slight shake at ~70 mph speed, particulary noticeable through the steering wheel. I've been reading the threads about similar ZR1 vibration, and wanted advice as to where to start troubleshooting. Seems like tire/wheel balance is the first step, then rotors & resonance next.

In order to rule out wheel/tire assembly balance as the cause, what Hunter road force reading is considered acceptable? My experience with other cars has been that a Hunter road force number below 10 lbs is good and is necessary. A number up around 20 lbs will cause an easily noticeable and annoying shake at hgihway speed. What have others experienced with this? Thanks for your input.

-Paul

JTE

Have the wheels dynamically balanced. The road force balance is inadeguate.

Glenn Quagmire

What is the difference between the two...never heard this before?

Streetk14

A Road Force balance (as in Hunter GSP9700) is a dynamic balance.

The difference between the Hunter machine and a regular tire balancer is it's ability to load the wheel/tire assembly and simulate the load one sees on a car driving down the road. In addition to measuring imbalance like most tire balancers, it can also measure wheel/tire assembly run-out and "road force".

To put it in simple terms, a tire's sidewall is like a spring. The problem is that tire stiffness varies as it rotates -- meaning some areas of a given tire are stiffer or softer than others. So going down the road at 70 mph, a perfectly balanced tire can still have vibration caused by this sidewall stiffness variation. The Hunter machine can detect this and help the operator compensate for it.

If any wheel/tire on your car has excessive road force readings, the GSP9700 can help you match the tire and rim so that you end up with the best possible match and lowest road force. This will make the car ride smoother than any regular balancer can.

And for what it's worth, Hunter's standard for passenger car tires is around 26 lbs or less of road force. I'd like to see 15 or so in my personal cars, but sometimes that isn't possible unless you want to start replacing wheels or tires.

Streetk14

Some good reading for those who don't understand what road force is: http://www.gsp9700.com/technical/4127T/4127t.htm

Glenn Quagmire

Thanks for the thorough explanation! I'm pretty familiar with the Hunter RF balancers, as I make sure that all of my aftermarket wheels are done. However, I'm not familiar with dynamic balancing, as JTE mentioned above. How is it different than the "inadequate" RF balancing?

Streetk14

I'm not sure what he was talking about -- and I'm not sure he did, either

There are 2 types of tire balance -- static and dynamic

Dynamic balancing just means the wheel/tire is balanced on 2 planes (usually one weight on the inside lip, one weight on the outside lip). The weight locations depend on the wheel design. The idea behind dynamic balancing is that it eliminates both "up and down" shimmy and "side to side" shimmy. In short, it makes for a smoother ride and has been the standard way to balance tires for YEARS.

Static balancing is old-school and just uses 1 weight in the center of the wheel. Static balancing can only eliminate certain frequencies and should be avoided.

I don't think JTE knows what the Hunter Road Force machine is or does, which is why I posted that. I think he meant that static balancing was inadequate, and I'd agree. The Road Force balance is the best thing out there and uses the type of technology that up until a few years ago was only used by tire manufacturers and OEM suppliers.

Oh, and pretty much any modern tire balancer can do either a static or dynamic balance, for what it's worth. A dynamic Road Force balance is the best you can get, just make sure whoever does your tires really knows how to use the GSP9700. Hope that clears it up!

Glenn Quagmire

I really appreciate you making sense of this for me. Now I can pretend like I know what I'm talking about.

JTE

Not cool buddy. Not cool at all.

GOLD72

That's so old school that I have not seen a static (bubble) tire balancing fixture in a shop in many decades!!!! To call it a machine would be to disgrace the definition of machine.

Reciprocal

Maybe he meant dynamically balanced on the car. He never said. It's old school too, but they jack up the corner, use a motor to spin the tire up and a strobe light to freeze the position of the wheel where the weight goes. Tape a weight on, repeat, trial and error until you get the right amount of weight put on. It balances the rotor and axle together with the wheel.

JTE

I was NOT referring to static balance. I was talking about making sure they are completely zeroed with a dynamic balance.

Streetk14

Wasn't trying to be rude.... but it was obvious to me you aren't familiar with the most current systems of vibration control -- and that's what this is about.

A tire that is dynamic balanced at "zero" can still have a noticeable vibration. That is where road force and tire/rim matching comes in. It is something that CANNOT BE DETECTED on a regular balancer and makes a world of difference.

Streetk14

I'd also like to add, this is what I was originally responding to. It really makes no sense at all..... sorry.

Glenn Hillhouse

the G M service manual explains it this way. Static out of balance causes bounce.
Dynamic out of balance causes waddle. We call it shimmy. I had both on my 2013
427. Michelin or G M would not help because of the after market wheels. after 6 weeks
of trial and error I had the rotors balanced which took care of 90% and then I balanced
the tires and wheels and rotors on the car . and now I have the perfect ride at 100 +.
I did try road force balance. It did not work for me.

mirage2991

post resurection is frawned uppon in this establishment

dougelam

A side from balance issues road force results help match tires to eliminate a tire pull condition. A radial tire pull condition will almost always pull to the good tire. A road force machine will show this by the amount of force it takes to compress the tire similar to the weight of the car. The more force it takes shows that the one tire is in a sense harder than one that has a lower force value. We all know that when we have a tire that is low on air it will pull that way alerting us that we need to pull over soon before destroying a good wheel.

On Corvettes a tire pull usually means new tires so road force measurements aren't as important but will reveal an out of round tire/wheel and as stated earlier irregularity in a tire.

Streetk14

With rotor balance issues on the ZR1, nothing you do to the tires will eliminate it. Normally, force-matching the wheel/tire on a Road Force machine will get you the smoothest ride possible. Being that a lot of these ZR1 vibration problems stem from the rotors, they tend to be a different animal all together.

And yeah.... this is an old thread.