Bad vibration at 110mph

[jamesmost]

my mechanic laughed at me when it told him i had a bad shimmy .......@110mph

not noticable @ other speeds.....

do u think i should go with the hunter road force balance as first line of defense???

or should i be looking at something else //?????James

[maxnix]

I would look at clean hub runout first, then true the rotors, then spin the wheels and measure balance and both runout specifications, then mount the tires and balance again and check for roundess and sidewall damage.

Eliminate the underlying possible causes first.
Modified by maxnix at 10:40 AM 10/17/2008

[Kiven422]

Yes rotors can cause vibration... right now mine are warped much more on LF than RF and I can feel how it offsets the wheels as they spin

[Unnatural1]

I'd probably laugh if you came to my shop too.

But, then I'd ask for more details. Do you feel the vibration in the seat/body mostly? Or is it mostly in the steering wheel? I'm assuming this is a new development; meaning that it didn't vibrate before and you've changed nothing and this has just started. Are there any noises associated with this that you can recall?

Typically, out of balance tires will cause a vibration at a very specific speed much lower than 110mph. And you stated that you did not notice any issue at lower speeds. That's not to say that there is not a tire/wheel issue. I'm also assuming that your tires are speed rated for over 110mph? Was this vibration during braking from 110mph or while cruising at 110-illegal-mph?

The more details you can provide about it the better we can help.

[Q45tech]

Road force imbalance show up at 2nd, third, and fourth harmonics. 55>110> 165 mph. The funamental speed depends on the EXACT load circumference and how that interacts with the chassis resonance frequency.

All the things change with temperature as the EXACT circumference changes minutely. Same with tire PSI as the exact circumference changes.

The question is whether a primary defect has another secondary defect........1,2, or 3 different BAD spots on tire, wheel, or rotor and how when timewise they interreact.

http://www.micropoise.com/engineering/

Tires for airplanes and Nascar are the only ones usually tested to 200mph.

Aftermarket wheels are usually not STIFF ENOUGH to not cause problems at high speeds from periodic flexing.............why oem wheels are strong and ugly.

http://www.vibratesoftware.com...l.htm

http://www.vibratesoftware.com

Download Free 14 day software to analyse your car

[jamesmost]

Road force imbalance show up at 2nd, third, and fourth harmonics. 55>110> 165 mph. The funamental speed depends on the EXACT load circumference and how that interacts with the chassis resonance frequency.

All the things change with temperature as the EXACT circumference changes minutely. Same with tire PSI as the exact circumference changes.

The question is whether a primary defect has another secondary defect........1,2, or 3 different BAD spots on tire, wheel, or rotor and how when timewise they interreact.

http://www.micropoise.com/engineering/

Tires for airplanes and Nascar are the only ones usually tested to 200mph.

Aftermarket wheels are usually not STIFF ENOUGH to not cause problems at high speeds from periodic flexing.............why oem wheels are strong and ugly.

http://www.vibratesoftware.com...l.htm

http://www.vibratesoftware.com

Download Free 14 day software to analyse your car

Good Info Tech.... Im gonna start with a Hunter ro9adforce balance.'I did just change the bearings in my SPL UCA's = did not have an allignment since --will do as well.My BBS wheels have been tru to me for many years now w/o issue....James

[mcrews]

gotta ask........what's it doing at 109mph?

kinda retorical.......... but also is it subtling building up?

[Unnatural1]

Road force imbalance show up at 2nd, third, and fourth harmonics. 55>110> 165 mph. The funamental speed depends on the EXACT load circumference and how that interacts with the chassis resonance frequency.

Yes I understand all that, but he specifically stated that this vibration was NOT noticeable at other speeds lower than 110mph. There are a multitude of possible issues here without getting more info. Which is why I asked.

Of course, that doesn't mean that the 1st harmonic was noticeable to the driver. Road force balancing is not a bad place to start and probably the second thing I check after inspecting the car and making sure there are no other obvious issues; suspension, steering, etc....