Tuesday, April 10, 2012

Determining Wheel & Tire Vibration

A common problem faced by owners of light cars with light wheels is high speed vibrations.  We faced a serious vibration problem at the last Lotus Cup race and wanted to determine the source.  Typically the following areas can be the cause:
  1. Wheels
  2. Tires
  3. Balancing
  4. Suspension
After returning from the races, we conducted a comprehensive set-down on our car.  We scrutinized the suspension components to see if any parts had come loose.  We were testing our new raceUPRIGHTS and new Delrin Bushes so we checked everything closely.  Nothing was loose or found to contribute to the vibration problem.  We then turned our attention to the ETHOS wheels that we had used.

We decided to send the wheels that we ran and were suspect to our supplier, Tom Merrifield, for measurement.  I called Tom to discuss the issue and he was open to conducting a Run-out test on the wheels.  Poor run-out in wheels could be from either poor manufacturing quality or track/road damage.  We decided to measure these wheels to see if they were out of spec.

Tom made a nice video showing the test method. See below:

He found that the wheels had less than .004" of run-out.  According to Tom, vibrations can not be felt under .015" of run-out.  We are well under this amount.

This leaves the Tires or Balancing.  Since the tires are from Yokohama, the quality is generally very high.  I spoke with the tire supplier and he was also confident that the tires were OK.  We've run them many times with good success.  Of course since we did not test them, we're not 100% confident.  In our mind, this left Balancing as the most likely source.

We arrived at the event with a set of scrubbed-in tires that we had locally mounted and balanced on a set of ETHOS.  They performed with no problems and Glen set the Fastest Lap of the Weekend.  We bought a new set of tires, at the track, and had them mounted and balanced to a new set of ETHOS. These vibrated badly around 70mph.

Balancing done at the track is usually difficult because of time constraints. There is usually a line of racers waiting for their turn, so the poor guy balancing never really gets enough time.  This was the case at this first race.  The tire supplier graciously offered free mounting and balancing so had their hands full!

Our local wheel balancer, Frank, advised that plenty of lubrication is needed for these tires and that proper time needs to be taken along with careful balancing to get these light wheels and tires sorted correctly.  He also agreed with the run-out spec that Tom follows.  We're attending this weekend's race with new tires and old ones that Frank balanced to the same two sets of ETHOS wheels that we ran last time.  Running the old tires (that vibrated), balanced by Frank, will determine if the track balancing was the problem.

What's the moral of the story? Get an extra set of wheels and use a local tire balancer who will take the time to install and balance your race tires before you leave for your track event.  Follow this rule and you won't likely have the same headache that we faced.

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