2008 Track Width Rule

[Tirewarmer]

Can someone explain this to me:

 

21) Increase in track width greater than 3 inches due to non-OEM axles, control arms, brake

rotors/hats, wheel spacers, hubs, wheel offset, and/or camber adjustment +6 (measured from

the center of each tire at ground level)

 

Where exactly are we measuring? The outside shoulder of the tire on each wheel vs stock? Or the center of the tread that contacts the ground on each wheel vs. stock?

 

So basically the center of the shoulder(outside) or the center of the tread (underneath). Yes, my miata does have 8 inch wide wheels.

[kbrew8991]

as I read that, I'd start measuring from the center of the tire (and not contact patch)

 

I'm sure Greg will be along to confirm/deny shortly though

[Greg G.]

You would measure from the midline of the tire tread surface as close to the ground as you can get the tape measure (or at the bottom of the tire if put up on jack stands). This would be the only measurement that could be used to compare OEM track width to modified track width and take camber and all of the other factors listed into account. A measurement from the "shoulder" of the tire would be taking tire width into account also, and tire width, as you know, is a completely different assessment.

[Tirewarmer]

Thanks. I'm good measuring that way.

[JCraven]

You would measure from the midline of the tire tread surface as close to the ground as you can get the tape measure (or at the bottom of the tire if put up on jack stands). This would be the only measurement that could be used to compare OEM track width to modified track width and take camber and all of the other factors listed into account. A measurement from the "shoulder" of the tire would be taking tire width into account also, and tire width, as you know, is a completely different assessment.

 

Hmmm, We could and probably will get fairly different measurements using the two methods above. Can each racer choose the method by which their track is measured?

 

I'm curious of course - from an impound perspective. If someone protests a car, do they choose the method?

 

In some classes , I believe the track is measured from the middle inside of one tire and the middle outer of the other tire on both the front and back sides and averaged so the toe in/out is averaged out. The measurement is done in the middles of the tire to reduce the camber effect.

 

Joe Craven

NorCal PT Director

[Greg G.]

You would measure from the midline of the tire tread surface as close to the ground as you can get the tape measure (or at the bottom of the tire if put up on jack stands). This would be the only measurement that could be used to compare OEM track width to modified track width and take camber and all of the other factors listed into account. A measurement from the "shoulder" of the tire would be taking tire width into account also, and tire width, as you know, is a completely different assessment.

 

Hmmm, We could and probably will get fairly different measurements using the two methods above. Can each racer choose the method by which their track is measured?

 

I'm curious of course - from an impound perspective. If someone protests a car, do they choose the method?

 

In some classes , I believe the track is measured from the middle inside of one tire and the middle outer of the other tire on both the front and back sides and averaged so the toe in/out is averaged out. The measurement is done in the middles of the tire to reduce the camber effect.

 

Joe Craven

NorCal PT Director

 

Joe, you have valid points. Practically speaking, I would assume that most cars would be on the ground when measured. It will be up to the tech inspectors and Race Director to do the actual measurement, and probably measuring in front of the contact patch, and behind the contact patch, then taking the average would give the most accurate measurement. If one is accurate with the measurement of the midline of the tire, then taking midline measurements on both sides will yield the same result as measuring the inside of one tire and the outside of the other. Since it would be easier to measure the inside-outside method, I would assume that it would be used more commonly. For the most part, this is all academic, since most of our cars never come close to 3 inches anyway.