Measuring tire diameter with VAG-COM?

[JJDubya]

Had a blowout yesterday. OE sized 235/40R18 Toyo Proxes 4 on the front right (with at least 35K miles on it ... they were on there when I bought the car) died due to a shredded sidewall. Replaced with the brand new (OE) Dunlop SP Sport01 spare and was on my way.

I know running mismatched tire diameters side to side is not recommended. And, I know Audi specs that tires should be within 4/32" of each other (it isn't clear if this is the difference in tire tread or tire diameter). Regardless, I am wondering if there is a way to use VAG-COM to measure tire diameter (either directly or indirectly). I imagine measuring blocks that report revolutions per mile or per minute or something similar... perhaps pulses from the ABS sensor at each wheel? From that data, one could calculate the tire diameter and determine how close all the tires are. Do those measuring blocks exist?

I ask because I am faced with the decision to buy one shaved Toyo Proxes 4 from Tire Rack (if they are even still available) or replace all four tires (and possibly spare to have opportunity to rotate tires to avoid this situation in the future). Any advice?

Thanks,

JW

[Pufftrees]

Its not recommended, its not going to hurt anything though. I wouldnt worry about it too much, just replace all 4 when you have the money/are ready.

Also, i dont think vag-com has any way to 'measure' the tires. You could probably create some formula using the speed sensors, but your thinking wayyyyy to far into this.

[lyleswk]

Just jack the car up and do it the old fashioned way. I would use what I think is a surveyer's tape measure (plastic covered cloth around a wheel)that is flexible (not sure where I picked it up) becuase it would lay flat against a tire vice a carpenter's metal tape measure. There are also flexible cloth one's that you can get at a fabric store.

[JJDubya]

Also, i dont think vag-com has any way to 'measure' the tires. You could probably create some formula using the speed sensors, but your thinking wayyyyy to far into this.

Perhaps, but it would be quite scientific! Do you happen to know what measuring blocks indicate the speed sensors?

[JJDubya]

Just jack the car up and do it the old fashioned way. I would use what I think is a surveyer's tape measure (plastic covered cloth around a wheel)that is flexible...

Certainly the least complicated method. If I find a dead end with the VAG-COM, this would be the way to go. Thanks lyleswk...