I've seen many threads on tire size. I had to prove to a GM dealer one time that what he thought were oversize tire's, in fact were not ... they were going go void a warranty issue!
Anyway if you go to this tire size calculator http://www.1010tires.com/TireSizeCalculator.asp it says our tires are 29.53" in diameter. When you go right to the spec sheet at Michelin http://www.michelinman.com/assets/pdfs/doc_ltxms.pdf it states 29.7"

My point and I'll shorten it here, the 245 / 65 / R17's from Michelin to Goodyear, Toyo, etc, are mostly all different. Some not by much, some are up to an inch difference. When you go to a different diameter tire, you change the revs per mile, that in turn change your odometer, speedometer readings and could affect braking and other safety systems on the vehicle.

Typically when you swap tire brands, your safe within the guidelines. When you go to over or under-size tire's, whatever your looking for, If your interested to keeping as close to stock ride as possible, before you buy a tire, go to the manufacturer's web site and look up the spec's. Don't take a tire shops word for it unless you trust them... some of them do not know

If people would simply remember what the tire size means this isn't that hard to determine.

245 = width of tire in mm
65 = aspect ratio or proportion of tire height to width

That means the factory tire height is .65 x 245 = 159.25 mm

Divide by 25.4 to calculate inches. That means 6.27 inches

Multiply by two since you have a top and bottom portion of the tire (12.54 inches)

Add to 17 inches for the wheel and you get 29.54 inches

That assumes the tire is mounted on the manufacturer's target rim width. If you mount it on a wider rim - you'll get a slightly flatter tire. On a narrower rim - a slightly taller tire.

245 = width of tire in mm
65 = aspect ratio or proportion of tire height to width

That means the factory tire height is .65 x 245 = 159.25 mm

Divide by 25.4 to calculate inches. That means 6.27 inches

Multiply by two since you have a top and bottom portion of the tire (12.54 inches)

Add to 17 inches for the wheel and you get 29.54 inches

That assumes the tire is mounted on the manufacturer's target rim width. If you mount it on a wider rim - you'll get a slightly flatter tire. On a narrower rim - a slightly taller tire.

Thanks for the input and the math makes total sense, but I was only stating that different tire manufactures have different sizes. Even with one manufacture you cant count on a specific tire size to be consistant with the different style tires they offer. Because of this, doing the math or using the available calculators will get you close to a proper fit, but sizes will vary based on tire style and manufacture.

I definitely agree with you that different manufacturers have different styles, widths, etc. In theory a manufacturer's sizing would reflect whether it had a different shape or design. But I have seen tires with the same claimed size have very different tread width. Note that the width rating of a tire is not the tread width but the width of the tire body.

Also you must remember that in manufacturing you have various tolerances and environmental variants. Being a flexible material I am sure the actual circumference from tire to tire varies quite a bit.

If you go onto Tireracks website, they have full specs of all the tires for the RL and include the Overall Diameter and a Revolutions per Mile calculation. They have the OEM tire listed as 29.4" and 704 Revs/mile. A 1 inch decrease in diameter equates to 728 rev/mile (a 3% increase).

The Ridgeline they will be using for tackling Baja this year will have 33-inch B.F. Goodrich tires. I'm wondering how the CaRR people are getting 33 inch tires on the Ridgeline.

The CaRR Ridgeline runs on 33-inch B.F.Goodrich tires specifically designed for the demands of off-road racing.

They look cool on this non-Ridgeline truck so I'm thinking they would look cooler on the Ridgeline.
Cool tires on Dodge Ram (http://www.edmunds.com/media/roadtests/firstdrive/2005/dodge.ram.powerwagon/05.dodge.ram.powerwagon.r34.500.jpg)