Speedo/Tach/Wheel Size/Mufflers!

[Sparty92]

Ok....

So I just drove my friend's 2005 Mustang GT. He's got 19" CCW wheels, 295/35/19 in the back. Not sure what the front's are.....I think 275/35/19. Anyway....

He has the SLP Loudmouth axle-backs on the car and they sound great! I could not detect ANY drone at 1,800 - 2000K....(70mph)...but it did come on around 80mph, and it was LOUD.

My car has the stock 17s. At 2K, my car is doing 70mph. I have 3.55 gears, and I think he does too.

Here's my question:
How far out of whack is his tach/speedo due to his 19" wheels? He has not done anything to correct it since putting on these wheels.

My concern is that I might get the drone down at 2K with my stock setup, and I DON'T want that to happen!!

Any gearheads/math nerds able to calculate the difference in RPM in relation from his 19s to my 17s?

Quick 2nd question: where's the cheapest/best place to buy the SLP Loudmouths?

Thanks!

 

[ct07gt]

http://www.discounttiredirect.com/direct/brochure/info/tmpInfoTireMath.jsp

This link will show you any differences caused by tire size changes. There is .11 miles per hour difference on your speedometer, so you should have the same results as your friend.