Yes it does, the speed rating tells you basically that the sidewalls can handle air pressure, torsion and temperatures at speeds equal or less than the speed rating. If you drive a tire past it's speed rating the sidewall becomes too soft and could bent easily if the steering is turned abrubptly or could explode easier due to the softer than normal sidewall texture at that higher than rated speed.
I am looking for a gadget they sell for trucks that depending on the tire diameter it corrects the speedo reading. Let me check if it is available for cars and if that is the case then the tire diameter would not mess your tranny changes points.
Here is the gadget for trucks, I need to find out if there is a counterpart for cars.
http://www.jcwhitney.com/webapp/wcs/...&storeId=10101
http://mikeegan.stormpages.com/Tru.html
http://www.superlift.com/33002I_1.pdf
http://www.superlift.com/print/insta.../33002IN_1.pdf
ALl the links that I have found point just to truck applications. But it would not hurt to ask the manufacturer if a version for automobiles could be available.