How does the change of diameter of ones wheels and tires effect the gearing ratio of our transmissions? With a turbo engine, should one try to shorten or increase the "gearing"? TIA

it all depends on your powerband and if your looking for top end or low end. ie: 1/4 mile w/ big tyres-higher et and higher mph.
correct me if wrong but thats what i believe.

Bryan

from my understanding small daimeter wheel/tires will "spool up" faster but will have a lower top speeds. Large diameter wheel/tires will "spool up" slower but have much higher top speeds. It's a trade off. I'm sure by checking the se-r gearing and final ratio and for what purpose 1/4 mile 1/8 mile you can figure out what wheel/tire is best.

smokemup.com (http://www.smokemup.com/auto_math/index.php) This site has a good auto math section.