Getting drag radials and gears and need info on what combo. I have a 94 a4 car and I see everyone goes w/3.73's. I'm ok with that ,but what tire size works the best 26,27,or28 tall tires and what RPM's in the traps. If I went with 28 would a 3.90 be better?

 

Use a gear calculator to help figure it out. You want to cross the 1/4 mile line at your highest horsepower leve (read red-line) to get the most out of the car.

http://www.izook.com/gearcalc.htm

 

Actually you want to be slightly past you peak horsepower as you go thru the eyes if your looking for maximum ET, it costs a little mph. Your car will be geared for better acceleration and moving all that weight. The stock elim car I dabble with we geared it foe about 1000' and let it "hang on" thru the end of the quarter. That is an extreme example for s purpose built car.

 

Without knowing what kind of HP you are making, the RPM at which you are making it, and the redline on the engine, no one can even attempt a guess.

 

What he said.

 

Red line is a misused term. To me a red line is where my rev limiter is set to keep the valves from floating. I don't shift at the red line. I shift at a preset rpm which is usually at or just past your peak HP. When you shift, the rpms drop and torque is used to bring the car back to peak HP. After a shift, the rpms should drop to where torque peaks. There's a lot of fine tuning to get these numbers perfect with cam profiles, transmission gearing etc.

As mentioned above, a properly set up drag car will cross the finish line at or just before the shift point in high gear (no OD) allowing the rpms to go over the peak hp as you cross the finish. I shift my car at 7000 rpm. My rev limiter is set to 7600 rpm. My shift light comes on just past the 1000' mark and I go through the traps at around 7200 rpm. There's no need to build power after that point or to run out of power before the end of the finish line.

The best suggestion for your car first depends on what it does now. What's your current tire size and gear ratio? What rpm do you currently go through the traps at and in what gear? What rpm do you shift at? With that kind of info, a better guess as to what may work better would be easier.