My car has 3:15's. How much difference between the 3:73's?
Gear ratios are straight-forward math, no voodoo involved.
3.73 / 3.15 = 1.184 ; or about 18% increase.
That means that at any given engine RPM and transmission gear:
- there will be 18% more torque reaching the rear wheels
- the rear wheels will be turning 18% slower; meaning the car will be moving 18% slower
18% is significant / noticeable
18% more torque means it will feel quicker and more responsive. 18% slower means you have to run the engine 18% faster to travel at the same speed, which burns about 18% more gas. Your overall gas mileage won't go down that much though because there is a big mix of conditions in real driving.
Remember there is no magic; the engine is still producing the same torque and horsepower. With the change in gearing, each gear will run out quicker so you'll have to shift quicker and get into the next higher gear sooner.