Honda Car Forum

A lot of speed shops lower the final drive ratio to increase torque. Is there a part one can by and install that will increase the final drive ratio, which would decrease torque, but also decrease engine speed and improve fuel economy?The 2005 Civic hatchback was only sold in an Si model and this model was geared for speed rather than fuel economy.A lot of speed shops lower the final drive ratio of cars to increase torque. Generally speaking, this trades speed for fuel economy.I'd like to go the other direction: is there a part I can buy and have installed that will increase the final drive ratio. This would decrease torque, but also decrease engine speed and improve fuel economy?A couple of people answered this question by pointing out that larger tires are a way to go to increase the drive ratio, and they are bang on, but on this particular model, the tires already pretty much fill the wheel wells.

Larger tires would be the cheapest way. You would have to measure your time over a mile though to check your new speedometer behavior just so you don't get a ticket.

I wouldn't try it, the ratio was engineered to provide maximum mileage while still providing a usable final gear. Its possible that you could see some small improvement however, its very likely to cause more problems then its worth expecially considering that this WILL void a major part of your warranty. Its cost prohibitive, depending on the labor cost its probably not going to net you much in the way of actual savings anyway. If you really want to increase gas millage though, your best bet is to get a PCM (computer) reprogramming. NOT Hypertech or any of those other goofy $300 devices. Google it, you'll find much more information. You might also want to try adding a cold air intake, these are fairly cheap and can be bought locally. They will net you a decent 5-7HP MAX increase and increase gas milage as well.

i own a shop,and you can do this by changing the tires and rims on it this changes the final drive ratio faster than anything does,,tires and rims determine what the final gear ratio is going to be,,good luck hope this help,s.

Running a higher ratio diff will not necessarily improve fuel economy this is because to run at a certain speed requires the engine to produce x amount of horse power at a certain no of revs if you understand that the higher an engine can rev the more power it will produce so by lowering the revs the engine may not produce enough power to push the car along at the throttle settingused before so now with the higher geared diff you have to increase the throttle setting to maintain the same speed and by so doing you use more fuel The same thing happens when you find your car is faster in fourth gear than it is in fifth because fifth gear is an overdrive gear for economy not power as the civic is a small car with a small engine in increase in the overall gear ratio would only lead to disappointment

So far I have not heard of any aftermarket final drive gear which will increase the final drive. Maybe you can refer to your Honda/Acura dealers & check whether there are OEM final drive gears from other Civic models. It may or may not fit in.An increased final drive will increase the max speed but will decrease overall torque & pick up speed. Whereas decrease in final drive will improve torque & pick up speed while decreasing the max speed.To improve fuel consumption, the most practical way is to tune your ECU to produce less power output & torque output. Some aftermarket ECUs enables you to switch between different driving mode. Example, frugal mode, sport mode, track mode. Down tuning of power output will ensure better consumption. Of course you must also step less on the gas pedal & have a relaxing drive like a old man.

It simply will not be cost effective.