Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com - View Single Post - Largest Tire Diameter on a 6th Gen Civic (for lower RPM)

cackalak · 11-10-2009, 11:58 PM

I could've told you from day 1 that increasing the tire size would decrease your MPG's. Same deal on my truck. Stock size = 31" tires. Went to 32's and saw a 2MPG drop (on three different trucks).

Few factors here. (sorry if it's already been discussed---I just skimmed through). The biggest is the rotational mass. Even at the same weight, weight further from the center will require more power. Given the tires will weigh MORE with increased diameter (in most cases), it will rob you of efficiency.

As already mentioned, gearing might not be favorable. There was a guy who swapped in a 4.9 FD into his Integra and saw a 2MPG INCREASE (29MPG to 31). He is not the first one. Reason stated was that even though the RPM's increased, at higher speed, it made the engine work more efficiently. Aerodynamics plays a big role when you get up to speed, and higher RPM meant he was cutting through the wind easier vs. at lower RPM, he had to gas it more to maintain speed.

So the key is, find out where the best balance is. IMO, they got it right from the factory, as far as that goes.

11-10-2009, 11:58 PM	#34 (permalink)
cackalak Honda Join Date: Jun 2009 Location: Rockies Posts: 9 Thanks: 3 Thanked 0 Times in 0 Posts	I could've told you from day 1 that increasing the tire size would decrease your MPG's. Same deal on my truck. Stock size = 31" tires. Went to 32's and saw a 2MPG drop (on three different trucks). Few factors here. (sorry if it's already been discussed---I just skimmed through). The biggest is the rotational mass. Even at the same weight, weight further from the center will require more power. Given the tires will weigh MORE with increased diameter (in most cases), it will rob you of efficiency. As already mentioned, gearing might not be favorable. There was a guy who swapped in a 4.9 FD into his Integra and saw a 2MPG INCREASE (29MPG to 31). He is not the first one. Reason stated was that even though the RPM's increased, at higher speed, it made the engine work more efficiently. Aerodynamics plays a big role when you get up to speed, and higher RPM meant he was cutting through the wind easier vs. at lower RPM, he had to gas it more to maintain speed. So the key is, find out where the best balance is. IMO, they got it right from the factory, as far as that goes.