Low Fuel Economy

[coaster]

i recently changed the wheels on my vt commodore from the 18's it had on it when i bought it to a set of 15's i had sitting around (hit a rock on the highway and damaged a rim and tyre, so just bought new 15's instead of new 18's and getting the rim fixed). anywho, going from the 18's with 235 tyres to 15's running 205 tyres has knocked about 0.5L/100kms off my fuel usage. i'm now down to under 8.5L/100kms

did by chance u change ur diameter of ur wheels and tyres? Lower rolling circumference will have and effect on your odometer therefore your l/100 rating.

[mad082]

size difference was minimal (speed difference between gps and speedo isn't really any different to before, so maybe a 1% difference in size), but the difference in the way the car drives is noticable. the car accelerates better, brakes better, requires less throttle to hold speed on the highway and coasts for longer when you lift off and the exhaust note is different. you can barely hear the exhaust on the highway now. given that the new tyres and wheels are lighter, and the contact patch of the tyres is drastically smaller, it isn't suprising there was a gain in economy. with the 18's on the contact patch was roughly equivalent to having an extra tyre. that's a fair bit of extra rolling resistance.