Please don't close this topic Mod's - and please everyone no arguing I'm not trying to prove anything, start an argument, slag people off etc etc.........just a simple discussion on why a change to 18" should cause a drop in mpg.
Right then.....Today I drove into town with the 18" wheels on the car. Mostly m'way and the rest town traffic. Cruise control on the motorway, set at dead on 70mph (8.4 miles of the journey). Now I now it's only 25miles, but this reslut bears out exactly what I discovered over a previous 160 mile journey - a drop of about 2-3 mpg.
18" Honda Altimo wheels.
Falken ZE912 225/40/18 tyres at 38psi all round.
Overall Diameter 637mm
Weight of wheels and Tyres 22.4kg
16" Honda wheels.
Michelin Primacy 205/55x16 tyres at 33psi front, 30psi rear.
Overal Diameter 632mm
Weight of Wheels and tyres 17.2kg
Factors that are different;
DIfferent make of tyres.
Rolling radius up from 1985mm to 2002mm so the speedo reading is out by (only) 0.79%
18" wheels & Tyres are 5.2kg heavier
With 18" wheels:
I got back home, changed the wheels back to the original 16" ones, and repeated the journey exactly, driving exactly the same way (Miss Daisy mode)
With 16" Wheels
So anyone who is better than maths at me, please reassure me that I have not decreased my mpg. Personally I reclon the heavier wheels may well be the cause. 5kg heavier each corner. Thats like me strapping on 5 bags of sugar to each wheel, that has to make a difference, shirley
Now behave
Right then.....Today I drove into town with the 18" wheels on the car. Mostly m'way and the rest town traffic. Cruise control on the motorway, set at dead on 70mph (8.4 miles of the journey). Now I now it's only 25miles, but this reslut bears out exactly what I discovered over a previous 160 mile journey - a drop of about 2-3 mpg.
18" Honda Altimo wheels.
Falken ZE912 225/40/18 tyres at 38psi all round.
Overall Diameter 637mm
Weight of wheels and Tyres 22.4kg
16" Honda wheels.
Michelin Primacy 205/55x16 tyres at 33psi front, 30psi rear.
Overal Diameter 632mm
Weight of Wheels and tyres 17.2kg
Factors that are different;
DIfferent make of tyres.
Rolling radius up from 1985mm to 2002mm so the speedo reading is out by (only) 0.79%
18" wheels & Tyres are 5.2kg heavier
With 18" wheels:
I got back home, changed the wheels back to the original 16" ones, and repeated the journey exactly, driving exactly the same way (Miss Daisy mode)
With 16" Wheels
So anyone who is better than maths at me, please reassure me that I have not decreased my mpg. Personally I reclon the heavier wheels may well be the cause. 5kg heavier each corner. Thats like me strapping on 5 bags of sugar to each wheel, that has to make a difference, shirley
Now behave