Ernie Rogers
Veteran Member
Hi, guys,
Okay, so I got pretty philosophical last time. This time, I will try to be more practical. Using the "New" Jetta for a model, I tried calculating the changes in mileage you might get by making some changes with the tires. Here are the results:
Case A: Normal Jetta with Mich. Energy tires, Crr = 0.009
--> 47.5 mpg at 60 mph. (38.2 mpg at 70 mph.)
Case B: Bigger tires, change diameter from 24" to 25"
--> 48.1 mpg at 60 mph.
Case C: Raise pressure from "normal" 30 psi up to 40 psi.
--> 51.7 mpg at 60 mph.
Case B+C: Increase tire diameter and raise pressure.
--> 52.2 mpg at 60 mph.
Case D: Buy cheap tires, more resistance, Crr = 0.012.
--> 42.9 mpg at 60 mph.
So, you can see how your choices affect mileage. I bought some cheap tires last fall, returned them for the satisfaction-guaranteed refund a month later, then paid more for the best I could get. I feel better, but I am still paying for the tires.
This forum has an earlier post on how to measure your own rolling resistance-- a good way to settle any questions. My Michelin Energy tires (25.6 inch dia.) at 40 psi were found to have Crr = 0.0065.
Ernie Rogers
Okay, so I got pretty philosophical last time. This time, I will try to be more practical. Using the "New" Jetta for a model, I tried calculating the changes in mileage you might get by making some changes with the tires. Here are the results:
Case A: Normal Jetta with Mich. Energy tires, Crr = 0.009
--> 47.5 mpg at 60 mph. (38.2 mpg at 70 mph.)
Case B: Bigger tires, change diameter from 24" to 25"
--> 48.1 mpg at 60 mph.
Case C: Raise pressure from "normal" 30 psi up to 40 psi.
--> 51.7 mpg at 60 mph.
Case B+C: Increase tire diameter and raise pressure.
--> 52.2 mpg at 60 mph.
Case D: Buy cheap tires, more resistance, Crr = 0.012.
--> 42.9 mpg at 60 mph.
So, you can see how your choices affect mileage. I bought some cheap tires last fall, returned them for the satisfaction-guaranteed refund a month later, then paid more for the best I could get. I feel better, but I am still paying for the tires.
This forum has an earlier post on how to measure your own rolling resistance-- a good way to settle any questions. My Michelin Energy tires (25.6 inch dia.) at 40 psi were found to have Crr = 0.0065.
Ernie Rogers