generic question
11-30-2009, 03:27 PM
#1
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generic question this doesnt pertain to fbodies or GM.
But my buddy has a f250 superduty 99 model. he just put a 6 inch lift and 37inch tires.
He has stock 373 gears. He just told me that if he puts in 4.56 gears, he will get better gas milage, because the truck will think that he has stock size tires on. does this make sense?
But my buddy has a f250 superduty 99 model. he just put a 6 inch lift and 37inch tires.
He has stock 373 gears. He just told me that if he puts in 4.56 gears, he will get better gas milage, because the truck will think that he has stock size tires on. does this make sense?
12-01-2009, 07:09 PM
#4
It's not a matter of what the PCM sees, its a matter of simple mechanics.
12-01-2009, 09:26 PM
#5
How do you figure that? If he keeps the same size tires and changes gears, his mileage will get worse. The driveshaft will have to turn more to turn the wheels, which equals more RPMs, equals more gas used.
It's not a matter of what the PCM sees, its a matter of simple mechanics.
It's not a matter of what the PCM sees, its a matter of simple mechanics.
His highway mileage might increase because he will be turning lower rpms at highway speed, but if it is lugging the truck it will get worse. And, the engine will have to work HARDER due to lack of net tq in city driving, therefore getting worse mileage in the city.
His comment about the pcm is that the rpm vs mph will be off, so the miles he's putting on the odometer aren't the actual miles he's going. Therefore, any attempted to use a trip meter to determine mpg will be wrong.
12-03-2009, 08:30 PM
#7
His tire size became considerably TALLER than stock. In essance that numerically lowers the "final" gear ration. The same concept is used when guys run a crazy rear ratio like 4.56 and have to use a 28" tall tire to keep the rpms down vs mph so they can still cross the 1/4 mile in their 1:1 gear (4th for six speed, 3rd for auto) without going beyond redline.
His highway mileage might increase because he will be turning lower rpms at highway speed, but if it is lugging the truck it will get worse. And, the engine will have to work HARDER due to lack of net tq in city driving, therefore getting worse mileage in the city.
His comment about the pcm is that the rpm vs mph will be off, so the miles he's putting on the odometer aren't the actual miles he's going. Therefore, any attempted to use a trip meter to determine mpg will be wrong.
His highway mileage might increase because he will be turning lower rpms at highway speed, but if it is lugging the truck it will get worse. And, the engine will have to work HARDER due to lack of net tq in city driving, therefore getting worse mileage in the city.
His comment about the pcm is that the rpm vs mph will be off, so the miles he's putting on the odometer aren't the actual miles he's going. Therefore, any attempted to use a trip meter to determine mpg will be wrong.