Gearing/tire question
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Gearing/tire question
Hi guys
I have a 2000 f150 4x4 with a 4.6 extended cab
I needed new tires and went with something a little bigger then what was on the truck
Original was 265/75/16
New tires. 285/75/16
Now the question is my truck feels like im pulling a trailer meaning its down shifting on hills faster and like to maintain a certain speed and i feel like i have to really push it hard to get to 70 75 mph and be in the drip down gear for what feels like for ever to get it there. I guess maybe over thinking it since i just dropped a lot of money for a new transmission. Since i put bigger tires on it should i maybe think about puting a new set of gears in the rear end? What do you guys think?
Thanks
Camble
I have a 2000 f150 4x4 with a 4.6 extended cab
I needed new tires and went with something a little bigger then what was on the truck
Original was 265/75/16
New tires. 285/75/16
Now the question is my truck feels like im pulling a trailer meaning its down shifting on hills faster and like to maintain a certain speed and i feel like i have to really push it hard to get to 70 75 mph and be in the drip down gear for what feels like for ever to get it there. I guess maybe over thinking it since i just dropped a lot of money for a new transmission. Since i put bigger tires on it should i maybe think about puting a new set of gears in the rear end? What do you guys think?
Thanks
Camble
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Joined: Sep 2006
Posts: 7,907
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You did not think this through.
The approx. difference in rolling diameter is 1.181 inches.
1 inch = about 300 rpm.
300 x 1.181 = 354 RPM less RPM for the same gearing and engine RPM at same road speed.
This put you 'down lower' in the engine torque curve.
And now you not happy with the results that should have been expected.
You would need to replace front and rear with enough lower gear to recover the stock RPM or more.
As it is now the computer does not know the tires were changed and still shifts at the points programmed for the stock tire size.
You must replace both front and rear with the same ratio so all wheels turn at the same RPM when in 4x4.
Even then you have not accomplished much except pushing more rolling resistance of a larger tire.
Good luck.
The approx. difference in rolling diameter is 1.181 inches.
1 inch = about 300 rpm.
300 x 1.181 = 354 RPM less RPM for the same gearing and engine RPM at same road speed.
This put you 'down lower' in the engine torque curve.
And now you not happy with the results that should have been expected.
You would need to replace front and rear with enough lower gear to recover the stock RPM or more.
As it is now the computer does not know the tires were changed and still shifts at the points programmed for the stock tire size.
You must replace both front and rear with the same ratio so all wheels turn at the same RPM when in 4x4.
Even then you have not accomplished much except pushing more rolling resistance of a larger tire.
Good luck.
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