Physics Question with gears

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06-12-2009, 08:22 AM

tkdtim

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Year: 1993 2 door

Model: Cherokee

Engine: 4.0L H.O.

Physics Question with gears

Using this page and the Find RPM chart:

Constants:
MPH = 55
Transfer Case Ratio = 1
Tire Diameter = 31

Variable
Axle Ratio = 3.07 ; 4.10
Transmission Ratio = 1 (4th gear) ; 0.79 (5th gear)

Heres the deal. 4th gear with 3.07 gears is approximatly the same RPM as 5th gear with 4.10 ratio at the same speed. Does the engine care what gear its in at the same RPM?
Could you just drive in 4th gear and save 5th for overdrive instead of re-gearing? Any adverse effects?

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06-12-2009, 08:30 AM

BuckB91XJ

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Year: 1987

Model: Cherokee

Engine: 4.0 liter RENIX I-6, DIY Cold Air Intake, 2.5 FM Exhaust, 3 Core Radiator

I absolutely CAN do this. The only thing is that the 4.10 gears would be much better to have for off roading and if you have larger than stock tires. You theory works fine for once you get the rig moving but with larger than stock tires and stock gears it will require more "go pedal" to get the rig moving each time so you'll be using more fuel. Good use of the noggen and basic math to show other guys how this works.