RPM's at 70
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Senior User
Joined: Oct 2006
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From: The Casa
RPM's at 70
With my 35's on my truck my truck is a turd,it takes for ever to pick up speed.
Well last week I put on some 31's so it would fit in the garage,well i took it out and with those doughnuts on my truck it is able to pick up speed fast and mabye even "halls ACE."
So I need to regear,and was just wondering what rpms yall turn at highway speeds.
Thanks guys
Well last week I put on some 31's so it would fit in the garage,well i took it out and with those doughnuts on my truck it is able to pick up speed fast and mabye even "halls ACE."
So I need to regear,and was just wondering what rpms yall turn at highway speeds.
Thanks guys
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Joined: Mar 2008
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here's two formula's for you to calculate what your present or expected rpm will be if you are wanting to change tire and or gear size:
RPM x tire diameter divided by final gear ratio x 336 = MPH
example: 2600 RPM x 35 (tire diameter)=91000
4.56 (final gear ratio) x 336=1532.16
91000 divided by 1532.16=59.39 MPH
or:
MPH x final gear ratio x 336 divided by tire diameter=RPM
example: 60 MPH x 4.56 (final gear ratio)=273.6 x 336=91929.6
91929.6 divided by 35 (tire diameter)=2626.56 RPM
dont forget you need to calculate your final gear ratio by knowing what your trans ratio at its highest gear is. most are 1:1, but say if you have OD you would first multiply the OD ratio x rear axle ratio ( example .80 x 4.56=3.65) to calculate your final gear ratio.
walt
RPM x tire diameter divided by final gear ratio x 336 = MPH
example: 2600 RPM x 35 (tire diameter)=91000
4.56 (final gear ratio) x 336=1532.16
91000 divided by 1532.16=59.39 MPH
or:
MPH x final gear ratio x 336 divided by tire diameter=RPM
example: 60 MPH x 4.56 (final gear ratio)=273.6 x 336=91929.6
91929.6 divided by 35 (tire diameter)=2626.56 RPM
dont forget you need to calculate your final gear ratio by knowing what your trans ratio at its highest gear is. most are 1:1, but say if you have OD you would first multiply the OD ratio x rear axle ratio ( example .80 x 4.56=3.65) to calculate your final gear ratio.
walt
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Joined: Feb 2004
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From: The Shenandoah Valley
Mine has 31/10.50-15s and stock 3.50 gearing, C-6 and it turns up about 2700 at 70 as I recall.
You pay a big price for those big tires every mile you drive.
Anytime you put larger diameter tires on you are going to slow acceleration for several reasons, more rubber and belt (takes more to wrap a larger circle) and the fact that this added weight,plus the weight of the added sidewall is all added on a larger circle, which has to be spun up from lower speeds. Once up to speed, it all takes greater effort to slow down as well as it has greater momentum. The bigger tires, greater weight, also change direction less willingly due to a greater gyroscopic effect.
Imagine taking a 2 foot 2x4, grasping it in the center with your right hand, and twisting it in circular fashion back and forth like a propeller. Now do it with a 3 foot piece of 2x6.
You pay a big price for those big tires every mile you drive.
Anytime you put larger diameter tires on you are going to slow acceleration for several reasons, more rubber and belt (takes more to wrap a larger circle) and the fact that this added weight,plus the weight of the added sidewall is all added on a larger circle, which has to be spun up from lower speeds. Once up to speed, it all takes greater effort to slow down as well as it has greater momentum. The bigger tires, greater weight, also change direction less willingly due to a greater gyroscopic effect.
Imagine taking a 2 foot 2x4, grasping it in the center with your right hand, and twisting it in circular fashion back and forth like a propeller. Now do it with a 3 foot piece of 2x6.
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Joined: Apr 2004
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Scroll down to second calculator. Just because the tire SAYS 31 inch don't mean it is. Check your loaded radius with standard air pressure. 1 inch doesn't make much of a diff.
37s and 4.56s...seems off unless you have OD.
Novak Conversions - Gearing & Gearing Math for Jeeps
37s and 4.56s...seems off unless you have OD.
Novak Conversions - Gearing & Gearing Math for Jeeps
