Auto tranny ?

RUBINOT

RUBINOT

Caught the Bug
Own my first Jeep with a Automatic Transmission, always had a manual transmission.

Anyway 2014 Jk Sport is stock w/3.73 and 225/70/16 tires, for now.

Anyway my question is, what is a normal RPM at 75 mph for the above set up. I'm at 2900, is that correct.

We drove to Colorado (Frisco) from St. Louis averaged 18.3 mpg, but it is up hill all the way;)

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Fir-na-tine

Fir-na-tine

Caught the Bug
cld0196 said:
Own my first Jeep with a Automatic Transmission, always had a manual transmission.

Anyway 2014 Jk Sport is stock w/3.73 and 225/70/16 tires, for now.

Anyway my question is, what is a normal RPM at 75 mph for the above set up. I'm at 2900, is that correct.

We drove to Colorado (Frisco) from St. Louis averaged 18.3 mpg, but it is up hill all the way;)

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Click to expand...

Using the link
http://www.advanced-ev.com/Calculators/TireSize/

The rpm data you provide shows you have a 3.21 geared JKU not a 3.73.......plugging in the 3.73 gearing puts your rpm's at 3310@75 mph....plugging in the 3.21 gearing puts your rpm's at 2848@75mph much closer to the 2900 rpm's that you observed driving at 75 mph on your trip.

Tire size 225/70/16 = 28.4"

~Woodrow~
 
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RUBINOT

RUBINOT

Caught the Bug
Hummmmm, interesting. I paid for 3.73 and it was on the window sticker. I'll have to check the rear diff.

But otherwise rpm that high is normal. Manual tranny (6 speed) was about 2500.

We just turned 1300 miles, so auto is still very new to me. I still keep trying to shift, but after driving Jeep CJ YJ TJ and JK for 35+ years it's a hard habit to break:thumbup:

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RUBINOT

RUBINOT

Caught the Bug
Ok, I dont see at tag on the rear diff to indicate what gears I have.

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RUBINOT

RUBINOT

Caught the Bug
Hummm still confused. Oh well going to enjoy vacation and figure it out when I get home.

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RUBINOT

RUBINOT

Caught the Bug
Yeah, the chart shows 4.11 no 4.10 and 3.31 not 3.21

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Mabar

Mabar

New member
cld0196 said:
Own my first Jeep with a Automatic Transmission, always had a manual transmission.

Anyway 2014 Jk Sport is stock w/3.73 and 225/70/16 tires, for now.

Anyway my question is, what is a normal RPM at 75 mph for the above set up. I'm at 2900, is that correct.

We drove to Colorado (Frisco) from St. Louis averaged 18.3 mpg, but it is up hill all the way;)

Sent from my SPH-L710 using WAYALIFE mobile app
Click to expand...

Are you sure about the 225 x 70 x 16? Stock Wrangler Sport tires are 225 x 75 x 16. If you have 75's then your tire diameter is about 29".

Your 2014 Automatic is a 1 to 1 ratio in 4th gear, and 0.83 to 1 in 5th gear (overdrive). That is a 17% RPM reduction in overdrive.

So if you use this calculator:

http://www.advanced-ev.com/Calculators/TireSize/

and assuming you have a 3.73 differential gear ratio, you can figure your RPM's at any speed in 5th gear (overdrive) by entering 3.0959 for your differential gear ratio (3.73 minus 17% is 3.0959).

According to that calculator your RPM's should be about 2690 at 75 mph in 5th, or 3241 in 4th gear.

Mabar
 
RUBINOT

RUBINOT

Caught the Bug
Mabar, thank you

You are correct on the tire size 75 not 70, my mistake.

Thank you for the info, makes me feel much better.

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HILLZ

HILLZ

Member
hmmm stock tire size here in Australia for the JKU Sport is 245/75R17. that's why Australia is the best... :cheesy::thumb::rock:
 
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