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Unread 06-16-2013, 11:53 PM   #16
PaXJ
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Quote:
Originally Posted by cj7guy View Post
4.10 if it had the factory tow package?
My post above. Mine did not have the tow package. I do belive in 07 all auto's came factory with 4.10.

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Unread 06-16-2013, 11:59 PM   #17
PaXJ
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This is a pretty accurate discription on the specs of 2007 JK/JKU
http://www.jeephorizons.com/tech/2007_tk_spec.html
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Unread 06-17-2013, 02:14 AM   #18
Rtone1583
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Quote:
Originally Posted by cj7guy View Post
The stock JK speedo is using GPS to determine my speed?
It doesn't use GPS for speed indication.

At the very least, the computer uses input from the speed sensors (consists of a tone ring and sensor) located at each wheel along with parameters for a given gear set and stock tire size to indicate speed. There is no longer a mechanical connection between the speedometer and any of the systems that were at one time used to measure vehicle speed.

The tone ring is mounted to the hub. Tire size effects how fast the tone ring spins. Smaller tires it spins faster, larger tires it spins slower.

However fast the tone ring is spinning, the sensor sends that information to the computer which uses that information along with the programmed gear ratio and tire size (and possibly other parameters) to provide an indicated speed on the speedo.
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Unread 06-17-2013, 09:09 AM   #19
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Quote:
Originally Posted by Rtone1583 View Post
It doesn't use GPS for speed indication.

At the very least, the computer uses input from the speed sensors (consists of a tone ring and sensor) located at each wheel along with parameters for a given gear set and stock tire size to indicate speed. There is no longer a mechanical connection between the speedometer and any of the systems that were at one time used to measure vehicle speed.

The tone ring is mounted to the hub. Tire size effects how fast the tone ring spins. Smaller tires it spins faster, larger tires it spins slower.

However fast the tone ring is spinning, the sensor sends that information to the computer which uses that information along with the programmed gear ratio and tire size (and possibly other parameters) to provide an indicated speed on the speedo.
Good explanation except for the gear ratio part.
Gear ratio won't affect distance traveled per tone ring revolution.
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Unread 06-17-2013, 10:14 AM   #20
Rtone1583
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Originally Posted by ronjenx View Post
Good explanation except for the gear ratio part.
Gear ratio won't affect distance traveled per tone ring revolution.
Correct. But the computer does use the gear ratio as part of the formula for computing speed.
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Unread 06-17-2013, 10:33 AM   #21
ncb
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Wheel speed is wheel speed. I have a six speed JK and a gear change made no change in the speedo.
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Unread 06-17-2013, 03:47 PM   #22
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Quote:
Originally Posted by Rtone1583 View Post
Correct. But the computer does use the gear ratio as part of the formula for computing speed.
How can you say correct to my post, then say gear ratio is needed to calculate speed?

Speed and distance depend on tire diameter and tone ring frequency. It matters not what gears are installed.

The OP could have had his answer days ago if he had jacked a tire and spun it 2 revolutions.
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Unread 06-17-2013, 04:33 PM   #23
cj7guy
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Originally Posted by ronjenx View Post
The OP could have had his answer days ago if he had jacked a tire and spun it 2 revolutions.
I thought this would be a really simple question to answer.

Assuming that the jeep is 100% stock...with revs of X and Speedo reading of Y in 6th gear, that means axle gears are the following ratio....regardless of whether I'm running 44" tires or running 26" bicycle tires.

But that's not how it went down.
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Unread 06-17-2013, 04:57 PM   #24
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Quote:
Originally Posted by cj7guy View Post
I thought this would be a really simple question to answer.

Assuming that the jeep is 100% stock...with revs of X and Speedo reading of Y in 6th gear, that means axle gears are the following ratio....regardless of whether I'm running 44" tires or running 26" bicycle tires.

But that's not how it went down.
...because that's not how it is.

Doing it your way, to solve for axle ratio, you need to know:
Tire Diameter
Transmission Ratio
T-case Ratio
RPM
MPH

It is a simple question to answer.
It just requires a tiny effort on your part. (Measure your tire diameter, or jack a tire and spin it 2 revolutions.)
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Unread 06-17-2013, 05:38 PM   #25
cj7guy
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Originally Posted by ronjenx View Post
...because that's not how it is.

Doing it your way, to solve for axle ratio, you need to know:
Tire Diameter
Transmission Ratio
T-case Ratio
RPM
MPH

It is a simple question to answer.
It just requires a tiny effort on your part. (Measure your tire diameter, or jack a tire and spin it 2 revolutions.)
2007 Sahara, 6spd manual,
stock
stock
stock
RPM in photo
MPH in photo

What's the answer?

I think we're getting lost in the weeds. I don't have some crazy custom rig. It's a freaking bone stock Sahara. A stock JK Sahara in 2007 had like 2 or 3 possible ratios in the axles. My revs seem a bit high, so I already know it's one of the shorter ones. Does nobody else ever look at their tach on the highway? With a group of gearheads that pay attention to their rigs this would take like 3 minutes around a lunch table, nobody would need to check tires or anything else. A simple process of elimination based upon what is greater than and less than the other 1 or 2 available options.
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Unread 06-17-2013, 05:42 PM   #26
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Quote:
Originally Posted by cj7guy View Post
2007 Sahara, 6spd manual,
stock
stock
stock
RPM in photo
MPH in photo

What's the answer?
So, you don't want to go out to your Jeep to get the tire diameter?
I guess there's nothing we can do for you. It will take some effort from you.
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Unread 06-17-2013, 05:48 PM   #27
ncb
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Google search Wrangler JK gear rpm chart.
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Unread 06-17-2013, 07:57 PM   #28
pismo61
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4.10s if you have stock size tires.My 2013 is at about 2500-2600 rpm at 70mph.My 6th gear is .80 to1 yours is.84 to1.
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Unread 06-17-2013, 11:17 PM   #29
Rtone1583
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Quote:
Originally Posted by ronjenx View Post
How can you say correct to my post, then say gear ratio is needed to calculate speed?

Speed and distance depend on tire diameter and tone ring frequency. It matters not what gears are installed.

The OP could have had his answer days ago if he had jacked a tire and spun it 2 revolutions.
The formula for determining MPH is:

engine RPM X tire circumerence divided by final drive ratio X gear ratio X 1056
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Unread 06-18-2013, 12:21 AM   #30
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Quote:
Originally Posted by Rtone1583 View Post
The formula for determining MPH is:

engine RPM X tire circumerence divided by final drive ratio X gear ratio X 1056
Remember, you were describing how the computer determines what speed is to be displayed on the speedometer.

All the computer needs to know is distance per tire revolution ( for the miles part), and how long it takes to make one revolution (for the per hour part). It gets this data from the ABS tone rings.

If what you say is true, the mph would be wrong when coasting downhill with the engine at idle; when the automatic's torque converter is slipping; when either transmission is in a gear other than top gear, (if top gear is what is assumed); etc.

As mentioned in a previous post, people who change gear ratios and don't reprogram, don't see a different error in the speedometer.

A 30" tire travels about 7.85 feet per revolution.
That's about 672.6 revolutions per mile.
If the tire rotates at a rate of 672.6 times per minute, the speedometer will show 60 mph.
I don't see any gear ratio or engine rpm data in that.
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