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highway rpm's with big tires

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Old Jan 14, 2014 | 09:26 PM
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Default highway rpm's with big tires
soooo its perfectly fine to highway drive at 3000 RPM on 33" tires and a stock geared 8.25?

serious question. I've been keeping it at 2000 @ 55mph.
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Old Jan 14, 2014 | 09:41 PM
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Use the pull-downs...
http://www.grimmjeeper.com/gears.html
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Old Jan 14, 2014 | 09:49 PM
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3000 rpms on 33 at 70mph on stock gears does not sound right to me... im on 31's but i turn 2000 rpm at 65mph by gps... it says about 72mph on my speedo
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Old Jan 14, 2014 | 10:02 PM
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at 2000 for me it reads 55 but is actually 50 ,and at 3000 it reads 75. I'm not sure 3k on 33's is safe for my xj..
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Old Jan 14, 2014 | 10:11 PM
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Originally Posted by SeriousOffroad
if i did this right, it says,
1887RPM @ 4th gear @ 70mph
2516 @ 3rd gear @ 70mph
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Old Jan 14, 2014 | 10:18 PM
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Well, for what it's worth I just did an 1100 mile trip in my XJ on 33's. Kept it in 3rd for most of the way, right near 3k RPMs at about 80mph. No issues, trans fluid looks fine.
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Old Jan 14, 2014 | 10:19 PM
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Why is it spinning at 3k on the highway with stock gears? You sure they are stock? That's more like 4.88 territory.
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Old Jan 14, 2014 | 10:23 PM
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Originally Posted by mr white
Why is it spinning at 3k on the highway with stock gears? You sure they are stock? That's more like 4.88 territory.
you could be right. the guy before me rebuilt the axle and who knows if its stock or not. :/ is there a way to calculate that?
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Old Jan 14, 2014 | 10:30 PM
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You can Jack the car up and count how many spins of the pinion to one turn of the wheel. Or you can remove the diff cover and count the teeth on the ring and pinion which would be more accurate.
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Old Jan 14, 2014 | 10:35 PM
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Originally Posted by mr white
You can Jack the car up and count how many spins of the pinion to one turn of the wheel. Or you can remove the diff cover and count the teeth on the ring and pinion which would be more accurate.
Oh duh. Thanks.
Last edited by spiral_energy; Jan 14, 2014 at 10:49 PM.
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Old Jan 14, 2014 | 10:55 PM
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Originally Posted by mr white
You can Jack the car up and count how many spins of the pinion to one turn of the wheel. Or you can remove the diff cover and count the teeth on the ring and pinion which would be more accurate.
Remove the diff cover and count. Unless you have a set of stock wheels/tires laying around, bigger tires will throw your ratio off if you do the tire spin/pinion rotation way...
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Old Jan 14, 2014 | 11:07 PM
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pull the diff cover, the ring gear will be stamped with each tooth count or ratio numbers.

kinda like this.
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Old Jan 14, 2014 | 11:11 PM
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Originally Posted by roninofako
Remove the diff cover and count. Unless you have a set of stock wheels/tires laying around, bigger tires will throw your ratio off if you do the tire spin/pinion rotation way...
How so?
Angular velocity will be faster on the 33 than the 29 but one turn will still be one turn.
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Old Jan 14, 2014 | 11:29 PM
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Originally Posted by mr white
How so?
Angular velocity will be faster on the 33 than the 29 but one turn will still be one turn.
Consider the tire to be the final gear in the driveline
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Old Jan 14, 2014 | 11:37 PM
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Originally Posted by roninofako
Consider the tire to be the final gear in the driveline
That won't affect reading the gear ratio via pinion to axle. That only affects speed / accuracy of speedo
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