[robncar]

Originally Posted by pielet97

This was the first trip from Cali to Indiana, I just bought it. I compared the trip odometer to the fuel used and only got into the 14's twice, in the mountains. It is a Rubicon, and I don't think there is a conversion box. I did notice the the speed was indicating about 5mph faster than the GPS, at 75mph(speedo).

We agree the RPMs won't change with gearing, so you're saying the speed is slower and the mileage is less than shown? I'd agree to that. After doing some math, and assuming the 5mph at 70 is exact, my mpg would go to 14-17. About 6.6% less, or 1mpg.

With your statement, only a 5% change in rpm, you're assuming the fuel flow curve is linear, and we all know it is not. You don't burn twice the fuel at 2000 as you do at 1000, and 2K-4K. Just not true, it burns significantly more as the rpms increase.

There are aftermarket solutions to "tune" the tone ring signal to correct your speedo. TruSpeed from Superlift comes to mind.

That 5% change in RPM may be significant in O/D. The engine will be in a more efficient RPM band at the slightly higher RPM. You may use more fuel lugging the engine at the speed and RPM than at a higher RPM with the right gearing to achieve the same vehicle speed. The fuel curve may not be linear but I was really discussing efficiency, that 5% wouldn't kill MPG. The better behavior of the O/D (less hunting, downshifting, etc.) and additional available power may be a push in terms of MPG as a trade-off.

[jeffb_79]

Originally Posted by RubiconRazorbac

I can tell you right away, at least in this case, the relative weakness of the R&P is minimal compared to the inherent problems with the driver.

Not to mention the size of the tires.


Go with 5.13s and you'll be happy.
Go with 4.88s and you'll wish you had gone with 5.13s.

[Peterpsc]

I have an o6 auto w/37s and 5.13s. I also have Dana 60s front and rear but from a gearing and drive-ability point of view...it's better than stock. Go with the 5.13s if possible. The 5% statement above is accurate...no problems w/ high RPMs with the OD we have.

[YOGI1]

Hey thanks for all of the replie's I am going to order 5:13's tonight as they are on sale at 4 wheel parts unless there is a problem with superior r&p they are on sale for $171.00 a set right now up to this point I have always used motive gear as I worked at a distributor and we paid cost for everything we bought can anyone tell me about superior gear's?

[robncar]

Originally Posted by YOGI1

Hey thanks for all of the replie's I am going to order 5:13's tonight as they are on sale at 4 wheel parts unless there is a problem with superior r&p they are on sale for $171.00 a set right now up to this point I have always used motive gear as I worked at a distributor and we paid cost for everything we bought can anyone tell me about superior gear's?

We've been running Superior 4.88's for four years now without issues.

[Jerry Bransford]

Originally Posted by YOGI1

Hey thanks for all of the replie's I am going to order 5:13's tonight as they are on sale at 4 wheel parts unless there is a problem with superior r&p they are on sale for $171.00 a set right now up to this point

5.13 is a good decision for your particular transmission and the 35" tire size, you'll like how it performs once the 5.13 gears are installed.

[mudb8]

Originally Posted by 00jeepred

i know a kid with a rubicon who has 5.13's and 37's with a manual trans. and he goes through r&p gears like water. In the process of going to d-60's. at that low of a gear the pinion is so small that there is not alot of tooth contact.

so... yer telling me you can tell the difference in gear ratios by looking at the amount of tooth contact on the r&P?



humor me and tell me how high these gears are....

[2006_Sport]

I wanna see this response.

[ZIMM18]

so can you run 5.13's in the stock rubi axles with the factory elect. diffs?? i have an 05' rubi LJ with 315/75/16's with stock gears right now and looking into installing new gears as well.

[mudb8]

Originally Posted by ZIMM18

so can you run 5.13's in the stock rubi axles with the factory elect. diffs?? i have an 05' rubi LJ with 315/75/16's with stock gears right now and looking into installing new gears as well.

yep, 03-06 rubi's can run 5.13's , they are air lockers...

07+ rubi's can run 5.38's and are electric..

[00jeepred]

Originally Posted by mudb8

so... yer telling me you can tell the difference in gear ratios by looking at the amount of tooth contact on the r&P?



humor me and tell me how high these gears are....

I never said i was able to tell. It not the tooth contact per say its more of the pinion is smaller and you have less teeth on the pinion. There for you have less teeth contacting the ring gear. so there is less teeth to spread out the force. So there for it is easier to chip or break a tooth on a lower geared vehical.

[robncar]

Originally Posted by 00jeepred

I never said i was able to tell. It not the tooth contact per say its more of the pinion is smaller and you have less teeth on the pinion. There for you have less teeth contacting the ring gear. so there is less teeth to spread out the force. So there for it is easier to chip or break a tooth on a lower geared vehical.

Let's talk pinion teeth, shall we? In this case 1 tooth...

Dana 44:

4.88 = 44/9 (ring/pinion = 4.888)

5.13 = 41/8 (ring/pinion = 4.125)

[DocMojave]

Im in the process of that whole tire/gear/brake upgrade myself. I had 33"s with stock ring & pinion, I upgraded to 35" and 4.88 but I drive 90% street/freeway and 10% off road and I don't do any serious technical trail driving at all (although I intend to get off road more frequently). Actually Ive averaged 3000 miles a year in the past decade. I can tell a big difference with the 4.88 gears, its much smoother and quicker.

[mudb8]

Originally Posted by 00jeepred

I never said i was able to tell. It not the tooth contact per say its more of the pinion is smaller and you have less teeth on the pinion. There for you have less teeth contacting the ring gear. so there is less teeth to spread out the force. So there for it is easier to chip or break a tooth on a lower geared vehical.

unless the gears are improperly set up, the first thing to bust will be an axle or other power transmitting items.

show me a 5.13 that broke on 36's along with what else also busted, then I'll show you 3.07's that busted on 29's.....