Anyone using 4.88's???
Thread Starter
JK Junkie
Joined: May 2007
Posts: 2,288
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From: Treasure Coast, Florida
I have an 07 Rubicon with the Auto transmission. I put a 3" lift on it and 35" tires. The power was lacking of course and as soon as funds allowed I bought a set of 4:88 gears.
I was actually concerned about the gears being to low as I have a set of 4:56 in my Blazer with 36" tires and it is a bit to much for hiway driving. I needed this Jeep to be good for everyday, not just off road use so that was a big fear of mine and I spent a lot of time thinking about it.
Last week I had the 4:88 gears installed replacing the stock Rubicon gears.
In the past week I have put 1200 miles on it with a trip to and from Memphis from Indiana. I can honestly say that I noticed no performance improvement over stock at all. On paper, there may be some improvement over stock tires/gears but my seat of pants gauge tells me I f-ed up and should have went with the 5:13 gears as I did hope for a performance improvement. IF you want stock like performance with 35" tires, 4:88 gears are for you. If I could do it over again, I would go with the 5:13 in a second.
For those wondering, the 35" BFG MT and the 4:88 gears made my Speedo 4 mph slower than reality as confirmed by my GPS. On a full tank of fuel dedicated to interstate only (mostly flat, no mountains) driving (at 75 MPH on average) I got 14.3mpg.
I was actually concerned about the gears being to low as I have a set of 4:56 in my Blazer with 36" tires and it is a bit to much for hiway driving. I needed this Jeep to be good for everyday, not just off road use so that was a big fear of mine and I spent a lot of time thinking about it.
Last week I had the 4:88 gears installed replacing the stock Rubicon gears.
In the past week I have put 1200 miles on it with a trip to and from Memphis from Indiana. I can honestly say that I noticed no performance improvement over stock at all. On paper, there may be some improvement over stock tires/gears but my seat of pants gauge tells me I f-ed up and should have went with the 5:13 gears as I did hope for a performance improvement. IF you want stock like performance with 35" tires, 4:88 gears are for you. If I could do it over again, I would go with the 5:13 in a second.
For those wondering, the 35" BFG MT and the 4:88 gears made my Speedo 4 mph slower than reality as confirmed by my GPS. On a full tank of fuel dedicated to interstate only (mostly flat, no mountains) driving (at 75 MPH on average) I got 14.3mpg.
JK Enthusiast
Joined: Feb 2007
Posts: 260
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I have the 4.88's with a 6 speed & 35's. I am happy with the results and think that 5.13's would have been overkill. I have heard differently about the auto they say 5.13's are better but the 4.88's and 5.13' both will be fine. I think 4.88's with 35's are perfect if you want to run 37's go with the 5.13's. 
JK Enthusiast
Joined: Mar 2007
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JK Super Freak
Joined: Nov 2006
Posts: 1,053
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From: Rockville, MD
i have 4.88's in my rubi with a manual tranny and 35's
it drives great, i couldnt be happier
the choise for me was easy 4.88's are a better combo for the 35's
the 5.13's a hair too deep if you drive on the streets a lot
although not a concern yet, but the pinion gear on the 4.88 gear set is much thicker then on the 5.13 gearset
if you are going to stay with 35's go with the 4.88's you wont regret it
it drives great, i couldnt be happier
the choise for me was easy 4.88's are a better combo for the 35's
the 5.13's a hair too deep if you drive on the streets a lot
although not a concern yet, but the pinion gear on the 4.88 gear set is much thicker then on the 5.13 gearset
if you are going to stay with 35's go with the 4.88's you wont regret it
JK Newbie
Joined: Mar 2007
Posts: 12
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i have 4.88's in my rubi with a manual tranny and 35's
it drives great, i couldnt be happier
the choise for me was easy 4.88's are a better combo for the 35's
the 5.13's a hair too deep if you drive on the streets a lot
although not a concern yet, but the pinion gear on the 4.88 gear set is much thicker then on the 5.13 gearset
if you are going to stay with 35's go with the 4.88's you wont regret it
it drives great, i couldnt be happier
the choise for me was easy 4.88's are a better combo for the 35's
the 5.13's a hair too deep if you drive on the streets a lot
although not a concern yet, but the pinion gear on the 4.88 gear set is much thicker then on the 5.13 gearset
if you are going to stay with 35's go with the 4.88's you wont regret it
There you go - Manual Tranny 4.88's are a nice improvement with 35 inch tires - Auto Tranny with 35 inch tires there is little / no improvement.
JK Enthusiast
Joined: Mar 2007
Posts: 427
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JK Newbie
Joined: May 2007
Posts: 19
Likes: 0
From: tarpon springs, fl
4.88's
I have an auto rubicon unlimited, with 35" cooper sst tires. With the stock
4.10 the performance was slugish and arround 12-13 mpg. After installing
the 4.88's, it's no tire burner but there is a big difference in arround
town drivablity. For the better and 15-16 mpg. On the interstate it holds
its speed much better. GPS- 72mph at 2600 rpm. I'm completly satisfided
with the 4.88's, my gearshop where the change was made is a jeep (4.88)
owner and this was his recomendation.
Peter
4.10 the performance was slugish and arround 12-13 mpg. After installing
the 4.88's, it's no tire burner but there is a big difference in arround
town drivablity. For the better and 15-16 mpg. On the interstate it holds
its speed much better. GPS- 72mph at 2600 rpm. I'm completly satisfided
with the 4.88's, my gearshop where the change was made is a jeep (4.88)
owner and this was his recomendation.
Peter
JK Newbie
Joined: Jul 2007
Posts: 42
Likes: 0
From: Temecula, CA
Here is a message I sent to a member who pmd me this week regarding the same topic. His question was along the lines of how do the 4:88s compare to stock performance. A few details it is an auto 4dr with dana 30 front axel and 44 rear, a 3" tereflex suspension lift, 35X12.5X17 Toyo OC M/T (they sit at 34" when mounted), no other mods to note at this point.
I never drove a stock JK. I had the tires and lift on before I picked it up. I struggled with which gears big time. I went with the 4:88 because there really was not a huge mathmatical difference when it came to RPMs and speed. However, I originally ordered 5:13s but right before they installed them they called me and convinced me that I should do the 4:88. This was their reasoning-first, the font dana 30 axel is barely acceptable for 35s and any extra torque would really put it at risk. Second, the pinion, as you know has one less tooth and is weaker. They had already had one JK come back with messed up 5:13s. It had 35s. It seems like I read about a forum member breaking 5:13s also with 35s... Last, again the performance gains are minimal and were not enough to outweigh the risk of breaking gears. That is what convinced me to switch.
With that said, I am not overly enthusiastic with the performance. First gear is better-mid range is ok and the top end doing 65-75 is definately better. I can again use OD and maintain highway speeds. I guess I was expecting more though. I am assuming it is slightly better than stock at this point-again I have never driven a stock JK.
Now the question is would I do the same thing again. The answer is yes.
Here is why. The gear shop really got in my head about breaking gears. The 100 extra RPMs really still are not worth it. Next, I am not confident that the performance is all due to the gears. I think the JK is a bit under powered as it is. The reason I say that is because even with the RPMs up there is still a lag in power and throttle response, I don't think that is because of the gears. I have the stock intake and exhaust still and really no other performance mods at this point. From my past experience I think with the basic air flow mods (intake/exhaust) and maybe a chip (which I am not sure I will do) I think I will be right where I think it should be.
One thing to consider is the fact that my goal was to improve all around driving more so than off-road crawling and such. Although based on the gear shops comments I still think I made the right choice. Also, once you are in low range the difference in performance of the gears is minimal. Also, for what is worth, the person I talked with at Superior pushed me towards the 4:88s as well. For my goal of improved daily driver.
I never drove a stock JK. I had the tires and lift on before I picked it up. I struggled with which gears big time. I went with the 4:88 because there really was not a huge mathmatical difference when it came to RPMs and speed. However, I originally ordered 5:13s but right before they installed them they called me and convinced me that I should do the 4:88. This was their reasoning-first, the font dana 30 axel is barely acceptable for 35s and any extra torque would really put it at risk. Second, the pinion, as you know has one less tooth and is weaker. They had already had one JK come back with messed up 5:13s. It had 35s. It seems like I read about a forum member breaking 5:13s also with 35s... Last, again the performance gains are minimal and were not enough to outweigh the risk of breaking gears. That is what convinced me to switch.
With that said, I am not overly enthusiastic with the performance. First gear is better-mid range is ok and the top end doing 65-75 is definately better. I can again use OD and maintain highway speeds. I guess I was expecting more though. I am assuming it is slightly better than stock at this point-again I have never driven a stock JK.
Now the question is would I do the same thing again. The answer is yes.
Here is why. The gear shop really got in my head about breaking gears. The 100 extra RPMs really still are not worth it. Next, I am not confident that the performance is all due to the gears. I think the JK is a bit under powered as it is. The reason I say that is because even with the RPMs up there is still a lag in power and throttle response, I don't think that is because of the gears. I have the stock intake and exhaust still and really no other performance mods at this point. From my past experience I think with the basic air flow mods (intake/exhaust) and maybe a chip (which I am not sure I will do) I think I will be right where I think it should be. One thing to consider is the fact that my goal was to improve all around driving more so than off-road crawling and such. Although based on the gear shops comments I still think I made the right choice. Also, once you are in low range the difference in performance of the gears is minimal. Also, for what is worth, the person I talked with at Superior pushed me towards the 4:88s as well. For my goal of improved daily driver.