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-   -   TJ with 285/75/16, 4.56 or 4.10 and A/T (http://www.wranglerforum.com/f282/tj-with-285-75-16-4-56-or-4-10-and-a-t-120610.html)

ckalogris 11-01-2011 10:37 AM

TJ with 285/75/16, 4.56 or 4.10 and A/T
 
Does anyone have this setup? Can you tell me the rpm you get at 60mph? Any pics?

Jerry Bransford 11-01-2011 10:38 AM

What model year TJ do you have? Through 2002 the auto was a 3-speed which became a 4-speed in 2004.

ckalogris 11-01-2011 10:43 AM

you have a point there!
it's 2005, with an OD

Jerry Bransford 11-01-2011 10:52 AM

Ok, that tire size is equivilient to 33" which means, because you have the 4-speed which has a very high overdrive ratio, your axles should be regeared to 4.88. 4.56 would not raise the rpms enough to let the engine run without lugging. You'd likely get worse mpg with 4.56 and you'd definitely not like how it drove with 4.56... you'd be constantly switching the overdrive off.

ckalogris 11-01-2011 11:03 AM

From what I have been reading, I have seen that 4.56 is the ultimate for me, since I get on the highway 2-3 weekends per month (travelling @ 60mph). Moreover I was told that 4.88 is very small and sometimes is destroyed under pressure. 285/75/16 is approximately 32.5", so my rpm will be a little bit higher than that @ the same set up and 33" (that is why I also want to know about 4.10).

Jerry Bransford 11-01-2011 11:09 AM

Quote:

Originally Posted by ckalogris (Post 1710200)
From what I have been reading, I have seen that 4.56 is the ultimate for me...

What you have been reading was either incorrect, was not for your particular transmission, or you misinterpreted it. Yes 4.56 is what would be appropriate with the 5-speed manual transmission but you need the slightly higher rpms of 4.88 for your 4-speed automatic.

ckalogris 11-01-2011 11:14 AM

What about that I was told that 4.88 is very small and sometimes breaks under pressure?

Jerry Bransford 11-01-2011 11:16 AM

Quote:

Originally Posted by ckalogris (Post 1710229)
What about that I was told that 4.88 is very small and sometimes breaks under pressure?

Again, what you were told on 4.88 gears breaking is not correct. That was a very early rumor back in the 90's when 4.88 first came out for our axles but it was soon proved unfounded. 4.88 is very commonly run by many Jeepers and it does fine. I am running 4.88 and have run 4.88 in two different Wrangler TJs for about the past ten years.

ckalogris 11-02-2011 04:20 AM

what setup do you currently run? will I be able to go on highway with 4.88, or I will see 3,000rpm at 60mph?

Northwest4x4 11-02-2011 04:36 AM

33s are not that big and 33s wont be breaking anything...

XJ Knight 11-02-2011 05:50 AM

Quote:

Originally Posted by ckalogris (Post 1712455)
what setup do you currently run? will I be able to go on highway with 4.88, or I will see 3,000rpm at 60mph?

Jerry Bransford's Jeep Profile :: Geezer Jeep II

Jerry Bransford 11-02-2011 10:44 AM

Quote:

Originally Posted by ckalogris (Post 1712455)
what setup do you currently run? will I be able to go on highway with 4.88, or I will see 3,000rpm at 60mph?

Why do you keep thinking the 4.88 rpms I recommend will be causing screaming high engine rpms? :confused: I would not be repetitively recommending 4.88 to you if they would do that.

You would only be turning over 2400 rpms with your particular 4-speed automatic transmission at 70 mph with 33" tires and 4.88. Your 4-speed's overdrive has an extremely steep .69 overdrive ratio which is why I keep telling you that you need that 4.88 axle ratio to overcome it.

At 60 mph, as you asked about, you'd only be turning over 2057 rpms with 4.88.

One last comment that might help. After my '97 TJ was stolen, I bought my present '04 from a friend and it came with the same transmission you have, 35" tires, and 4.88 gearing. The engine lugs (rpms are too low) so I keep having to turn the overdrive off. With my 35" tires and 4-speed automatic, I'd be much happier with 5.13 or 5.38... 4.88 is not enough gear for 35" tires with this particular transmission. My present 4.88 would be ideal for 33" tires however. The previous owner admitted he screwed up by only installing 4.88 gearing with 35" tires, 5.13 or, and likely better, 5.38 would have been ideal.

ckalogris 11-03-2011 04:23 AM

thanks for all your tips! I will go to 4.88...
:)
Christos


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