Do you remember what RPM 4.56 would be turning at 75mph? Was it very significant or no?
Gears and lockers
- Thread starter tristan6555
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Do you remember what RPM 4.56 would be turning at 75mph? Was it very significant or no?
A 33" tire is going to have an effective rolling diameter of about 32"
NV3550/32"/4.56=2801rpm @ 75mph
NV3550/32"/4.88=2998rpm @ 75mph
I daily drove 33s/488 for many years over 100k miles and never once wanted less gear.
Good to know. Still adjusting to mine and wasn't sure if I overgeared it. 3.07 to 4.88 is an entirely different vehicle.
This is very will trodden territory. Historically, people have been undergeated for several dumb reasons that never seem to go away.
Do you think difference between an A/T less aggressive/ lighter weight tire and an M/T more aggressive/ heavier weight tire would justify 4.56? Or are they pretty well a useless gear ratio?
I've never understood why folks who own the Swiss army knife of vehicles are automatically lumped into the category of being ill prepared for emergencies. If you know you have something that is oddball, different, difficult to source, then buy some fucking spare parts.
The inner splines at the carrier have convinced us many times over that 27 spline will bite you in the ass when you least need it to. Even if you couldn't predict whether a 27 spline set up would break at the inner or the outer, you still want nothing to do with them breaking at the inner.
My 1st gear is 4.46:1 with 5.13s and 35s and it is as useful on pavement as the OEM 4.46:1 with 4.10s and 30.5s was.
That's not a granny low. A granny low is 6.55:1 or 7.05:1.
During my time with 488/33s, I was routinely taking off in 1st and shifting a bit below 4krpm.
Yep. I went 4.56 specifically for this and it's 2750 at 75mph. 3120 rpm at 85mph. My tires are 285/75R16 with an actual rolling diameter of 32.6". This size is also a pretty common actual diameter with most of the 33s for 15" rims.
The difference is 5th between 4.88s and 4.56s is almost exactly 200rpm. It's not the end of the world either way and that 200 rpm does bring you a bit further up the power curve closer to 3200rpm peak torque and from about 115hp to about 130hp at WOT at 75mph. @jjvw has a very good logic to this. For me I wanted to keep the engine rpm under 3k at 75mph and get 4th gear up the curve at 50mph enough to hold gear on a steep section of I70 - which it did going from 2113 to 2350,
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My three sets of 33s never had an effective rolling diameter that large.
I'll have to force myself to use 1st gear take-offs more and see how I like it in a few days. Currently waiting on some revolution gear oil for post break-in.
If we are thinking of the same section of 70 at the tunnels, I was frequently able to hang on to 53-54mph at the top of the hill with my deeper gearing. And that old combination did better in that spot than what I have going on now.
Indeed we are. On the 4.10s I couldn't ever quite hold 50 in 4th.
I didn't just do the 4.56s though. I also have 1.7 roller rockers, a shorty header, CAI and I've done some tuning on WOT spark and fuel for that altitude in HPT. I'm able to cruise through there at over 65mph in 4th now. I have very little in terms of armor or weight adding mods, and usually run my hard top. If I get held up and have to drop much below 50, I'll usually have to kick down to 3rd for a minute.
I'm not sure what "in a pinch" means to you, but I don't consider a junkyard option terribly convenient if I break a shaft while out on the trail.
The simplest answer is to have spares if you are worried about breaking a shaft or u-joint. None of that refutes the benefits of running stronger 30-spline inners.
Why do you want your cruise RPM so close to peak torque? This is not common practice. Down shifting should be expected for passing or very steep grades.
Because I want a jeep that can start to get out of it's own way. Because some of us have figured out how to build a jeep that does not behave like a Jeep a thing because you don't understand.
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