Just Went to 33s / Do I Go to 4.30 or 4.56 ?

[Heavy D]

If you’re running 33s only I would swap the 3.73s for some 3.45s. You know, personal preference and all.

Completely agree with "personal preference"
However you are the 1st person in the history of man that has ever said My Jeep needs a taller gear ?

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[Camaroboi13]

Completely agree with "personal preference"
However you are the 1st person in the history of man that has ever said My Jeep needs a taller gear ?

Works just fine in my wife’s Wrangler on 35s ?‍

Honestly in my opinion a 33” tire is not even a tire change. That’s what, 3.8%? Not even enough to change the speedo. This is coming from a guy on 37s with 3.73s and loving it. Your mileage may vary.

 

[JTGuy]

I went 37s and 4.88s and it's the best thing I ever did. If I was ever going back to 35s I would not change the gears.

 

[Jakef7]

Now that’s what I’m talking about! Big thanks!!! Of course I’m running the slightly shorter tire, so I’ll be running a little bit higher, but that’s not bad at all.

I’ve been going by this chart I found online. You have 4.56’s with a 33 inch tire and you’re running 2150 RPMs at 70mph. According to this chart, you should be running at 2698 RPM, unless this chart is calculating everything for 7th gear and not 8th because it is considered “overdrive”. Anybody out there familiar with this chart?

 

[ShadowsPapa]

I’ve been going by this chart I found online. You have 4.56’s with a 33 inch tire and you’re running 2150 RPMs at 70mph. According to this chart, you should be running at 2698 RPM, unless this chart is calculating everything for 7th gear and not 8th because it is considered “overdrive”. Anybody out there familiar with this chart?

Gotta be an old chart - there's too many of that sort floating around.
No way I am running over 2200 at 70 mph

 

[bleda2002]

I’ve been going by this chart I found online. You have 4.56’s with a 33 inch tire and you’re running 2150 RPMs at 70mph. According to this chart, you should be running at 2698 RPM, unless this chart is calculating everything for 7th gear and not 8th because it is considered “overdrive”. Anybody out there familiar with this chart?

Please stop posting this chart. Its for the JK with 6 speed auto, not the JL/JT with 8 speed auto so its completely wrong and provides false info.

 

[Jakef7]

Please stop posting this chart. Its for the JK with 6 speed auto, not the JL/JT with 8 speed auto so its completely wrong and provides false info.

Thank you for clarifying the chart. Please understand that I wasn’t trying to provide false info. I only posted it hoping someone would be familiar with it because I wasn’t sure what platform it was for or where the calculations came from.

 

[JTGuy]

With the 8 speed the chart is closer to 80MPH speed in 8th.

 

[Zachanadandy]

I can say that getting into, and holding, 8th gear is no longer an issue. The tranny now runs right through the gears up to 8th and holds it there unless you get heavy on throttle.

I don't know where anyone got the impression that this is how an 8 speed should behave? It's a double overdrive with 7th being equivalent to the top gear in most transmissions. That's why a stock JL has 32s paired with 3.45s. It's not supposed to hold 8th under load. Be it a hill or a headwind it should be in 7th. Why gear it so low that it's in 8th at any speed over 40mph? It runs through the gears alright, and is out of shifts by the time it reached half of freeway speed? 3.45 and 32s is equal to 4.10s and 37s. Even the JTs standard 3.73 and 32" combo is equal to 4.10s and 35s. Sure if you never drive over 65mph you aren't losing much by running super deep gears thanks to the double overdrive, but most road trips have the cruise set at 85mph in our Jeeps so I'll keep my gearing on the taller side like it is from the factory.

 

[ShadowsPapa]

I don't know where anyone got the impression that this is how an 8 speed should behave? It's a double overdrive with 7th being equivalent to the top gear in most transmissions. That's why a stock JL has 32s paired with 3.45s. It's not supposed to hold 8th under load. Be it a hill or a headwind it should be in 7th. Why gear it so low that it's in 8th at any speed over 40mph? It runs through the gears alright, and is out of shifts by the time it reached half of freeway speed? 3.45 and 32s is equal to 4.10s and 37s. Even the JTs standard 3.73 and 32" combo is equal to 4.10s and 35s. Sure if you never drive over 65mph you aren't losing much by running super deep gears thanks to the double overdrive, but most road trips have the cruise set at 85mph in our Jeeps so I'll keep my gearing on the taller side like it is from the factory.

Someone finally said it.
The first 6 are non-overdrive with 6th being 1:1 ratio or equivalent to direct drive.
BOTH 7th and 8th are OVERdrive gears.

8th is the cherry on top of the whipped cream on that sundae.
These are not meant to stay in 8th.
8th is more for non-windy, fairly flat terrain where not a lot of torque is required.
When you get either fast enough for the wind resistance/drag to be an issue, it's going to dro out of 8th, same for a hill or towing.
You frankly shouldn't think at all about seeing 8th when towing, or even driving 80+ (due to drag/wind/air)

There's an obsession with staying in 8th - maybe "because it's there" but that's all wrong.

I have a T5 in my SX4 - 5th of course as most Jeep people know is the OD gear, 4th is "high" or 1:1, or direct drive.
I can use 5th cruising on the highway, fairly flat, not a lot of wind, and moderate highway speeds. But get going fast or in hills and I need to drop to 4th to maintain speed.
I never use 5th when using cruise control in that car.

Back to - there's a reason Ford and Chevy pretty much said "no overdrive" when you hit tow mode.

 

[Zachanadandy]

Someone finally said it.
The first 6 are non-overdrive with 6th being 1:1 ratio or equivalent to direct drive.
BOTH 7th and 8th are OVERdrive gears.

8th is the cherry on top of the whipped cream on that sundae.
These are not meant to stay in 8th.
8th is more for non-windy, fairly flat terrain where not a lot of torque is required.
When you get either fast enough for the wind resistance/drag to be an issue, it's going to dro out of 8th, same for a hill or towing.
You frankly shouldn't think at all about seeing 8th when towing, or even driving 80+ (due to drag/wind/air)

There's an obsession with staying in 8th - maybe "because it's there" but that's all wrong.

I have a T5 in my SX4 - 5th of course as most Jeep people know is the OD gear, 4th is "high" or 1:1, or direct drive.
I can use 5th cruising on the highway, fairly flat, not a lot of wind, and moderate highway speeds. But get going fast or in hills and I need to drop to 4th to maintain speed.
I never use 5th when using cruise control in that car.

Back to - there's a reason Ford and Chevy pretty much said "no overdrive" when you hit tow mode.

And the beauty is under low loads like tail winds or down hill stretches of freeway you still see 8th at 80+. My JTM will cruise at 83mph and 2k rpms in 8th half way across the desert thanks to the typical tail wind heading east...on 37s with the stock 4.10s.

 

[Heavy D]

I wanted my engine and drivetrain to rev in the ranges it did when it was OEM.
The 4.56s may be a tad deep for 33s but should be dead-on with 35s (which are my next move).
I do know my Jeep is much more enjoyable to drive with the new set-up and my fuel mileage has improved considerably.

I also have a guy that lives down the road from me that does not wave back when I go by his house so I'm doing donuts in front of his place as soon as new gears are broken in... These donuts would not be doable with the factory gearing.

 

[Zachanadandy]

I wanted my engine and drivetrain to rev in the ranges it did when it was OEM.

3.73s and 32s is equivalent to 33s and 3.85s, 4.56s aren't even close to the same revs as stock. It won't be dead on with 35s either. That would be 4.07s. The math is simple. 4.10s would match 35s to the stock revs. I felt the revs were too high in the wife's stock xr with 4.56s and 35s, no interest in 33s and 4.56s personally.

 

[LouisvEarlleJT]

4.56s with 33’s is going to tank your mileage and have your motor screaming down the road. Though, yes, you will “take off” quicker when you start moving.

What keeps your revs “in the OEM range” is the proper shift points in the transmission.

 

[Jakef7]

4.56s with 33’s is going to tank your mileage and have your motor screaming down the road. Though, yes, you will “take off” quicker when you start moving.

What keeps your revs “in the OEM range” is the proper shift points in the transmission.

This is not true. Heavy D has this exact setup and his motor isn’t screaming down the road. And he has stated that his mileage has actually improved.

I know a few above have stated that 8th isn’t really supposed to be used etc.. However, by re-gearing with lower gears, it will make 8th a lot more usable. With 3.73, my truck stays in 7th a lot on the highway and rarely falls into 8th. However, by doing a 4.56 it will now use 8th and be running close to the RPM that it was running with the 3.73 in 7th.

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