Slow top speed

Rob5589 · May 7, 2017

Drew said:
It's a 3.07 dana 30. The lowest gearing for dana 30 is 3.55 correct?

The question is kinda confusing but no, 3.55 is not the lowest gearing. If you are referring to the carrier, yes 3.55 is as low as it can take unless you get a thick gear set. The rear carrier will need to be swapped as well or use a thick gear. A thick gear on the rear will also likely use a special cross pin to allow placing the c clips.

Brantley · May 7, 2017

UpperMI said:
No, you can get Dana 30 gears as low as 5.13 if you want. I have 31's with 3.73 gears and this is a low as I would go for 31's. Since you have a manual tranny I would put 4.10 or 4.56 gears in. If you plan to go up to 33's you should go with 4.88 or 5.13.

5.13 would be way too low for 33's with his 4.0 5-speed. 4.56 is ideal and the only other option I would consider is 4.88 but most people don't want to rev that high, so 4.56 is the best overall recommendation for 33's unless he wants to go to 35's someday.

4.10 is ideal for the 31's he has now, 4.56 will be better for the 33's he's looking to get.

UpperMI · May 7, 2017

Brantley said:
5.13 would be way too low for 33's with his 4.0 5-speed. 4.56 is ideal and the only other option I would consider is 4.88 but most people don't want to rev that high, so 4.56 is the best overall recommendation for 33's unless he wants to go to 35's someday.

4.10 is ideal for the 31's he has now, 4.56 will be better for the 33's he's looking to get.

5.13 gears yield an engine RPM of 2,669 in 5th gear at 70 mph with 33" tires. How is that way too low? My jeep is happiest cruising at 2,500 - 3,000 rpm.

Just as a comparison, 4.56 gears yield 2,373 rpm with the same set up at 70 mph. 4.88 gears yield 2,539 rpm at the same setup.

Brantley · May 7, 2017

UpperMI said:
5.13 gears yield an engine RPM of 2,669 in 5th gear at 70 mph with 33" tires. How is that way too low? My jeep is happiest cruising at 2,500 - 3,000 rpm.

Just as a comparison, 4.56 gears yield 2,373 rpm with the same set up at 70 mph. 4.88 gears yield 2,539 rpm at the same setup.

That would be because you have a 42RLE 4-speed auto with a .69 overdrive. Drew has a 5-speed NV3550 with a .78 overdrive. With 5.13 and 33's, he would be doing 3200-3300 at 75 on the highway. Around 3050 at 70.

UpperMI · May 7, 2017

Brantley said:
That would be because you have a 42RLE 4-speed auto with a .69 overdrive. Drew has a 5-speed NV3550 with a .78 overdrive. With 5.13 and 33's, he would be doing 3200-3300 at 75 on the highway. Around 3050 at 70.

No, I have a 5 speed NV3550. Same transmission as the OP. I use the Grimm Jeepers calculator for the RPM numbers.

Look at the HP and torques curves. Peak torque doesn't even start until you reach 2,800 RPM and runs thru 3,600 RPM. At 2,800 RPM HP is under 130 BHP.

Brantley · May 7, 2017

UpperMI said:
No, I have a 5 speed NV3550. Same transmission as the OP. I use the Grimm Jeepers calculator for the RPM numbers.

View attachment 15598

Look at the HP and torques curves. Peak torque doesn't even start until you reach 2,800 RPM and runs thru 3,600 RPM. At 2,800 RPM HP is under 130 BHP.

Grimmjeeper's number is incorrect for the NV3550's overdrive ratio. It's .78, not .73 as Grimmjeeper shows. There was a variety of NV's installed into other trucks, some of them had .73 overdrives. The Jeep model had .78. That makes a rather large difference in calculated highway rpm. 5.13 would be too low for 33's with the 5-speed.

UpperMI · May 7, 2017

Brantley said:
Grimmjeeper's number is incorrect for the NV3550's overdrive ratio. It's .78, not .73 as Grimmjeeper shows. There was a variety of NV's installed into other trucks, some of them had .73 overdrives. The Jeep model had .78. That makes a rather large difference in calculated highway rpm. 5.13 would be too low for 33's with the 5-speed.

That error explains it.

Mudguard2004 · May 7, 2017

You drive a Jeep. Why on earth would you want to go over 80 mph? Keep in mind you're driving a brick. If you have to swerve in the slightest, you'll be rolling down the highway in the wrong way. Coming from someone that sold their 240z sports car for a TJ, this is a totally different game! Top end is not our deal. Of course, my 240z couldn't handle the rubicon either! Slow and capable is MUCH more fun! JMHO!

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Brantley · May 7, 2017

Mudguard2004 said:
You drive a Jeep. Why on earth would you want to go over 80 mph? Keep in mind you're driving a brick. If you have to swerve in the slightest, you'll be rolling down the highway in the wrong way. Coming from someone that sold their 240z sports car for a TJ, this is a totally different game! Top end is not our deal. Of course, my 240z couldn't handle the rubicon either! Slow and capable is MUCH more fun! JMHO!

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While I agree that he shouldn't be driving 80+ regularly for safety reasons, there's no reason he shouldn't be able to mechanically. I drive 70-75 all day long for Texas speed limits. I could still do it before regearing but the new gears made it much nicer to do. It's a good thing to do, regardless of what top speed is being driven.

Rob5589 · May 7, 2017

Mudguard2004 said:
You drive a Jeep. Why on earth would you want to go over 80 mph? Keep in mind you're driving a brick. If you have to swerve in the slightest, you'll be rolling down the highway in the wrong way. Coming from someone that sold their 240z sports car for a TJ, this is a totally different game! Top end is not our deal. Of course, my 240z couldn't handle the rubicon either! Slow and capable is MUCH more fun! JMHO!

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I wasn't gonna say it but, yea

lovemachine · May 7, 2017

Why drive over 80mph? Well, sometimes it's not safe to drive under the flow of traffic. And sometimes I HAVE to drive 80mph.

I have gotten my jeep at 90mph, and it was perfectly safe.

Brantley · May 7, 2017

lovemachine said:
Why drive over 80mph? Well, sometimes it's not safe to drive with the flow of traffic. And sometimes I HAVE to drive 80mph.

I have gotten my jeep at 90mph, and it was perfectly safe.

Some highways in some areas just love to move fast. Going 20 mph slower than everybody else usually isn't the best way to deal with it.

As far as swerving at 80 on the highway...I've driven a lot of vehicles and I don't think there's a single one of them that would do very well swerving at that fast of a speed. A TJ exaggerates that a little bit with the shorter wheelbase but I don't think there's a single vehicle in existence that's very safe to be making quick changes in direction at such a high speed. Maybe a race car.

Mudguard2004 · May 7, 2017

Don't get me wrong! I'm totally with you guys that want to go faster! I'm from the San Francisco Bay Area (where the minimum speed is over 75 mph) , one step below the Los Angeles area! I love keeping up with the locals! Just saying that we've moved to Jeeps. There is a difference. I've REALLY had to make s change of perception. As a Jeep owner, I can go pretty much anywhere. But on the freeway, I've got to suck it up and let the sports cars (and other -idiots - I was one of them!) pass me by. That's ok! I'd rather climb a mountain than go 80 on the freeway!

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RALLEN71 · May 13, 2021

Best gear ratio for top speed and acceleration in my 05 wrangler tj 4.0. With 35" tires and a 4" lift. Heavy tires will slow you down

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Slow top speed

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