Highway speeds and RPM’s

[tmd07]

I have a ‘98 4.0 32RH with 4.10 gears. This Jeep went through a frame swap and I swapped in the 4.0 and 32RH. The Jeep is originally an SE and had the 2.5 and AX5. I decided to keep the 4.10 axles/gears on there thinking this would be the best option. I’m currently running 31” tires. I’ve gone on the highway a few times and my RPM’s seem to be very high. I have confirmed the transmission is shifting through all gears and the torque converter is locking up after 3rd gear. When I get up 65mph I’m at 32~3300 rpm’s. Does this seems right for my setup? My speedometer is off by like 3mph after I put in what I thought was the correct Speedo gear but that’s a different situation (I went off those charts and it’s not the correct gear). I have also double checked that I actually have 4.10’s as well. Will going to a 3.73 help much? Not saying I want a highway Jeep but I would like it to be lower Rpm’s for temp reasons and helping the fuel efficiency any way I can.

 

[jjvw]

Regear to get closer to 3k rpm at 75mph..
32rh/30.5”/3.73=3082rpm @ 75mph
32rh/30.5”/4.10=3388rpm @ 75mph

Or keep the gears and change to a 35" tire...
32rh/34"/4.10=3039rpm @ 75mph

Pick your poison.

 

[CharlesHS]

As JJVW posted above; 4.10 at 3039 rpm at 75 mph with 35" tires; sounds like a good idea.
Sell the 31" tires and recoup several hundred $$ towards paying off the $1500 plus for the 35" tires.

 

[macleanflood]

If it was only $1500.

Thread 'So you want to run 35" tires on your TJ?'

Oct 19, 2016

I felt this thread was necessary at this point. We see a lot of people on the forum who insist on running 35" tires, but probably don't know how to do it properly, or what's required (other than just the tires and lift).

For anyone considering adding 35" tires to their TJ, first take into consideration that this is no small feat. You're going to need at minimum several thousand dollars set aside. Sure, there's ways to do it on the cheap, but if you plan on off-roading your TJ at all, you'll want to do it right.

I'm going to give you a run down of what you'll need to properly run 35"...

• Chris
• Replies: 177
• Forum: TJ Resources

• 

-Mac