RPM Too High???
JK Junkie
Joined: Jan 2008
Posts: 2,232
Likes: 0
From: SoCal
why don't you agree with the gear calculators? this one agrees with your numbers exactly:
http://www.4lo.com/calc/gearratio.htm
plug in 35's, 5.13's, 2500rpm, transmission ratio .69 (OD), transfer case ratio 1, and you get 73.6mph.
i am guessing the OP has a 6-speed (.84 OD).
comparing an auto to 6-speed is really apples to oranges, especially when talking highway speeds (OD ratios are so different).
http://www.4lo.com/calc/gearratio.htm
plug in 35's, 5.13's, 2500rpm, transmission ratio .69 (OD), transfer case ratio 1, and you get 73.6mph.
i am guessing the OP has a 6-speed (.84 OD).
comparing an auto to 6-speed is really apples to oranges, especially when talking highway speeds (OD ratios are so different).
Thread Starter
JK Newbie
Joined: Dec 2006
Posts: 9
Likes: 0
From: Jacksonville, FL
Sorry it took me a while to post a reply to answer some of the questions. I sent the original topic while driving in hopes that I would have input waiting on me when I got home. You all are the best...thanks!!!
OK here we go.
I have a 6-speed
Speedometer is not fixed after the bigger tires, but I am using a GPS to monitor speed. This has also been checked at several traffic control radars and it is working correctly.
2850 is the RPM for 70 MPH
3000 is the RPM for 73 MPH
To the reply about my research: I tried my best and have been sitting on the edge of my seat for over a year trying to decide on which package to go with. I have seen numerous posts about 4.10 gears being a dog with 35's and I have seen posts saying that it is okay with 4.10's. I also looked at the various gear charts and tried my best to figure something out.
My only real concern right now is that this increased RPM is going to cause excessive wear and tear on my vehicle. It is a DD, so I have reason to be concerned. I will say this- It is sooooo much friggin fun with the 4.88's in the city and on the trail. I would think that 4.10's would be a little bit more of a pain....but indeed livable. 4.10's would probably work out better if I had a 2 door.....but I think the added weight of a 4 door would be too much.
If the general consensus is that I am worried for nothing...thank you. Really thank you! I have had the Jeep for about a year and a half and it is a ton more fun now than I ever imagined
OK here we go.
I have a 6-speed
Speedometer is not fixed after the bigger tires, but I am using a GPS to monitor speed. This has also been checked at several traffic control radars and it is working correctly.
2850 is the RPM for 70 MPH
3000 is the RPM for 73 MPH
To the reply about my research: I tried my best and have been sitting on the edge of my seat for over a year trying to decide on which package to go with. I have seen numerous posts about 4.10 gears being a dog with 35's and I have seen posts saying that it is okay with 4.10's. I also looked at the various gear charts and tried my best to figure something out.
My only real concern right now is that this increased RPM is going to cause excessive wear and tear on my vehicle. It is a DD, so I have reason to be concerned. I will say this- It is sooooo much friggin fun with the 4.88's in the city and on the trail. I would think that 4.10's would be a little bit more of a pain....but indeed livable. 4.10's would probably work out better if I had a 2 door.....but I think the added weight of a 4 door would be too much.
If the general consensus is that I am worried for nothing...thank you. Really thank you! I have had the Jeep for about a year and a half and it is a ton more fun now than I ever imagined
JK Enthusiast
Joined: Jan 2008
Posts: 416
Likes: 0
Sorry it took me a while to post a reply to answer some of the questions. I sent the original topic while driving in hopes that I would have input waiting on me when I got home. You all are the best...thanks!!!
OK here we go.
I have a 6-speed
Speedometer is not fixed after the bigger tires, but I am using a GPS to monitor speed. This has also been checked at several traffic control radars and it is working correctly.
2850 is the RPM for 70 MPH
3000 is the RPM for 73 MPH
To the reply about my research: I tried my best and have been sitting on the edge of my seat for over a year trying to decide on which package to go with. I have seen numerous posts about 4.10 gears being a dog with 35's and I have seen posts saying that it is okay with 4.10's. I also looked at the various gear charts and tried my best to figure something out.
My only real concern right now is that this increased RPM is going to cause excessive wear and tear on my vehicle. It is a DD, so I have reason to be concerned. I will say this- It is sooooo much friggin fun with the 4.88's in the city and on the trail. I would think that 4.10's would be a little bit more of a pain....but indeed livable. 4.10's would probably work out better if I had a 2 door.....but I think the added weight of a 4 door would be too much.
If the general consensus is that I am worried for nothing...thank you. Really thank you! I have had the Jeep for about a year and a half and it is a ton more fun now than I ever imagined
OK here we go.
I have a 6-speed
Speedometer is not fixed after the bigger tires, but I am using a GPS to monitor speed. This has also been checked at several traffic control radars and it is working correctly.
2850 is the RPM for 70 MPH
3000 is the RPM for 73 MPH
To the reply about my research: I tried my best and have been sitting on the edge of my seat for over a year trying to decide on which package to go with. I have seen numerous posts about 4.10 gears being a dog with 35's and I have seen posts saying that it is okay with 4.10's. I also looked at the various gear charts and tried my best to figure something out.
My only real concern right now is that this increased RPM is going to cause excessive wear and tear on my vehicle. It is a DD, so I have reason to be concerned. I will say this- It is sooooo much friggin fun with the 4.88's in the city and on the trail. I would think that 4.10's would be a little bit more of a pain....but indeed livable. 4.10's would probably work out better if I had a 2 door.....but I think the added weight of a 4 door would be too much.
If the general consensus is that I am worried for nothing...thank you. Really thank you! I have had the Jeep for about a year and a half and it is a ton more fun now than I ever imagined
Hey man,
That sounds about right...I have a 2 dr stick with 5.13's running on 35's (technically 34.2's, measured at 33.75's) and I'm running at 2750rpm at 65mph...it's a lot of gear for the tires I have on there right now (in fact almost every single car goes around me when taking off from a light), but I was thinking of the future 37's when I got mine regeared.
I also had this question in mind too, because feeling the stick while driving, 2500 rpm seems to be the point where the engine really starts kicking, as I can feel much more vibration coming from it over that engine speed. I found a shorter route to work and now run no faster than 55mph for better economy and lower engine speeds.
Colin
I'm gonna be running them on 33"s with an auto for a while so it should be pretty interesting.
JK Jedi
Joined: Nov 2006
Posts: 5,831
Likes: 2
From: SoCal, USA
Here's a good thread that should ease your fears about your 4.88's
https://www.jk-forum.com/forums/modified-jk-tech-2/4-88s-5-13s-auto-24446/
https://www.jk-forum.com/forums/modified-jk-tech-2/4-88s-5-13s-auto-24446/
JK Freak
Joined: Aug 2007
Posts: 665
Likes: 0
From: (714)
These high reving 6 bangers are fine at 3K for extended periods...in fact....you truely can run quite some time right up to the redline and be fine...if they weren't the redline would be below 3K RPM...the only thing that will suffer is your fuel mileage 
