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[JMT]

Did I say I love my new gears? There is nothing like proper re-gearing for everyday driving enjoyment. It can’t be beat. I can’t say enough about it. I didn’t know what I was missing. You can do all the mods that people can see and try to be happy that way, but you might be underestimating daily driving fun! @AndyG was right. I’m so glad I had a shop do it that is reputable. I passed vehicles while pulling a trailer. It’s crazy

 

[jazngab]

Did I say I love my new gears? There is nothing like proper re-gearing for everyday driving enjoyment. It can’t be beat. I can’t say enough about it. I didn’t know what I was missing. You can do all the mods that people can see and try to be happy that way, but you might be underestimating daily driving fun! @AndyG was right. I’m so glad I had a shop do it that is reputable. I passed vehicles while pulling a trailer. It’s crazy

So funny that you post this now....I dropped off the jeep for regear today and told them 4.10 as I "thought" I had made up my mind. Can't stop thinking if I'm choosing the right gears so of course I research some more and now I think I'm going to tell them 4.56 because it seems like everybody in every jeep forum that had faced the same decision went 4.56 and were so glad they did. So I don't think it'll be too horrible driving at 2800 rpm at 70mph on 31s as I don't do a ton of highway driving (only to get to off road parks) and I'd move up to 32s once these are done (or sell them if I get an itch lol).

 

[JMT]

I’m 2850rpm at 70mph in 6th. It doesn’t bother me. It did a little at first. But not anymore. I love it, on 33’s of course.

 

[jazngab]

I’m 2850rpm at 70mph in 6th. It doesn’t bother me. It did a little at first. But not anymore. I love it, on 33’s of course.

I believe that’s what I would be running at on 31s 70mph 5th gear with 4.56. Trying not to “fear the gear” lol

 

[jjvw]

Bump it up if you think you'll be running 32s. My 70mph is just about 2800rpm and I do this often.

 

[JMT]

@jazngab, 456 all the way

 

[Ron Hall]

Also, looking at the pics the Jeep looks pretty level in the photos with the new wheels. Very pleased with it. Looking at the pics, you guys think I could run 32's or 33 in a 10.5? And if I do that am I going to need to change my gear ratio to avoid it being sluggish?

Here is my Rubicon with 2.5 0ME and 1.25 BL. The KO2 tires are 33x10.5X15 on8 inch rims. My 4.10 axles are just ok with those tires. 4.56 or 4.88 would be better. Sorry about all the tools and clutter in the photo I had just chaged the lift and was checking height.That lift combo really drives great

 

[DrDmoney]

I believe that’s what I would be running at on 31s 70mph 5th gear with 4.56. Trying not to “fear the gear” lol

Don’t be afraid here’s the numbers. 31” tires AX-15 on the left NV3550 on the right (didn’t know which one you have) 4.10 left 4.56 right

 

[jjvw]

Don’t be afraid here’s the numbers. 31” tires AX-15 on the left NV3550 on the right (didn’t know which one you have)View attachment 79544

If you entered 31 as the tire size, then the rpms will be a bit higher in real life. Take an inch off to better reflect reality.

 

[DrDmoney]

If you entered 31 as the tire size, then the rpms will be a bit higher in real life. Take an inch off to better reflect reality.

You definitely need to measure for accuracy

30’s it is

 

[jjvw]

You definitely need to measure for accuracyView attachment 79545

The measurement is the hub height x2.

 

[jazngab]

Yea I’ve been playing with the Grimm calculator. I put NV3550 wide ratio, NP231, 4.56, and both 30 and 30.5 tire diameter. Been getting numbers around 25-2600rpm at 70. I had @Jerry Bransford say that it should run around 2750 at 70. I had @Westtown Willy give me his real world number of 2550 at 70 on 33s 4.56. So my guesstimate is that I would run 2800-2900 real world numbers which I would be fine for me since everyone says it’s ok to run “higher” rpms even tho it’s in the powerband. And it would only be while I had 31s. Thanks all.

 

[Jerry Bransford]

Yea I’ve been playing with the Grimm calculator. I put NV3550 wide ratio, NP231, 4.56, and both 30 and 30.5 tire diameter. Been getting numbers around 25-2600rpm at 70. I had @Jerry Bransford say that it should run around 2750 at 70.

I generally use the Grimm calculator to give rpms to anyone asking for them. So something doesn't sound right that there'd be that much of a discrepancy. That 2700-2750 at 70 is what I saw at 70 mph with my AX-15 and 4.88 gears with 35" tires. I commonly quote those rpms from personal experience.

 

[jjvw]

The biggest discrepancy in comparing rpms is going to come from inconsistent tire sizes. With a large group of people each using different methods, that measurement is going to be a very soft number. I find it to be an interesting problem.

 

[JMT]

The biggest discrepancy in comparing rpms is going to come from inconsistent tire sizes. With a large group of people each using different methods, that measurement is going to be a very soft number. I find it to be an interesting problem.

What's the best way to measure the true diameter of a tire?

I know you can't just measure a tire on the ground under vehicle weight.

I'd think you have to either lift the tire off the ground and measure two or three diameters (less reliable) OR measure the remaining tread depth around the tire, average it and subtract from the original true tire measurement (more reliable).

 

[jjvw]

Hub height x2 = the effective rolling diameter

Or...

Enter your specs into Grimmjeeper and adjust the tire size until it matches a known (and accurate) speed and rpm combination. This should be the most accurate.

An important thing to be aware of is that Grimmjeeper's OD for the nv3550 is not correct. GJ lists .73, whereas Novak, Advance Adapters, others list it as .78. it's a small discrepancy, but it makes a difference in the math.

I have emailed GJ to correct this, but I didn't get a response.

 

[Farmergreg]

You could drive a distance, say three revolutions of the tires and do the math to get back to a loaded radius of the tire.

 

[JMT]

Hub height x2 = the effective rolling diameter

Or...

Enter your specs into Grimmjeeper and adjust the tire size until it matches a known (and accurate) speed and rpm combination. This should be the most accurate.

An important thing to be aware of is that Grimmjeeper's OD for the nv3550 is not correct. GJ lists .73, whereas Novak, Advance Adapters, others list it as .78. it's a small discrepancy, but it makes a difference in the math.

I have emailed GJ to correct this, but I didn't get a response.

Ok, I was successful with changing the tire size until it matched a known speed and rpm. So my 33's are essentially 32.2" currently.

For my knowledge, how do you measure the hub height? The hub is what the wheel turns on, but where am I measuring from? I've tried to find this out there, so apologize if it's a stupid question. Just not apparent to me.

 

[jjvw]

32.2" sounds about right for a 33.

The hub height is just the height of the center of the wheel from the ground. A tape measure and a level will get you close. Be sure to measure a tire that is connected to the speedo sensor.

The GJ method is the same as farmergreg's method.

 

[bobthetj03]

couldn't you measure to the center of the axle tube for hub height?