Grim Jeeper calculator not working

[D M]

The grimjeeper calculator is not working for me properly. Am I missing something? All my entered information is correct, Im trying to see the difference between 33s with 3:73 and 4:56 gears. Here is what I got
NV3550 Wide Ratio
NP231/NV231/NVG231
No Underdrive

It tells me that 2500 rpms in 4th gear is 82 mph. Not true at all, my speedometer is correct and it reads 64 mph in 4th at 2500.
What am I doing wrong?

 

[L J]

What am I doing wrong?

Entering the correct value for your tire size?

I used 31.5 with 3.73s and got 63 mph.

 

[Steel City 06]

The grimjeeper calculator is not working for me properly. Am I missing something? All my entered information is correct, Im trying to see the difference between 33s with 3:73 and 4:56 gears. Here is what I got
NV3550 Wide Ratio
NP231/NV231/NVG231
No Underdrive

It tells me that 2500 rpms in 4th gear is 82 mph. Not true at all, my speedometer is correct and it reads 64 mph in 4th at 2500.
What am I doing wrong?

Are you sure you weren't looking at 5th gear?

 

[jjvw]

Measure the height of the hub and double that number. The easiest way to do this is to put a tape measure next to the axle tube where the tape touches the tube is the center of the hub.

 

[TheBoogieman]

Try to get it to 6,000 rpms in 5th gear (chart) and see what your top speed actually is. My Jeep won't go over 93 mph.

 

[Steel City 06]

Try to get it to 6,000 rpms in 5th gear (chart) and see what your top speed actually is. My Jeep won't go over 93 mph.

TJs have a governor at 150 km/h or 93 mph. The engine will cut out at that speed. Rev limiter is around 5200 anyways. Regardless, the top speed (if the governor is bypassed) of TJs is limited by engine power versus wind resistance rather than gearing.

With a 5 speed, 5.13s, and 35s, theoretically you could get to 130 mph before hitting the rev limiter in top gear. But you would probably need a supercharged stroker to have enough power to get there.

 

[jjvw]

Try to get it to 6,000 rpms in 5th gear (chart) and see what your top speed actually is. ...

Why?

 

[Mr. Bills]

The grimjeeper calculator is not working for me properly. Am I missing something? All my entered information is correct, Im trying to see the difference between 33s with 3:73 and 4:56 gears. Here is what I got
NV3550 Wide Ratio
NP231/NV231/NVG231
No Underdrive

It tells me that 2500 rpms in 4th gear is 82 mph. Not true at all, my speedometer is correct and it reads 64 mph in 4th at 2500.
What am I doing wrong?

Using published tire sizes will lead to incorrect Grimm Jeeper results. Measuring loaded radius (ground to center of hub) and doubling that number to get a value for tire diameter will be closer for gear calculator purposes but still not exact.

See this post for an illustration:

https://wranglertjforum.com/threads/tire-size-measurement-methods.38648/page-5#post-641879

 

[mrblaine]

The grimjeeper calculator is not working for me properly. Am I missing something? All my entered information is correct, Im trying to see the difference between 33s with 3:73 and 4:56 gears. Here is what I got
NV3550 Wide Ratio
NP231/NV231/NVG231
No Underdrive

It tells me that 2500 rpms in 4th gear is 82 mph. Not true at all, my speedometer is correct and it reads 64 mph in 4th at 2500.
What am I doing wrong?

There is only one variable to enter that is subjective. The rest is basic math. We know that the driveshaft turns 3.73 times to turn the ring gear 1 time if you have 3.73 gears, we know that the engine turns over 1 time in Drive to output 1 driveshaft revolution and we know the t-case is 1-1 in 2 or 4hi.

That only leaves one thing to fuck up if you can jot down a MPH at a specific RPM and that's tire size. If what you see on the dash doesn't match the form on GJ, that only means one thing.

 

[pagrey]

This is not a tire size issue. @DylanM345 simply misread the chart. The chart says 66 with the incorrect tire size of 33", big deal that's 2 mph. If the value of 32.5" is entered then it shows 64 which is correct. 2 mph makes little difference when considering gears.

 

[Steel City 06]

With a 5 speed, 5.13s, and 35s, theoretically you could get to 130 mph before hitting the rev limiter in top gear. But you would probably need a supercharged stroker to have enough power to get there.

My wild guess for power requirements might actually work out mathematically for 31s (but maybe not 35s). In this example I will use a 5-speed TJ on 31s and 4.0 gears.

I believe a TJ on 31s could do about 100 mph with the stock engine near the top RPM (close to peak HP). IN this example, 100 mph would be around 4600 RPM in 4th. It would take a long time to get there, for sure. But even a lifted TJ with a stock 4.0 can sustain 90+ without too much issue.

Power requirements due to drag are proportional to the cube of velocity.

So if a TJ can sustain 100 mph using all 190 engine hp, we can estimate the power requirements at 130 mph to be (130/100)^3 times the power requirements at 100 mph. Thus, we would expect to need about 2.2 times as much power, or about 417 hp.

A Golen supercharged stroker does right around 410 hp, which would be very close. So with a 5 speed, 4.10 gears, 31s, and a supercharged 4.6, I suspect a TJ could hit almost 130 mph, at around 4700 in 5th gear.

 

[jjvw]

This is not a tire size issue. @DylanM345 simply misread the chart. The chart says 66 with the incorrect tire size of 33", big deal that's 2 mph. If the value of 32.5" is entered then it shows 64 which is correct. 2 mph makes little difference when considering gears.

Because there is no value in understanding how to use a tool correctly.

 

[pagrey]

Because there is no value in understanding how to use a tool correctly.

It led to several posts that have no value in understanding the original issue, in fact your post suggests tire size was the issue which is false so I guess it has negative value in this case.

 

[D M]

Because there is no value in understanding how to use a tool correctly.

Well, I think I am using it properly, I put my tire size at 32.2 which is what my KM3s are measured out to. 4th gear at 2500 rpms is now 82 instead of 80. Something is definitely wrong here

 

[D M]

It led to several posts that have no value in understanding the original issue, in fact your post suggests tire size was the issue which is false so I guess it has negative value in this case.

Are you experiencing the same thing I am?

 

[JDS123]

With 32.2 and a 5 speed, this is what you should be getting.

4.56

3.73

 

[Steel City 06]

Well, I think I am using it properly, I put my tire size at 32.2 which is what my KM3s are measured out to. 4th gear at 2500 rpms is now 82 instead of 80. Something is definitely wrong here

That makes perfect sense for 5th gear, not 4th

 

[D M]

With 32.2 and a 5 speed, this is what you should be getting...

Nope,

32.2 with 4:56 in 5th gear at 750 rpm on my chart = 23mph
32.2 with 3:73 in 5th gear at 750 rpm on my chart = 31 mph


What the ****

 

[D M]

That makes perfect sense for 5th gear, not 4th

yeah, for some reason thats on 5th gear

 

[Steel City 06]

yeah, for some reason thats on 5th gear

Is column 1 not what you’re getting?

It shows those speeds on 5th gear