Rubicon Stock Speedometer Tire Size

97' 4 Popper

97' 4 Popper

Opened a Can of Worms
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I need new tires and realized that the Rubicon speedo can't be calibrated with a new gear tooth. I am aware of yellowbox and speedohealer. That being said I have read conflicting posts on here, some say 245 is most accurate to speedo, others say 265 or a 33. Anyone have first hand experience with this? Lets say I wanted to choose a tire size in relation to the speedo. I can't get 245 in load C so I am either going to 265s or storing the moabs away and doing a 31/10.5/15.
 
What tire size do you have now? Use GPS and determine how much it's off and go from there? Typically, most vehicles from the factory read fast on the speedo by about 2 mph at highway speed. I can't confirm the Rubicon specifically reads fast on the stock 245/75/16s, but if it were like most vehicles, it would. I have seen a few say it's more accurate with 33/s or 265s, but really the best bet is to just do the testing yourself with GPS.

Stock 245/75 will read about the same as a set of 31x10.5s. 265/70s would read the same as well, and 265/75s would slow the speedo down a bit. I don't see how 33's would be accurate, that would put the stock tires off by 5 or so mph at highway speed from the factory and that doesn't seem correct. That would be roughly 8% off on the factory 30.5" Rubi tires.
 
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JKP said:
It's dead on with the stock 245s.
Click to expand...

This is what I assumed but I never bothered to test it and have read conflicting posts.

machoheadgames said:
What tire size do you have now? Use GPS and determine how much it's off and go from there? Typically, most vehicles from the factory read fast on the speedo by about 2 mph at highway speed. I can't confirm the Rubicon specifically reads fast on the stock 245/75/16s, but if it were like most vehicles, it would. I have seen a few say it's more accurate with 33/s or 265s, but really the best bet is to just do the testing yourself with GPS.

Stock 245/75 will read about the same as a set of 31x10.5s. 265/70s would read the same as well, and 265/75s would slow the speedo down a bit. I don't see how 33's would be accurate, that would put the stock tires off by 5 or so mph at highway speed from the factory and that doesn't seem correct. That would be roughly 8% off on the factory 30.5" Rubi tires.
Click to expand...

245/75/16 is my current size. I'm so anal about wanting to maintain the originality of the LJ that I'm having a hard time with this. 245s aren't available in load c, 31s are the next best option but would result in me having to store the Moabs away. When I measured my TJ’s 31s next to 245s they are both 29 inches at the same psi. Another option is getting a 15 inch look alike Moab. I even considered that in my desperation.

Once the weather gets better and I can go back to working on the jeeps I will buy my tires and will do three tests with a GPS app

Speed difference between gps and speedo at 65 mph
~control test with 31/10.5/15 with the correct 33 speedo tooth on regular TJ
~with 245s on Rubicon
~with 265s on Rubicon


Depending on how much the difference is I will think about getting a speedohealer.
 
I bought a speedo healer for my Rubicon when I first got it but found that the 265s were almost dead on (32”ish) on stock gears so I didn’t bother to install it until I regeared.
 
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Jamison C said:
I bought a speedo healer for my Rubicon when I first got it but found that the 265s were almost dead on (32”ish) on stock gears so I didn’t bother to install it until I regeared.
Click to expand...

Well that's definitely reassuring. I was already frustrated with not being able to get 245s, so if I can circumvent the speedo issue that would be nice.
 
97' 4 Popper said:
This is what I assumed but I never bothered to test it and have read conflicting posts.



245/75/16 is my current size. I'm so anal about wanting to maintain the originality of the LJ that I'm having a hard time with this. 245s aren't available in load c, 31s are the next best option but would result in me having to store the Moabs away. When I measured my TJ’s 31s next to 245s they are both 29 inches at the same psi. Another option is getting a 15 inch look alike Moab. I even considered that in my desperation.

Once the weather gets better and I can go back to working on the jeeps I will buy my tires and will do three tests with a GPS app

Speed difference between gps and speedo at 65 mph
~control test with 31/10.5/15 with the correct 33 speedo tooth on regular TJ
~with 245s on Rubicon
~with 265s on Rubicon


Depending on how much the difference is I will think about getting a speedohealer.
Click to expand...

You won't be doing too much crazy wheeling on 245's I don't think....if you want to maintain originality, I'd just get a set of SL 245/75s.

Yes, 31 and 245/75 are essentially the same size. I'm pretty certain the 265s will be the one spot on. I would really not worry about it this much though. 265 and 245 are so close, neither makes any real difference other than reading a mile or two off.
 
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97' 4 Popper said:
Well that's definitely reassuring. I was already frustrated with not being able to get 245s, so if I can circumvent the speedo issue that would be nice.
Click to expand...

I hadn't realized GoodYear had discontinued the DuraTrac in a load range C 245/76-16, but it looks like they have. You could always go with a P-rated all-terrain such as a Yokohama Geolander AT G015, Toyo Open Country AT III, or Bridgestone Dueler AT Revo 3, if you're comfortable running a P-rated tire.
 
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Mine wasn't close to accurate until I put on 33s. Internet lore says the early '03s were calibrated for a larger tire size that never made to production, but Jeep didn't correct the speedometer until later.
 
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machoheadgames said:
You won't be doing too much crazy wheeling on 245's I don't think....if you want to maintain originality, I'd just get a set of SL 245/75s.

Yes, 31 and 245/75 are essentially the same size. I'm pretty certain the 265s will be the one spot on. I would really not worry about it this much though. 265 and 245 are so close, neither makes any real difference other than reading a mile or two off.
Click to expand...

Lol I don't do any wheeling period unfortunately, here in New York there are very few trails and they are too easy for a Jeep, I take my bike instead. :cry: In a few years though hopefully I will be able to travel out west.

I'm looking around now for a SL, but I believe the load C would be better suited.

deadbeat son said:
I hadn't realized GoodYear had discontinued the DuraTrac in a load range C 245/76-16, but it looks like they have. You could always go with a P-rated all-terrain such as a Yokohama Geolander AT G015, Toyo Open Country AT III, or Bridgestone Dueler AT Revo 3, if you're comfortable running a P-rated tire.
Click to expand...

I would probably avoid a p rated tire to be honest.
 
I read reports on various forums back in the day that suggested '03 and '04 Rubicons read a little high, and my own experience agreed. My '03 was about 4% high from the factory, or about 3 mph high at 70. That moved to about 5% or 6% as the tires wore, about 4 mph high at 70. (I got 60k out of the original MTRs)

It became much closer when I moved to 32s, with no other correction.

I'm pretty sure I have read that the '05 and '06 Rubicons had more accurate speedometers from the factory.
 
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245/75/16 is close to 265/70/16.
265/75/16 is an inch taller.

There is some calibration that can be done to the speedo.
I had a neighbor that was a Mopar tech.
He tried to adjust mine ('06), but 33s were out of it's adjustable range.
 
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SSTJ said:
I'm late to this thread, but I found one Load Range C in 245/75/16, and several SLs in that size.

Table is here. (Scroll down a bit.)
Click to expand...

The tire on the chart says not available when you click on the link. Anyways it looks like I'm going with 265/75/16 Cooper discoverers.

In case anyone is interested according to a GPS app I used the Rubicon with 245s shows up as running 1-2 mph slower. Tj with 31s, 3.73 and correct speedo tooth according to all the charts, 1-2 mph slow as well.

I got a decent quote on tires and balancing I just need to figure out what track bar im going with up front I'm leaning towards JKS. Not looking forward to drilling out the mounts.
 
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LONGJP2 said:
There is some calibration that can be done to the speedo...33s were out of it's adjustable range.
Click to expand...

I just posted a thread on how to calibrate the speedometer on TJs with the NGC PCM (2005-2006) with the DRBIII:

https://wranglertjforum.com/threads...-the-ngc-pcm-2005-and-2006-model-years.69512/
Both 33" and 35" tires are in the settings:

10-jpg.412429


However, gearing stops with 4.56:

11-jpg.jpg
 
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