Starting to regret bigger wheels and tires….any words of encouragement ??

[Zandcwhite]

Funny I’m averaging 11.2MPG on my BFG K02s 37 C loads right now in my 392. It’s painful with premium fuel near $5.00 in SoCal but I’m happy and the pedal is still touching that medal on the daily

I would love to get 18-19 highway at least but that’s not going to happen. I accept the compromises of owning a V8 but would be pissed with a 2.0/3.6 getting close to 13-15MPG.

With the 2.0t and 37x12.50 Yokohama x-mt’s on 4” lift, winch, compressor, tools, and recovery gear always in the Jeep we average 17-18mpg. We both drive on the fast side, 80-85 on the freeway. Unfortunately for the V6 guys, it seems their mpg takes a much bigger hit when going to large tires.

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[Jamrock]

Thanks David, that's what I was thinking, but sometimes we need a little confirmation. I'm feeling much better now.

Let us know how it works out. That will help someone who reads the thread in the future.

Remember to post some before and after pictures.

 

[Strommen95]

This statement may perhaps benefit from further clarification.

It's not clear if you meant what you said or did not say what you meant.

In any case here are two scenarios presented for the sake of discussion.

1) If you have 33" tires mounted on the Jeep but have programed the system to calculate for 37" tires the display of mpg will be greater than real life. This is because for every mile the Jeep thinks it travels on the 37" tires it will have actually only traveled approximately 89% of that distance on the 33" tires. So, if your display says the Jeep averages 20mpg you are really getting about 17.8mpg.

2) If you have 37" tires mounted on the Jeep but have programed the system to calculate for 33" tires the display of mpg will be lower than real life. This is because for every mile the Jeep thinks it travels on the 33" tires it will have actually traveled approximately 112% of that distance on the 37" tires. So, if your display says the Jeep averages 15mpg you are really getting about 16.8mpg.

Yes, what I said was intentional. Your scenarios assume the display is not factoring extra weight and resistance of larger tires in the equation. However it does, it does factor extra weight/resistance into the equation (the equation isn't 100% accurate due to difference in tire weights of the same size, tread, PSI, etc.)

 

[Yellow Cake Kid]

...Your scenarios assume...

I am going to guess that you have been referring to the instantaneous or current mpg display rather than the ("trip") average mpg display mentioned in the two scenarios I described.

 

[oldcjguy]

With the 2.0t and 37x12.50 Yokohama x-mt’s on 4” lift, winch, compressor, tools, and recovery gear always in the Jeep we average 17-18mpg. We both drive on the fast side, 80-85 on the freeway. Unfortunately for the V6 guys, it seems their mpg takes a much bigger hit when going to large tires.

LOL! I don't average that with my stock 2.0T steel bumper Rubi. I average around 16-17 keeping it below 75 on the highway, 65/35 city/highway. I guess it really depends on where you live. But I'm not in it for the mileage and I probably have more of a heavy foot too.

 

[Somefun]

Did anyone upgrade brakes or is the stock heavy duty brakes sufficient?

I’m looking at doing that now. I went from the stock Rubicon rims and 33 to Fuel 17/ 12.5 with Nitto trailgraplers and they’re about 40 lbs. more per wheel. You can definitely feel the brakes are not as good. I was looking at installing APB four piston calipers. Problem is the 14” rotor won’t clear the rim so I need to talk with them about their 13.5” but they were at Sema this week. So I’m gonna reach back out next week.

 

[Headbarcode]

I know you agree the ECU is self-learning but to re-iterate when bigger tires are first put on the shifting will definitely be rough. What you were seeing is most likely from the ECU needing to adjust. That's my humble opinion and only explanation. With all due respect, placebo affects just about everybody in some way over their lifetime. I can't say your anecdotal experience is wrong but I can confidently say my mechanical knowledge about transmissions strongly disagrees and my personal experience testing different sizes with my Tazer was different than yours aswell.

Given you didn't have any warning signals or worse issues, like not being able to use cruise control for example, aswell as shifting getting better anyways, I agree, a sensor obviously wasn't the issue. The article brought up those symptoms as a way to diagnose a faulty sensor though. Not as a symptom of wrong tire calibration. While I don't know what calibration means specifically in the context of the transmission sensors, it doesn't say tire calibration and proper tire calibration certainly isn't mentioned as a possible remedy. Tazer themselves have a financial interest in telling us their product will help shift points, so for them to say differently is quite a strong statement in my opinion.

What we read on the display is just math. It's why the speedometer will be off with bigger tires, because its only input is a mathematical equation around the circumference of the tires. Meanwhile the VSS in the transmission reads speed by measuring the rotational speed of gears in the tranny, which is why the ECU knowing your proper gearing and not tire size is incredibly important. In essence, the transmission always knows how fast you're going regardless of what the digital display says. A similar comparison would be gas mileage. If you have 33s on but wrongly calibrated for 37s, gas mileage on the display will be awful. In contrast, if you hand calculate it by dividing your gallons by miles driven, one will see their real gas mileage is much better than what the display said. So it doesn't matter what the display reads, the information given to the ECU is still coming from the transmission itself.

On the day that I picked up my Jeep, it had exactly 6.1 miles on the clock. I distinctly remember thinking "either the JK transmission was horrible or the guys on the forum are smoking some bad stuff" because it wasn't shifting as brilliantly as I had read here. It wasn't long into that 2.5 hour ride home before it straightened up nice and I took back my previous thought. Days later, I received my paper copy of the manual and ocd made sure that I read it cover to cover.

Here's my personal experience, and bear with me, I like analogies. During the beginning of that maiden voyage, the Jeep was acting like me when engaged in too deep of a conversation before having a chance to soak up some caffeine to sharpen my brain. It was off, but not wtf off. Immediately after my tire size increases, it felt like it just got a lobotomy. All the fun of driving it was sapped out. It was quite a bit worse than how it was acting fresh out of the factory.

I actually owned the tazer before the Jeep. My main reasons for buying it was to disable ASS, adjust tpms thresholds, and to open up use of the lockers in all drive modes. I knew it could change tire sizes to straighten out the Speedo, but I was skeptical of having read some other members posts about its affect on the shift points. I'm used to the much older vehicles that I owned most of my life. A quick tweak and a reboot later, and I was floored at how quick and drastic of an improvement it made. My giving it a 90% over 100% improvement is because there'll always be some felt parasitic loss of acceleration and braking performance. Shorter gears would be needed to chase down that last 10% of factory like performance. And I'm not at all talking about mpg here. That goes away and stays there unless the Jeep gets reverted back to stock.

I am very aware of the placebo affect. And yes, it shows its ugly face with everyone from time to time. I occasionally recognize it in the posts I read here. It's one of the markers that stand out to me that help decipher the mechanically experienced members from the usual DIYer's. And I'm not at all knocking the latter, we all come from all walks of life and professional backgrounds.

I was a truck and heavy equipment mechanic in the private sector for far too many years. My father's business and where my childhood to my mid thirties were spent. It was all older equipment that predated the crutch of scanners and laptops that do everything shy of chasing the tools. Putting food on the table hinged entirely on personal observations and systematically going through the process of elimination. I've also seen the insides of many transmissions, but I'm talking about 80's and 90's vintage non synchro triple countershaft units out of Mack's. The most sophisticated they got was if they had a pneumatic solenoid for hi/lo instead of a 2nd stick. Even on the rest of the equipment I worked on, they never included anything more fancy than fly by wire throttle, but still I only saw them for strictly mechanical fixes.

Point of this babble is to simply explain my bred-in ability to separate fact from tricks of the mind. At the same time, I'm limited on the knowledge of the computer side of things. Since you're a transmission guy, the most sophisticated unit I ever opened up was a 4L60e out of my 96 Chevy 1500. It snapped the "star basket" that contains one of the clutch packs on my way home from work in the middle of the night and put it in limp mode. That was some years back, but I remember looking at all those wires and valve bodies thinking of how easy I had it with the simpler (in my mind) fully mechanical units.

I'm genuinely curious about why some of us are getting results on both sides of a fence that shouldn't exist when speaking of one JL to another. I fully admit that I'm probably wrong if my words are being taken as saying that tire size has a direct affect on shift points. That was never my intent. I should specify, that in my personal experience, changing the tire size in the Jeeps system is having a domino affect on immediately improving the transmissions behavior. My Jeep's 2.0/8-speed combo has resisted the need of a shorter set of gears all the way to 38x13.5's, but is now a possibility after swapping to 40x13.5's. Fuel economy is not a high enough priority to limit how my Jeep is being built, but I have noticed that my 19.1 mpg average calculated by hand with 38's has dropped to 16.5 with the 40's. Most of my mileage is stop and go vs highway. About a 90/10 ratio. Time spent in 8th gear has become less frequent as the tires got taller and overall pep at any speed has been surprisingly good, but I've definitely found the line in the sand on this last jump in size. A set of 4.88's may be in my jeeps future, but I may hold out for larger axles.

 

[OllieChristopher]

Since you're a transmission guy, the most sophisticated unit I ever opened up was a 4L60e out of my 96 Chevy 1500. It snapped the "star basket" that contains one of the clutch packs on my way home from work in the middle of the night and put it in limp mode.

I installed a chip in my 94 Silverado that changed the shift points. I believe your Taser is not much different (although much fancier with more features).

The new 8 speed may have a "learning program" built in. However, when you change the tire size and other parameters through your programer it is going to naturally change the shifting just by nature of feeding the ECU new data.

If you were to just install the larger tires and did nothing, then you would have been disappointed with the performance. I recently went from 3:25 to 3:75 gears and TruTrac in my 05 GMC Sierra. It even has the 5 speed manual. First thing the gear shop told me was to get a programmer for it. I got all kinds of error codes and my little shifting light was going crazy. Once I installed the programmer it was like a new truck.

There is not a snowballs chance in hell that 2 identical Wranglers side by side (one with Taser and one without) are going to perform or shift the same with larger tires.

 

[oldcjguy]

I’m looking at doing that now. I went from the stock Rubicon rims and 33 to Fuel 17/ 12.5 with Nitto trailgraplers and they’re about 40 lbs. more per wheel. You can definitely feel the brakes are not as good. I was looking at installing APB four piston calipers. Problem is the 14” rotor won’t clear the rim so I need to talk with them about their 13.5” but they were at Sema this week. So I’m gonna reach back out next week.

Try a better brake pad first. HUGE difference in stopping power with better pads.

 

[JDub11]

This post went slightly off track. If you are not happy with the performance then a regear will help with that. I'd your not happy with the mpg then you should drive slower. On a positive not I bet your jeep looks way more bad ass with those 35s. Gotta pay to play. Now to keep this post off topic. I'm not calling anyone a liar, but I would love to ride with these people claiming crazy milage. They must drive down hill with a tailwind at 55 mph every where they go. I've driven multiple jls and neither the 2.0 or 3.6 showed more then 20mpg on the lie o meter. My wife's grand cherokee is lucky to average 21, and it's not a brick with huge tires. I've also seen the same person on here claim 15 to 17. then diff post 17 to 18. then diff post 21. My point being take othe people's mpg numbers with a grain of salt.

 

[PavementWarrior]

definitely time to slam it to ground, put some low profile tires and get a grumper. Front axle removal will speed it up too

 

[MOPAR Boy]

I recently put on 35’s on my 19’ JLUR 2.0 with no lift, fits amazingly and definitely looks more like a real Jeep now, but when I ran stock, is was a race car especially on the highway.. now it feels like it’s struggling to shift or maintain higher speeds, i know heavier tires would effect speed and mpg’s , but was hoping it still drove closer to normal, I have an appointment to get the speedo recalibrated to the correct tire size at the dealership, hoping that helps… any input or suggestions would be awesome

The new Jeep Wrangler ‘Xtreme Recon’ model comes factory equipped with 35 inch tires, and the Stelantis boys fit it with 456 gearing. I assume you are running 410?

https://media.stellantisnorthamerica.com/newsrelease.do?id=22862&mid=

 

[OldJupiter]

This post went slightly off track. If you are not happy with the performance then a regear will help with that. I'd your not happy with the mpg then you should drive slower. On a positive not I bet your jeep looks way more bad ass with those 35s. Gotta pay to play. Now to keep this post off topic. I'm not calling anyone a liar, but I would love to ride with these people claiming crazy milage. They must drive down hill with a tailwind at 55 mph every where they go. I've driven multiple jls and neither the 2.0 or 3.6 showed more then 20mpg on the lie o meter. My wife's grand cherokee is lucky to average 21, and it's not a brick with huge tires. I've also seen the same person on here claim 15 to 17. then diff post 17 to 18. then diff post 21. My point being take othe people's mpg numbers with a grain of salt.

Hey look at this. Stock Sport Tires Steelies in NYC/NJ/PA of all places.

 

[Strommen95]

However, when you change the tire size and other parameters through your programer it is going to naturally change the shifting just by nature of feeding the ECU new data.

There is not a snowballs chance in hell that 2 identical Wranglers side by side (one with Taser and one without) are going to perform or shift the same with larger tires.

How do you feel about ZF never mentioning tire size being relevant to shift logic? How about Tazer acknowledging their own product does nothing for shift points? It's honestly amusing that so many posters on this forum go against the manufacturers word on their own products.

To repeat myself in nauseam, tire size or circumference has no input on the transmissions shifts. The transmission on its own will respond to the heavier load bigger tires present and inevitably adjust. To be more specific, there's a vacuum modulator that measures the load on the engine every time you drive. The transmission manually reads the load thanks to the vacuum modulator. The input is from the VM and not what tire data the ECU has. The VM is also what tells the transmission to not reach 7th or 8th gear when there's too much of a load to do so safely. Similar to how a bad VSS and wheel sensor will affect shift points, a bad vacuum modulator will affect shifting aswell.

Given I've presented mechanical facts throughout this thread aswell as two reputable sources, I'm going to bow out until somebody presents more than just their opinion. Something that verifies tire calibration is relevant to shift logic.

OP, I should've mentioned sooner there's zero downside to owning a Tazer. Understand I'm a nerd, splitting hairs here and enjoy talking about this stuff. The Tazer does a lot more than just correct your speedometer. It's worth buying.

 

[blnewt]

Try a better brake pad first. HUGE difference in stopping power with better pads.

Hopefully there will be more true performance pads available soon for our JLs, Hawk has a front pad set , haven't seen any rears though, AFAIK that's the only real performance pad that's out there so far. The Powerstops have been out for a while but IMO they're not a real performance pad, a bit more bite than stock but not much more.

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