Tazer JL Mini Tire Size Adjustment + Shift Points/MPG

[IndustrialAction]

I installed my Tazer about a week and a half ago when I moved up to 35s. Specifically Nitto Ridge Grappler 35x12.50x17s (which are actually 34.76" according to the interwebs). Once I got the Tazer installed I adjusted it accordingly.

Since then, my MPG has dropped from 14 to 12 [90%+ of my driving is in-town]. Now I expected that to happen. After-all, my new wheel/tire combo is a lot heavier than stock so I'm not really too concerned about it (though it really does suck to see it so low). I verified the speedo against GPS speed and speed checking apps and they all match so that part is good.

That said, I think the shift points are off. The RPMs hang too high before shifting and I find that I have to let off the gas to get it to shift into higher gears when going 50-60+. I see the RPMs at 3k+ and I know it should be shifting but it seems to stay there too long. I can manually shift it but I am expecting an auto to do it on its own properly.

I'm running a 3.6L auto

Has anyone else found that their shift points are off? If it isn't changing gears properly it would definitely affect performance and MPG. I don't want to continue to play with the size options because the speedo is correct at the 34.76" setting.

I'm running 11.06 right now

Definitely interested in hearing what others are experiencing since using the Tazer for tire size adjustments

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[Rhinebeck01]

@IndustrialAction

How many miles since you installed the 35's and did the speed recalibration.

Regardless of whether you had dealer do the recalibration or did it with a Flash Cal or Tazer JL the results would be the same.

Basically, what I am saying is what you are seeing has nothing to do with the programmer, programmer's firmware version, etc..

With that said listen up to anyone with 35's, regardless of what programmer tool was used...

 

[IndustrialAction]

@Rhinebeck01

I'd say it's been ~150 miles since then. I've seen mention of people 'getting 8th gear back' and such when using a programmer (Tazer often mentioned) to make the proper adjustments so that sparked my inquiry here. The shift points are noticeably different now but my expectations (which admittedly are subject to being incorrect) were that once the programming was done, the Jeep would behave as it did before the tire swap with regards to the engine behavior.

 

[Rhinebeck01]

@IndustrialAction

Again, nothing to do at all with the programmer used for speedo calibrating.

You did say your speedo is now reporting correctly as programmed

You may need to drive more miles for the tranny to re-learn... and have shift points that do the deed better for you.

Often guys that move to 35's and such do not realize that indeed the tires will impact gas mileage and shifting dramatically.

I'm sure guys with 35's. etc. will chime in and tell you what they are seeing.

.

 

[islandtees]

@Rhinebeck01

I'd say it's been ~150 miles since then. I've seen mention of people 'getting 8th gear back' and such when using a programmer (Tazer often mentioned) to make the proper adjustments so that sparked my inquiry here. The shift points are noticeably different now but my expectations (which admittedly are subject to being incorrect) were that once the programming was done, the Jeep would behave as it did before the tire swap with regards to the engine behavior.

Programmers don't get 8th back when going to larger tires. You will have to regear to get it back. I have 37's and get 8th once in a while and I have a Tazer. I will be regearing soon.

 

[butcho]

I get close to 16MPG with 35's after recalibration on a Sport and 95% city driving. This is done via the miles driven and quantity of gas pumped, not by what the dash computer says.

You didn't say how you're calculating your MPG so I would make sure you're using a accurate method since you're now recalibrated correctly. Incidentally, did you pick 35" or 34.76 ?

 

[IndustrialAction]

I get close to 16MPG with 35's after recalibration on a Sport and 95% city driving. This is done via the miles driven and quantity of gas pumped, not by what the dash computer says.

You didn't say how you're calculating your MPG so I would make sure you're using a accurate method since you're now recalibrated correctly. Incidentally, did you pick 35" or 34.76 ?

Just going off dash calculations/display

 

[WranglerMan]

When I got my JLU Sahara I was getting 22 Hwy and 19-20 going back and fourth to work ( All Stock ) saw 8th gear all the time.

Fast forward with some mods, I added a 2.5” lift and 315 KO2’s and at first did not have my Tazer and average MPG’s on the EVIC were all over the road as the JL did not know how to calculate with the bigger tires but 8th gear faded and only saw it on calm non windy days going mostly flat but sometimes up hill then I added the Tazer shortly and set my tire size and did several GPS checks and the MPG’s settled down and after a few tanks of gas I did the math and my average dropped to 18-19 running back and fourth to work so I lost about 2 and 8th gear was still not that frequent even after a few hundred miles

But wait more mods, I then added a steel bumper, winch and that added about 200 lbs more and you guessed it the mileage calculated again dropped and I now get 16-17 so another 2 miles gone and 8th gear is a distant memory and it stays in 7th most of the time and sometimes it does hesitate shifting and the tach revs alittle but not that much and I can only attribute it to a cold engine and all the rolling mass weight I added over stock, I still have a rear bumper to get and figure I will be at about 16 when it’s all said and done but hey it’s a Jeep

I doubt the Tazer has anything to do with the shifting and more than likely it’s the rolling mass of big tires and drag, gotta remember your Jeep did not roll off the line with those big heavy wide tires

 

[jerseymike]

When I got my JLU Sahara I was getting 22 Hwy and 19-20 going back and fourth to work ( All Stock ) saw 8th gear all the time.

Fast forward with some mods, I added a 2.5” lift and 315 KO2’s and at first did not have my Tazer and average MPG’s on the EVIC were all over the road as the JL did not know how to calculate with the bigger tires but 8th gear faded and only saw it on calm non windy days going mostly flat but sometimes up hill then I added the Tazer shortly and set my tire size and did several GPS checks and the MPG’s settled down and after a few tanks of gas I did the math and my average dropped to 18-19 running back and fourth to work so I lost about 2 and 8th gear was still not that frequent even after a few hundred miles

But wait more mods, I then added a steel bumper, winch and that added about 200 lbs more and you guessed it the mileage calculated again dropped and I now get 16-17 so another 2 miles gone and 8th gear is a distant memory and it stays in 7th most of the time and sometimes it does hesitate shifting and the tach revs alittle but not that much and I can only attribute it to a cold engine and all the rolling mass weight I added over stock, I still have a rear bumper to get and figure I will be at about 16 when it’s all said and done but hey it’s a Jeep

I doubt the Tazer has anything to do with the shifting and more than likely it’s the rolling mass of big tires and drag, gotta remember your Jeep did not roll off the line with those big heavy wide tires

what did you set the tire size to? I have 315 KO'2s and not sure to test as measured or what the spec is. I ended up setting with a similar percentage as what it is stock....ie stock KO2s spec at 32.8 but measure 31.5 installed and the tazer when first married to the jeep read 32.520 on the EVIC.

I then calculated: 32.520/32.8 = .9915 which I then multiplied by 34.4 to get 34.106 and set the jeep with tazer as close to that as possible.

speedo is very close (about 1mph faster than actual), trip miles are slightly lower than expected based on google maps

I know that most manufacturers error speedo to faster than actual so figure this is close but could not find in the tazer instructions how to properly set tire size

 

[WranglerMan]

@jerseymike I have my tire size set at 34.49 running Tazer 11.06 firmware and did GPS speed checks with two separate apps ( Speedbox and Waze) and after a few adjustments and settling on the 34.49 I am spot on at 30, 50 & 70 and my hand calculated mileage for the last three tanks has been 16-17 mpg and thats a mix of city and highway driving here in Houston as I work downtown, I am curious as to what it would be on a long highway trip so time will tell but I figure it would be 18-19 at best and if I got that on the highway with the lift, tires winch and bumper I would be totally happy

 

[jerseymike]

@jerseymike I have my tire size set at 34.49 running Tazer 11.06 firmware and did GPS speed checks with two separate apps ( Speedbox and Waze) and after a few adjustments and settling on the 34.49 I am spot on at 30, 50 & 70 and my hand calculated mileage for the last three tanks has been 16-17 mpg and thats a mix of city and highway driving here in Houston as I work downtown, I am curious as to what it would be on a long highway trip so time will tell but I figure it would be 18-19 at best and if I got that on the highway with the lift, tires winch and bumper I would be totally happy

thanks, I'll try that out

 

[WranglerMan]

thanks, I'll try that out

Also keep in mind tire pressure affects it to some degree, my KO2 315’s chalked out at 29-30 lbs

 

[jerseymike]

I upped it to 34.4 and it did seem better on the way home, shifts up a little quicker as expected. GPS up to 50mph is accurate

I keep my tires at around 38psi....was already getting 16-17 mpg, which will probably be a little higher with this new ratio and earlier shifting

 

[LLRubylady]

I just put on 35 ridge grapplers and i thought it was just me but my shifting sees off. I am in a manual rubicon.

 

[Rhinebeck01]

I just put on 35 ridge grapplers and i thought it was just me but my shifting sees off. I am in a manual rubicon.

@LLRubylady

The discussion here regarding automatic transmission, shift points being off, pertains only, to those with automatic transmissions.

Your speedometer will be off, though. You will need to go to the dealer and get your JL programmed in regard to tire size. Once you do this your speedometer will be correct.

SO, do keep in mind that your speedometer is presently not telling you the correct speed you are traveling.

.

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