Jeep Wrangler Tuning and Tire Recalibration Explained

Jeep Wrangler JK’s have a throttle management system often referred to as Drive-By-Wire. Unlike older throttle management which consisted of the gas pedal attached to linkage that directly controlled the throttle body, the throttle body is managed electronically in a Drive-By-Wire system. Under these new systems, when the accelerator is pressed the movement is registered by the ECU (Engine Control Unit). This in turn regulates the actuator motor in the throttle to respond per the demand. The transfer of information produces a delay often referred to as throttle lag.

There are a variety of tuning options available that help address the lag. Systems like the Pedal Commander Throttle Response Controller, provide four distinct modes to take advantage of the electronically controlled system which include:

• Eco: For maximum fuel conservation, this mode reduces the start/stop acceleration to a very slow, gradual increase for optimal fuel consumption
• City: Like Eco, this mode focuses on fuel management, but is better suited for stop and go city traffic
• Sport: This mode decreases the throttle delay for a quicker response and sportier feel. It’s important to note it does influence fuel consumption
• Sport Plus: Maximizes the quickest throttle response available, for a very quick acceleration, but resulting in very poor fuel economy

In addition, each mode has eight different levels of sensitivity for further customization. The controller is designed plug into the throttle position sensor and offer a plug-and-play installation without a permanent modification.

Engine tuners or calibrators adjust the ECU to accommodate a modification so your rig can take full advantage of the new parts. Typically, these low end tuners are used to re-calibrate the speedometer when larger tires are used. This is helpful to display the correct speed you’re going, and also the shift points are corrected so the ride doesn’t seem sluggish. They can also be used for the following additional modifications.

• Reading and clearing check engine codes: This is helpful if you get a check engine light. Reading the code is the first step to diagnosing and solving the problem
• Adjusting the engine idle: This is important if you plan to use a winch, adjusting the engine idle will help with the power demand from a winch under heavy load
• Accessory customization: You can customize accessory options like daytime running lights, head lamp delays, horn chirps etc. Options typically accessible in other Jeep trim levels 
• TPMS: You’ll be able to adjust the Tire Pressure Monitoring System, setting it to zero if you’ve removed the tire sensors and don’t want to see the tire pressure light, or if you would like to set the threshold limit very low because you need to air-down while on the trail 

More advanced tuners can allow you to make further adjustments and display important engine performance data while you’re driving. The intended use will help determine the level of tuner you’ll need.

Another common engine tuning modification is a throttle spacer. This is a thick piece of aluminum you bolt between the throttle body and intake manifold. The additional space creates an increase in air velocity coming from the throttle body into the intake manifold. The spacers are also typically threaded along the inside, and this twists the air rushing into the intake manifold which creates more velocity. 

This ultimately translates into a crisper throttle response on the low end which means from a stopped position the initial acceleration has a quicker response. This is especially helpful for Wranglers utilizing more low-end torque. The spacers typically rob some performance on the top end, but most Wranglers never excel in top-end performance anyway. 

In addition, some throttle body spacer manufacturers claim there is also a slight improvement in gas mileage. Anywhere from 1-2 mpg. These estimates are debatable, especially since the increase in low end throttle response typically translates in a more aggressive start from a stop position which demands more fuel. Nonetheless, this an inexpensive modification with very little drawbacks, and it’s something that can be easily installed/removed if you don’t like the results.

Aftermarket air intakes have always been a debatable modification. These intake systems are designed to increase air volume coming into the intake manifold and shield the air source from the hot engine bay to retain a cold, denser air intake. The theory is great, but most modern engine management systems monitor the air volume and adjust the fuel delivery accordingly which affects the engine’s performance. This adjustment period might take some time which is why there’s an impressive initial reaction when the intake is first installed and then tapers off in time as the ECU re-calibrates itself for the increase in air volume. Air intake systems also claim an increase in fuel economy which is also debatable for the same reasons. 

In addition to the debatable performance, open element air intake systems can introduce a couple of problems. The first is the introduction of water. If you plan on doing any type of water crossing, an open element system has a higher likelihood of taking in water. If water is taken into the intake manifold, it could be catastrophic for the engine since water can’t be compressed. This will lead to bent pistons and significate engine damage. Some aftermarket air intake systems counter this problem with a sealed enclosure. Aside from the danger of water intake, some open elements utilize oils on the filter to help with the filtration of the air. The theory of having larger cell openings in the filter allows for more air to come through, but also dirt. Oil looks to counter that by trapping the dust and dirt. The problem with oil on the air filter is the potential of the oil working itself onto the MAF (Mass Air Flow) sensor. This is a delicate sensor that monitors the air coming into the engine. If it becomes coated with the oil from the filter, it can be easily damaged. 

There are some cases in which an aftermarket air intake system works and is beneficial. The first is if it’s paired with a tuning chip. The tuning program recalibrates the ECU to take advantage of the increased air volume to produce more horsepower and better fuel economy. Typically, these uses are more beneficial on paved roads/highways. If you plan on driving mostly on paved roads and higher speeds, this combination might be useful and something to consider.

When you upgrade the size of the tire, you also increase the overall circumference of the wheel. That means the wheel will travel less rotations to cover the same distance as the smaller tire. Therefore, both your speedometer and tachometer will be incorrect and need to be recalibrated. If you don’t recalibrate your Jeep to take into account the increase in tire size, then the shifting points will be incorrect and result in sluggish performance. In addition, your speed will be inaccurate and could cause miscalculations while on the road, running the risk of a speeding ticket.

In order to properly recalibrate your Jeep after upgrading the tire size, you need to measure the tire. Most manufacturers don’t have an accurate interpretation of what the Jeep community has labeled as a 33”, 35” etc. tire. Often tire measurements fall in between those sizing guides, and it’s critical to get an accurate measurement. In order to start, the tire should be inflated to your desired running PSI. Once you’ve determined that and properly inflated the tire, measure the height of the tire from the ground. You’ll find the size isn’t exactly the projected 35” for example. It will most likely be 34.5” or even less. This is the number you’ll need to plug into the calibration program.

As mentioned previously, you’ll need a reprogramming tool like the SUPERCHIPS flashpaq. This tool will connect to your Jeep’s OBII port and allow you to enter the tire’s new size in order to recalibrate the speedometer and tachometer. The Flashpaq can accommodate tires up to 42”, so the system is very versatile and easy to work with. The color touch display is intuitive and will walk you through the process. Once complete, your Jeep will have the correct tire dimension needed to calculate the rotations and properly display the correct speed in addition to correcting the shifting points for optimal performance.