At the start of 2025, we met to talk about the setup window on the B7. After a year of running the car, we still hadn't figured out a baseline setup for carpet and felt like something was missing. We decided to stop guessing and measure the car. First, we took one of our 2023 B6.4 models and measured the roll centers, then did the same for the B7. We fed that data into our CAD software so we could intersect lines and analyze the results, which is when we began modifying the B7's geometry.

The big difference between the B7 and other brands comes from its narrow pivot and long arms. This setup raises the roll centers. In my opinion, this is what narrows the tuning window on the B7. Like everything, tuning the roll center is a give and take. Generally, a higher roll center makes the suspension stiffer. Any time you had stiffness or bind, you add potential for mechanical grip. On some carpet tracks, this is where we have an issue. A high rear roll center tends to "jack" the chassis and plant the outside tire in a corner. It also moves the "instant center," the car's leverage point for rolling, much closer to the chassis compared to the B6.2, shortening the lever. That makes the roll quicker but harder to control. It's like using pry bars to lift a heavy rock: a short bar moves it fast but without much control, while a long bar lifts it more smoothly and with more confidence controlling that movement.

Why does the rear roll center matter? The rear roll center is arguably the most important part of the suspension setup. As a racer, you need to decide when you need more off power grip and when you need more on power grip. This is much easier said than done. I have a saying that I have been coaching for years, "slow in equals fast out". I would argue that the most important part of the corner is the exit.

On carpet, sometimes you get full traction, where the outside tire grips, the suspension reacts quickly, and the chassis jacks up, lifting the inside rear tire. On a fast 180-style track, this can actually help by promoting rotation, but on a smooth, flowing track where you need to drive through the corner, it can be a real disadvantage. We've found that in almost every corner except a "dot 180," the car jacks on entry and gets loose. To find grip, we pull the throttle, but then the car goes straight and won't turn. To get steering back, you lift the throttle and repeat the cycle, turning an easy corner into a frustrating connect-the-dots exercise. It's slow, and worse, it kills your confidence. Generally, this is when you need more off power grip and less on power grip.

A lower rear roll center will allow you to control the roll with more confidence. That roll is what loads the outside tire and makes grip. You could say you are controlling traction. This is when drivers are using the throttle and the wheel to steer the car. A lower rear roll center will jack the chassis down. This can have the feeling of "in the track". The chassis jacking down takes the roll centers and the CG with it. In my opinion, you want the chassis as close to the surface as you can be without scrubbing speed from the chassis contacting the surface.

The B7 geometry can excel on tight tracks with a bunch of 180, and fast lap times. the B7 geometry works. The car jacks the chassis and makes the inside tire light which promotes rotation. This design works great on slicks, where side bite comes only from the contact patch. Getting the right tire load and contact patch is crucial for slick racing. However, it's less ideal when the tire generates side bite, like on carpet.

This is why the setup window has become smaller on the B7. There are other aspects to the equation, but I believe this is the most important. To find your setup quicker, I would ask a couple of questions. Does the car need more grip early in the corner or late? If the car needs grip early. Lower the rear roll center. You need more downward angle on the lower link from the outer hinge pin to the inner hinge pin. You can achieve this by lowering the pills or lowering the rear hub. Both of these changes will have an effect on down-travel so keep that in mind. The most aggressive way of lowing the rear roll center would be using a wider hanger and a shorter A-Arm.

Kingpin Inclination (KPI)

KPI is another important update in the B7 design. Like caster, it improves straight-line stability by keeping the front wheels pointed forward. Its self-centering ability is notable, and sometimes it's better for the car to exit corners driving more "square". This can be an issue if you need the car to drive more "round" on throttle. KPI can also affect scrub radius, but here the focus is on how it impacts the rear.

When combined with caster, KPI pushes the inside front tire down, adding to its load. This creates a "wedge" in the chassis that also puts extra load on the outside rear tire. This wedge can add to the "jacking" of the chassis. While this might seem like an advantage, it's not always the case. In a fast, sweeping corner, extra load on the outside rear tire usually means more grip. So, the real question is: do you need more grip off-throttle or on-power?

"Square" = More grip on throttle-Car goes straight

"Round" = Less on throttle grip-Easier to turn on throttle

Our RC cars use an open differential, which directs power to the tire with the least load. This can lead to "diffing out" when the inside tire has less load but gets all the power, reducing the car's forward speed. It can also make the car feel like it's about to spin out or steer into the pipe. This is where the jacking of the chassis can be troublesome on some circuits.

As a result, many racers have gone back to using the B6.1 caster blocks and spindles, which are lighter than the B7 versions. On tight 180-degree tracks, more KPI can help improve rotation because of the jacking. If you're running a lot of KPI, and need less rotation, lowering caster can help get rid of some "wedge". The B7 parts also allow for a steeper front camber link angle, making turn-in more aggressive, but too steep can impact bump, so watch out for that. Overall, we've found the older front end delivers the most consistent, linear steering in most situations. If you prefer the B7 parts, the new T7 parts have the ability to run 0 KPI.

"Keeping The Car Flat"

How many times have you heard this, "the car stays way flatter"? Most, including myself, instantly think about roll. I have learned that most elite racers are talking about the pitch axis. The pitch axis is the weight shift front to back.

Fast drivers excel at a many key skills, one of which is managing the car's behavior along the pitch and roll axis. This is a crucial aspect of driving that often doesn't get the recognition it deserves. The AE's current geometry adds stiffness to the roll axis but not the pitch axis, causing the car to shift a lot of weight from front to back. This point will become important later in this article.

In rear-wheel drive cars, the rear roll center sits lower than the front, which matters because the rear tires push the car forward. The B7 geometry changes this front-to-rear roll center balance compared to other models, making it more like what you'd expect in an all-wheel drive setup. In a fast, sweeping corner, the rear should ideally roll first and more, hopefully pulling the front along with it. This balance between front and rear roll centers plays a big role in controlling weight shift along the pitch axis, and it's one of the challenges the B7 geometry can present in certain situations.

In mid-2025, we had a few test days to try out different setups. We brought three cars: a B6.4, a B7 with B6.4 geometry, and a standard B7. On this day and layout, the B6.4 was the fastest, with the B7 close behind. The B7 took some getting used to because of its different driving style, while the B7 with B6.4 geometry was the easiest to drive but slightly slower. Both B7s were similar in performance, but the B6.4 was clearly quicker. Since that wasn't an option, and we saw promise in the B7 if we could dial back some of its jacking and rotation.

This is where the B6.1 3-gear transmission came into play. I had some concerns about the B7's 5-gear transmission. Reliability was one issue, but my main worry was the backlash it had. In the CNC world, backlash is called "loss of motion", when a machine moves in one direction, then switches, and there's a delay before it starts moving the other way. Elite RC racers are like CNC machines, hitting their marks on the track repeatedly, and any loss of motion can affect their ability to stay precise.

While I still think improving the throttle and brake feel was important, what we discovered might be just as crucial, if not more. The old 3-gear setup moved the motor back significantly, creating a new weight bias that balanced the car on its pitch axis with the narrow hangers and long arms. With the motor positioned farther back, the car didn't shift weight as much. We believe this rearward weight shift helped the car absorb some of the energy that was causing the chassis to jack up, keeping it "flatter." So far, this is the best performance we've seen from our cars with the B7 geometry.

In 2025, Brandon took part in five events, each with a different 2WD car and geometry. In Canada, we ran B6 arms front and rear with a brass front bulkhead. At RC One, he used a .050″ spring steel chassis and a 5-gear setup with B6.4 geometry. The April Fools Race was his only dirt event, and it seemed like he really enjoyed spending time with friends and running on dirt. I'm pretty sure he went back to B6.4 geometry for that race. The final two events were at Island RC—first with a modified B7 chassis, B6.4 3-gear, and B7 geometry, then at carpet nationals with our chassis, B6.4 3-gear, and B7 geometry. That setup has been our best yet for the current AE 2WD. While 2025 didn't have much racing, it was packed with work as we designed, modeled, and tested many things, especially when it counted most, on race days.

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B7 Rear Roll Centers

Rear roll center tuning on the B7 plays a critical role in how the car generates grip, steering, and overall balance on carpet. Changes in rear pivot width have a direct effect on rear roll center height, with wider rear pivots lowering the rear roll center and narrower pivots raising it. Testing across multiple configurations showed that even small changes in rear roll center can significantly alter how the car behaves on power, through the corner, and over varying track surfaces.

The first configuration evaluated was the narrow rear pivot setup, which raises the rear roll center. This higher roll center produced a car with a large amount of rear grip when throttle was applied, but it limited on-power steering. The rear tires stayed heavily loaded, which made the car feel secure and predictable, particularly in sections of the track with bumps or uneven carpet. On tighter layouts or tracks that require frequent direction changes and short corners, this setup can be advantageous. The elevated rear roll center helps keep the car stable and minimizes unwanted rotation, but it also makes it harder to aggressively drive the car through the corner when maximum lap time is the goal.

Lowering the rear roll center by switching to wide rear pivots produced a noticeably different driving characteristic. With the rear roll center lower, the car gained on-power steering and became easier to rotate while still maintaining throttle through the corner. This allowed the car to be driven harder into the corner and pushed closer to the limit without becoming unpredictable. On higher-grip, flowing carpet tracks such as PDX, this configuration proved to be more effective. As the rear roll center was lowered, the car responded better to throttle input, carried more speed through the corner, and rewarded a more aggressive driving style. The improved ability to drive the corner rather than slow down for it made this setup particularly well suited for tracks where momentum and commitment are key to achieving fast lap times.

While the wide pivot configuration excelled on higher-grip surfaces, it did reduce overall rear grip compared to the narrow pivot setup. On surfaces where the carpet is worn or does not build as much tire grip, this reduction in rear grip can become noticeable. To address this, a third configuration was tested using wide rear pivots combined with a B7 rear arm and a -4 hub. This arrangement effectively created an intermediate rear roll center and track width relationship, blending characteristics from both previous setups.

This hybrid configuration added rear grip compared to wide pivots alone while maintaining more stability and consistency than the narrow pivot setup. On lower-grip or older carpet, where tires struggle for grip sometimes, this balance proved to be especially effective. The car maintained predictable rotation and usable on-power steering without feeling loose or overly aggressive at the limit. The result was a setup that could be driven confidently while still allowing the driver to push lap times as the track conditions demanded.