Urban RC

Here’s some in-depth information on the car and electronic package I used to win the 2022 UTS Championship! The entire season was hosted at Urban RC, a small medium to medium-high grip epoxy surface (similar to asphalt) track. The surface here requires a lot of steering so this setup is tuned for that. We only run the 17.5 blinky class here so this information will be especially useful for anyone running their XRAY X4 in similar conditions, but I’m sure that a lot of the information will be applicable on other surfaces and for other classes.

Suspension - I ran the basic shock package of 350 oil with 4x1.1 piston all round, combined with a 2.5-2.8 front and 2.7 rear spring. This works great in almost all conditions based on my own experience as well as feedback from our team drivers, and I would definitely recommend this as a starting setup for all asphalt tracks. Sometimes I like to use 375 rear shock oil (still with 350 front) for a bit more high speed steering at the expense of off power and low speed steering.
Roll centers and sway bars - these 2 settings go hand in hand so I thought I’d discuss them together. I ran 3mm under the front arms and 3.5mm under the rear arms, a little higher than the kit setting, which freed up the car in the corners and made it more reactive for this technical track. Sometimes I’ve liked 2.5mm under the front arms depending on the track layout. This reduced initial steering slightly but allowed the front end to dip more into the corners, and at the same time reduced front tyre overheating. Combined with this, I used the kit 1.2 rear sway bar but a softer 1.1 front sway bar which made the front end more round with less pitching between off and on power, allowing the car to roll nice and smoothly around the corner.

Weight bias - As usual on asphalt, I ran a more rearward weight bias (F49% R51%) for more rotation and overall steering.

Bump steer and ARS - I ran a slightly higher than usual bump steer shim of 5mm which made the car easier to drive and also easier on the tyres in the super hot weather. It freed up the front end and increased corner speed everywhere. I ran 6.5mm of ARS shim which gave about 0.3-0.4 toe gain under compression, although this also depends on your rear caster and shim under the rear hub. I feel that more toe gain gives you more off power but less on power steering. This setting is very sensitive and depends a lot on your driving style. I used only 1 degree of static toe in which is a special setup for Urban due to the surface. On other tracks I would probably use 2 to 2.5 degrees.

Caster - as usual, 4 degrees of front caster which gave the best balance between on and off power steering. I used 4.5 degrees of rear caster which just freed up the rear end by shortening the wheelbase and also slightly shifting the weight bias even more rearwards.

Downstop - I used a pretty aggressive downstop setting of 6mm front and 4mm rear which gave a 1.5mm difference in front to rear axle height when taking the shims under the hubs into consideration. The higher front downstop value increased the initial steering of the car at the expense of a bit of corner speed, but it was faster for my driving style. The lower rear downstop value increased off power rotation.

Flex - as typical on asphalt, a split top deck worked best. I cut all 3 ridges in the rear of the top deck and didn’t use a T-brace for maximum rotation. I used all 4 shoulder screws to stiffen the car slightly, which allowed the car to carry more corner speed. The usual motor mount screw setup for asphalt is 2 screws in the rear, but I’ve found that adding an extra screw just behind the spur gear has a big effect on handling, it sharpens the car up a lot and allows it to get out of the corner quicker. In this setup I also used the M lower arms. I have experimented with using the H arms before which slightly increases the reaction and corner speed of the car but in the end I chose to revert back to the M arms since I believe these have a wider setup window for the various conditions I would face throughout a race day outdoors.

Others - I used the kit 0.5mm under the front hub, and 1mm under the rear hub for a bit more steering into the corner but less steering out of the corner, which best suited the balance of the rest of the setup. I used narrow hexes all round for more overall traction. The H rear body posts greatly increase the reaction and stability of the car, especially in chicanes and high speed sections.

Electronics - I used the proven combination of the Hobbywing G4 motor paired with the G2S speedo. This motor is by far the most popular choice for our series. With the locked 2850 KV rule, I chose to gear the motor slightly shorter than normal for this race since the layout basically had no long straight. I would normally run a 48 pinion (3.9 FDR) but I used a 46 pinion (4.1 FDR) here. I have previously made a separate post all about this motor. Speedo settings were pretty standard for blinky racing, you may choose to use a little bit of drag brake (3-7%) depending on your driving style but I’m used to running without drag brake for stock. Keep in mind that a higher drag brake value will increase motor temperature.

D. Quek

Source: D. Quek