Chassis
The main chassis setup of the Micro RS4 is similar to that of your average pan car. It's a basic fiberglass deck that supports the bumper, front lower bulkhead, and rear pod. The 2-piece upper deck supports the front upper bulkhead and provides a large area for mounting electronics. Batteries are mounted to the upper deck by a battery mount and a couple of body clips. You have the option to use preassembled packs or individual AA cells. The motor sits right behind the batteries and mounts to the chassis with an aluminum motor plate. Sitting in the very front of the car is a baby foam bumper cute enough to make anyone say, "Awwww."

Suspension - There actually isn't much to the suspension as it has a very simple design. Up front, lower arms are incorporated into the lower bulkhead and remain stationary. Steering knuckles at the end of the arms are allowed to slide up and down. A ball joint at the top of the knuckle snaps into the upper arm and holds the knuckle firmly in place. Hinge pins in the upper arms provide a pivot point in the bulkhead. Both upper arms extend past the hinge pin and connect to their independent spring shocks.

In the rear, the chassis itself provides the suspension. Working much like a T-plate, though not independent from the main chassis, the rear suspension works entirely on chassis flex alone. An additional spring shock in the rear provides extra rebound.

Drive Train - The seemingly-simple, single-belt drive line is the most complex part of the Micro RS4. Within the drive is an impressive set of differentials. The rear utilizes a bevel gear differential. A solid axle goes through the diff to drive the left wheel and the diff drives the right wheel -- very similar to a pan car. Up front, the Micro uses a sealed pinion gear diff and mini universals!!! A long belt runs on the pulleys of the diffs along the right side of the Micro. Since the entire chassis flexes as part of the rear suspension, a tensioner is useless on this type of car, so small bushings are used as a guide to keep the belt on the pulleys. Finally, all the go parts are supported by a full set of ball bearings.

Steering - The steering is set up in a fashion where the servo sits flat across the chassis. The servo is held down by a small piece of servo tape. The servo is then centered by a servo centering tool which pokes through the bottom of the chassis and guides the servo horn toward its center. From the horn, a floating steering rack, which has been slotted so that it is able to slide up and down as the front suspension compresses, connects the two knuckles with ball joints. The optional servo horns allow the use of a standard-sized servo or a mini servo. I opted for the mini servo as it takes up less space and conserves weight, aiding the car's acceleration and improving top end speed.

Body, Wheels, and Tires - HPI was kind enough to provide all three highly-detailed bodies for our test Micro. The selection of a BMW M3, Dodge Viper, or Nissan Skyline are available as of now. The decals come pre-cut, so no trimming is required. Sweet!

The Micro also includes three different sets of wheels for you to choose from. With the option of a five-spoke, six-spoke, or mesh wheel, you have the choice of a custom look for your Micro.

A relatively sticky compound rubber (which still needs to be glued) hugs the rims and provides good traction on the asphalt. A medium/firm stick-on insert lines the rim and maintains the integrity of the tire.

Testing
Testing of the Micro RS4 was conducted here at the offices and parking lot of Xtreme R/C. Our short carpet, obstacles, table legs, and chairs made for a perfect running area to test agility. The parking lot is your run of the mill, black asphalt. It's a little dusty, but home nonetheless.

Acceleration - The acceleration depends on gear ratio, battery power, and motor. I used the 11-tooth pinion with a custom 6-cell battery pack and the stock motor. To my surprise, the Micro RS4 was able to spin the tires as it left my feet. Acceleration was crisp and controllable -- nail the trigger, and the Micro was gone!
Rating: 4

Top Speed - Top speed of the Micro RS4 was relatively impressive in its stock outfit with a 6-cell. According to the radar gun, the Micro topped out approximately 19mph! Not too shabby for a little guy! Drivability at top speed for the Micro was exceptionally stable for such a narrow stance.
Rating: 4

Braking - Braking was also good. The LRP Quantum Pro Reverse provided plenty of braking power to stop the little car. The Micro tracked straight under deceleration. No veering was noticed, nor did it spin out under hard braking in a corner. From a topped out, high speed run, the Micro went from 19 to 0 in less than 4 feet!
Rating: 4

Low-Speed Handling - At low speed, the Micro had a hint of understeer and a
considerable turning radius for a car its size. In a tight spot, such as the office at work, be sure to have reverse.
Rating: 3.5

High-Speed Handling - The high-speed handling was much more interesting. During a high-speed cornering maneuver on throttle, the rear end of the Micro likes to come around just a bit. Off throttle, the car was stable into the corner and hard out of a turn on throttle. For such a small car, it handled very much like its larger 1/10-scale counterparts.
Rating: 4

Tuning - With the Skyline body, I was able to use a slightly wider track. The front track was increased from 94mm to a 98mm and the rear was increased from a 97mm to a 101mm. This was all done simply by pulling the wheel off the car, rotating the wheel, and then sliding the wheel back on the hub with the notch in a different slot. There are three widths in the front and four in the rear to choose from.
Rating: 3.5

Damage - As much fun as the Micro was, I couldn't help but hit everything, including Dave's feet. No damage was done to the car, but the office quickly became a mess. Guess I shouldn't tell Mike about the...uh, nevermind.
Rating: 4.5

Conclusion
The Micro RS4 is an absolute blast to drive around. It's far too much fun to pass up. With a friend, it would be even more interesting, and not that much room is required to play! More than likely, you can probably set up a track right on the patio in your backyard. I can't wait to see a class of Micro RS4s at the track.

With a miniature car that's 4WD, accepts all your standard-sized equipment, and has tremendous upgrade potential, how could you go wrong? You will be able to find the Micro RS4 in the local hobby shop for about $120. So what are you waiting for? Go! Go now! Why are you still reading this?