Brakes -   This should be the most important design aspect to ponder. After all, for mini-quads safety considerations should be foremost and braking performance is key. Three things to consider- disc or drum, lever or foot actuation, and cable versus hydraulic.
     Disc brakes have better wet braking characteristics and are usually hydraulically actuated (another good thing). But drums are relatively inexpensive and still work decently, certainly for a mini-quad.
     All the machines reviewed have a hand lever actuating the front brakes. New riders can readily make a connection between hand levers on a quad and bicycle brake controls and therefore levers are easier to use in that respect. Also, the fact that they can see the controls is an added benefit.
     A few have a conventional style foot pedal actuating the rear brake which has some real advantages. Two aspects of the foot brake make it appealing- no matter how tired the hands are, stomping on the brake pedal will still make it stop. Also, why not get used to the conventions of a full sized machine right off the bat?
     Cable actuation has several drawbacks- cable drag makes it harder to pull the brake lever, brake balance between the front wheels is more difficult to obtain, and cable actuation requires continual adjustment. Of these issues the harder lever pull is the most significant given the little hands that end up pulling em.

Carburetion -   The most important carburetion feature is actually related to the throttle. Thumb, or push type throttles are the most popular offering, which is probably preferably to the twist throttle anyway. The operation of twist throttles is not intuitively apparent to most kids. As far as safety goes, in an unintended acceleration situation a rider is inclined to IN-crease the amount of throttle by the motion of the wrist as the arm straightens- obviously a bad thing in an already bad situation. Further, it then becomes difficult to let off the gas by rotating the throttle back. The downside to a push throttle is the fatigue that usually sets in quickly on a new rider’s thumb.

Adjustable throttle stops are common. By adjusting a screw on the thumb throttle the amount of maximum throttle opening can be controlled which effectively controls maximum power, and thus speed. An additional means of limiting power utilized by many is an exhaust restrictor donut. If air can't get OUT of the engine, it can't get IN either- and the amount of air is directly proportional to the amount of power an engine can produce.

Automatic electronic chokes are also fairly common, making starting less of a guessing game when it comes to choking the throttle. Most carbs are Mikuni’s which implies that jets are readily available when and if time comes to start modifying the engine.

Fuel Capacity -   Fuel capacity is significant only if your planning on taking long non-stop trail rides. It’s a pretty good bet that most young riders will run out of gas before the tank does. Keep the tank topped off before going riding and even the smallest tank will provide hours of non-stop fun. Most even have reserve settings on the petcock.

Height -   Overall height is basically reflective of the height of the handlebars which is ultimately a rider’s personal preference. Height is a relatively poor indication of center of gravity height- a better measure might be ground clearance (hyperlinked).

Length -   Length is usually just the wheelbase plus half a wheel diameter at each end plus whatever plastic sticks out beyond that. By itself, it’s kind of a moot measurement when it comes to vehicle dynamics. See "wheelbase" for more pertinent details.

Lubrication -   Automatic oil injection versus premix are the options. Anybody that’s been bitten by an oil injection system that failed will tell you premix is the only way to go. However, with a reliable, well-maintained machine it’s hard to knock the convenience of oil injection. Just don’t forget to keep an eye on the reservoir level- some even have a low oil warning light. If it makes you nervous, you can still mix your own- just disconnect and plug the reservoir feed line.

Seat Height -   Seat height by itself is only part of the picture. Sure, on a two-wheeler it’s important (you don’t reach, you fall down). But on a mini-quad a more significant characteristic is the difference between seat height and foot rest height. A rider should be able to sit with his knees slightly bent, so that he can stand when needed with some flex left in the legs. Unfortunately this measurement is usually omitted; sitting on the candidate machine is the best measure anyways.

Starting -   It’s hard to argue about the virtues of electric start. It’s almost too easy to start these machines (that’s why they have keys). Should the battery get run down a kick starter backup should breathe life back into it. Assuming the thing is in a good state of tune, kick starting (or even pull starting) is not the chore most envision it to be. Of course, if racing is the name of the game, batteries and starters mean unwanted extra weight.

Suspension, front -   Unlike high tech full sized quads, the suspension of a mini-quad is generally designed to provide comfort over performance. Most of the machines feature a single A-arm design (as opposed to double A-arm). The lack of an upper A arm results in very large camber change during suspension travel, but in a quad designed for kids it’s just not a significant issue. Shocks that have pre-load adjustment are handy for dialing the machine in for a rider’s weight. The heavier (or higher flying) the rider is, the more pre-load you’d want. As far as travel goes, 2" is plenty for probably 90% of the riders out there. But if racing is on the agenda, there are some that have as much as 5-6".

Suspension, rear -   They’re all swing-arm style with a single coil over shock. Pre-load adjustment that some models feature is important (more so than on the front) since most of the rider’s weight (especially during jumps) is over the rear end of the quad.

Tires -   Tire size is the same for front and rear, and are of the tubeless pneumatic type. Two sizes predominate: a 145/70-6 which is a 14-1/2" diameter tire on a 6" wheel, and a 16-8x7 which is a 16" diameter tire on a 7" wheel. Replacement tires in either size are readily available.

Transmission - The type of transmission popularized by snowmobiles is most common on these little quads- CVT, or continuously variable transmission. This system uses a V-cross section belt enclosed under an engine cover to change the transmission ratio based on engine speed and load. It offers good performance at low speed as well as high. The other type of transmission used by some is the classic centrifugal clutch. One ratio is all you get, but the engagement has a more positive feel than the CVT. Final drive is via chain on all (no shafties).

Weight (Dry)-   From a lightweight 130 lb to almost double that, the most common weight for a mini-quad is about 200 pounds. A good rider to machine weight ratio ideally shouldn’t exceed about 3 to 1, not only for kids but for full sized machines as well. Putting a 50 lb child (an average weight for a 6 year old) on a 200 lb machine is pushing that limit, but it gives plenty of room for growth. A reasonable test to validate appropriate machine weight is whether the rider can pick either end of the machine up off the ground.

Wheelbase -   Traditionally, longer wheelbase means better high speed stability. The compromise is that a shorter wheelbase is more agile. On a quad designed to barely exceed single digit speeds, wheelbase becomes a non-issue. A more significant consideration may very well be whether the quad can be placed transversely on a utility trailer, and fortunately they all should (so you can buy another, and put it on the trailer too).

Width -   Just like the popular commercial, wider is better. Since overall width on a quad is basically associated with track width, the wider the machine the more unlikely it will be to tip. Unless it’s taken to an extreme there’s really no downside.

Lights -   Brake lights are almost a necessity for obvious reasons, as long as the young rider isn’t fascinated with watching his own brake light turn on and off. However, there are mixed feelings regarding real, operational headlights. Some contend that it promotes riding at night or in poor visibility conditions. Others praise it for the added visibility it adds to the machine for other riders.

Ground Clearance -   Ground clearance can become a real issue when riding rutted trails- with such small diameter tires and large diameter axle hardware it's easy for the machine to high center and get stuck. Specifications usually define this measurement from the ground to the engine, however it's usually the rear sprocket or brake that's the real issue.

Max Load -   Most machines have max load capacities well in excess of the weight the machine was specifically designed for. If you’re planning on romping the little quad around the yard (to the amusement of your friends and neighbors) then you may want to pay a little more attention to this attribute.