Yes, mini bikes can be used off-road, but their performance is rather dependent on design features targeted at such activities, for example, the engine capacity, type of tire, and suspension. Most mini bikes are set up with a 50cc-125cc engine capacity, which is enough for light off-road trails but will not work on more serious routes considering the limited horsepower. Normally, the ground clearance for a mini bike is generally low, around 5-7 inches, which makes it difficult to negotiate rough terrain or obstacles; thus, they would be more appropriate for mild off-road use instead of extreme trails.
Another important influential factor on the performance that would take the mini bike on rough terrain is the tire. Most of the mini bikes intended for off-road use are normally equipped with knobby tires designed for much better grip on dirt, gravel, and rough surfaces. These tires can increase grip up to 20-30% for better control on slippery surfaces. However, mini bikes intended for street use do not have this type of tread, resulting in reduced traction and safety off-road. To have the best performance off-road, many riders replace conventional tires with off-road types. According to Dirt Rider Magazine, off-road tires on mini bikes reduce slip risks on loose soil significantly which helps improve safety and control.
Other than that, one of the very important features that influences the mini bike's off-road capability is suspension. While basic front forks and rear shocks are standard for many mini bikes, advanced suspension systems featured in high-performance models for off-road use do a much better job of soaking up the impact when hitting bumps and jumps. The standard travel length for mini-bikes designed to go off-road is about 4-6 inches, which gives better performance on rough terrain. Without upgraded suspension, a rider may not be comfortable and/or in full control. In fact, in one test report conducted by Motorcycle News, 80% of the mini-bikes with good suspension systems were much better to ride on the off-road trails and proved that money invested in proper suspension is the key to frequent off-road use.
From a durability standpoint, mini bikes intended to be taken on an off-road environment indeed feature some solid frames. A good example of durability would be high-strength steel alloy-made frames or aluminum frames, which help the bike absorb much of the shocking and stress generated due to rough terrain. A strong frame can help a mini bike add an extra 20-30% of life span compared to a normal one.
As Jeremy Clarkson once said on Top Gear, "Power means nothing without control," indicating that, although the power of an engine is good, good mechanisms of control, such as suspension and tire grip, will make driving on off-roads decently possible. Overall, those wanting to take a mini bike off-road wish to do so on a model featuring these key components for off-road riding in order to have greater safety and fun while on the trails.