Efficient and stable skate board

A skateboard comprising a deck(S) and a rolling unit comprising:

• a truck (12) comprising a plate (122) connected to a lower face of the deck(S) and a tab (124) extending from the plate (122) and comprising a rack (1242);
• a box (14) pivotally connected to the plate (122);
• a transmission (16) comprising a pinion (162) and a driving bevel gear (164) connected to the pinion (162) so that they are rotatable with each other, wherein the pinion (162) is located out of the box (14) and engaged with the rack (1242), wherein the driving bevel gear (164) is located in the box (14);
• an axle (18) comprising a middle section extending in the box (14) and two ends extending from the box (14);
• two wheels (22) respectively connected to the ends of the axle (18);
• a hollow shaft (24) wrapping the axle (18);
• two driven bevel gears (28) engaged with the driving bevel gear (164);
• two unidirectional bearings (26) respectively supporting the driven bevel gears (28) on the hollow shaft (24);
• a primary input gear (32) connected to the hollow shaft (24) so that they are rotatable with each other;
• a primary output gear (34) connected to the axle (18) so that they are rotatable with each other;
• and
• an acceleration mechanism (40) arranged between the primary input and output gears (32, 34).