Abstract: The present invention relates to an undercarriage equipped with a coreless rubber crawler in a chain drive configuration, and more particularly, to a track system undercarriage for a skid loader in which an auxiliary axle and an auxiliary sprocket are provided to solve the problem of load concentration at the contact points of a coreless rubber crawler, which is adopted to reduce the total load of a vehicle. A gear chain is provided surrounding a main axle and the auxiliary axle, so that the load is dispersed over a large contact area of the coreless rubber crawler, thereby relieving internal stress concentrations at the sprocket and the coreless rubber crawler, and significantly improving the life span of the coreless rubber crawler.