Answer :

Moved the axle to the rear of the platform. 
Made them out of wood and leather. hope this helps

According to unverified historical data, chariot appeared about 3000 BC in Mesopotamia, and from 1770 BC they became a major part of military tactics. This military "weapon" from Asia Minor has spread to Egypt, where changes have been recorded, both in decoration and in construction. Namely, the Egyptians moved the chariot axis to the rear of the platform, and covered the axle with metal parts, to reduce friction between the axle and the wooden wheelhub. In this way, the driver would stand closer to the axle, which would make it easier the load on the horses and improve performance, speed, mobility, etc. Also, the performance has been improved by using leather and wood. Leather pads are placed on the back of the horse, so that yoke can be attached to them. Also, leather girths around the horse's abdomen, this would increase friction and prevent the yoke from slipping. Using wood in the making of chariot would help chariot be lighter, hence faster and less load of horses, and it would be easier to shape them when making them dip in hot water.