Maybe so on paper, but the properties of Kevlar, both 49 and 29 type, plus Dyneema is one of high elongation.

In the late 80's early 90's when my model race car lifestyle prevailed, I tested many belt materials for my handbuilt belt drives. A Kevlar corded belt with a urethane matrix worked very well and was proven to be most efficient in these electric cars. The cars would see more speed, longer run times from the batteries and slightly better acceleration. The drawback to a kevlar/urethane belt was failure. These belts were very life limited and would not tolerate high power motors. The belts would stretch under hard acceleration or loads like a collision or hit from the rear instantly stopping the tires from rotating. With high output motors the pulley would skip over the teeth and basically time was lost. After this occurred failure was within minutes. On the opposite end were fiber reinforced belts with higher tensile strengths, while slower they did survive for longer times and were not as prone to slipping.

Not condemning or praising the belt drive. However consider that we are now seeing performance automotive tires with carbon fibre reinforcements as opposed to the previous aramids (kevlar).

PK