Why do runners carry different weight in 'terms' races?

Local racing fans usually call non-handicaps as 'terms' races. However, most of the so-called 'terms' races are in fact weight-for-age races. The Prix de l'Arc de Triomphe held in France on 7 October 2001 is a good example. Among the runners, one of them was a five-year-old carrying 131 lb. Eight were four-year-olds with six carrying 131 lb and the other two carrying 128 lb. Another eight were three-year-olds with six carrying 123 lb and the other two carrying 120 lb.

The variation in the weight is as a result of the application of the weight-for-age allowance. In this race, four-year-olds and up must carry 131 lb while three-year-olds carry 123 lb, enjoying a weight pull of 8 lb. Besides, fillies and mares carry 3 lb [there is an allowance for fillies and mares in all French races of 1.5 kg (3.25 lb)] less than colts of the same age. That is why runners of the same age carry different weight in the same race.

Another example is the Bauhinia Sprint Trophy race 2001. All four-year-olds and up in that race carried 126 lb except Crystal Charm which is a mare and received 3 lb and King Of Danes which is a three-year-old and received 5 lb, thus carrying 121 lb.