Q: what identifies a Vintage MX Bike? A: Motocross Bikes fall into two eras.
on the left have a shorter suspension, made up to 1974. Then the shocks
began to get longer and slanted forward. We refer tp the latter half
of the 70s as "Evo" becvause the suspension evolved to make
rough ground easier to negotiate, and to accomodate courses with jumps.
For each of these two categories there are size classes, age classes,
and an assortment of additional ones like XR75s, women and four strokes.
Size claasses are based on the engine capacity, e.g. 125, 250 amd Open
which essentially means 360, 380. 400, 450 etc. And age classes are
based on the rider's age - guys over 40, over 50, etc. Each class has
two motos, and from that the day's result for that class is ca;culated
using he Olympic system of low score wins. Study the chart below and
not how the bikes changed as the 1970 went by.