Vintage US MOTOCROSS

Q: what identifies a Vintage MX Bike?  A: Motocross Bikes fall into two eras.
Those 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.