This response will address race dirt bikes and ignore the entry level air cooled 4-strokes such as the TTR's, CRFxxxF's, KLX's, etc. The 4-strokes tend to be a little better on fuel and pollute less as a rule. Gone are the days of 4-strokes lasting forever and being bullet proof. The race 2-strokes and 4-strokes enjoy a similar reliability history with the 250's being somewhat worse due to the high RPM's they run. 4-stroke power delivery is more desirable by some groups due to the low end torque and smoothness. There is still a small weight penalty (5-10 lbs in many cases) with 4-strokes. Probably universally the most undesirable aspects of the 4-stroke race dirt bikes is the fact that 1) they can be very difficult to start, 2) parts and accessories typically cost 2X to 3X as much (rebuild parts, after market exhaust, etc.) as 2-strokes. 3) the horrific costs associated with valve jobs (titanium) and the frequency some brands will require this repair. Why did the 4-strokes all but replace the 2-strokes in Motocross? The AMA changed the class rules such that a rider will get the most power from 4-stroke in a given class. It is rumored that the AMA sold out to the EPA. To put it another way, the power of a 2-stroke 125 does NOT equal that of a 4-stroke 250. The power of a 2-stroke 250 does NOT equal that of a 4-stroke 450. The AMA has pretended it does in an effort to kill the 2-stroke. The 2-stroke is alive and well (and often preferred) in the freestyle MX sect as well as the off-road market (GNCC, hare scrambles, enduros, etc). These 2-stroke bikes are plentiful among the European mfr's such as KTM, Husqvarna, Gas Gas, etc.). Yamaha's YZ250 is still available as well.
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The two main types of dirt bikes are motocross and trail bikes. Yamaha, Kawasaki, and Honda all make these types of dirt bikes.
The materials that were originally used to make dirt bikes included rubber, plastic, steel, and aluminum. These materials are used to make those bikes today.
Homeowners insurance does not cover dirt bikes. There is dirt bike coverage that can be purchased. Dirt bikes are not required to be licensed in order to use them. Make sure that your dirt bike coverage stipulates that it is covered upon theft because not all policies include theft.
all the materails used today for dirt bikes
YAMAHA About all manufactures make an SX or MX bikes
Basically because they can, and because the dirt bikes make it possible. They're light enough, powerful enough, and can take the beating well enough.
Depends on the make and model of the bike. Some motocross bikes have 4 gears while most of the cross country thumpers are 5 or 6 speeds.
A 2-stroke dirtbike will be powered by a 2-stroke engine and a 4-stroke dirtbike will be powered by a 4-stroke engine. For the same power, the 2-stroke will be a lighter bike. For the same weight, the 4-stroke will be a weaker/slower bike. The 2-stroke is likely to use more fuel and make more noise. The 4-stroke will run cleaner and quieter.
Brand wise, it is KTM. The make a wide varity of dirt bikes in both two and four strokes. They have everything from kid's bikes to enduro bikes to MX bike. They are by far the best.
For 2009, KTM still has the following 2 strokes:50, 65, 85, 105, 125, 150, 200, 250 and the 300.
sometimes if you need a new one try eBay of course or go to this company called UFO plastics they make new plastic for dirt bikes really cheap