Another vague question.
Most road bikes have a wheel size of 28" / 622 mm / 700C.(these are all different names for the same size) Older bikes can have 27" / 630 mm wheels.
If you're asking about what size you should have, do a net search for "bicycle fitting" and you'll find plenty of help.
MAYBE - , frame size has nothing to do with tire size. Style does, and if its a mountain bike, it will not work with a 27 (road racing) wheel and tire. Brakes will not fit.
depends the age and size
CC refers to the engine displacement or in other words how big the motor is. Larger cc engines produce more power then a low cc engine can. When racing dirt bikes they require the engine size to be near the same size so that everyone has an equal chance in the race. For example: Racing a 125cc bike against a 500cc bike would be a one sided race. The 125cc bike would not have a chance against the power a 500cc bike puts out.
A bike that is a 125 CC has an engine size of 125 cubic centimeters. A 125 CC bike is usually used for off road travel.
the speed depends on how well tuned the bike is and also the size of the engine.
Depends. Usually, for a bike to be road legal it has to be registered, insured, inspected, able to pass certain standards of noise, braking, lights and such. Any bike - regardless of engine size - that fulfil these requirements can be road legal. If it doesn't, then it isn't road legal.
There are several sizes available. Most are 622 mm bead seat diameter.
Talk with a salesman, let them help determine what size dirt bike is appropriate for your. Be sure to tell them what you will be doing, play riding, racing, dual sport rides, etc. Select a model that is suitable for your skill level taking into account the bike's handling, power and size. Sit on the bike to make sure it is the right size and test ride each bike. Also, consider buying a used dirt bike.
That would be different from bike to bike. Get a vernier caliper and measure it.
It's more like a kid's street bike. It's not a freestyle bike because it doesn't have any platforms and no front brake. It's not really a racing bike because it has a Gyro rotor, although there's nothing really stopping you from using it in a race. Another thing about the bike is the wheel size is an odd ball 18" (as opposed to 20").
Do a net search for "bicycle fitting" and you'll find plenty of help.
The Leader Kangero frame is a track frame. The medium size has a 53 cm. seat tube, and a 55 cm. top tube. Both measurements are center to center. The large size has a 55 cm. seat tube and a 56 cm. Which size would fit someone 5' 9"? This would depend on the intended use. If it is to be used as a pure track bike for racing on a Velodrome, then definitely the Medium size would give a good racing position. However, is the bike is for use as transport on the streets, the Large size would result in less drop from the top of the saddle down to the handlebars. Compare the measurements above to the bike you currently ride.