BMX BIKES
Any well maintained bike is ok to start with, for club day racing that means mountain bikes, street bikes (without pegs), anything with two wheels will do so long as it meets the rules below.
Kid's bikes can end up with bits left on them from old brackets (bells or horns) to aerials (does anyone out there remember those neat big yellow aerials with an orange flag on them!) or even busted pedals... take them off or fix them ... all they will do is bite chunks out of you or your competitors when you crash.
Ok, it sounds kind of dumb but you'll have two of these, but the size is optional when starting (but not once you're competing nationally!)
Little guys will ride anything down to 12inch, yes our youngest riders can be down to 3 or 4 years old! The standard BMX wheel is a 20inch and the cruiser class is a 24inch or over ... a standard mountain bike wheel is between 26 and 29 inches.
More can be said about the wheels you ride than pretty much anything else in BMX but some basic facts are obvious..
Make sure your tyres are pumped up, generally about 40 - 60psi for kids, more if you're heavier, and remember to make the back harder than the front, to give more traction on the front... rear wheel slides are ok, front aren't.
Tread is optional, some is good ... big knobblies (MTB) are bad, you'll roll off them, the harder the track the smoother your tyres can be. Again .. more tread on the front than the back!
Width. For a 20inch the fat 2inch+ tyres aren't necessary unless you're over 70kg. Most of the serious junior riders on mini frames are on skinny little 1 & 1/8" tyres as they are faster.
For a standard frame BMX try 1.75" on the front and 1.5" on the back. The front should be as fat or fatter than the back.