Q. Scooter is good, but why rear tyre are so small,is it maxi scooters - Burgman Street?

We must first know that scooters are meant to be a city commuter. Keeping that in mind. The small rear tyre (by radius) is probably to reduce weight and also give better pickup from stand still. Which is very ideal for city commuting and Short rides, as it gives the impression (illusion) of having a strong torque (and power) which isn't a bad thing in city. Foreign companies tend to follow this patterns and they are actually good enough for most city commutes. But I prefer the Indian brands in scooter section because they know the Indian roads, us people very well. Although scooters are meant to be city commuter, Indian Brand(Companies) knew well we will be using it for almost all purpose like, Touring, Commuting, off-roading, agriculture workhorse, etc. So they usually make front and rear wheel same radius, with a Powerful low end torque.

Actually great! Tyres are small but provides better grip on roads.

Yes