I have this doubt from 4-5 years.
When a 1.2 L car can deliver a mileage of 15KMPL with nearly 1000KG weight.
Y cant these 100CC 100KG bikes cant give 100KMPL atleast.
considering the weight, ratio of capacity to mileage, it should be atleast 150KMPL. Also, power, it should be nearly 15 to 20Bhp.
Y bikes take more fuel to deliver less mileage and less power even though it has less weight.

Nice thought buddy. Even I have the same doubt.

The maruti a-star gives a mileage of 39.4 km/l, which is approximately the same as bikes.

Maruti Suzuki A-star breaks own record of fuel efficiency

one of the main factor is RPM ..

as cars have bigger engines, so it doesnot have to spin as fast as bike's engine for a same output, but bike's have smaller engine so for same amount of workdone as done by car a motorcycle engine has to spin alot more than a bigger car engine.
so finally
a car's engine spins slower for same work thus reducing friction,and other loses.

i usually travel in my car at RPM between 2k to 3k.. while at the same speed motorcycle engine has to do 5K-6K spins...

correct me if i am wrong??

The number of cyclinders, the RPM levels, the way the fuel burns in the engine, are some of the answers...

OT: My statistics professor always said this, a man and a women can make a baby in 9 months.... but can a man make a baby in one month by having 9 women?