How do i calculate the torque

yes it is .

use the formulae:

torque= total load * wheel radius

total load= the load to be carried + the self weight of wheels +self weight of motor +self weight of other vehicle components.

vineethkumar1987I am making a project where i use a DC motor to move a load of 100kg fitted over 2 wheels one front and other rear. The DC motor will be fitted to the hub of the rear wheel and the wheel diameter is 21 inches. If I have to move the load horizontally at a speed of 60km/hr then what will be the minimum torque required?
The DC motor will be selected based on the torque hence I cannot give you the RPM and Power now.

Is it possible to calculate the torque based on these data

There are two very different issues here. The torque reuied to hold a steady speed horizontally is only friction dependent. Theoretically, in the absence of friction and wind resistance, no torque is required because of inertia.
e.g. A satellite does not require any force to keep it in orbit. It is moving in a horizontal path at constant velocity.
However, the torque required to attain that speed from a state of rest in a given time is quite different.

#-Link-Snipped-#: doesnt the load split up on 2 wheels so dont I have to half the weight while multiplying with the wheel radius.

#-Link-Snipped-#: Sir cam you please tell me atleast what will be the power of the DC motor that I will have to use here??

vineethkumar1987#-Link-Snipped-#: doesnt the load split up on 2 wheels so dont I have to half the weight while multiplying with the wheel radius.

#-Link-Snipped-#: Sir cam you please tell me atleast what will be the power of the DC motor that I will have to use here??

The load does split up. However, this will not be equal.Since the person is sitting virtually over the rear wheel bulk of the load will be on this. For design it will be best to assume all the weight is on the rear wheel. Friction coefficient and other info can be got from calculators here:
<a href="https://hpwizard.com/tire-friction-coefficient.html" target="_blank" rel="nofollow noopener noreferrer">Tire friction and rolling coefficients</a>

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why don't you make a rough sketch of your design and post it here, it will make discussions very easy.