Minimum torque for 20 kg robot (53pound)

I'm wondering if the tracked robot I'm building will have enough torque...
It weighs 20kg( really max)
wheels radius (wheels and tracks) 4.5cm  1.8in
I have 2 motors giving 2000 rpm, 0.2n.M 28.3in-ozf
I wanted to use a 1:1 ratio for doing speed, and a 2:1 for climbing. max speed at 1:1 about 20kmh, 12mph.
but surprise, when I try stopping the motor with my hand, I don't feel its that powerfull, and its getting me worried a bit for the capacity of the robot. I have a bit of place for a few pulleys to do a gearbox if needed, cause I'd like to try making it going up stairs.
So, here is my question: What minimum ratio do you thing It needs, to be unstopable?
If some of you have allready compared torque, weight...
Thanks a lot,

Samuel

Here you goTorque Calculator

Here you go

Torque Calculator

Very usefull caculator!

Very usefull caculator! Thanks

No problem, they have some

No problem, they have some more in the site if you look.