I'm going to buy a torque wrench for some high-torque bolts in my car. I need a torque wrench to torque bolts from 130 nm (95.8 lb-ft) to 160 nm (118 lb-ft). I found some torque wrenches which support a range of 30 - 210 nm. However, I found a problem with all of them and that is the length of wrench. All torque wrenches of this range (even the most expensive ones) are about half a meter long (20 inches).
Now, imagine you want to torque a particular bolt in your car to 160 nm (118 lb-ft).
Torque = Force x Distance >
160 nm (16.31 kg/m) = Force x 0.50 (meter) >
Force = 16.31 / 0.5 = 32.6 kg (about 72 pounds)
Do you think an average human arm can exert such a force (72 pounds) to a torque wrench handle?
Why don't they make torque wrenches a bit longer?
I don't think adding an extension to the wrench would be a good idea because you may damage it.
I have a torque wrench of the same dimensions that you are talking about and can operate it without a problem.
While I can pick up a weights a lot heavier than 72lb (32kg), you will find that operating a torque wrench on the higher settings is not just about using your arm. You will likely hold it with both hands and use your whole body to move the wrench to give a smooth action to the movement. It may be that you keep your arms straight and use your legs to move you or you lean to pull on the wrench, but it will rarely be just your arm doing the work.