I have been searching for explainations and formulas on this subject but have been hard pressed to find what I am looking for unfortunately. I would be appreciative if anyone could either provide some answers or any external resources they could point me to which has detailed information on this subject. I do not have any background in Physics but I do have some Math background. Let me setup the stage first before I ask my question. This is just background so no time is lost in any misunderstanding of what I am asking. +++++++++++++++++++++++++++++++ The small combustion engine generates a force on the piston forcing it to a downward motion. The piston is connected to a rod known as a "connecting rod" and this is attached to a particular location on the crank. The force will cause the crank to rotate and this generates varying levels of torque (torque = length x force) at the crank with varying speeds (RPM). Generally the engine will transfer both the speed and torque to the rear wheel through three levels. First is the primary drive, which will consist of a gear at the end of the crank and a large gear attached to a clutch. The clutch allows the engine to vary the speed/torque transfer at any RPM through the transmission, however in this case let's assume it's never engaged. The gear ratios are used to do two things which is to transfer both torque and speed to the rear wheel. Small engines generate low torque at high speeds so we need to lower the speed and raise the torque. This is where the gear ratios come into play. The primary drive will consist generally of a smaller gear on the crank and a larger gear on the clutch. Torque will be magnified and the speed will be lowered based on this ratio. A transmission does the same except it has several rows of gears to adjust what action it takes as it depends on the current gear. The torque can be raised and speed lowered in lower gears while it can raise speed and lower torque in higher gears. The final or secondary drive is what attaches to the end of the motor and to the rear wheel. Depending on the type of motor and the output of torque from the engine the ratio will vary. Generally, the ratio is to lower speed and raise torque to the rear wheel. ++++++++++++++++++++++++ Now, here is my question. The gear ratios which multiply the speed of the engine are fixed. I.E. for any RPM I can know the speed of the output shaft. The same is NOT true for torque, correct? Torque is lost through friction and this I know can be very complicated depending on the environment / lubercats, etc. I am however looking for general information or formulas for torque and have a few specific questions. 1. When gears change direction, is torque lost? Any general idea of how much? 2. Given the type of setup between gears, what is the relationship to torque loss? i.e. A primary drive with a Chain Setup vs. a Gear Setup. The chain setup will rotate the same direction. I have heard that chains transfer torque better than gears, why is this, is it due to the direction or is it the contact of the gears making less friction than the contact of teeth? Is there any generic method of torque loss (i.e. ~2% for chain and ~5% for straight cut gears) 3. Does the weight of the gears affect torque transfer? Is there a formula? NOTE: I realize some will likely be lost to friction of the bearings in the engine. I am more interested in Chain vs. Straight Cut Gear setup, especially as the primary drive setup (which would be a short chain than used on a secondary drive setup). Any information or resources are helpful.