a lot of ATV's now have LSD's too, which drive up shock loads and torque cycling too, especially wheel off ground applications. I bet shaft sizes we done for none LSD setups and lower power/eweights and have been upgraded past htere limitations
If you want some help Formula SAE/Student cars use...
I have seen a few SAE papers on this that may be of use if you have access to them, based around the design of housings for Formula SAE torsen differnetials. May be of use as these are bike engined single seat cars, so will use a very similar chain driven differential rear axle
couple of other reasons missed
1) outer CV joints do create a 2nd turning moment due to angle. This was indicated with the FBD discussion but not expanded on. When at different angles (unequal length) this creates a difference in turning moment accross the axle which is proportional to torque...
