[maclaren]

Just so everyone knows.

Coefficent of friction is not static value with rubber. As the weight per square inch decreases the coefficent of friction actually goes up. This was proven by several different experiments that are posted in the thread that you mentioned. So assumeing 1.6mu is fine for baseline calculations but will vary depending on how you implement it. The mu vlaue could increase by 20%or more depending on implementation.

So the euqation is:

mu*Normal force="Tractive Force"

If you normal force stays the same but your mu goes up by 20% you will see a 20-30% greater tracitve force thus

1.2mu*Normal Force = 1.2Tractive Force

(I use the term tractive force to mean the force that you must apply to break staic friction and start relative motion between the ineracting materials.)

Just so you know manual labor the outback tracks have a pivot wheel so you don't get the full length of engagement on the tracks. So change 60 inches of engagement to about 30 inches but it is still 5 times the engagment of a 6wd robot.

I hope some day to do an exhaustive experiment to settle this question once and for all but I don't have the time or the money right now.