My L3700 SU has R4s and the rears are filled with what I think is beet juice.. Not really sure, The dealer did it when I bought the tractor new in 2011 ish. Anyway.. When It gets cold, The rears get flat spots in them when it sits outside. The first 10 or 15 minutes I can feel them as i use the machine.. It goes away with use.. But besides putting the tractor in a heated garage.. is there a way to remedy this .. ? more air ? Or is it just a matter of the rubber on the tire hardening in the cold and it is what it is ?