I've got a DR650 with an air-cooled engine. I know that continuous idling can overheat the engine. I'll probably do average speeds of less than 12 mph on dirt because I'll be going dual-up with my wife most of the time and do not want to spill this bike with her on the back. I anticipate that we are going to spill at some times and want to keep the speed low to lessen the impact. Even on logging roads and hard packed gravel roads around here you will find mud and soft dirt and sand. I already know what a DR650 with stock tires will do in this terrain. Going slow allows time to assess these conditions in advance and find a way to steer around them in many cases. In addition, we want to enjoy the scenery. No hurry to get anywhere. How slow can an air-cooled engine go before overheating kicks in and what detrimental effect does overheating have on an air-cooled engine? I do realize that ambient air temperature will affect heating but lets assume a worse case air temperature of 70 degrees F for this scenario.