Originally Posted by contango

From the other side of the equation (I ride MTB although mostly on roads and trails). If you're likely to go a lot faster than him then you need to either keep your speed down or find other riding buddies. On my MTB I can get to a friend's house which is a whisker under 5 miles away in sub-20 minutes if the traffic isn't too heavy but I'd probably struggle to maintain 20+mph for 30 miles. If you want to set that pace you'll leave him behind which will end up being less fun for both of you.

5 miles in 20mins is 15mph, 5 miles in 25mins is 12mph. Unless he sets his speed so as not to arrive dripping with sweat he'll probably struggle to maintain 20mph for even a couple of miles.

Last year I did a 150 mile tour with a friend who was much fitter than me and on a touring bike. Most of the way I set the pace. My friend's natural pace was probably 50% or more faster than the pace I set, but the ride was about the company as much as the distance. Had he just taken off and dropped me we might as well have done the ride individually.