After looking through a number of ironman (*) running race courses, it seems all of them are laid out to run through cities, which implies paved/asphalt roads. Is that because this way it makes it easier (better) for spectators? Or is there another explanation? From my limited experience (hobby long distance runner/cyclist and occasional swimmer) it sure feels like it's much better to run on trails and dirt roads than on paved ones....
(*) I'm referring to the distances, not the brand
Usually it is a logistics issue. Consider the same question, as to why almost all marathons are usually pavement/road based.
It is very hard to find 26.2 Miles of trails.
Then consider the case of an Ironman distance race, where the prospective host city must find suitable swimming for 2.4 Miles, and 112 Miles of bike route that can be secured/closed.
Then require it to be on trails? Good luck finding such a place.
Ironman Wisconsin in Madison, WI has a multiple mile segment run on sort of dirt trails. My memories of that race from 2003 are sufficiently faint that I do not remember which segment was on dirt, but I remember the dirt trail.
Ironman Couer D'Alene, Idaho had a sort of trail/path segment on the run as well, same faded memory excuse on more details.
I recall reading that the old Roth Challenge Ironman distance race was mostly run on trails. This memory was in the context of the Hoyts, (A father son team, where the son has Cerberal Palsey, and his dad has done many marathons and ironman distance races) and a complaint that his running time was terrible due to the off road nature taking a toll on his running wheel chair he was pushing.
On a side note, the Hoyts are just amazing.
A long off-road course is difficult to design. You have to find a course that is wide enough to handle large crowds and in good enough condition to avoid injury. Finding a suitable course that is marathon-length is very difficult.
The XTERRA off-road races manage to do this, although they are not Ironman length. Nationals next weekend in Utah is 1.5K swim/28K mountain bike/10K trail run. XTERRA also holds trail run-only races as long as 25K.
