Yes, it is. When you look at finish times of several top marathons and several top Ironman triathlons -- each of which we've competed in -- you'll see that an Ironman marathon can be faster, on average.
The marathons at Ironman Austria, Ironman Switzerland, New York City Marathon and Chicago Marathon are all in the 4:25 range. Ironman New Zealand and RnR Arizona Marathon are nearly identical at about 4:35, on average. RnR San Diego Marathon's average finish time of 4:52 roughly equals the average of 25 Ironman marathons, and is only a few minutes faster than Ironman marathons in Lake Placid, Canada, Florida and Arizona.
Very interesting, all fact-based, nice trivia, but still, perplexing . . . how can it be?
It's a bit of an illusion, actually.
A first reality check is our own experience running marathons on each of these courses. Our regular marathon times were roughly 40 to 45 minutes faster than on Ironman courses. Our fastest marathon was a 2:54 in Boston; the same year we ran a 3:36 personal best Ironman marathon in Lake Placid.
The next check is comparing the average of 25 top marathons -- 4:24 -- with the average marathon at 25 top Ironman triathlons -- 4:50 -- a difference of 25 minutes.
The reality is, there's more to an average marathon finish time than meets the eye. A very recent trend has shown more women than men run regular marathons; but Ironman triathletes tend to be male. Women's regular marathon times are slower than men's; see our analysis of New York City marathon results and number of runners per age group, for example. In contrast, it's not uncommon for men to represent 75% or more of the field at an ironman triathlon. And the men run faster ironman marathons.
We'll be presenting a side-by-side age group marathon comparison shortly. Until then, you have to admit, it's pretty interesting that an ironman marathon can be faster than a regular marathon.