But in 2016 I'm doing two ultramarathons that are both on trails. In April I'm running the Hawkeye 50k in Solon, IA; and in May I'm trying to survive the Booneville Backroads Ultra 100k. So far, I've run 2 marathons so these will be a challenge. Even more, they're on trails and gravel, and are a long long way to run.
Vibram makes a few different kinds of trail-type shoes. Here are my thoughts on the options.
For running, they're about the most comfortable VFF's I have other than the KMD sport. (My ideal VFF's would be this sole with the KMD upper.) The sole give great protection from rocks and gravel, without feeling too thick. I definitely prefer it to the Trek sole that came on previous trail models like the Trek Sport or KSO Trek.
Unfortunately, possibly due to getting a bum pair, I can't hardly wear my Spyridon MR's anymore. After wearing them casually and running 30-40 total miles in them, my MR's began to feel like I had rocks in my shoes. What I finally figured out is that the glue that holds the insole material down, balled up under my feet and cause irritation. I'm hoping it's only my pair that does this. (My friend has had a pair longer than me and doesn't have this issue.) After months of not wearing these shoes, I finally decided to do some surgery and try to fix it. So I made slits in the insole material and started getting the glue balls out. But unfortunately I haven't been able to get the material glued back down without irritation. So there's no way I can wear these for 50-100k of running.
Trek Ascent (& LR)
So I decided to try a different kind for the trails. After already getting the Trek Ascent LR's last Spring for hiking and casual wear, I decided to try the regular Trek Ascent for running the trails.
The sole of the Ascent is aggressive! It is great and protective without being too thick. It has probably the best grip of any VFF's I've worn. They are the shoes I plan to run my ultra marathons in, and I'm excited to see how they do. The one caveat is that, unlike the Spyridon sole, they aren't great for road running. The rubber is so hard on the sole that the Ascents begin to hurt my feet when I wear them on roads for very long. So I'm saving them for the trails.
Bonus - KSO Trek
Do any of you run trails in VFF's? What ones do you like?