I am a minimalist runner and was wondering if anyone races in xc flats for trail marathons or ultras. Besides cushion and support are there benefits for one or the other?
I can’t think of too many shoes that would be more uncomfortable to wear for a trail marathon or ultra than a pair of flats. What advantage are you hoping to gain versus wearing your everyday minimalist trainers?
Not sure… That’s why I’m asking if there is any.
If it’s a loose, muddy, slick or uneven rough terrain, trail shoes have a little more traction. XC spikes, might be a little extreme. They are really intended for wet grass and hard pack single track.
Protection from thorns and sharp rocks.
I am a minimalist runner and was wondering if anyone races in xc flats for trail marathons or ultras. Besides cushion and support are there benefits for one or the other?
No one. But you can get a racing trail shoe. Saucony Peregrine is one. Still need the protection from rocks and roots.

Or the Asics Fuji Racer
http://www.runningwarehouse.com/ASICS_Gel_Fuji_Racer_3/descpageMRS-AFUR3M1.html
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As others have said, a minimum amount of root/rock/debris protection would be nice. Merrill and New Balance have a few minimalist options. Brooks PureGrit and and Saucony Kinvara TR would be worth looking at if you didn’t want to go to a more traditional trail shoe.
I have a set of NB 507 rubber spikes, they are fun shoes to run on in the spring for hills/trails, short stuff. I really couldn’t see there being enough in that shoe for an ultra, nothing but tread, laces and a bit of fabric.
Maurice
For the best of both worlds I suggest you try on pair of Brooks Pure Grit 3’s. I think you will like to rugged sole, level of prtoection and minimalist feel.
I’ve ran up to 25k in older NB 101s (the ones with a rock plate) which are basically a XC shoe. If I was running a trail marathon, I wouldn’t hesitate to use them and wouldn’t expect any issues. I currently prefer Nike Wild horse and kiger (sp) trails shoes just due to the feel of them, but no functional difference over the NB 101s IMO.