Yep, the terrain is the difference in the two times: the marathon was flat and fast.  The 50k had a steep *bonk* from mile 25-31. 

It didn't occur to me that McMillan did the calcs beyond the marathon distance. Thanks for pointing this out.

Not sure how this compares in validity but this one goes to 200K:

Race Predictor

The WMA Age-Graded Calculator also goes to 200K on the roads and has the added feature that you can input any distance or at least any distance 200K or less.

My unscientific methods for judging 50 mile pace:

1) Easy pace for approximately 30 miles on equivalent course both technical and elevation wise.  My 50 mile PR is 7:19 (8:48 per mile) on a moderate trail course.  3 weeks before I ran 35 miles at 8:48 pace on the same course.

2) Ultrasignup - No not the crazy race predictors or athlete scores, but by looking at multiple finish times of athletes running other courses you have run.  The key here is multiple finish times.  I can spend 2-3 hours browsing results before I have an idea of how I think I can finish.

3) Running strengths - over time I've been able to determine an equivalent race pace based on my strengths and weaknesses with elevation, technical, etc.  If you really suffer on hilly or technical terrain compared to flat terrain you may need to calculate a ratio...

I have never finished a 50-miler, but I've started 2 and learned a lot.

Frankly, if you are doing real marathon training (50+mpw), you should be able to finish a 50-miler running most of it.  A few 30-mile training runs and B2B long runs should suffice in preparation.  Practice your fueling, which is a change from marathon training.

I found the low end of my easy pace to be a good goal pace for the 50-miler.  I DNF'd both of my attempts around 34-36 miles, 6:50ish per mile to that point, but that was due to my hip/sciatic nerve issues being aggravated by the time-on-feet, nothing to do with conditioning.

I have never finished a 50-miler, but I've started 2 and learned a lot.

... 

I found the low end of my easy pace to be a good goal pace for the 50-miler.  I DNF'd both of my attempts around 34-36 miles, 6:50ish per mile to that point, but that was due to my hip/sciatic nerve issues being aggravated by the time-on-feet, nothing to do with conditioning.

As I moved the low end of my easy runs from nines to tens, maybe even closer to elevens I dropped my 50-mile time from 7:30ish to 6:30ish.  I think, but cannot prove, the long tempo runs were just as important as the endurance stuff.  There is a tendency, something else I cannot prove, to run the easy stuff too fast and the fast stuff too easy.

Put in the endurance runs for the distance at hand; apply "endurance>strength>speed" and all those little nagging things will go away -- you will be trained for the effort and distance.

Following up on "training at 50M pace"...McMillan's calculator suggests that 50M pace is 1:15 slower than marathon pace.  I take that to mean pace "on identical conditions with equivalent training".

 

My road marathon pace is 7:22.  Being that my 50M is on trails, lets just say that same marathon effort is 8:30 pace on the trails.  So using McMillan I would add 1:15 and estimate a 50M trail pace around 9:45/mile.

 

If the logic makes sense, then here's my question.  I have a road marathon coming up right before the goal 50M race and would like to run the road race as a training run.  It's not a very good proxy, but it'll be a good supported long run (plus, its paid for already).  I think I should shoot for the "equivalent effort" pace of 8:30 as my 50M training pace in the road race.  How would you run it?

I was never able to get any of the pace calculator/predictors to fit what I did -- totally envious that you can.  If it wasn't a total hijack, I would ask how you track pace on trails so well (seriously not a question, I rarely wear a watch, let alone a GPS thingie).

What is the 50-miler?  You mentioned Rocky--Rocky could be totally runnable, but t-storms could mess with things... bbbyyy

I used a flat-and-fast road marathon as a last long tempo run three weeks before a mostly gravel road 50-miler, then an easy two-hour run the following Saturday (two weeks before the ultra).  What sort of taper (two-week, three-week, ???) do you use?

^^^ Good stuff here, this is all right on. And yeah, it should really be called Rooty Raccoon.

I have a road marathon coming up right before the goal 50M race and would like to run the road race as a training run.  It's not a very good proxy, but it'll be a good supported long run (plus, its paid for already).  I think I should shoot for the "equivalent effort" pace of 8:30 as my 50M training pace in the road race.  How would you run it?

Makes sense to me. How long is "right before"? The closer it is, the easier it should be.

Thanks! i want to stick this on my wall! aiming at 50 miles in the spring. longest race yet was 38 mi. biggest issue after that 60K was cramping but it was a timed race and i could have continued. i am considering a 40+ mile training run. does anyone train at this distance?

For fifty miles it seemed like 32-35 miles on roads or 5-6 hours on trails was plenty.  When you get beyond 30 miles without a good underlying endurance base, you need to pay close attention to recovery during each training week.  During training you need to (should?) be able to run consecutive long-run weekends, which, I suppose, turns this back to -- are you training to run the whole thing (terrain permitting)?

I thought... (weakly and with lots of wandering and almost no justification):

One 30-35 mile road run (5-6 hours on trails) would get you through a 50-mile whatsit.

Two --- would, maybe, let you run just about all of it.

Three -- run the whole thing and maybe be thinking of down into the single-digit hour stuff.

Four -- racing instead of running.