Pace Advice from Experienced Marathoners

A brief look at your logs shows you've done plenty of work this year to not let the enforced lay off in the last couple of weeks drop your fitness, you just had a slightly longer taper period :-)

I like to attempt to negative split races, in your case I'd suggest heading out the first half in 9:00 m/m (if that's what you've been averaging in your long runs, start there). when you hit the half way point if you're feeling good and your HR is stable, step it up to 8:45m/m.  Reassess at mile 18 both HR and RPE.  If you're able to pick up any then do, but by this time you'll be getting tired, make it through miles 18 to 23 maintaining 8:45 and you'll be good to hang on the last 3(point 2) :-)

Common mistakes,( or rather mistakes I have made!):

1. Feeling great from mile 10 to 15 and picking up the pace too much and going way past my overall pace time, by mile 19 the wall smacked me right in the chops, the last 7 that day were probably the toughest (and slowest) miles I've run in a marathon.

2. Going "b to the wall" as an experiment, actually achieved my fastest ever half marathon time in the middle of this marathon, but again it was completely unsustainable and hurt, a lot, hanging on to the end.

Lastly, if this is your first marathon, try to enjoy it, and soak up the crowds/atmosphere as much as you can,  you've trained for it and I'm sure you'll love it.  If you get there and things seem harder or to hurt more than you expected, slow down, take in the race, learn from it and get through it, better to finish and learn from the experience.

I might try starting out around 8:50-9:00, let your body warm up for the first 10k and settle down from the adrenaline rush, then see about settling into about 8:45. Unless you start having pain that should be about right. It's much easier to negative split than start out too fast and try to recover. Plus watching your pace fall off is mentally draining, and those last couple miles are as much about mental toughness as training.

That week of low volume isn't going to hurt you a bit. It takes about 3 weeks off to lose conditioning. Make sure you have a solid nutrition and hydration plan, stick to your plan, and have a great time.

For me the most difficult miles are 16-20.  I am past the halfway point and it feels like no man's land.  I guess this is more from a mental standpoint than physical.  Of course the last part of the race is going to hurt but knowing that I have only got 30-40 more minutes to go makes the pain tolerable.

I race by feel and only looked at my Garmin 3 times during the marathon.  Although McMillan predicted  a faster pace I decided to follow the 3:30 pace group but moved ahead by Mile 3.  It 'felt' too slow and I didn't like how the uphills and downhills were managed.  By mile 18 I was confident with how I was feeling and just kept running.  Managed a 3:21 with a neg split (which I always do).

I agree with starting with around 9:00 min/miles to start and taking stock of how you are feeling at the halfway point.  I do think it is better to base pacing off of McMillan and past races w/ MPW.  I don't think that basing marathon pace off of long run pace is ideal.  I ran 80% of my mileage (including long runs) at a 8:50 to 9:10 min pace and ran the marathon at a 7:47 pace.

As everyone has said, going out conservatively is a move you will never regret.

I run based on perceived exertion rather than by pace so, I go out "easy" and allow myself to establish a nice rhythm and then evaluate throughout. 

I don't think you have enough information to determine a solid answer.  Your injury is a total wild card, and while your running mileage seems to be consistant, it's far from ideal to help predict a long race like a marathon.  You're realistic in throwing out the 8:14 prediction of McMillian, so that's a good start.  Lots of people can do well in a half marathon on lower mileage, but the lack of mileage tends to catch up to people after the 20 mile mark of a marathon.  Without sufficient mileage, I wouldn't expect to race much faster (if at all) than the pace of your 20 mile long runs.  It may seem like it's "only" 6.2 more miles...but trust me, it is the longest 6.2 miles of your life if you're riding the edge...and even longer if you go over that edge.

So I'm with everyone else that you should start conservatively in the first 15-18 miles if for no other reason to be cautious of your knee.  Your 20 mile long run pace is a good starting point.

I was told of a 10-10-10 plan prior to my last marathon and like the idea. 10 miles  10-15 sec of desired pace- 10 miles at desired pace- 10k everything you have left. This is assuming you have a rough idea of pace, which you probably do off your 20 mile runs. I like the idea but didn't follow properly. My last 10k went from everything I have left to just hold on. Not to say the plan didn't work I just went out my first 10 miles at pace instead of 10-15 sec slower. Still managed to hold on and break goal time.

Although only you know how bad your knee is and how much it will hinder you.

Lots of good advice in here already, and there's fairly good consensus too. Something that we don't know is how your fitness and weight are relative to when you did the 1:42 HM. Everybody has you heading out in the 8:45 - 9:00 range, and that seems about right - you could tend towards the faster or slower end of that range depending on where you are compared to a year ago. But the main thing is to really put the brakes on in the first few miles. It may feel ridiculously easy, but you just have to resist the urge to get carried away. You could use HR for a reality check, if that will help.

Don't worry about the effect of the extra rest. You'll be fine. Just take care of your knee.

Good luck, and we'll look forward to reading your RR.

Thanks all.  I'm glad first of all to hear that most folks don't think the unplanned layoff will totally crush me.  Just to be clear, though, the total impact is going to be the entire last 2.5 weeks, not just the one - I'm only going to get in about 18 miles over that time frame. Getting the knee healed is the priority.

Regardless, I'm going to plan on starting off at 9:00 for at least the first half and tweaking from there.  The consensus seems to be that (i) that's likely still possible, and (ii) that's not egregiously conservative.

Thanks for helping me feel comfortable with the plan.

One more thing to add: take a look at the course beforehand so you know where the hills are.  Plan in some flexibility on your pace for the uphill sections.

The toughest course I've done was downhill or flat for about the first 8 miles, uphill (rolling) until mile 23ish, then a steep downhill to the finish.  Very hard to pace properly.

Yes, if the planned pace feels too hard, then ease off to a comfortable effort.

But don't play it the other way. If the planned pace feels too easy, don't speed up to an effort that seems fine. That's probably the more common occurrence. In that case, simply stick to the planned pace, and enjoy how great you feel.

I just wanted to thank the folks who chipped in last week.

I completed the marathon in 3:58. My six official splits were all in the 9:00-9:10 range. My unofficial watch-based mile splits had more variation - ~8:50s early (very long gradual descent on old railroad path), 9:00s in the middle, with a two jagged 9:30s thrown in around 19 and 23 or so as I was struggling a bit.

I still feel like something has been 'off' this week; my HR and RPE have been much higher than they should be at a given pace, both compared to previous training runs and previous races.

Either way, though, I got through and beat 4:00.  Thanks for helping make sure I didn't overdo it early.  I can't believe how sore my legs were the first two days afterward.

Congrats... sub-4 for a first marathon is pretty dang good!

I will relay what I was told prior to my first marathon...

First 10 miles: if you feel like you are putting forth any type of effort your are going too fast
Second 10 miles: it is going to start to hurt a little bit, you are now putting forth some effort to maintain pace
Last 6.2: Now the race BEGINS, now is where all that training you have done comes into the picture.

I followed this idea the best I could and boy did it hold true..

It's very hard if you have a competitive nature but your first marathon should not be for time, but for the experience.  Find a pace bunny that's around 9 and stick with him/her.  If you feel that you're pushing it, fall back.   I've messed up a number of marathons by going out too fast in the beginning.  I have a really difficult time holding myself back.  I never feel like I'm running fast at the beginning but I do.  The only way I've found to control it is to stick with a pace bunny.  I agree that the last 6 miles where the race begins.  If you get there and are feeling good, pick up the pace a bit.  

Marathons are significantly harder than half marathons.