How to pace my long runs?

I'm confused about what pace I should be doing my long runs at for a marathon! I tried to do the Manchester marathon last year, but definitely was trying to do too much too fast and got injured after my 20 mile long run! Am trying again this year; and am just confused over how fast/slow long runs should be ran? Any advice will be much appreciated!

Put a recent race time into a calculator such as McMillan Running.

It will give you reasonable estimates of your times for other distances, and suggested training paces.

I have a similar problem. thankfully no injury so far, but i'm having trouble determining what "marathon pace" should be. Some of my runs have sections of X miles at marathon pace, or at half marathon pace. My last race was a half about 18 months ago, and before that my last (and first marathon) was nearly 3 years ago, in which i completely crashed, so I don't think either are particularly helpful indicators for pace, plus I think i'm probably fitter already than I was for either of those races, given i've already had a period of 4-5 months steady prep before starting my current marathon plan.

i'm using recent parkrun times as a guide to marathon pace (via mcmillan) but the greater the difference in race distance the lower the predictive accuracy.

So my question is whether, in training at"marathon pace" to use:

a) my 3 year old crash and burn marathon time

b) my 18 month old half marathon time

c) my 5k race time, extrapolated to marathon via mcmillan

d) my "goal" (for goal, read, idealised, preferred target) marathon race pace.

suggestions? my gut tells me the correct pace to use should be somewhere between C and D, given that A and B are too old to be of any meaningful use. I'm currently setting the "marathon pace" runs in my training to be slightly faster than that predicted by C, but not as fast as that needed for D, with the theory that the pace will approach D as I near race day.

A couple of pointers about long runs and general pacers for Jemmet and AgentGinger:

First of all, you need to have good base fitness before you can extrapolate performances to marathon pace. So if you run 55+ miles a week, then Mcmillan and similar calculators will start to become more accurate, obviously if you don't have a base level of fitness, then maintaining a marathon pace for more than a few miles is going to be hard.

The golden rule of long runs is that they shouldn't be any more that 25% of your average weekly mileage, so 20 mile runs are overdoing it if you aren't running 70-80 miles a week.

There's a few reasons to do long runs, and they can be used to stimulate different physiological developments. The one most people are aiming for with the long run is to develop base aerobic ability, if so, then pace isn't necessarily a concern and so the miles should just feel comfortable this can vary from week to week depending on what other training load your body has had to deal with.

So, your easy pace is better thought of as a range and hitting an exact figure itsn't usually necessary unless you are trying to mix the long run with other physiological targets.

I've never heard of that 25% golden rule. That would mean I'd never get my 20 milers in ! 

Or a half marathon for that matter.......

I'm with Cougie on the 25% rule.  I only ran an average of 48mpw (max mid 50s) for my last marathon and ran (6 x 20m or longer).

 A general rule that I follow is that if your pace starts to slow towards the end of a LSR then you started too quickly.

If you have built up through 14, 16, 18 mile runs then you should have an idea of what pace you can hold for 20 miles.

If you still feel good after 16/17 miles then you can always increase the speed a little (don't get carried away) in the last few miles.

I always do my first 20 miler at MP+70s(ish) and then on the others I try to put in blocks of MP efforts, but only do that once you are used to them.

Good luck

Yeah-I think I definitely do them too fast! I like the feeling afterwards! And I feel it helps me physologically to know I can run at my desired speed on the day if Ive already done it before!

Going to look at Mcmillian running now!