Running 18.3 miles a week and having a time goal is a recipe for disaster.

You're going to hurt if you go out at 3:30 pace.

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https://markmcdermott.substack.com

Get up to holding at least 100k for 3 straight weeks. Do this by adding 10% every week til you get there

When was that 20k?

Last weekend. I run a 20k pretty much every weekend.

I figured if I ran a 20k on a confortable sub 4:30min/km pace, I should be able to go the distance on a 5:00min/km pace?

No, not the case?

https://www.mcmillanrunning.com/


I plugged in your 10k time. It predicted your 20k time on the money. Says your marathon time is 3:07. But as others have said, that's most likely assuming you're doing the necessary volume in training.

Nice!


3:30 will hurt way more than it should, because, of course, you don't have the volume.
You should be able to hit it though, maybe even a a good bit under it.

While this is clearly a silly thing to do, at least run it smart and truly embrace a negative split strategy. Go out at 3:30 pace and don't speed up until well into the second half. If you're feeling it at 20, I'd say go for it.

Try not to injure yourself.

Yeah, def don't want to hurt myself for this lol. The second half kick might be my best bet then?

Either you'll pick it up at mile 20 and have a negative split or you'll barely hold on or slow by then and be thankful you started easy.
Either way, it'll hurt, but the first way will hurt much less.


Next race, do a proper build and use that for a PR to be proud of.

You def have the engine for it - I'd say - but your legs will probably fail you at some point. Hopefully closer to 40k than 20k :-) As others have said - be religious about keeping your 5min/km pace - which will (should!) feel like a breeze for 20k. After 25k-30k I guess your legs will start hurting and you will perhaps struggle to maintain pace, but it will be WAY easier to keep it up if you have been diligent about not going over pace early in the race.

As en example I had my first marathon on similar conditions as you. I'd run very little, but biked a fair bit. Had an ok engine but no running-legs. Made the mistake of going to hard first half - split something like 1:34/1:35 first half. Struggled the next half and came in around 3:27. I guess I could have gone a couple mins faster with better pacing, but was still happy.

Don't listen to the guys saying you cant run a marathon on limited training. You CAN - you just wont run to your potential and your legs will hurt :) I agree - though - that a marathon is much more fun with better training-base! I've gotten a few years of some ok running and am (hopefully) closing in on a 3 hr marathon within a year or so. In conclusion; volume works! :-)

Awesome! Thanks for the advice :) and same here, ton of biking and little running.

I'll stick to 5:00min/km for as long as I can :)

Should, based on a pace calculator, yes. Will, based on experience, no. You have the speed, I think you lack the miles on your legs. Up your training miles and it's very doable.

Tracking this thread. Make sure to post your results when you are done.

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Charity is injurious unless it helps the recipient to become independent of it. John D. Rockefeller Sr.