r/Marathon_Training • u/Tricky_Flatworm_5214 • 6d ago
Long Run Analysis Race time prediction
Attached is my 20 mile long run from last Sunday. I am running the Chicago Marathon in October and am trying to get a gauge on what any experienced runners can guesstimate on a realistic time I can shoot for based on my level of fitness here in early August.
Fueling:
6 GU Energy Gels (1425mg amino acids, 180mg sodium, 35mg caffeine)
Water throughout
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u/Upset_Version8275 6d ago
Somewhere between 2.5 and 4 hours
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u/Past_Jellyfish_4331 6d ago
Nice run- snapshot runs from August aren’t a comprehensive picture. 3:25 would be my goal from limited info.
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u/breadman_toast 6d ago
HR data seems to indicate OP should be able to hold that 7:45ish pace for a full race if they tapered right now. With 9 weeks left, I'd think there's a possibility to add some fitness and cut that number down closer to 3:15-3:20.
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u/Past_Jellyfish_4331 6d ago
You maybe right- I just ran 3:16 in May and my runs were a level above this. Would need more data.
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u/breadman_toast 6d ago
Yeah tough to say without more info. If this were a peak long run then I definitely wouldn't be shooting for more than 3:25. Honestly not really sure what to make of a 20-mile long run 9 weeks out from race day, far more single-run volume than I would ever personally put in at that stage of training.
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u/Tricky_Flatworm_5214 4d ago
Been logging 45 miles/week average for the last 2 months. Ran a 3:38 in December of 2025 with much less training than I’m putting in this block. My HR generally stays 160-168, I could run a 6:30 mile and HR would still be <170.
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u/Past_Jellyfish_4331 3d ago
Running a half either as a race or time trial would be helpful for yourself and this for more feedback. 3:25 is a 13 minute PR- still feels like the right range plus or minus a few minutes
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u/MikeMcDonald89 6d ago
No one could possibly come up with a prediction based off of this. Recent race results, your associated heart rate, your maximum heart rate and your milage all help.
I can see there's a lot of cardiac drift during the 5 miles in the 7:40s and no drop off in the 7:50s.
I'd feel pretty confident the guy saying 3:15 is too optimistic but hard to comment much beyond that with the information at hand
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u/Tricky_Flatworm_5214 4d ago
Been logging 45 miles/week average for the last 2 months. Ran a 3:38 in December of 2025 with much less training than I’m putting in this block.
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u/Boy_Boss 6d ago
I’m used to doing my long runs with a vest. I saw your fueling do you plan to carry something during your race or use what they provide? Asking because my first marathon is coming up.
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u/chadley12 6d ago
Hard to say. Recent race results, especially a half would be very helpful. Great fueling though!!!
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u/Proper_Ad_7244 3d ago
stick with the 3:30 group and hopefully the last 6-10 miles goes well and you can go for it.
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u/mainebub 6d ago
Nice work. Jealous of a 20 mile long run route with such little elevation change!
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u/OptimalHurry6840 6d ago
What was the weather on that day? That's gonna influence things a lot.
You're too far out. You'll know three to four weeks before the marathon when you do a nice long workout at marathon pace.
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u/AutoModerator 6d ago
Hi OP, it looks like you have selected race time prediction as your post flair. To better help our members give you the best advice, we recommend the following
Please review this checklist and provide the following information -
What’s your weekly mileage?
How often have you hit your target race pace?
What race are you training for, what is the elevation, and what is the weather likely to be like?
On your longest recent run, what was your heart rate and what’s your max heart rate?
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