Right IF to target for 3-4hr Marathon Mountain Bike races?

For the 1st time, I’ve dedicated a MTB racing season to marathon (vs XCO) mountain bike races. Thus far, my distances range from 26-40+ miles (ie, no 100mi Leadvilles!), all with a lot of climbing, and all start with an extended hard climb. In XCO, I knew to run just below threshold for 90 mins. I know it’s an overly-general question, but what IF range is sustainable/optimal for these type of marathon MTB races? Thank you!

This was a helpful blog post for me: How To Build A Pacing Plan For Long Events - TrainerRoad Blog

Others may be able to add deeper insights, but I found that a good starting point.


Having just done three 3.5hr XCM races last month (which is shorter than my usual goal race, thus I took note of how the numbers differed) I averaged between 0.83 and 0.88.

I think if you don’t blow yourself up early 0.85 is pretty reasonable, assuming you’re reasonably well conditioned.


Anecdotally, a couple years ago I did a 50mi XCM with 4k+ of climbing. It was a 2 lap course and I went out way too hard and set many “All Time x231” power records in lap 1. That was me trying to stay with the front group. Lap 1 ended up being a .84 IF, with a 25 min section of .92 IF :grimacing:. That came back to haunt me because lap 2 was a .73 IF. Total for the race which lasted 3:38 hours was a .79 IF. Better pacing would have likely resulted in something in the low to mid .80s IF. Not going out too hard is my piece of advice!


This seems very optimistic to me. The SS progression thread talks about progressing 90% to 60 straight minutes up to possibly 2 hours. Doing .85 for 3.5 hours would be impossible for me. I know it’s normalized versus average, but as someone who can do 90% average for 90 mins straight, I think I’d struggle to maintain .75 for 3.5 hours. Looking at how my rides over 3 hours play out, I did .8 at most, but mostly around .75. Most of those weren’t race efforts, but still, .85 seems stout. I’d say you are more than “reasonably well conditioned.”

The key is workout vs race here.

I also do long SS, though I would expect to get off after a Polar Bear, or other 90-120min SS 90% session and be ready to go again a day or two later.

The 0.88 race was stage one of a stage race (following prologue the day before) and the day after was “only” 0.83.

The week before was 0.83 but if you take out the final 6km with river crossings it was 0.88. both left me pretty fryed.

Again, I said it’s down to conditioning. I should also caveat it with how hard you want to push yourself.

ETA: I also contributed to the thread above. I used to be in the more conservative camp, but I am realizing that it’s possible to push a bit higher. It’s a dangerous game though.

Do folks who pace these events by IF have a variability index (VI) number in mind?

For example, I did a hard (for me) 3:45 gravel ride with lots of climbs last year. I ended up at 0.87 IF, but average power for the ride was much lower @ 0.62 of FTP. That put my VI at 1.4 and it was HARD :grimacing::grimacing::grimacing:

Pacing is not my strong suit. I’m sure 0.87 IF with a lower VI would have been that much harder. I have no idea how to use this info to pace better this year :rofl:

I’m the same on the pacing front, but knowing the course helps as well. If you know where the passing spots are going to be on Lap 2, you’re in much better shape.

e.g. The Sea Otter XL is 100km this year (qualifies as an XCM, no?), The last 3 miles of each lap is a climb. The first half of each is a single track climb with big patches of sand mixed into the single track. It might be worth it to burn a match to get position before the single track and ride it at your own pace before it opens up. Or just take it for what it is knowing you have some in the tank for the last 1.5 miles of up hill before the finish.

So can one burn a match, recover, fuel, and hydrate before one has to burn the next one? :man_shrugging:

Obviously different type events, but for a Half-IM bike leg, most people would target a .75-.80 IF….but they need to run 13.1 miles after. Those bike legs tend to be 2.5+ hrs for the majority of the field.

A lot will depend on your fitness and capabilities, but I would guess targeting a .8-.85 IF would be about the right range.

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Day one two weeks ago, average 0.88 (first 90min at 0.94) but it was largely 4wd track and passing options weren’t crazy difficult.

Day Two single track early and we didn’t start hard enough. The first half was something like 0.88, but the second half ends up being slower anyway but you’ve lost too much time.

I think 0.85 is a good target.

I aim for about 0.75-0.78 for 6-7hr XCM (depending how my fitness is going).

I am pretty retentive on making sure my FTP is set close to MLSS.

This is key! If you’re using solely AIFTP detection then your IF targets should a bit lower.