Century Time Trial (imperial century)


I’m doing a Century Time Trial in the summer, so I’ve plugged it into the Plan Builder and I’ll follow that with regards to training. It’s flat c 1500ft/500m over the entire century and it is a circuit that we ride 4-5 times.

The question I’m wondering is other than riding a few century time trials does anyone have any suggestions how to calculate my power for the duration - which will, I’m hoping, be in the region of 5hrs. It’ll be my first TT over 10 miles. But I regularly ride century & 200km rides, on a road bike but with a different mind set and agenda so not really an ideal comparison. Also this is the first season I’ve had a power meter too.

EDIT: I’ve got a target time in mind, but I’m really wondering how I can calculate a target power that I can hold for 100miles be that 75% of FTP or 92% of FTP anyone with any experience of that rather than targeting a time, setting power & finding that is either way over or way under what I could have achieved. EG Brad Wiggins had a bash at the hour when he knew he could hold 440w for 60 min and hold it in aero position that gave him sufficient W/CdA to be on the money for a result.
My aero position will as good as I can hold, my FTP will be what it will be on the day so if FTP is the power you can hold for 1 hr what is the percentage of that you can hold for 5 or 6 hours?



You have a target time there that will give you a target speed. There are a couple of webtools (.e.g. this) out there for calculating your likely required average power based on your personal metrics.

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Good point :+1:
I’ve put that as much as a mental stake in the ground.

If you have your historical power/time curve then you can compare the predicted average power with your historical numbers to see if they are compatible.

The model demands a CdA figure. Looks like my wife will be taking photos from the front & I’ll be getting the graph paper out to calculate my frontal area.
Sadly I don’t have any realistic data (mainly Strava estimates of power) yet. I’ll pick up data through the season but doing a century in a TT position is something I really only want to do once (ha ha ha). Or sitting on the trainer for 5hrs is not top of my To-Do list either

I guess I was hoping there was a rule of thumb along the lines of FTP-10%/hr type guestimate so for 2hrs = FTP-20% 5hrs = FTP-50%

Would use 70.3 pacing as a guide, as overall event duration is similar. Typical advice for a 70.3 bike leg is somewhere between 75-85% of FTP. With stronger athletes being towards the top end of that scale, partly because they’ll have better fatigue resistance, and partly because they’re faster and therefore out there on the course for a shorter time. 5 hours is a fastish 70.3 time so I’d say 80-85% is a good target.

Also worth noting that a lot of people find a significant difference between FTP in the TT and road positions. So you need to either test in the TT position or at least do enough some practice races to get a feel for what’s achievable. My experience has been that enough time on the TT bike, plus a good fit, can get those differences down to very little or nothing, but I know others really struggle.

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I would plan for an Intensity Factor (IF) around 0.80 based on the info below.

Source: The Power Meter Handbook by Joe Friel.

Also check out this article.

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Cheers @rkoswald - that ties nicely with @cartsman (thanks too). And coincidentally if I’ve a moderate CdA according to @simonicusfacilis modelling page (not that kind of modelling) that should be do-able for the 5hr target and if I do that should allow me to negative split as I should have something in the tank for the second half - if I’ve fuelled well enough!

Have you done any 10s on your TT bike, and with power? You can calculated your likely cdA from that.

@splash I did a few last season (a hub based as opposed to crank but I guess the difference isn’t worth shouting about). Does MyWindSock have that functionality?

I can’t remember where I’ve seen it unfortunately, maybe you have to google it :smirk:

Bestbikesplit might be useful too?

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This is my data from a 100mile TT last year, around 76% FTP avg pwr. My target was to go sub 4hrs 30.

I would advise though that you will likely fade no matter how you try to pace it. I regretted not starting a bit faster and if i was to do another i would go out harder and plan to reduce power incrementally every 20 to 25 miles. Leave negative splits to the pro’s. Long TT’s are as much an art as they are a science.


http://bikecalculator.com/ gives estimates based on various inputs without you having to guess a CdA figure. It asks you to specify the position you plan to use - hoods, drops, etc.

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