Ironman bike pacing

Ok, I know there’s lots of info out there but I’d appreciate some advice from the good people of tritalk. IMCH will be my first tri with a power meter. I’ve been using it for about a year , mainly in time trials but usually retrospectively. The only time I used it so far on the fly to cap my watts was during a 12hr TT last year and it really helped me pace it well in pretty windy conditions. At the Outlaw I was very conservative and this worked well, but I’d like to try to find out how far I can push my watts/IF and still be able to run off the bike.

So, yesterday I went out and rode my first proper longer training ride with my bike pretty much set up as it will be for IMCH and rather than riding a flat route I tried to do one that had some hills as half of the IMCH bike course has some lumps. Ended up riding at 195W average power, 212W NP, IF 0.79. Am I right in thinking that IF should be somewhere between 0.7-0.8? I felt ok at the end of the ride, not fresh but not completely wiped either. Have not investigated but is it possible to have IF as a displayed metric on a Garmin and if so, any use?

Stronger cyclists, like you, should be up at 80%.
Weaker ones, like me, would err on the side of caution.

The rides below were on extremely similar courses, a mash up of the East Cheshire J series of time trial routes, climbing not over 300m.

2:33:55 89.7km 35km/h
143bpm ave, 156bpm max
93rpm ave
233W NP, 0.83 IF

2:36:22 85.3km 32.6km/h
130bpm ave, 145bpm max
86rpm ave
212W, 0.76 IF

First ride was my first outing over 90 minutes on the TT bike, immediately after a 1.9km swim, with deep section wheels and an aero lid.

Second ride was done an hour after waking, training wheels, flappy (warm) clothes, normal helmet and with a few positional changes.

I was wrecked after the first ride. I attempted a run off, but bailed after 5km and walked home. The position wasn’t right and it was my first brick in years.

I felt “okay” during the ride, but off the bike?
Not a chance.

Second ride, having a few more TTs and even a triathlon under my belt, plus some position adjustments, I felt much more comfortable.

The time of day limited the Watts I was putting down for the HR, but I could have easily rode that distance again at that power output (or I felt like it at the end!)

In fact, I cleaned the bike down and put everything away and felt like I’d not ridden, that’s how easy it was.

We are talking about tiny differences here, so make sure your FTP is correctly set and you’ve done a few rides at your target FTP% (IF) in race gear etc.

RE: Garmin.
I think there is an IF showing, but I have one screen with the following;

10s power avg

Set up the alerts to buzz you if you go above a certain threshold.

RE: Powermeters.

Like the 4% trainers, these are definitely “cheating”
I rode a 25 this weekend and used it in anger for the first time.
My VI was 1.02, so massively within my target range.
Just a shame it was windy/raining/hailstones and I’d ran a parkrun PB about three hours before.
Really struggled to hold FTP.

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Last week I did a 100km hilly ride, with 2500m climbing with an IF of 84.6%, followed immediately by a 12km zone 2 brick. Run was fine, around 5m/km pace, but IF was too high for a good run during an IM

IMCH Last year, my IF was 71%, for a 5:28 bike - I had a crap ride due to getting hydration wrong in the heat, but I had a reasonable run

I think that an IF in the range 74%-78% is about right for me


Short answer - between 0.75 and 0.8 IF is ‘correct’ for an IM.
There’s a run/walk/crawl matrix out there somewhere. (On TP.)

Apparently I can’t include links so google how to cheat power IM bike training peaks, or something like that.

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Thanks for the replies gents.

Pretty sure my ftp is accurate at the moment and hopefully will be raising it a bit over the next 8 weeks. I have not done any bike / run bricks yet. Probably next week, will start seeing what that’s like.

Matt, don’t know if you mind sharing what your weight / ftp was last year when you did IMCH?

This thread is far too informative and civilised.


In this new high tech age everything is recorded

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Remember it’s much better to undercook the Ironman bike and regain on the run. The opposite offers you no route back :boom:

Over 0.8 is not a good strategy for most AGers; I have been there.


search this for a training peaks link how-to-cheat-by-using-a-power-meter-in-an-ironman/

I still can’t post links either.

This suggests .75IF.

Most of my IM’s have been ~190AP/200NP, mostly flat courses, for some reason I can’t find the NP for Wales & Bolton *2.

For my last serious effort in Barca 2016 Garmin reckons I was about .69 so definitely steady, but I did run a fairly easy 3:38 after with some walk breaks.

My FTP is ~290W depending on the time of the year, couldn’t get near that on a 20 min FTP test, but a rested 25 is doable, so in reality I’d say that .69 maybe should be just over .70


You are also looking for a VI as close to 1.00 as you can get it.

An NP of 80% of FTP (0.8IF) is useless if the VI is 1.45.

Ok, found the article but can’t post it yet. Will do so when I can. I had read it before, but thanks for pointing me back to it. I’ve had a play around with my Garmin and have changed the display to show IF and 3 second power. I’ll give it a go this weekend and see how easy it is to ride at a set IF. I’ll have a go at 0.70 and see where that gets me.

0.7 will be a piece of pie!
But that’s what you need to find out…all about running off the bike.

Might not be able to post links, but you can post images! :wink:

The thing to remember in this table is that you need to know your estimated finish time before you can use it to guide on suggested IF. That’s where something like BBS comes in. If you’re a beast and going to bike close to 5hrs, then 0.72 IF is “safe”. However if you’re going to bike 6.5hrs, then you’ll have massively overcooked it.

It’s a vicious cycle. If 0.75 IF means you’d likely take 5hrs30, you’re then likely overbiking (given that’s for proven strong IM runners), so would need to dial it back, but in doing so you’re going to go slower. 0.74 might cost you 10 extra minutes, and now you’ve just moved up to the “walk it in” band!

I have to be honest, I have no idea how people are saying to bike up towards 0.8 in a full distance. That’s about my general mid-range target in a 70.3!

I did 0.67 in my one and only IM. I’d aimed for about 0.7-0.73 (the latter was what I’d done in my 100TT simulation). However on the day I knew anything more than what I did would have been too much. RPE still factors. That 0.67 was still good enough for under a 5:20 bike split, and a sub10 overall.


And/or circle. :wink:

Totally agree with the post though. 0.8 has got to be an elite performance. Which is all of us right? (Clears throat)

They’re one and the same :man_shrugging:

So I went out on my long ride today and set up my Garmin with IF as a metric to keep my eye on. Made the mistake of starting my ride with two friends who are both currently much faster than I am on the bike. After about 10 miles I waved them off but by that time the displayed IF was already 0.81.

I spent the next 80 miles trying to back it down, which I did do and at the end the IF was 0.77. The ride was a straight out and back so I did pretty well to get it down despite a head wind on the return, but the two halves were quite unbalanced from an IF point of view. Although it was only the first 10-12 miles where I really went over, this had a pretty big knock on effect for the whole ride and 0.77 is still too high for me.

Going to have to bike well below 0.75, get my ftp back up over the next 8 weeks and not over cook the hills. The second two points I didn’t need an IF metric to tell me, but pretty handy to have something to gauge my effort in real time.

The IMCH bike course is two loops with a flat and presumably fast first half and a lumpier second half. I had the idea of hitting the first half of each loop a bit harder and then slowly recover on the hills. This is now a pretty obviously insane thing to do.

A few stats here. TSS way too high.


I did pretty much the same…added IF to Garmin and set off on my long ride, albeit on my tod. Wasn’t really watching it after the first couple of km and overcooked the first 80k with IF at 0.87 :thinking:. Eased it back for the second half, probably due to fatigue but IF came out as 0.81. TSS was 320.

This was my first long ride this year on my TT, which I think accounted for some over exuberance, along with the great weather :sunglasses:. I felt pretty good at the end apart from sore neck, but wouldn’t have fancied running a marathon, so guess that’s too high.

Will try and be more disciplined next time and aim for 0.75. No point having the tool if you ignore it…:joy:.


These expensive speedometers are great, aren’t they?


Get the VI stat on there, too.
Then set up some beeps.
That’s where the real fun/boredom starts.
No more coasting downhills, literally soft pedalling uphills.

I’m quitting the Sunday club rides for the next four/five weeks.
Just me and the TT bike testing 78-85% IF.

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Yes, good idea. I’ll see if I can set alarms for upper/lower range to focus the mind.

I always say to the uninitiated that the secret to endurance sport training is a high boredom threshold! :crazy_face:

EDIT: Is there any way to see VI on Garmin Connect for a particular ride? Was curious what mine was today and it shows everything else TSS/IF etc. but not VI.

9 weeks til IMUK, did my gym winter training with power and would love to bite the bullet and get one now rather than relying on keeping HR upper Z2.

I have a suspicion I’m riding under .7 (FTP near 300W but estimated power on Strava around 180) but body/heart doesn’t dare go faster based on feel.

If going to get one should get it now to be useful, but If I don’t get a power meter now will likely be inevitable to get one next year, number one on the wish list above race wheels/time trial bike/kit etc