IF for a 8-9 hours gran fondo

Hi all,

On June 8th I will ride the “Trois Ballons” Gran Fondo in France: 210km (130mi) and 4,400 vertical meters (13,000 feet).
It is a mass start with c. 4,000 riders, so riding to the first climb will be hopefully mainly sheltered in the pack. Then 6 medium to long climbs: http://www.grandtrophee.fr/epreuve.php?C=22#course.

I’m trying to figure out how to pace this as % of FTP so I can enter that into best bike split to come up with a pacing. (knowing that BBS doesn’t include the lower wattages that I expect to need when in the wheel of someone as I will not riding alone all day) Expected finish time is in the range of 8.5-9.5 hours (I hope :smile:) with a 9h40m cut off time to finish within the “gold medal” category for my age group. So finishging in 9h40 or faster is definitely the goal.

For sake of completeness: 42y old, 58kg, 1m70, 225W FTP and doing some 5h-7h long rides to get accustomed to the long duration.

Any suggestions on pacing?

If it’s useful for you, I completed recently a similar gran fondo (185km and 3700m) and my IF was 0.77.

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Last year, I did two 100 mile/8000 ft. century rides at 0.77 and 0.78 IF which worked well for me but for 130 miles, I’d likely back that down a bit more.

It may also depend on how much variability you will allow to go harder up climbs. Keep in mind IF is the normalized power relative to FTP - some people mix that up with average power when they quote % they rode at.

I rode my own pace to not get sucked into too much hammering in groups - both cases were right around 175W actual average power, while NP was around 203W for both. I rarely pushed over FTP and longer climbs were mainly tempo. I think the more you keep the variability under control, the higher you can push average power, but you will get a better time pushing a little harder on hills and easing off a little on descents. This year I might push that direction a little more, but not much - no fun to blow up!

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I use NP indeed, not average power.
I indeed want to prevent that with 100km to go, my legs are (amost) shot. Then it will be a miserable last part of the ride and I want to have fun and ride as fast as I can over such a long ride. So the plan is to rarely hit FTP and if that means I have to let other riders go, fine by me.

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Looking at a few of my big days out

La Marmotte (probably the most similar) IF0.76 (179km 5000m 10h22) I really blew up in this and died a 1000 deaths on the Glabier
Fred Whitton IF82 (184km 4000m 7h26)
Liege Bastogne Liege IF0.71 (271km 4400m 11h37)

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my first 4 hour ride last weekend was @ 0.76IF and that was a BIG ride and I was very fatigued and pretty done the last 20 mins

What is your power so far on 7 hr rides…this will not be far off your target. However if you have no long term ride data the I suggest a more conservative 0.6 for 9 hrs and 0.62 for 8 hrs (checked according to online calculators)…or around 135 watts which is ave not normalized (which might be 10-15% higher) . ok sounds low but can be easy to maintain this in the bunch…but then increasing to 150w-160w on the climbs which look hard!

I mainly did LSD on long rides up to 8h in the range of 0.50 - 0.65 IF, which worked fine: i was somehat tired from being in the saddle for so long but the legs were fine, not even remotely close to cramps. Tomorrow I have a 165km gran fondo through the Belgian Ardennes hills (much shorter climbs) which I’ll use to get a better grip on IF and nutrition strategy. I do this ride with some friends who typically stop at each feeding station for 10 min which I don’t plan to do for the Trois Ballons gran fondo.

thanks all for the replies.

For what it’s worth:

  • La Marmotte 2. July 2016: 173 km, 4,721 m elevation gain, 7h 57m, 214 NP (71% of FTP), 0.72 IF, 417 TSS.
  • Tour du Mont Blanc 15. July 2017: 324 km, 7,826 m elevation gain, 14h 1m, 202 NP (67% of FTP), 0.71 IF, 712 TSS.
  • Jotunheimen Rundt 29. June 2018: DNF at 248 km, 2,860 m elevation gain, 7h 19m, 225 NP (75% of FTP), 0.76 IF, 428 TSS.

I would say an IF around 0.70-.075 makes sense.

Best BIke Split.

I’ve done the long version of Levi’s Gran Fondo (~118 miles, 10,000+ feet of climbing) three times, and my IFs were:

  • 0.73
  • 0.79
  • 0.74

Good luck


He will still need to know his IF, but I doooo love me some BBS.

I just did my first Fondo. 103 miles, similar FTP to yours, I did .73 and it didn’t have anything left in the tank by the time I finished. I think I got a little behind on my nutrition, but I think .7-.75 as others have stated is a good goal.

I did a 120mile group ride last Feb with only half your amount of climbing in 8hrs at an IF of .68 and had enough in the legs to enjoy the whole ride. Mind you I’m not far of ,twice your weight and really suffer when the road points up.

Yes, it works for me.

First test done during a gran fondo this weekend: 160km with 2,500vm.

My quark reads 5ish % higher than my Tacx Neo, so I have an ego inflating 235-240ish FTP on my bike using the Quark. 6h00 ride, av.power 140W, NP 185W (pushed hard on the hills, and rode the flats easy).
Nutrition went very weel, 2 bottles with Maurten 320 and some gels along with some more solid foods. Quite some stops though when waiting for all of the group to catch up. Was able to push north of FTP until the end, no cramps or excessive fatigue. Next week a similar hilly ride at 110mi with a smaller group so hopefully less stops and definitely aiming for a more consistent pace. Based on last weekend, an IF of .70 should be doable for les Trois Ballons.

Here’s my ride from BWR a few weeks ago.
7:46 moving time
0.75 IF (367 ftp)
443 TSS

I believe that I paced this ride/race/fondo/death march perfectly. I did have three flats, which resulted in an additional 40ish minutes of resting time… Maybe that helped with me feeling so good?

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So I commented earlier on what I thought was my perfect IF for 100 miles - around 0.77, based on multiple prior century experiences, and also realizing that an IF of 0.86 had put me at/just past my limit on 75 mile Battenkill course.

Went into GFNY last weekend feeling good - and for 83 miles, I was executing perfectly to my most of my plan.

Goal was target of 180 avg/210 NP/0.78 IF:
Mile 42 - 175 avg / 200 NP / 0.75 IF (just before bear mtn)
Mile 50 - 183 avg / 210 NP / 0.78 IF (after bear mtn)
Mile 83 - 178 avg / 204 NP / 0.76 IF (more tough climbs but trying to be careful to save some for end to finish strong)

Consistently 10 mins ahead of my time last year throughout the course ckpts.

I then failed spectacularly at 83 miles in with stop and get off the bike leg cramps that hit me repeatedly. First insides of thighs, then back hamstrings, then top of thighs, eventually all randomly, sometimes front and back at once if leg bent, cramping to limp to the finish riding at 0.50 IF and losing 25 minutes over my time last year. I’ve never had them hit so badly. Watched over 200 riders pass me in the last 17 miles, ending at 163 avg/193 NP/0.72 IF.

I believe it was a massive hydration failure on my part - only one 24 oz bottle for first 50 miles on a day that got much hotter than expected. This was the only place I deviated from my plan.
I intended to drink two bottles 44 oz total and refill both at 50 miles. When I realized I wasn’t drinking that much an hour in, I figured maybe I’d go to ~65 miles instead, fill there, and then increase water intake later when hotter. But then after making that decision, I stopped at 50 miles for quick leak as I originally planned. So I just filled one bottle after needlessly rationing myself, and now those two had to go 50 miles or take another stop. Stupid stupid stupid… didn’t stick to a solid plan, hoarded water/nutrition for no good reason, and worrying about a possible second 30 second stop killed my ride. I estimate I was down about 8-9 lbs of weight at the end and just dehydrated badly by the end. I knew better from what I’ve read, heard on podcast, experienced myself when newer to this - yet I totally blew it on a chance for my best ever century on a tough course. Maybe this time finally lesson learned?

So, to say it again - IF is important, but so is hydration and nutrition :disappointed:


Maybe the moral is “Never kick the hydration can down the road”. If you know you are behind you should do something about it NOW.


@Enrico Good luck tomorrow!!

After reading through your thread, I wanted to post on my 1st 100 mile fondo. Perhaps my experience will help someone else. I did (1) ~80mile ride to see how my body would feel, but prior to that my longest ride was around 50 miles. I had planned to conservatively average around .7 IF based on the examples above. I figured out the wattage range I wanted to maintain, set up my computer to show 5 minute power in addition to my usual 5sec, and intended to watch it over the ride.

Perhaps not surprisingly I ended up with a group of faster riders and didn’t stick to the plan. By the finish I was properly wiped, but still standing. In retrospect, I think I was lucky I held it together. Eating as much as I could stand and drinking way more often than usual probably saved me from cramps and bonking completely.

Highlands Gran Fondo (NJ / NY)
182 avg, 226 NP, .87 IF (260 FTP), 433 TSS
5:45, 101miles, 8500ft

My last ramp test was about a month ago, so maybe my FTP should be higher. Anyway, I have another fondo tomorrow, going to try and keep the IF lower and see how that feels.

Thanks everyone for sharing their experiences.

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