First, there are a ton of threads on IMMT gearing just do a search.

You can use an adapter like this with your short cage derailleur https://www.wolftoothcomponents.com/products/roadlink

I did the MT and if I had to go do the race again I would go with a 50/34 and 11-28. I would consider going with a 11-32 too. For reference I'm 71kg and my FTP is 320W.
Based on what you described I would not go with a 53/39 unless you enjoy walking the marathon.

A cassette will be $60 tops... You don't need top of the line $250 Red.. A PG1170 or even 1130 will work just fine. Used ones are even cheape!

Also don't get hung up on 90 rpm. You can can go much lower than that over hills and you will be fine if you train for it.

If you have a smart trainer you can simulate hills by doing 5-10 minutes intervals at 80-90% FTP with 60-70 rpm in ERG mode. With a regular trainer you just put it in a huge gear and you get the same effect. Point is: specificity in training.

2:45/3:00 bike at IMMT on a 53/39 with 11-28 (21.9mph). I strategically backed off lap 2 due to losing 40% of my nutrition.

Most of the lovely course is rolling, it is the climb past the casino at the end of the lap that I needed the lowest gear. If you are confident rider, you could max out the 55 on the rollers, like when you descend into St. Jovite.

I think you would be fine with a 42/28 for the few miles up past the casino. A chance to pop out of the saddle to stretch and use some different muscles. if you are worried, the earlier poster has the right idea about getting one of those adapters from wolf tooth to extend your rear derailleur and handle a larger cassette.

i've done the full five times and did not have the right gearing the first year and suffered the second loop. put on an 11/32 and made a huge difference:) good luck. you will love the whole experience:)

Thanks Charlie...what were you running up front? 50/34 or 53/39 or 55/42, etc.?

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My other car is a Felt. DFL>DNF>DNS.

"There will come a day you won't be able to do this, today is not that day."

I've done IMMT twice, on two different cranks (new bike). 2016 I wasn't as strong as I am this year and I ran a 50/34 up front and a 11/28 in the back. Thought that was a perfect setup for my ability at the time (5:50 bike, 11:30 overall) as I didn't suffer and had a good run. This year, new bike, I ran a 53/39 with an 11/28. I was much stronger this year and I didn't feel like the more teeth in the front hurt me uphill and I certainly liked the 53 for the flats (a lot of the course). I think the 11/28 is your best bet, it worked pretty well for me (biked a 5:16, ran my ass off, passed ~800 people on the bike). Of course it depends on your ability but if my times sound like what you are targeting I can tell you those setups are gonna workout just fine! Good luck, enjoy that beautiful course!

I have a friend (6.5 hour bike) that did it quite comfortably this year with a 50/34 11-32

Unless you are more than 4.4W per kilo FTP, then just get a 50/34 with a minimum 11/28, ideally 11/32 if you are less than 3.5W per kilo FTP. All kinds of people will say that they were fine with massive gearing and they think they are cause they get through the bike, but all that high crank torque low rpm riding and power levels above what they should bites in the last 10 miles of the run. Don't be one of those athletes. There is no shame in lower gearing. Don't believe it? Chris Froome uses a 38x32 low gear on almost every mountain stage in the grand tours and he even used it in the Marseilles TT that ONLY had a short 1K 10% grade. Are you stronger than Froome? If not, you know the answer.

Hey, thanks for the response.

The situation, for me, is one of cost as well as necessity. I have a felt IA 10 with 55/42 and 11/28 Sram red etap right now. But I have the short cage derailleur for which the max is 28 in the back. My options, in the OP, were to reduce the chainrings or get the medium cage derailleur and a new cassette. Both are PITA options and the latter is just about $900.00. I'm actually leaning toward the more expensive option and swapping out the rear der and getting a new cassette. Anyone run this course with 55/42 and 11/32?

At 20 min, according to Strava, i'm at 1.8W per kilo. Note...am fat...losing weight for this race...appx 50 lbs.

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My other car is a Felt. DFL>DNF>DNS.

"There will come a day you won't be able to do this, today is not that day."

I am also not one of these '4+ watt/kg' guys...
I'm more like 3.2 w/kg.
I've done MT several times now, and seem to get by OK with a 50/34 and 11-28. But I may swap out my rd to a medium cage next year and put on a 32. I was able to get up all the rises staying seated, but it is a little bit of a grind for me, I would have used the 32 each time if I had it.
I'm 5'10, about 182. I need to lose weight too... :(

53/39

Do you have a power meter?

Yep. Quarq.

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My other car is a Felt. DFL>DNF>DNS.

"There will come a day you won't be able to do this, today is not that day."

Are you sure your Quarq can take compact crank. Check the BCD, 110 is for compact chainrings. You cheaper option may actually be the WiFli rear derailleur.

FWIW My FTP was just about 4.0 W/Kg last year at IMMT with a 34/27. I had no issues on the steep parts but still got out of the saddle for a few short sections. I did the 70.3 this year at a FTP of 4.1 W/Kg with the same gearing, I didn't even question trying to switch to a different cassette even though I was pushing more watts since it was a 70.3.

You are targeting an aggressive weight loss. You could make huge progress on that side but fall short by 10lbs (and still be a huge win for you dropping 40) and have that be a big impact on w/Kg. Either way you won't be sorry with extra gear.

I am gonna have to disagree with you and stick with my original post. I was pushing ~3.2 w/kg and was fine on 53/39 with 11-28. Was I a 100% happy camper at the end of the run? No. Are you ever at an IM? No. If you are you didn't empty the tank. I ran a 3:34 OTB (ran a 4:02 in 2016) and felt damn good. I'm not Chris Froome, I agree, but you don't need to be pushing crazy w/kg to run a 53/39. Remember Froome has to last 3 weeks and we get to drink beer the next day. Just keep yourself in control on the Chemin Duplessiss and the highway hill. Spin to win baby!

1.8w/kg is going to make it a pretty tough day without proper gearing. I don't doubt that you will lose 50 pounds by race day—that's very achievable—however it will be hard to increase your power while doing it. Not saying it can't be done, but it's very hard to do both effectively.

Assuming 200w/240 pounds, you may hit 210/190, or 2.4w/kg. Target power for the race would probably be around 140w, or 1.6w/kg. You'll still need all the gearing you can get. You may need to do both the crank and cassette to be able to get through there optimally.

Comparatively, I did it in 2013 at 3.3w/kg, with a race target of 2.0. Gearing was a 53/39 with a 12-32 10-speed cassette. It wasn't too bad coming up Duplessis. I was able to keep below 250w (my upper *upper*, *almost* never go past limit) for all but 5 minutes. Cadence did get pretty low—often below 50 during that period above 250w. But again, it was only for 5 minutes total.

Could I have used easier gearing? Yes, I would have loved to have a compact crank. Did I absolutely *need* it? Not in this case. I still had a pretty consistent ride (1.06 vi) and finished in 6:05. http://tpks.ws/H1pt8

So if you've got a lower target, you're probably going to need more gearing, unless you specifically train for this section of road and/or sacrifice other parts of the bike (pushing less power to save some juice for the hills). Either way, you will be slower without the right gearing.

I could do the math on this, but I would just ask the question of how important is it to finish this as quickly as possible? If you want to save 5-10 minutes (wild guess) I would do what you can to ride a 50/34 with a 11-32. The Wolf adapter is cheap, and totally worth a try as a first step though!

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George Dedopoulos | @geodee | geodee.com | Team Atomica | Toronto Triathlon Club