IMUK is not a 1.02 VI course 
I pretty much perfected riding
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Coincidence I’ve just come across this when considering a summer trip to Scotland. Suddenly IMUK looks like a 1.00 course
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Cheers folks 
This is what I was so disappointed to realise after a few years in the game.
I started doing long distance stuff as I am v slow at shorter distances (amongst other reasons) and thought I would be better at long.
I now realise that if you aren’t quick at shorter stuff (especially running) you aren’t going to be quick at longer stuff. 3.30/kms is sprint pace for me.
edit for a bit of misery.
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I think this is another way a polarised type model for training helps. In that if your doing your hard stuff with the capacity to go hard it makes your top end faster, rather than being being a bit too fatigued so it feels hard but isn’t that fast/high power.
There’s obviously a real need for race specific preparation, which may well fit into Seiler’s zone 2.
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one of the things i do in swimming, also something Solar banged on about back in the day was that unless you can swim flat out a 1:15 you aren’t going to be holding 1:30’s unless your name is @TTowel (he had some unusually very low sprint decay)
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My 100 PB is 1:17 dead and I could swim a 57:44 3.8km in the pool (okay, so that’s 1:31.2/100m)
I rest my case m’lord
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So? Gearing is important for anyone wanting to do well, or qualify for Kona, then not take their spot. Etc.
In that vein, and my bad gearing choices for the IMUK course…
…can you use an 11sp chain with a 10sp rear mech? It’s only the jockey wheels and the narrower chain should fit through. With the TT shifters set to tension mode (not the click one) I imagine it’d be easy to use the full 11 gears.
Does anyone have any experience of this?
(Also, thanks for the info @stenard )
My BMC has an 11sp Ultegra 52/36 to test out on the TT bike for now.
You can use 11sp chain on a 10 speed setup. In fact I’ve read it is preferable, manufacturing quality of 11 speed and materials/coatings have all improved. 10 speed is frozen in time.
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Eh???
But the chain is narrower???
I’ve just ordered an Ultegra 12-30 10sp cassette.
My DA cranks are 130BCD, so lowest inner ring I can do is 38 with those cranks.
Like I said, I’ll put my 52/36 11sp Ultegra cranks on for the next recce (hopefully the bottom bracket is the same standard…)
Pretty pissed off, as I’d just bought a Rotor noQ 53T chainring to match to my 39T DA one 
Bidding on a 52/36 105 crankset to save farting around, too.
Good job I didn’t win those disc wheels now!
The internal dimensions of chains haven’t changed for years, it’s just the external width so a 11sp chain should work fine on a 10sp set-up. having said that the reduction in external width is from thinner plates and the rivets no longer protruding which makes the chains weaker so I would always use 10sp for 10sp given the minimal cost of a chain.
Also bear in mind that if you’re playing with different cranksets & cassettes your rear mech needs to have the total capacity to take up the chain slack. If it’s a long cage you’ll be fine but if it short/medium there will be a limit.
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10 and 11 speed chains are interchangeable. Spacing is the same, the 11 speed chain is 0.5mm narrower, but doesnt affect performance
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This is the one thing that I do know!!! 
It’s an utter ballache - I don’t think my rear mech will take a 30 cassette with my current chain length, but we can but see!
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You may prefer the 39/53 - for most triathlon’s an 12-25 cassette and 39/53 would be a good combination
BB should the same.
I would probably swap for 11-30 cassette, however, it really depends how you like to ride. On a 12 I spin out around 65kph, while on an 11 I spin out around 75kph… however, once above 60 you could argue that assuming a good aero position may be quicker than pedalling
On my latest build I am using a 12-28 cassette, and really enjoying the ratio’s: where you need them they are closer together than an 11-30. the 15, 16, 17 in the middle of the cassette is a joy.
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Gearing is pretty much the biggest mistake everyone makes, they look at pro’s riding up a hill in 39x25 and think they should be able to do the same, ignoring the 10mph difference in speed.
But… don’t assume going across the board lower is better, you really want to optimise the gears for the cadences and powers you want to do, being forced either out of your preferred cadence or forced to put out more power than want, or ending up putting out significantly less power than you want can also screw the race - although obviously less bad than if you’re really having to “grind” up a hill.
So don’t be too drastic on the extremes if you’re going to be spending long sections stuck between large gaps elsewhere in the range. so make sure you have close ratios for those speeds you’ll be doing on the bulk of the ride (so make sure the difference in ratio in the 28-35km/h bits or whatever it is you’re going to be doing is right there in the middle of the rear cassette.
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It’s FLAT where I live, so a 55/42 23-11 is perfect (the 23-11 is on the race wheels), but I rarely/never get past the 13 as I’m quite a spinner.
I took a look at the spacing on the 12-30, before purchasing!
Bottom end is decent, but for climbing, the jumps are huge!
But then that’s how you want it, or certainly how I would.
Good thing is, thanks to you guys saving me from Google, I have loads of combos to try out.
I have a 50/34 on my winter bike, so I could even give that a go - but I would be spinning out on the A666 if I used that.
I wouldn’t stress too much about spinning out. I always gladly stop turning the legs over when this happens & allow myself a chance to eat/process food/rest. It’s a long day.
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I’ve had all the different cranksets at one time or another and think 52-36 combined with an appropriate cassette is the perfect compromise. You’ve got virtually the biggest gears of a 53-39 and almost as low 50-34. There always a trade-off in terms of jumps but (as Jim says) if you keep them in the right area then I think it’s worth it.
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Thanks @jibberjim - that’s really helpful.
I am hoping my power will be ~200W on race day.
Like others said earlier, getting that AP up and the spikes down, which I can achieve by spinning up the hills.
Cadence is ~91rpm.
The bulk of the ride is really downhill, nice TT sections, or stupid 2-3% drags.
The hills are short, with only one sharp one, but that’s where the power will be spiking.
The downhills are steep and require more skill than pedalling, all about guiding the bike through the corners and not scrubbing too much off, but just enough. I think there’ll be a lot of time to save on the first lap with that (second and third not so much with passing people)
With me living close enough to ride out and do a loop as my long ride, I can have a real play with gearing over the next four months.
I run an ultegra 12-30 on sram mech, the early 10 speed di2 and dura 10 speed mechanical.
All work fine, the sram red is prefect.
The shimano stuff, which is not supposed to work… is not quite as smooth but that could just be me…!?