My first no-brainer change is put a prior-gen Dura Ace 11-23 cassette on the bike. If you are averaging 27, then you are spending most of your time on the small few cogs. The smaller cassette will give you single-spacing through all the gears you will commonly use and make it easier to maintain efficient cadence.

If you were going to make a chainring change, then I would jump to something like a 56. That would let you run more toward the center of the cassette with cogs that are slightly less drag than the little ones (less change articulation).

Makes sense to me. I had a similar idea when I saw a report on chain line efficiency. The other bit of info you need to take into account is cadence. Without that lots of ratios will get you to any speed but you want the ratio with the best line at your comfortable cadence. What I would do is cruise around a bit at your 27mph then decide which gear ratio you prefer at that speed. Then it’s just using a gear calculator to replicate that ratio at a chosen place on the cassette. Get that ratio on your current set up and then comeback to double check the maths.

This gear calculator maybe? Does anyone have a better one?

Thanks all.

Sorry, I'd forgot to mention my cadence which from the events I've done is 86, so ideally I'd work it out based on that cadence.

I'll likely keep the cassette as it is for now and just try and work out the best ring for me.

Thanks for that calculator, I'd not seen that. It would be interesting what the savings are like as I know I was spending a lot of time lower down the block as I do tend to power the gear rather than spin it. Can't be very efficient on the smaller cogs.

To be fair if it genuinely only is about one gear then you don’t even really need a calculator.

I'm finding that a bit confusing on my phone

But the point is I don't know which gear (ring) it is that will work the best so it's nice to work out a few of the combinations to make a more informed decision.

I did say cadence, so my bad, but I meant as an outcome rather than a metric.

The whole thing is a lot easier, IMHO, if you know the existing gear combo that you want to replicate. Which presumably is 52x?

You've got a double. Planning on keeping it?

If so, I bet you could run a 56/42 combined with a 12-25 for flat courses and an 11-28 for hillier stuff. Flat courses you'll never be in the 11 or 12 really. Hilly courses may need the 11 and the 28 in the same ride to power down a hill and make it up.

If 1x, I'd say go 56t front and own a 12-25 and 11-28.

I'm about 1/2mph or so slower in flat stuff from you and when it is a touch hilly wish I had a 56t for the downhills. In training those wheels of mine have the 11-28 cassette. I've had issues on two loops I train on with a 30sec downhill with the 54t where I wish had that little little bit extra oomph.

Don't cheap on trying out cassettes at least. 105 is cheap enough and good enough to try out and sell what you don't like. I can understand the front rings costing enough for good ones to not desire owning a ton of them.

Yes, currently I have a 52. Basically what I think I need is the chainring that allows me to hold 27mph on the fifth or sixth cog on the sproket which I believe are 19t and 17t.

That is a 68-tooth chainring at ~85 cadence.

Yes, I was thinking of keeping the double, for now at least. I was just looking to keep the upgrade as cheap as possible so in my mind I wasn't going to touch the inner ring as I had no intentions of using it for the two courses I race. I don't have a 25t cassette, I'll have a look at that cassette to see how the ratios differ, closer ratios can't be a bad thing as when I get to a point I struggle above it cadence wise.

There was 9 seconds separating 7 of us last week and I was 3 seconds off placing 3 positions higher so every watt counts!!

Thanks. Wow, that has surprised me! So a closer cassette would be worthwhile by the looks of it.

You are obsessing about something that's pretty trivial. Plenty of pros going >30mph with a 53 on the front.

Chainline isn't the problem, rather the cog. If you are in the 11 or 12 a lot of the time, then you'd benefit (slightly) from a bigger ring. Otherwise don't bother. At 27mph and 87rpm you'll be in the 13-14t cogs. Since you have a double ring, the neutral point is to the right of the middle of the cassette.

For most people 87rpm is low for a 10mi TT, so you may wish to work on that.

Here are the combinations that will get you ~27mph on 85 and 90rpm (either side of your average cadence), assuming you're using 700x23's

85rpm:

54x13 (27.60mph)
56x14 (26.60)
58x14 (27.53)
60x15 (26.60)

90rpm:

54x14 (27.18)
56x15 (26.27)
58x15 (27.25)
60x16 (26.41)

I don't think you're going to be able to get your desired speed while in the 17t or 19t without going with a massive chainring and probably 1x. Going to a tighter cassette won't help because all of the cogs above are already in single tooth jump territory.

If you are sticking with 2x then as the chainring gets bigger you'll run into two problems: (1) chainring availability and (2) front derailleur clearance. At a certain point your FD is going to be as high up the hanger as it can get and won't clear the chainring.

PS If you want to keep the 11-28 but want smaller jumps in the gear you are using, you can switch to SRAM. They go 11-12-13-14-15-16-17-19-22-25-28 instead of Shimano's 11-12-13-14-15-17-19-21-23-25-28.

Thanks for that. Yeah, my cadence is usually higher when I time trial. I've basically not been training since Covid other than a ride out once maybe twice a week, sometimes not at all and with zero structure whatsoever. I'm putting my lower than usual cadence down to this. I only entered these races to get a marker down on these courses so I've got something to compare to for when I'm in full swing for IMW training next year. TBH I'm happy with how I'm going considering.

After considering what I've learned here I'm edging to maybe going for a 54t as it would likely be better for these races and also be something I could use for a flat tune up 70.3 I was going to do next year.

Also it sounds like the gains I was expecting aren't realistic, not that I really had an idea what the savings would be in the first place in all honesty. Big rings do look cool though!

I'd not seen that graph for the 1X but I'm sure I'd heard Josh Poertner say somehere that a 10t sproket has 40% greater frictional losses that a 12t srocket.

Thanks for that. I've downloaded an app and it's great for working out what you've highlighted above. Plenty of things highlighted here for me to consider for sure.