Should the fact I'll mainly be using a bike in ERG put me off going 1x

So in the process of building up a cheapo TT bike off ebay parts that while get some outdoor use but will probably be on the trainer 95% of the time.

For the type of outdoor riding I have planned 1x will likely be spot on with a normal range cassette/mech and bigger rings seem to be a little easier to track down in 1x, so I’d probably go 1x if only using outdoor but generally the advice is ride ERG in the small ring right?

What’d you do in my situation? Obviously not a huge outlay either way but got that kind of decision paralysis we all get some times!

Depends a bit on the trainer you have, and potentially your FTP on that trainer.

  • Some low to mid level trainers require shifting from low to high flywheel speed in order to hit the upper and lower power targets of a given workout.

  • Even if you have one with those limits, your rear cassette may have enough range, but it is not possible to estimate without more info.


Elite Drivo 1 and had planned a 11-25t cassette if that helps? I don’t think it’s great ERG trainer is it?

When upgrading from wheel on a while back wasn’t a huge amount of stock to choose from at the time!

Is this just for TR workouts?

I use my cross bike with 1x on a kickr core and NEVER change gear.

Recommendations for chainring choice are likely based on flywheel inertia as Chad eluded to. But that optimisation is suggested because most people have 2 chainrings, not because a particular chainring is necessarily 100% optimal. The most optimal chainring size could be 75t but that’s not realistic because most bikes don’t have that.

So I say, buy the bike you want and if it works for you outdoors then it can work for you indoors.


having said that, if the bike will spend 95% of the time on the trainer then why are you speccing it based on the outdoor terrain?

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The Drivo 1 is a decent trainer with plenty of high and low power capability, so I don’t think you will experience issues unless you have a very low FTP.

Per ERG, this is the Achilles heal of the trainer. It works but has a tendency to be slow to change resistance, as well as bounce around instead of holding a tighter target like other trainers. If you are doing more steady state stuff (a guess since you are talking about TT stuff), you will probably be fine.

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To better mimic riding outdoors, you always need to use the BIG chainring, erg mode or not. Using lower gears just makes riding a trainer even less like riding outdoors.

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I’ve been using my 1x bikes in erg mode for the last year and have had no problems. The only issue I might foresee is doing VO2 intervals in resistance mode. In 1x you either need to adjust the resistance or shift a bunch when moving between the 120% and 40% sections. In a 2x shifting between chainrings would replace some of the shifting in the back needed for the 1x. But I do everything in erg so it hasn’t been a practical problem for me.

I run a 48t front and outside an 11-36 cassette. Inside I have a 12-25 or 12-28. I started with a straight chainline but now sit in the 21 because my trainer is better able to control and adjust resistance with a slower flywheel speed. If you want to simulate flat outdoor riding (high inertia) be in one of the smaller cogs. If you want to get closer to climbing (low inertia) be in one of the larger cogs.

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Even in your largest gear, the inertia of trainers is much less than outdoors, even when compared to climbing slowly. The only reasons to change gears on a trainer are therefore 1) to spread the wear around, and 2) to keep within the trainer’s speed vs. power limits.

So why do people say to use the small front ring then?

Who says this? If I ever see a preference, its for the bigger chainring due to higher inertia to mimic outdoors

Going off this…

Set your gearing - In order to maintain smooth, even power across all of your power zones, you should maintain a mid-ring gearing in the rear cassette, and either a mid (if you have three) or inner (if you have two) front chainring. Your chain should follow a straight path from rear to front. This will also help you avoid hitting a wattage floor.

From here

Yeah this is a good point I do quite a bit of Zwift racing, too much if I’m honest, though picking up trainer road imagine I’ll be doing far less, and could always switch to the road bike on the trainer in those instances where it’s going to be using a wider gear range, probably makes the racing experience more realistic than doing a crit on a TT bike.

Interesting, I’ve not seen that before.

However, I believe that recommendation is based partly on the “wattage floor” but also on chain alignment. For example, the gear selected by choosing a mid-cassette cog and the small chainring could also be achieved with the big chainring and a bigger cassette cog. The chain wouldn’t run as straight a path but would still be perfectly functional. It’s nothing different to what the chain would be doing out on the road.

I’ve had no issues with zwift racing and free riding with my 1x. I have trainer difficulty / realism set around 40% and you can always adjust it as it is effectively ‘virtual gearing’ to get the low end you need for the steeper parts. I thought about getting an 11-36 for a vEveresting attempt as you are supposed to run the difficulty at 100%, but that is the only reason I’ve thought of for replacing my 11/28 / 11-25 aside from wear.

Because they don’t understand physics would be my guess.

It’s like the folks that suggest jacking up the front of the bike on a trainer to mimic climbing - all it does is give you numb nuts (if you’re a guy, anyway).