ArgoMan

Hey all. So, I am going with a 12-23 cassette (10 speed) on my new TT build. I ride mostly flat areas. To that end, I have inched very close to installing a 1x chainring. I have an Ultegra R8000 crank (compact, 165mm, 50-34.)

I've looked at various 1x chainrings. My question pertains to the size I should seeking. I'm thinking a 52 tooth would work well with a 12-23 cassette. But I'd like any input that you may have. Thank you!

PeteHski

How are we supposed to know how strong you are? Your proposal sounds sensible for flattish terrain, but you really should use a gear calculator and see if the speeds and cadence work for you.

ArgoMan

Wow, I didn't even know such a thing existed. Thank you! But by looking at a few, it seems that such calculators are somewhat confusing. I'll give it a shot.

PeteHski

I find this one the most intuitive:-

https://www.gear-calculator.com/?GR=...N=KMH&DV=teeth

Eric F 

If you don't need anything bigger than 52x12, nor lower than 52x23, it will work just fine. You're the best judge of whether or not that range is sufficient for your needs.

SoSmellyAir

In addition to the above, I heard that really hardcore TT riders choose their chain rings so that the most frequently used gear combination would have a perfect (i.e., parallel to top tube) chain line.

ArgoMan

True, even in my case (I'm not "hardcore", just beginning.) I have a 12x25, 9 speed set up that works really well. I typically only use 3 cogs, and never have any cross-chaining issues. This is one of my main concerns in using a 1x. It's a bit more centered. And I can't recall the last time I really needed a wider range of gears.

TMonk

You want the chain to be in the middle of the cassette when racing. So, pick a ring that will put you there at your desired cadence and anticipated TT speed. I ride a single 54t chain ring and an 11-28 cassette on my TT bike. I'm a reasonably fast time trialist and wish that I had a 56 TBH. But, then riding home up hill from Fiesta Island would suck even more

Iride01 

The gear calculators still won't tell you if you are able to push those gears or if they will be too easy for you. That will only come with your experience. And for me to be able to tell you I'd have to watch you ride and ask you what gear you are in at various times.

I fail to see the intrigue behind a person making their bike 1x. I'd want options. And that means a 2x or better. Nothing says I have to shift out of the big ring or the small ring. But I'd have the option to do so just in case I found that one little rise that needed a lower gearing when I'm worn out and not able to put much muscle into pedaling. It also seems that 1x systems come with their own set of issues that many DIY'ers have come asking questions about.

TMonk

A rider should be able to determine their approximate "cruising speed" during a flat time trial fairly easily. The rest falls in to place using the calculators once you know your speed band, which is probably going to be fairly small. At least in my experience. Another thing that helps with this is that most riders will not encounter a huge diversity of time trial courses. For example I have only ever time trialed on 4 courses, despite having done it many times.

Also as far as 1x, the advantages to TT are incremental. But, it's a discipline that rewards attention to detail, especially compared to road, which is too dynamic and variable to obsess over equipment IMO. I am sold on 1x for my TT bike. Aerocoach makes some great rings and other after market adaptations for TT bikes.

TMonk

Also ArgoMan I encourage you to post these types of things in "the 33" Road Bike Racing subforum. Activity is slow, but of the active posters there, you have some good experience and results in time trialing and will get a high proportion of quality responses.

ArgoMan

All very good observations. I went to a 1x because I had never used the smaller ring in several years. Heck, I can only recall one time where I used the largest rear cog. And I would experience FD rubbing at times, which I couldn't remedy. It drove me nuts! And this was using two different FDs. The 1x resolved that, obviously. It also made the bike a bit lighter, a tad more aero, and it looks really clean. And I can always throw the small ring back on if I expect to ride more elevated areas.

Iride01 

Hmm, you are right the OP did say this was for a TT bike. So there are a few extra considerations. I just assumed a normal road bike since that is the name of the forum. And the fact I only retain a small bit of the info I read in posts! <grin>

However cruising speed won't be of any help with the calculators if the OP doesn't know what gears they normally cruise in when at that speed. You'd think one does, but I'd bet many can't say for certain.

ArgoMan

I typically cruise using a 50T chainring and the 14 or 15 rear cogs. My speeds average at least 24-25 mph on the aero bars, on flat roads in non-windy conditions. But that's relying on a crappy Bontrager RideTime device that malfunctions quite a bit. Other than that, I'm clueless. I can probably up. maybe I need a power meter.

PeteHski

I was assuming the OP had some previous ride data with at least speed and cadence recorded. If not, then that’s where to start. Otherwise they might as well just guess a chainring size.

Eric F 

There are pros and cons for both 1x and 2x/3x. On a MTB, where small steps between gears are essentially inconsequential, a wide-range 1x is a simple sequential system that eliminates the potential for cross-chaining, and opens up the left side of the handlebar for other controls (dropper, lockout). On a gravel bike, some 1x users may bump into gearing limitations, and a 2x makes more sense for a wider range of gearing, and tighter ratios. That said, I've found I prefer the simplicity of 1x on my gravel bike. For a TT bike ridden on the same (or similar) flat-ish courses, a wide gear range is simply unnecessary. For a road bike, terrain often demands a wide range, and the importance of close ratios increases. I've done plenty of rides where I've used the full range of my gearing (53/39 x 11-29). Yes, some folks are running 1x on their road bikes, but I think we're still a long way form this becoming the norm. That said, if I lived in an area where I never needed the small ring, I would consider 1x for my road bike.

merlinextraligh

So add in a power/speed calculator like Kruezotter. For time trialing the number you need to know is your ftp. From that you can calculate the speed you should be able to maintain for a given grade.

With that you use the gear calculator to get the gear combo you need for your desired cadence.

Or just notice how fast you usually go doing. 2x20’s

Random11

This seems reasonable to me. Both of my bikes are 2x, but I ride often in Tampa and St. Augustine, which are flat, and when there never use the small chainring. If you're not using the small ring, and there are other benefits to 1x, that seems like the way to go.