I'm putting the finishing touches on a TT build, and I think I'm beginning to develop an unhealthy obsession concerning the number of teeth on my large chainring. Allow me to explain. I am using a "non-series" Shimano crankset (a RS510 crank, which is essentially a 105, but with solid crank arms, not the Hollowtech.) It's heavier than the 105 by about 1/2 a pound. But I went with it because it was the only 165mm set I was able to get within a reasonable price. But it's a "compact" model (50x34T). And that's where my unhealthy obsession has begun. I'm using a 12-23 (10 speed) cassette. With that lower number of RD cogs, I'm obsessing over whether I need a larger front chainring that has at least 52T. Am I defeating the whole purpose of employing a 12-23 cassette by going with a 50T chainring?

And my obsession has gone further in that I'm gung-ho on using crank arms that are no longer than 165mm. In that regard, I can't seem to find a suitable replacement for what I have without spending far more than I care to. So please help me end this agony! Am I obsessing over something trivial, or will switching to a crankset that has at least a 52T large chainring make a noticeable difference? I ride and compete on fairly flat roads. Thanks and sorry for my nuttiness!

Well, it is a bit of obsessing. But everyone delves into things to their own liking. To each his/her own. That being said…I don’t think you need to get a whole different crankset. (I’m not sure if that is a 1x or 2x set. Either way…) Just keep the 50T ring you have. Order a separate 52T ring. Swap it out depending on your liking, and the terrain of the area you train in, and the terrain of your next race.

Dan

Dan....thanks. You know what's crazy is that after I posted the message, I thought of exactly what you have recommended! The crank I have is, I believe, a heavier mimic of the 105 R7000. So, I think I can just get a large 52T 105 or Ultegra ring and just swap it out.

Thanks again!

If I may ask, where did you get the crank set? I heard Shimano is now offering crank arms down to 160mm. I'm more of a grinder than a spinner and I think 160 is about ideal for me.

Second, you may be obsessing, but I don't think you're wrong. 50 up front and 12 in back doesn't give you much top end. Of course, you really shouldn't even need it unless you're on a descent anyway, but when you are, it's always nice to be able to keep putting power into the crank.

One of my bikes I tried 150mm arms. That crank set came with a 50t big ring and it has a 11t on the rear. I run out of crank pretty quick on any noticeable descent.

Thanks Jen. I got the set on eBay. It's brand new. Really nice cranks. It's just that the crank arm are solid, and thus much heavier that the 105 counterpart. My road bikes use 172.5 and 170. I think 165 will be a good fit for me. But I think I will need at least a 52T large ring. I've decided to order one and just swap it out.

OK, thanks. I think crank arm length is one of those things that can fit a formula, but there are plenty of people who lie outside the norm. I'm one of them. I have short, stubby, but strong legs that don't like spinning very fast. So even though the formula says I should be at around 145-150mm, I absolutely hate that length. I just feel like I can't get any leverage.

Like I said, I have one bike with 150s now. I took it for a ride yesterday on a route I ride pretty regularly, at least the first 10 miles out and the same 10 miles back, I ride pretty regularly. So I know this route, and I know roughly how fast I should be on this route. My normal time on that 10 miles is right around 30-35 minutes, depending primarily on wind conditions. Yesterday, I was 40+ minutes.

The problem is that at a cadence that's comfortable, I don't have the leverage to maintain any speed. So to go faster, I have to pedal faster, but I can't maintain that faster cadence.

Now, my Shiv came with 165s. I want to try 160s with it, but I'm far more comfortable with the 165s than I am with the 150s. I can spin a little slower and just use power to maintain a speed.

So what I'm getting at is that I think you need to determine if you are more comfortable spinning faster or grinding slower. Then you can dial in arm length and chainrings from there.

Thanks. You're spot on. I'm going to "feel" it out. Very easy to swap out cranks. I can even buy just the crank arms!

As an aside, are you competing at Indian Wells in December? I know a lot of athletes around my area that will be giving it a shot and it's tickled my interest.

No. I did it last year. Doing the full IM in Phoenix in November. After that, I will likely call it good on the long distance stuff, mainly because of knee and hip issues. I'm still going to do sprints but will also do more aquabike events.

Just pointing out that 5mm = 0.196 inch. I mean look at that on a ruler. It isn’t much. That’s less than ¼ of an inch, about 3/16 of an inch. Unless you’re a weight junkie…the only strong argument I’ve ever heard for shortening up crank length (when the length you’re using is appropriate) was from a guy who frequently raced criteriums. Pedaling through the turns…with the shorter cranks…allowed him to lean into the turn more (while still pedaling), and thereby faster through the turn. — Dan

For determining the gearing, I always go back to "Am I spinning out my high gear at any point in the race?" -and- "What gears do I need for the worst climb in the race?"

Depending on the race I may have very different cassette and/or chainrings. I don't think there's one correct answer.

Very good advice. Thank you. I think I just need to get a cassette tool.

Absolutely correct, but also keep in mind that's on each crank arm, so effectively you have to double that. It's still a pretty minuscule amount but it could make a difference. For me, the only reason I'm considering just that small change is more of a fine tune in my Shiv. I'm really quite happy with the set up overall, but I can feel a little more strain in the leg muscles under certain conditions. Not often, and I definitely don't want to go too much. But particularly for a tri bike, it can help open up the hips for better breathing. It may not be a significant amount, but then again even tiny gains add up over 112 miles.
Super cheap on Amazon. I got the Bike Hand brand that has both the lock ring tool and the chain whip to hold the cassette in place for under $30. I've used it at least a half dozen times. There are only a handful of bike-specific tools I think everybody needs to do their own maintenance. That's one of them.