Hey all! I run a 52t large chainring. I'm reading about how alot of TT competitors are riding larger rings, like 55t. What ring size are you using and why? Thanks!

I have a 52 on my Shiv, which has 165mm cranks, but I have a 54 on my P2 that has 170mm cranks. I wish I could say I landed on that after hours of testing but the honest truth is that's just the way those bikes came. I have not, as of yet, played with changing chainrings. I find it much easier and economical to test cassettes.

I will say this, however, when I decided to try my hand at St. George, knowing that course is notoriously hilly (particularly Snow Canyon Road), the P2 was almost instantly eliminated from consideration. The smaller chainrings on my Shiv gave me better options for climbing big hills. Looking back, I didn't give up anything on the flats or descents with the Shiv but it was a much better choice for the climbs than the P2 would have been.

So, my take is you have a couple variables to figure out. First is how much power you can put down. If you're a monster, averaging a couple hundred watts over the course of a ride, maybe bigger is better for you. If you live and ride exclusively in flat-ish territory, maybe you can make better use of 54 or better.

My thinking is if you're on flat ground and holding a steady high effort pace, look at your cassette. If you're not on one of the three smallest cogs on that cassette, you don't need a bigger chainring.

But that's just me. I'm sure other, better educated opinions will chime in.

Big rings on TT and triathlon bikes: that's a marginal-gains thing. It's not about muscling big gears.

The idea is that with a bigger big ring, you mostly use the sprockets toward the center of the cassette, rather than the smallest ones, on flat and rolling terrain.

The most important advantage is that the jumps between adjacent sprockets are smaller (in percentage terms) past the smallest sprockets, which facilitates staying close to your ideal cadence and power output

Also, the chain line is straighter, reducing the friction that results from transmitting power through a chain that's twisted sideways.

Finally, friction losses are greater with the chain on smaller sprockets than on larger ones.

And you can really crush those long descents.

Crazy good responses. Thank you. I'm an oddball in that I run a 10-speed cassette on a modern frame (Cannondale Slice), with a DA friction shifter. The cassette is a 12-23. On the flats, which is essentially all I ride, I'm in the middle cogs of the cassette most of the time. Although I do find myself switching to the smaller cogs once I get going. My crankshaft came with a 50t-36t, but I switched out the large ring with a 52t. I think I'm going to keep it that way, for some of the reasons that are mentioned here. Also, my own research tells me that jumping to a 54-55t probably won't make a heck of a lot of difference. I'd be better off with a different cassette, as Jen mentions, assuming that's even a concern for me. I ride no hills, hence the 12-23 cassette. Plus - and this is a big PLUS - have you seen the price of the Shimano 53-54t rings? Crickey! Over at Jenson, they advertise an Ultegra 11-speed ring "from $19", but when you select a 53t ring, it's $165! The Dura Ace rings are upwards of $300!! I can get a new crankset for that price. Rotor seems to have some nice offerings at a decent price.

Ya, I'm of the idea that I buy cheap cassettes, like Tiagra, until I figure out what is the best ratio for whatever I'm doing. Then when (if) I wear that one out, I'll replace it with a higher end one.

This has to be the approach, considering the price of things. I also find that "lower" end components are just fine. I run a Tiagra RD on my TT bike. Works like a charm, doesn't hinder me in any way.

Sounds like you are not going to benefit from bigger rings.

And, if you go up to a larger ring, you'll need to change your inner ring to get the shifting working correctly.

And let's not forget that will also involve repositioning the FD, which might require recabling as well.

52 to 56t is a vertical change of 8mm. Usually that won't require a new cable.

Rather than spend $165 for a bigger chainring, feels like you could just use an 11t smallest cog on your cassette instead of 12t. 10t needs a microspline hub, but 11t and 12t are both usually just a bog standard HG hub.

Personally I use a 50t Evosid chainwheel that was $30 off amazon and an 11t-34t cassette that was $15 (Shimano CLARIS CS-HG-8) off eBay. I only have an 8s Deore LX derailleur, though.

I use a waxed chain and only ride 6 miles a day, so the increased wear of a smaller rear cog is irrelevant. Even if it wasn't, a replacement cassette is only another $15.

If this plan is for a 2x chainring setup, there is a potential issue. A few years ago on one of my road bikes, I went to a 54/38 chainring setup (from a 52/42). I quickly discovered that when on the (inner) small chainring, and the two or three (outer) smallest gears, that the bigger chainring interfered with the angle of the chain back to those small gears. The bike was still rideable…just couldn’t use those smaller/outer gears when on the small/inner chainring. The interference was just slight, but enough for the large ring to snag the chain. Then I figured that if I added a small spacer(s) between the two chainrings…just a washer on all the chainring bolts…that it created enough clearance. But THEN I discovered that the space between the rings was wider than the chain, and occasionally it would fall in that gap when shifting, resulting in no drive, and I’d have to stop and correct that mess. Eventually I went back to the 42 inner chainring because I got tired of dealing with it. I suppose the problem could have also been eliminated with a BB that had a longer drive side spindle. — Dan

Yes, which is why I used the word "might". You just never know what you could run into. 8mm isn't a lot but I've seen cables that didn't have even that much.

REALLY good explanations.

Interesting. So, I always look at gearing via gear-inches, because I know my needs there, and I'm always on the same crank length. However, IIRC(?), gain-ratio takes crank arm length into account, I think this was a favorite of Sheldon Brown and it's an option on their gear-calc page. Since you run different arm lengths, do you ever use gain-ratio? Or just pure on-bike testing?

OK, I have *no* idea what you're talking about.

LOL....whilst I greatly appreciate such information that Duragrouch gives, and I encourage it, it really flies over my head!

Not surprising, I realized later that gain-ratio is not just referenced on Sheldon Brown, he invented it, so may be a bit obscure.

Gear ratio, chainring to cogs, is just what it says, and doesn't take into account different size wheels. The same gear ratios on my 20" wheels will be inherently "lower" geared versus 700c.

Gear-inches takes gear ratio, AND wheel/tire size into account.

GAIN RATIO also takes crank arm length into account, along with gears and tire size; Longer crank arms give more leverage ("lower" gearing), but then the pedals have a larger circle to make (more displacement), just like with anything that makes the gearing lower, you need to move your feet farther (more revolutions), but not push as hard. So that's what gain ratio does, it also takes crank arm length into account.

Whole explanation on Sheldon Brown of current gearing descriptive systems, like Gear-Inches, Development in meters, etc., plus gain ratios (semi-long):
https://sheldonbrown.com/gain.html

Short form of above, if you already know the other systems:
The gear calculator on Sheldon Brown has a gain ratio option under "gear units":
https://www.sheldonbrown.com/gear-calc.html

I don't know my needs in gain-ratios, as I've never tried different arm lengths. I just know that with 170 arms, I need 21-85 gear-inch range, at least, at both ends. Touring with load and long climbs, I might need lower than 21.

Short version:

Gear ratio calculations for bike normally include three numbers: number of chainring teeth, number of rear sprocket teeth, and rear wheel diameter.

Each number actually represents a lever length. Higher tooth counts represent longer levers (the lever length is the distance from the rotational center to the point of contact with the chain). So does a larger wheel.

Sheldon Brown simply added crank arm length (the most obviously lever-like of the levers involved in bike gearing) to the calculation.

I think I get it now. I got a "D-" in geometry, if that matters. I want to move to 165mm - or less - crank arms on all my bikes. My inseam is 30 inches. But it's really hard to find 165mm cranks sets and arms for decent prices. As someone else commented, the reason is that "Pogi bought them all." That dude is a beast!

I was terrible at math. And I still don't understand why, when I turn a shirt inside out, it reverses back to front too.

Performance Bike has a current sale going on Tiagra cranks. 30% off ($105, down from $150). 165-mm to 175-mm arms, in various chainring combos.

I think that depends on whether you are reversing a shirt that fully opens in front, a buttoned shirt, so *when open* does reverse back to front, *horizontally*, versus no buttons like a T-shirt, which can only reverse *vertically*, so does not reverse back to front.

I was on an outing, started to rain, and my dad was preparing his rain jacket for me to wear, by rolling up the sleeves, only he was trying to roll them to the inside so wouldn't collect rain, and having difficulty. Me: "Why don't you turn the sleeve inside-out, roll it up to the outside, then turn it back rightside?" Him: "Why the hell didn't I think of that?" And he was a very skilled mechanical engineer, superb at 3D stuff. I was 8 years old. I didn't realize until my mid-30s that this, and other examples in my youth, indicated a superpower for 3D visualization.

You're dad was very smart. And it looks as if the apple didn't fall too far off the tree!