Hi everyone. My question today is what are the benefits of having a larger chainring? Also, for those of you who run big gears, what do you suggest? I currently run 48x15 and the next obvious one would be 48x14. But maybe that's still not a big difference for what I need. To give you an idea about my fitness level. Yesterday I pedaled an outdoor, windy, flat track going 20-21 mph for 1hr and 20mins, no water, no stopping, with at least 1 sprint for every 2 miles.

wear spread over more teeth +1t on a chain ring is a smaller increase , than -1t on a hub cog..


you can do the Math Y/N ? Front T divided by rear T is a Ratio... 40/20 is 2:1 ...

Many of us find "gear inches" and easy way to visualize gear ratios that the straight ratio fietsbob uses. It is also a language that has been around a ;long time. "Gear inches" (GI) is what a single wheel wopuld need to be to roll as far as one pedal stroke; in other words how far a high wheeler of 140 years ago would go (or a kid's tricycle). 70" is what a big high wheeler would be and also makes a nice all-around flat ground gear. Above 80" is starting to get big. 90s are full on race on the velodrome.

Your gear is 48 / 15 X 27" (roughly your tire diameter assuming common 700c) = 86.4", pretty big.

As for chainring size, bigger means bigger cogs also to achieve the same GI. Slightly heavier and very slightly more wind resistance but a little more efficient and long wearing. (An aside - running 1/8" chain, rings and cogs as opposed to 3/32" has many of the same advantages/disadvantages.) I run 1/8" and a 42 tooth chainring as I want to be able to go to good hill climb gears, am 65 yo and never had your kind of speed. In my racing days, the fix gear was primarily my poor weather/winter bike and after my first season of racing I rarely went higher that 42-15 at my strongest mid-season.)

Ben

that's only 1 step away multiply ratio by wheel nominal diameter.. ...

(not into single speeds anymore.. but a 16:38, 26" wheel & a 16:53 in a 20" wheel [ IGH 11th of 14 is 1:1.in the hub ] is pretty close to rach other..

Changing the large chainring by 1 tooth is a smaller percentage change of ratio than changing the small rear sprocket by 1 tooth.

Bigger chainring and sprocket = smoother action, less friction, and less wear.

Smaller chainring and sprocket = marginally less weight and marginally less aerodynamic drag. Negligible effect for everyday riding.

Other considerations are simply what is readily available, and what looks better to you.

The gear inches thing is often a useful comparison because a simple comparison of ratios assumes that the two bikes being compared have the same wheel size.


You can of course look it up on a gear calculator online, but I think it is always nice to understand what is happening and to be able to work it out yourself. The calculation is easy enough:

1. Take the number of teeth on the chain ring.
2. Divide by the number of teeth on the sprocket.
3. Multiply by the diameter of the driven wheel in inches.

Example: 49/17 x 28 = 80.7 inches.

This means that the gear ratio produces the same effect as if you were pedalling a directly driven wheel (penny farthing or unicycle) with an 80.7" wheel.

Technically, you should also factor in the length of your cranks, but as most modern bicyclists use cranks of 170mm +/- about 5mm, the effect is negligible. In the world of unicycling, we use cranks from around 75 mm up to about 170 mm and then it really matters.

Ok, this is actually what I wanted to know. Thanks.

For the experienced riders that have tried it all. What was your next move after 48x15? Did you make the obvious move of 48x14? The thing is you really don't know until you try it. Any suggestions?

I would suggest you focus on spinning your legs faster to produce more power/go faster instead of gearing up. Do you ride any hills?

Your listed speed and gearing puts you at about 80 rpm, which isn't super low but it's on the low end. If you could spin that gear at 90 rpm, you'd travel 22.5 miles instead of 20-21 in that same duration.

get yourself a Big Zen chainring, all the cool flatlanders are doing it.

Apparently it is not what the OP was looking for but since it became part of the discussion...I used Gear Inches a lot to help me make decisions about my own drivetrain and everybody seems to be forgetting that tire size, which does effect the actual wheel diameter, should be included to more precisely calculate G/I. I'm pretty sure I've seen a formula somewhere that factors it in, but that's one of the reasons, besides being kinda lazy, why I am content to use one of the abundant gearing calculators available on the interwebz.

And to be precise, seeing as how it was just mentioned that crankarm length ought to be included in one's gear calculations - No, that is not any part of figuring Gear Inches (or the European/Metric equivalent - "Meters of Development"). It is Sheldon Brown's gear measurement system called "Gain Ratio," which is the distance travelled by the bike divided by the distance travelled by the pedals during one turn of the crank, that does bring crankarm length into the equation....

I practice spinning as well. I have a spare wheel with a 17 on one side and 16 on the other. All of my strava segments are very similar from 17-15 except for top speed, but usually the "average speed" is always 20-21.


No hills, I live in Florida. I do enjoy climbing though whenever there's a bridge.

Tire size 25mm and crank arm length is 170. 28's are becoming really popular and I've thought about trying them out.

Nice, glad to hear you've got some experience and know what you want. The 48/14 is certainly a big jump up and is large enough to compete in endurance events at outdoor velodromes, just something to keep in mind.

For some context, I race a 51/15 in the Men's A's at the outdoor velodrome in San Diego, which is a similar gear to 48/14. It's certainly big enough for me to score points in races sometimes against national champs, former world champs and (occasionally) professional road cyclists. But there are guys who ride bigger gears and I happen to prefer a lower, "spinny" gear than some people. As with everything else YMMV, just providing some context. Needless to say the races are fast.