benjamin163

Hello, how would I work out the crossover between the gears on the larger chainring and the gears on the smaller one?
ie is 5th gear on the large chainring the same as 10th gear on the smaller one?
is there some mathematical formula?
Any help gratefully received.

sarhog

Click here Good luck.

GlennR

It's better to think of it as the small chainring is for climbing and headwinds while the large is for flat, tailwinds and desents.

You're never going to move through the gears in an exact progression. If you did then you would be constantly switching chainrings and moving up and down the cassette.

Litespud

that’s pretty much how I use the gears - I see them as a “high range” and “low range”, with a fair amount of overlap between the two. I generally use whatever range is appropriate to the conditions. I’ll switch chainrings if I run out of range, which buys me a few extra gears at either end, but my range overlap is such that either chainring will give me gearing options around the “middle”

Retro Grouch 

That's all that you need to know.

delbiker1 

There are going to be times when you feel like you are in between gears on the one chainring, you are either spinning too fast, too easy or too slow, too hard.. Time to shift to the other chainring. Generally, if shifting from the small ring to the big ring up shift 2 gears before going to the big. If going from the big ring to the small ring, downshift 2 gears before going to the small. That is what works for me. Sometimes I will have to shift another gear once I have changed from one ring to the other. On long rides, it makes a difference in expended effort when in the proper gear.

subgrade

Of course there is a formula - each individual gear combination has a ratio: chainring tooth count/cog tooth count. The tooth count is usually written on the cogs and chainrings; if not, you can just count. Then you can compare the ratios for each individual chainring/cog combination and see which overlap.

That said, the tool linked to in post #2 is very illustrative and easy to use.

fietsbob

Ratio math quiz: count teeth .. it's a number . use those numbers, calculate, to learn the ratio ...
like 44:11 is 4:1 50:11 ,,,, is 1: 4.545454545454...

rydabent

Or if you have a triple -------------small chain ring for up hills-----------middle ring for most riding---------------large chain ring for down hills or with the wind.

BoraxKid

Nope, wrong again. My triple is used thusly: big ring for most riding, middle ring for most climbing, small ring for extreme and/or loaded climbing.

c_m_shooter

There should be about 2 gears in the rear difference between chainrings. You shouldn't be trying to use them that way though. As mentioned above choose your chainring based on the range you need. Then fine tune your shin with the rear gears.

BoraxKid

If you want to work out the "best" shifting progression for your bike, this article, Gear Theory for Bicyclists, should explain it pretty well:

https://www.sheldonbrown.com/gear-theory.html

I believe that piece was written around the turn of the century, but most of the information still applies to bikes made in the 2 decades since. Good luck!

79pmooney

I couldn't get that calculator to run custom chainrings and cogs. (50-38-24 X 12,14-19, 21,23 9-speed) I hit :custom" but the chart just went blank. I saw no way to enter my sprockets.

OP, calculating your gears is the way to "get" what you need to do to find shift patterns that match your riding style. (It might even encourage you to change the gears top better fit. See my gear choices above. I've never seen my choices on a stock bike but I love 'em. Before I aged, I rode 53-42-28 X a variety of freewheels and cassettes, all having 13,14,15,17,19 and adding more cogs as the numbers grew.

I live around real hills, some quite steep and I love to climb. Having a bike that doesn't allow me to go up them doesn't work for me. (I've been known to pull out middle cogs and add 25 and 28 tooth cogs.)

Ben

caloso

Click and drag the chainring on the left over to the line to add a chainring. You can move them wherever you want on the range. Same with the rear cogs in the line below.

79pmooney

I've never liked ratios. Too hard to remember and keep straight. I find the ancient and granted archaic system of "gear inches" is the easiest to remember and visualize.

OP, "gear inches" is simply the wheel an early bike rider on the high-wheeler of the 1880s was riding. (Also your kid's tricycle.) Both travel one wheel circumference with one complete pedal revolution. The bigger the wheel the farther you went. So riders talked about the "wheel" they were riding. (And racing started right away because that is whet we male humans do.) Everybody "got " that bigger wheels were faster. (And with the need to straddle that big wheel in those high-wheelers, small people needn't apply for jobs as pro bike racers.)

Then chains came along. Suddenly anybody could ride any "wheel" they wanted. Since talking wheel diameter was accepted, people just kept doing exactly that, except now that "diameter" was the diameter of the equivalent high-wheel. Calculating it is simple measuring the outside diameter of the wheel you are riding and multiplying by the gear ratio used. (700c and 27" wheels with normal road tires come out close enough to 27".)

Chainring Teeth / Cassette Teeth X Wheel diameter (27" for most of us) = Gear Inches.

Say 39 teeth in front, 18 teeth in back: 39 /18 X 27 = 58.5" (or a higher-wheeler of just under 5 feet).

Gears over 100" are considered "high". Gears in the 60s, 70s and 80s "normal" for flat ground. Gears down to the 20s for climbing. Below that for fully loaded touring climbing.

(If you ever deviate from the common road wheels to say 29ers or folding bikes you will see where gear inches is much more useful than "ratios". You and your much smaller wife or kid can ride different wheeled bikes; both in 72" gears and pedal the same speed.)

Ben

shelbyfv

Recently, right here on BF I learned you can print a gear chart and tape it to your stem or bars!

79pmooney

Thanks! I'm a guy who wrote programs when mice still had fuzz and all numbers had to be typed. That you could just move chainrings on the screen - revolutionary! I took real pride in having instructions on screen that told the user what to type in (so I could use a program I wrote a year before and now needed again having not looked at it since).

79pmooney

I've been doing that with Excel gear chart a million years. (Well, not that long, but longer than Excel has existed.)

fietsbob

chain wheel : cog .. ratio x wheel diameter in inches, is 'gear inches'..

gear ratio x wheel circumference in meters is 'development' how far you go down the road, with 1 petal rotation..

cyccommute 

Yup. From fast road bike to dual suspension mountain bike to touring bike, I spend most of my time in the large ring in the middle of the cassette.

BlazingPedals

Sheldon Brown's gear calculator:
https://sheldonbrown.com/gear-calc.html

kingston 

I like the Mike Sherman calculator the best

bruce19

I do it differently. If you are in the big ring or small ring and pick you cogs to come up with the same or similar chain/inches you will get the same experience/result. At least that's been my experience. I choose my ring and cog based on the situation and what my legs are telling me. There's also the the idea that you can use the small ring and increase cadence rather than go to the big ring. It's the difference between using cadence vs power. If you deplete yourself using cadence you can replenish with food/water. If you deplete power you need rest to replenish. One let's you keep riding and the other ends your ride. At least that's the theory and my experience.

genejockey

I spent the time to make an Excel spreadsheet that calculates the ratios of all the gears on all my bikes, which was fun, but on the road it boils down to this:

1. Change gears to maintain preferred load and cadence.
2. Big ring till I'm going slow enough that it gets noisy, then switch to small ring and drop 2 or 3 cogs smaller depending on the chainring combo - 53/39 drops 2, 50/34 and 52/36 drop 3.
3. Stay in small ring till I'm going fast enough that it gets noisy, then shift to big ring and go 2 or 3 cogs larger, again depending on the chainring combo.

In the end, I go by cadence, load, and noise, and don't generally look down. I sometimes only know what ring I'm in when it starts getting noisy from cross-chaining.

hortan

Agree, same for us. But available cassettes of the popular brands have to be adjusted to larger sprockets in the last(smallest) 4 or 5 positions in our case. We use for the top gear in the cassette a 16 or 17 Sprocket (Miche)