What is a gear-chart, and how do you use it?

[lambbo]

I haven't gotten far enough in my life to consider chain-line (does that just mean it goes straight back in the middle gear?) or gear ratios...

If it's possible to explain simply, and provide an example, could someone do so?

I have a Roadini that needs new cassette, I have a 46/30 double up front, and currently I have what I think is an 11 speed shimano cassette with one gear missing to make it 10, and it's always ghost shifting, and I was thinking it's time to do maths and make smart purchases for the sake of nice shifting. 

Help?  Thank you smart people!

[Cyclofiend Jim]

Back in the day, the answer to many of life's question was "AASHTA", which stood for "As Always, Sheldon Has The Answer..." - 

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

Before the current state of the internet, Sheldon Brown was out there documenting and sharing and answering with generosity questions about all things bicycle. I miss him.

It is in his spirit that places like this exist. Be safe out there!

- Jim

[Drw]

What are your shifters?

[ted]

Jim has already given you all anybody really needs. But I’ll add a few thoughts/suggestions anyway.
If you are going to obsess over gear charts do measure the actual radius/circumference or your wheel inflated to the pressure you ride with you on the bike.
When making changes to a bike you are already using, paying close attention to what gear combinations you use in various situations, and where you find the steps between gears either too big or too small. This helps tie what the tables tell you to your reality.
Ignore what anybody else says about what gears they use unless you know them to be a lot like you, just because so and so uses some gear for something is no reason you should, and if they are a pro it’s rather a good indication you shouldn’t.

[aeroperf]

What Ted said.

Also, https://www.sheldonbrown.com/gain.html

Chain line just means taking the best shot at keeping the chain straight.

For a single speed it's easy - front chainring should line up with the rear gear.

For multi-speed derailleurs it is a best guess.

There are standards.  Road chainline is 43.5 - 45 Cm measured from the centerline of the bike.  That's what the front derailleurs are designed to move the chain around.

MTB chainline is approx 47.5 to 50 Cm.  On the rear cassette, it is measured from the centerline of the bike to the middle of the cassette.

Again, Sheldon is your friend.  https://www.sheldonbrown.com/chainline.html

[Philip Williamson]

I love and miss Sheldon, but this is the gear calculator I wish that I had designed: http://www.gear-calculator.com/

I’ve never printed a gear chart. I use the calculator to see some things about the gears I’ll get with cassette and rings I’m considering:
- Range of gearing. I like ~100” at the top, and ~30” at the bottom for most bikes. That’s about a 1:1 gear, with a 30t cog and a 30t ring with a 700/54 tire. Smaller tires or rims will give you lower gears for the same cog/ring combo.
- A ~72” gear around the third or fourth cog spot in the big ring. That’s my main gear, and the chainline should be pretty straight there.
- That the gears aren’t redundant between the two chainrings. It’s an OCD thing more than actual, since I’m never going to make three shifts to fine tune a 54” gear to get a somehow more perfect 52” gear. People used to wring maximum gearing out of 2 rings and 5 cogs and the thought of only getting six different gears made them itch. Try out 52/39 and five cogs and see what you get.

A good place to start is by setting up the calculator with the gears you have, and think about if you are happy with the gear jumps when you’re riding along at a good clip.

And when you buy a new cassette, get a new chain as well.

Philip
Santa Rosa, CA

[aeroperf]

And for ghost shifting…
Check your hub.  It should be designed for your rear cluster.  An 8-9-10 speed hub is slightly shorter than an 11 speed hub, and an 11-speed hub can be used with a 10-speed cluster but requires a small ring spacer.
If you have a 10-speed hub and you’re running an 11-speed cassette with one gear removed, that might put things off enough to  cause ghost shifting, because the distance between the 11-speed gears is slightly less than the distance between 10-speed gears.  For Shimano the spacing is 2.35mm for 10-speed to 2.18mm for 11.
But it is also possible the rear derailleur is set up a little off of where it should be.

[Steve Palincsar]

About ghost shifting -

• Are you friction-shifting?  Some (myself included) find it difficult-to-impossible to avoid ghost-shifting on 8 speeds and above but are happy friction shifting 7 speed or fewer.
• Are you referring to skipping under load?  A worn chain and cassette will do that.
• What exactly do you mean by "ghost shifting"?  My typical ghost-shifting scenario was I'd downshift approaching a stop sign or traffic light.  All would be well.  I'd stop, then upon starting up, when I'd put the drivetrain under load it would skip to the next higher gear with a BANG.  The basic reason is Hyperglide is designed to make shifting easy, so that the chain can happily ride on two sprockets at once (during the shift) without clattering.  So you friction shift and - lacking any clattering to signal that you're not 100% centered on the new sprocket - think you're fine.  You stop, and once you go to start and there's a big load on the drive train it jumps to the small sprocket.
• If you're index shifting and it skips on every shift are you sure you've got things adjusted properly?
  

As for gear charts: the basic idea is, convert the chainring / sprocket combinations to Gear Inches (i.e., the equivalent "high-wheeler" wheel size).  An example: 52x14 feels like -- essentially is -- the same* gear as a 48x13 for the same wheel.  They both translate to 100* gear inches.   With a 17" wheel, a 54x9 would give you the same* 100 gear inches.

[*rounded to an even integer, that is]

The calculation for gear inches is #teeth on the chain ring / number of teeth in back * wheel diameter in inches.  It's away of quantifying the "feel" of the gear for comparison purposes.   You can also do it French style: instead of converting to the size of the wheel, you convert to "development" which is the circumference: how far the wheel travels for one rotation.  A lower gear gives more mechanical advantage / travels less per rotation / is the equivalent of a smaller diameter wheel.

Once you know what the values are, you can lay them out in parallel rows or columns and visually see how they lay out.  Some gear calculators do this with charts, others leave it as numbers and let you compare.  Part of the idea is to see how the gears overlap.  Sometimes two different chainring/sprocket combinations come out to the identical or nearly identical gear.  Sometimes the shift from one to the other is huge.  When you cross from a large to a smaller chain ring if you want to get to the next gear in sequence a chart can show you how many shifts you need in back to adjust for the shift in front.

-

-- 
Steve Palincsar
Alexandria, Virginia 
USA

[John Hawrylak]

Lambdo stated: " I have what I think is an 11 speed shimano cassette with one gear missing to make it 10,"

Perhaps getting a 10 spd cassette would help, assuming you have a 10 speed hub.  Or a cassette which matches the hub you have  

John Hawrylak

Woodstown NJ

[lambbo]

Thank you all, this is really helpful.   

Jim, of course! I forgot about Sheldon, to whom I used to look to for all information.  Thank you. 

Including the tire makes sense, though I don't think I'm a conscious enough rider to feel the difference in ratio if I'm riding 32 or 35, but why not be accurate to start.  

Steve, thanks for the in depth response.  My ghost shifting is under weight, and given that I weight 230, it happens a lot.  My inherited cassette now has an additional 2000 or so miles on it, and I've been meaning to get a new wheel, so have delayed replacing the cassette until then.  I kind of forgot about how old it is.   I use Silver 1 friction shifters, but I also friction shift on my cheviot (9 speed) and it's flawless.  The rear der. is set up properly as far as I can tell...I wonder if given how much I may flex the bike, indexed would be better.     I'm going to look into an indexed downtube shifter for the rear (front is fine friction). 

Thank you all again, I'm going to comb through your suggestions a few times as i figure this out. 

[Steve Palincsar]

On 3/22/20 10:36 AM, lambbo wrote:

>
> Steve, thanks for the in depth response.  My ghost shifting is under
> weight, and given that I weight 230, it happens a lot.  My inherited
> cassette now has an additional 2000 or so miles on it, and I've been
> meaning to get a new wheel, so have delayed replacing the cassette
> until then.  I kind of forgot about how old it is.   I use Silver 1
> friction shifters, but I also friction shift on my cheviot (9 speed)
> and it's flawless.  The rear der. is set up properly as far as I can
> tell...I wonder if given how much I may flex the bike, indexed would
> be better.     I'm going to look into an indexed downtube shifter for
> the rear (front is fine friction).

If you're friction shifting 10 or 11 and you're getting ghost shifting,
don't be too surprised.  As I think I mentioned, I couldn't avoid it
with 8, worked fine with 7.  There's not that much difference in
thickness and spacing between 7 and 8, and that little bit was enough to
make it unacceptable to me.  10 is thinner/closer and 11 even more so. 
Yes, some can do it; but I don't feel bad that I can't, and you
shouldn't either, if that's the case.

It's also possible that at 2,000 miles the chain is worn out and now has
worn the cassette out.

[reynoldslugs]

Phil - that is a great online calculator.  It’s a great tool, but for rainy days and lockdowns, I love this analog go-to:

https://flickr.com/photos/41563482@N06/sets/72157658291314262

Best,

Max Beach

Santa Rosa CA

[Patrick Moore]

Did any of you ever carefully type out gear charts, cut them out, and tape them to your stems? I did!

I also used to calculate gear ratios during boring staff meetings, long ago.

[Philip Williamson]

Oh wow. That analog gear calculator is amazing.
I have a slide rule around - I’ll check Sheldon’s instructions on using it to calculate gears. I did it a couple times a long G.P. time ago.

Philip
Also in SR CA

[dougP]

I looked up "cyclo puter".  The name was trademarked in '75 but not renewed in '81.  That is one rare find.  But.....does it go to 11?

dougP

[lconley]

Yes, I did also. 

Alpine gearing - front step was 1.5 rear steps - the chart helped to know where the next half-step was that required a double shift. Much easier when there were only 5 rear cogs.

When I got my Paramount P-15 - it was half-step plus granny - the gear chart was not as necessary, plus hated to hide the Cinelli stem.

Laing

Delray Beach FL