When to change bicycle gears

October 16, 2007 2:46 AM

How/when do you change gears on a multiple-speed bicycle? Out of the 21 gears, there are 11 or so useful/unique ratios. So, do you stay in in one front ratio and only use the rear-derailleur until you have to shift down, or do you shift through the all the available ratios, double-shifting when necessary.

I have a 21-speed town bike (4x3), and most of my cycling is 'normal' road use (minor slopes). Sites like Mike Sherman's Bicycle Gear Calculator can create tables of gear ratios for my bike, given the correct data, including a nice chart of the ratios:

Gear Inch Chart and graph:
          (7)   (6)   (5)   (4)   (3)   (2)   (1)      |    11    13    15    18    21    24    28  ----+------------------------------------------3: 44 | 105.8  89.5  77.6  64.7  55.4  48.5  41.62: 34 |  81.8  69.2  60.0  50.0  42.8  37.5  32.11: 24 |  57.7  48.8  42.3  35.3  30.2  26.5  22.7  20                30          40        50     60     70    80   90  100--------------------------------------------------------------------------1:     1     2     3      4       5     6      72:                    1     2     3      4      5      6      73:                               1     2     3      4      5      6      7

So, If I had to shift sequentially up the gears, I would have to double shift at certain points (shift up on front, down at rear) which is a pain eg:
1.1 1.2 1.3 1.4 <> 2.3 2.4 2.5 <> 3.4 3.5 3.6 3.7

If I don't double shift, I end up with a big change at one point when I change the front ratio, which is unconfortable to say the least...


At the moment, I end up staying in one front ratio and only shifting the rear until it is really needed.. I notice when doing this that it is a bit noiser in the extreme ratios (eg 1.7, 2.7 and 3.1), possibly because the chain is more diagonal in these ratios. Is this bad for the chain/gears?

I also notice that a double shift up/down is a great crash of gears, (especially if made under pressure going uphill), with the chain slipping a couple of times until it catches, which suggests that that is also a bad thing to do...

So any hints on 'best practice'?
TIA

posted by nielm to sports, hobbies, & recreation (22 comments total)

You want to be using the gear selection that produces the desired gear ratio via the largest number of teeth on chain. More teeth holding on the chain means less stress, wear, and tear on the teeth.

Translated into practice, that means use the largest front gear wheel as the default, as this means you will automatically choose the largest rear gear that can produce the right ratio.

Only switch to the smaller front gears when you need too (ie steep hills). In these cases, you'll be using a large rear gear anyway, but once you get back up to speed, switch the front gear to the largest rather than getting a similar ratio by switching the rear gear smaller.
posted by -harlequin- at 3:11 AM on October 16, 2007

To add to that:
In my experience, it's the teeth on the rear gear wheels that get wasted. The front gears are so big with so many teeth to share the load that it's ok to be using the same (large) gear wheel all the time - it will still wear down much slower than the rear cogs that are each doing duty much less frequently, but have far fewer teeth.

A chain is much cheaper (and easier!) to replace that the rear gears (or any gears), so I suggest not being too worried about damaging the chain. The thing to watch in the chain is that as it wears, it stretches, particularly (I assume) if you're a strong cyclist who tends to use high gear ratios. A stretched chain doesn't distribute the force evenly among the teeth - it only grabs the first few, before it's slack, concentrating the force onto individual teeth, so a stretched chain will erode your gears much quicker. If you're cycling and your chain skips a tooth when you're not changing gears, that's a sign of a stretched chain and/or worn teeth.
posted by -harlequin- at 3:35 AM on October 16, 2007

Sounds like your bike could use some oil.
posted by alexei at 3:58 AM on October 16, 2007

You can do it however you want. However, most riders find shifting the front and rear to get to a new gear inconvenient and time consuming and thus put the front into a gear in which they can easily shift into a comfortable gear in the rear. Shift frequently though, even if you are on a little 100 yard elevation you want to shift to accommodate and then shift back. Keep your feet at 90 rpm or higher. Frankly, part of your issue is a too big rear sprocket. An 11-23 would give you a closer ratio and make it easier to find a comfortable gear without shifting the front. You really don't need a 28 in the rear with a triple.
posted by caddis at 4:36 AM on October 16, 2007

Caddis is probably right that an 11-23 would probably make gear changes smoother and easier. You're probably not climbing any mountains or doing technical mountain biking right? So that 24-28 is much easier than you need. (Consider that most road racing bikes have, as their smallest gear, a 39-23 or 39-25, which is way too low for everything but the steepest hills; and even a 24-23 is considerably lower than that.)

Alexei is probably also right: it sounds like your chain is probably too dry. Go buy some decent chain lube (something meant for bicycle chains, not grease or WD-40) and follow the directions on the bottle. You'll notice results immediately, particularly when you shift multiple steps rapidly. (If your chain is very noisy in any but the most extreme combinations, like 44-28, for example, it's definitely in need of lube.)

You don't want to try to move sequentially up each gear, rather, use your 24 and the lowest gears in the back first, then, when you get up to a certain point, maybe 24-15, move to the 34, maybe shifting down to larger cog (so you go to, say, 34-21) in the back simultaneously. Stay there until you're really moving, then shift to the 44, and use the smallest back cogs (11, 13, 15, etc.). And do shift frequently. You want your pedaling cadence to stay basically the same as much of the time as possible.

Try to avoid the most severe chain-crossing gears (that is, 24-11, 24-13, 44-28, 44-24), these lead to maximum stress and wear on the chain and cogs. You're right to think that you don't have 21 real ratios, rather you have all those combinations to achieve the maximum range of choices. Some of those doubled-up ratios are useful because you can sometimes get the same ratio but avoid a energy-sapping shift in the front, but generally, you should not expect to really use all 21 combinations.
posted by dseaton at 5:21 AM on October 16, 2007

I also meant to say that shifting isn't a science -- you don't need to use every gear every time -- it's really an art. You put it in the gear that feels right for the moment, sometimes that'll be one chain ring, sometimes another. As long as you're not in one of those cross-chained combinations, if you can pedal comfortably, you're doing the right thing.
posted by dseaton at 5:25 AM on October 16, 2007

IANLA (Lance Armstrong), but I was always told that the idea was to keep your chain straight (i.e., parallel to your bike frame) between your front and rear sprockets for maximum power efficiency and the least chance for slippage/broken teeth.

Thus, if you're using the large front sprocket, only use the first few rear sprockets. If you have to switch to the next few rear sprockets, switch to the next large sprocket, and so forth.

Or, to use the example I was given as a kid: There are 3 teachers for 7 grades. Teacher A teaches the youngest kids (grades 1-3), Teacher B the middle (3-5), and Teacher C the oldest (5-7). Teachers=front sprockets, grades=rear sprockets. The overlap in grades/gears allows for a smoother transition.
posted by Rykey at 5:36 AM on October 16, 2007

Ditto on keeping the chainline as straight as is practical. Better efficiency and less stress on all components involved.
posted by well_balanced at 5:42 AM on October 16, 2007

Ditto x 2 on keeping the chainline straight, I will use big ring at the front with only the smallest half of the rear sprocket and smallest front ring with the largest half of the rear sprocket. Using the middle ring will get me all 8 cogs on the back sprocket, without twisting the chain too much, a good cross-country gear.

Whilst some say double shifting is a pain, I've found that by using both gears I can fine-tune the exact gear ratio I need, which makes for more comfortable cycling. Unlike a car your legs have a very narrow range of comfortable and efficient rpms.

If all things are equal, definitely use more teeth, ie bigger rings, this also reduces chain slap.

Oh and try not to change much as you climb a hill!
posted by sdevans at 5:56 AM on October 16, 2007

Ditto x3 on the importance of a straight chainline, especially for the granny-gear (24 in front).

Since granny gear is really only there for the occasional stupidly steep hill, you should probably ignore it most of the time; when you do use it, use only 1.1 and 1.2. There's a fairly wide gap between 1.2 and 2.1 but you're quite unlikely to be spending much time in 1.2.

2.1 through 2.4 will all be OK, as will 3.4 through 3.7. Personally I'd pick 2.5 rather than 3.3 for the gear between 2.4 and 3.4, but that's just me.

You might also find things even out a bit if you swap your 34-tooth front ring for a 32-tooth one. Or, you could just ditch the derailleur altogether and spend serious dollars on a Rohloff hub :-)
posted by flabdablet at 7:05 AM on October 16, 2007

I'm usually a pretty big geek about memorizing tables to know the 'proper' next gear to use, but to be honest.... I just go with what feels right.

I've been riding the same bike since 1990 (a 14-speed) and I generally know that shifting from big-ring to little-ring is "worth" about 2 of my rear sprockets in terms of cadence (leg speed). So, if I'm just cruising along, and feel the need to shift in either direction, it's a flip of the left lever, and two clicks on the right lever in the appropriate direction. (Yeah, I'm still using down-tube shifters)

I tend to only change rings for considerable changes in slope though. YMMV.
posted by Wild_Eep at 7:40 AM on October 16, 2007

I should also add two things:

1.) In all of the 1970's era bike books that I read as a kid, (back when a "10-speed" was about as fancy as bikes /were/), the term for the type of shifting where you tried to maximize the number of combinations for the benefit of your legs was called "half-stepping", and serious bike-trekkers would write down the ratios and tape them to the handlebar for easy reference.

2.) In the early 90's, most bike chains became narrower, to help provide space for all of the extra cogs in the rear, as such, the 'no diagonal rule' became even more important. (The price of replacement chains also jumped 3-4x in price.)
posted by Wild_Eep at 7:46 AM on October 16, 2007

Let me just take a moment and contradict myself and several of the other posters above.

Yes, in the ideal world, you would always keep your chainline as straight as possible. BUT, there are plenty of situations where it's actually preferable to cross-chain. For example, say you're cruising along a nice easy flat section of road in your 34-15. Suddenly you hit a short hill and realize you need to quickly get to an easier gear. You should go to your 34-24 rather than your 24-18, just for example, because under tension, it'll be much easier to get to the gear that doesn't require a change in the front. Even though you'll be cross-chaining some in this combination, it's the right one for the situation.

However, if you have time to plan your shift a moment ahead of time, then go to the 24. (Like I said, shifting is an art, not really a science.)

Also, I disagree that you should always go for more teeth in the front. First, because chain slap isn't really a problem if you're on the road, so reducing it isn't really a big deal. Second, because, given equivalent gear-inches, it's easier to accelerate the gear with the smaller front chainring, which means more efficient riding for you. There are situations where it's good to be in a bigger front ring, of course, but you should not necessarily be there all the time.
posted by dseaton at 7:53 AM on October 16, 2007

Two things: Contradicting a comment above, it's bad for your bike parts to be in the large chainring up front as well as the larger cogs in back. This will cause the chain to drive at an angle across the teeth of the sprockets and cause your chain to both wear out quicker and to "saw" across the teeth, causing the sprockets to wear out quicker. On a triple such as yours, you're going to have their respective half-cogs available to the outside chainrings and most of the cog available to the middle ring.

Secondly, and I ride in an area with lots of steeper slopes, I try to stick more with staying in the middle of the cog in back, while choosing a chainring suitable for the "mode" that I'm riding in. If I'm generally having to climb, then I'll use a smaller ring in front so I have more climbing gears available without shifting up front. If it's flat or downhill, then I'll be on the big ring and choosing where to go from the middle of the cog, keeping my access to faster gears in downshifting.
posted by rhizome at 8:31 AM on October 16, 2007

Sure, you can build a spreadsheet to analyze exactly when to half-step crossover your granny... frankly, plates of beans spring to mind. Modern bike components and materials are very good. So good that worries about equalizing wear and maintaining chainline blahdeblah are pretty academic. On top of that, we now have reliable systems with 8, 9, 10 rear sprockets (in my early years of cycling, six was fancy - and no cycling on the lawn). Knowing exactly what gear you're in isn't all that essential any more. I'm assuming you're riding for fun, not for engineering course credits.

When you need a big jump in gear, change the front. When you need a subtler jump, change the rear. Done.

If you find you're bottoming out or never reach the top, consider different parts rings/sprockets as necessary.
posted by normy at 10:33 AM on October 16, 2007

I notice when doing this that it is a bit noiser in the extreme ratios (eg 1.7, 2.7 and 3.1), possibly because the chain is more diagonal in these ratios. Is this bad for the chain/gears?

The guy at my bike shop says this is fine, if you don't mind the rubbing noise. I personally enjoy the quietness of biking, so I avoid those situations when I can.

I also notice that a double shift up/down is a great crash of gears, (especially if made under pressure going uphill), with the chain slipping a couple of times until it catches, which suggests that that is also a bad thing to do...

Yeah, personally I stop pedaling so hard during shifts to allow the chain to seat properly on the new gear, before going back into full-force pedaling mode. This is annoying going uphill, because I sacrifice some momentum by letting up, but it seems like the right thing to do.

To answer your primary question, you have these tools at your disposal (two gears and a variety of ratios). Use them however it pleases you. Personally I keep my front on '2' most of the time, and shift only using the rear gears. If I am going up a huge hill, I'll downshift the front gear to '1', and if I'm going down a huge hill, I'll shift up to '3'. These don't happen too often.
posted by knave at 10:40 AM on October 16, 2007

given equivalent gear-inches, it's easier to accelerate the gear with the smaller front chainring

That's interesting, can you elaborate?

Yeah, personally I stop pedaling so hard during shifts to allow the chain to seat properly on the new gear, before going back into full-force pedaling mode.

For the rear, this shouldn't be necessary at all (see Hyperglide) (though my heavily warn components still appreciate the little break they get :P), but I believe that most modern components will still require clutching for front changes.

Caddis is probably right that an 11-23 would probably make gear changes smoother and easier. You're probably not climbing any mountains or doing technical mountain biking right? So that 24-28 is much easier than you need.

I dunno about that.. For a 2m circumference wheel, 42 front, 28 back, and 100 rpm, you are traveling at 18km/h. I ride a couple of sub 18km/h hills here in Toronto, and it's a pretty flat city. It's the 11 you don't really need, unless you're racing (~46km/h).
posted by Chuckles at 3:31 PM on October 16, 2007

a 39-23 or 39-25, which is way too low for everything but the steepest hills

So.. A road wheel is more like 2.1m, making a 39-23 a 21 km/h gear (at 100rpm). Lots of real world hills are steeper than that, for most riders.

And then there are the standing starts, which often happen every 200m when city riding..
posted by Chuckles at 3:49 PM on October 16, 2007

Ditto on the backing off pressure (clutching) when changing. It might be because of my pre-hyperglide training, but I find it helps.

Also pre-changing is an option: spot a hill ahead, power up, change down, then coast or go over-cadence for a few seconds until the gear "catches up".
posted by pivotal at 8:42 PM on October 16, 2007

Thanks all for your advice.

A clean and a lube helped a lot to smoothen the gear changes (it's a fairly new bike, and I cannot believe how skanky the chain had got after only a couple hundred km -- maybe it was over-oiled on delivery)

So, I guess in summary, go with what feels confortable, avoid extreme diagonal gears (1.6/1.7/3.2/3.1), and back off a little while changing (especially if double-shifting). Preferably, change front cogs in advance of when you need to..

I guess once I know myself, my bike and the roads better, I will get a better idea of when I can stay in the high ratio, and when I need to drop down to the middle.


From your replies, my cadence seems to be quite low. You guys talk about 90-100rpm. I guess mine is closer to about 70rpm (based on the linked charts and 35kph in top gear).
If I pedal faster, it actually tires me out more than using a higher ratio... I am quite tall and heavy compared to your average thin, lithe biker (195cm/6'5", 93kg/205lb/14st9)... maybe that has something to do with it... Or maybe I am just not fit enough :)
posted by nielm at 1:15 AM on October 17, 2007

The standard cadence that serious bike riders generally aim for is about 90. This does indeed feel weird and uncomfortable to casual riders (my normal cadence was about 60 before I found out that 90 was better) but once you get used to it, it's really nice: much, much less knee stress, because you always end up riding in a lower gear.

I found that the extra tiredness I felt after adopting a higher cadence just disappeared once I figured out that my pedal action was wrong. Concentrating on turning the pedals instead of pushing them cleared that right up, and gave me a nice power boost at the same time. Bicycles work much better when your legs are helping each other instead of fighting!
posted by flabdablet at 1:52 AM on October 17, 2007

I am quite tall and heavy compared to your average thin, lithe biker

You really want to protect your knees, so start spinning :)

Maybe I don't concentrate on turning the pedals enough, or maybe my 170mm cranks are too short, but I find that my muscles stall in the mid-90s, hence my basing things on 100rpm. Slower than 90 for an extended period, and I'll start to notice knee strain..
posted by Chuckles at 10:16 AM on October 17, 2007