Continuing Which gears combinations shouldn't be used? and How do I know what gear combinations should work without chain rasp on front derailleur?, which are rather generic questions and answers, let us consider in this very question the specific bicycle Raleigh CHESTER 21 2022 with frame size 50 cm. The bicycle has 3 front gears (1 = smallest chainring, 3 = largest chainring) and 7 rear gears (1 = largest sprocket, 7 = smallest sprocket). Which gear combinations are admissible in the sense that they do not cause excessive wear or switching issues? The best explicit list of combinations I found so far is very vividly depicted in http://www.whycycle.co.uk/images/gearCrossovers.png along with the explanation http://www.whycycle.co.uk/buying-a-bike/bike-jargon-buster/bike-gears-explained . However, this is still generic; especially the claim that the middle front sprocket can be driven with 6 rear sprockets is suspicious.

Can you confirm or reject the claims of that article concerning the combinations for a general 3×7 system? Is there a narrower list of combinations for the specific Raleigh bicycle in question? (According to the documentation, the derailleur is 21-G Shimano Acera, but a huge list on https://si.shimano.com/en/manual/search?series=ACERA has led me nowhere so far.)

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    Hi, welcome to bicycles! It would be helpful (since a cursory scan doesn't find it in the linked page) if you added the details of what size the sprockets (especially the chainrings) are.
    – DavidW
    Apr 24, 2023 at 21:33
  • @DavidW Unfortunately, the bike is not with me now (and it's going to take me days till weeks to get the bike and a ruler simultaneously). Therefore, we have to rely upon its description in German or its translation www-lucky--bike-de.translate.goog/Fahrraeder/Trekkingrad/… . They don't mention the sizes. When I get my hands on the bike, which sizes should I measure? The number of teeth, the two outer diameters (between the tops of the teeth), or the two inner diameters (between the bottoms of the teeth)?
    – user69411
    Apr 24, 2023 at 21:49
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    What matters is the tooth count on each sprocket; that's really the only thing that matters. The reason to ask, especially for the chainrings, is because the potential for interference at a particular angle (i.e. in a particular sprocket on the cassette) depends on the size of a chainring compared to the one next to it.
    – DavidW
    Apr 24, 2023 at 21:55
  • @DavidW Ok. It has just occurred to me that a ruler would not help unless I take off the two cassettes (aiming at measuring precisely), which is not going to happen before the bike breaks in some way. As for the teeth, I'm going to count them as soon as I can (not today, though).
    – user69411
    Apr 24, 2023 at 22:03
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    It all depends on chainline, so in addition to teeth count, offset of the crank and cassette matter too. The drivetrain will always be happiest with a straight chainline and ok up to a certain angle. Any rule-of-thumb risks being wrong for your specific scenario. bike.bikegremlin.com/1755/bicycle-chainline has some more info. One fairly safe assumption is that your bike chainline is set up so that the largest chainring will work on the smallest cog, otherwise you wouldn't be able to safely spin out your top gear.
    – shox
    Apr 24, 2023 at 22:23

1 Answer 1


While custom-personalised calculations for your specific bike might be nice, they won't help the next person to read the answers. So a more-useful answer is to show the method.

Start by working out how many teeth your bike's cogs have. I googled up a plausible page which says:

  • Crankset Shimano TY301 48-28T which is clearly a triple, so presume its a 38T middle ring.
  • Cassette Shimano TZ500 14-28T and appears to be 14/16/18/20/22/24/28 teeth.

Poke these values into calculators like Bicycle Gear Calculator for a visual result like this:

enter image description here

There are two combinations greyed out - 28:14 and 48:28, or “small-small” and “big-big” respectively. These are “discouraged” because the chain has to flex most to get here. However, they work fine. [Comment of the original-post author: in practice, the bicycle rider hears noises while cycling with these and close combinations, and it's difficult to shift to such combinations; so no recommendation in practice.]

We see there is one gear combination that is an exact duplicate. 28:14 is the same as 48:24 which means you have the same cadence, or “pedal feel”. So which one you might choose depends on what the terrain is, along with the wind and how you're feeling. These are the “hardest easy gear” and the “easiest hard gear”.

It would be reasonable to think the middle chainring is useless, because the large and small chainrings have minimal crossover and you could do all your riding in those, and forgo a middle ring. (This is the basis for a sub-compact double chainring on some bikes.) However, your fast speed should be “comfortable” when into the smaller rear cogs. This lets you change up the rear-cogs for a stop or a climb without having to change chainrings.

Changing chainrings at the front is always a high-pressure event, because the chain is under tension at this point in the path. So you have to back off the pedal pressure to shift. As such, it makes the ride smoother to shift mostly at the rear, and only change at the front when you have to.

Your bike has 7 rear gears, so the common thought is that the middle chainring can get to all of them without undue wear. The large chainring can totally be used on the large rear cog, but its under the most angle so minorly increased wear.

Your bike appears to be lower-entry spec. Its not rubbish, but is also not a fancy expensive one. The bike does not have a cassette, instead it has an older design of freewheel (hence the 14 tooth minimum). Parts for this grade are common and quite cheap, so if you need a new $30 block of gears every couple of years, that's a tenth what a fancy road cassette could cost. Same goes for common 7 speed chain – it's cheap and available. Don't stress yourself about wearing out the bike's parts, which will take thousands of kilometres to achieve and likely years.

Personally I just ride the bikes, and make sure to clean and lube my chain periodically. This does more to extend the transmission's longevity than anything else.

  • First, thanks! Second, it occurred to me that I had to specify the frame size to get proper tyre designations. I now added the frame size of 50 cm to the question. This implies 28-inch, Continental Ride City, 47-622 tyres. Could I kindly ask you to please adjust your answer in this respect? I think the calculator shows a slightly different result then.
    – user69411
    Apr 24, 2023 at 23:07
  • With the tyres named above, I think gear-calculator.com/… yields the proper™ result (the SL argument is minimal here; we can adjust it to our wishes): i.imgur.com/lfGZ3tX.png .
    – user69411
    Apr 24, 2023 at 23:15
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    @AlMa0 the tyre size has no effect on the relative gearing ratios. It only affects speed at a specified RPM. My whole point here of showing the method and links is that future readers can apply this to their situation and numbers, just as you've done. SE is not a one-and-done, its building a series of long-term useful answers for future readers as well.
    – Criggie
    Apr 24, 2023 at 23:24
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    Alright, thanks! Then do you mind then me editing your answer so that it simply matches the bicycle precisely (i.e., that the reader wouldn't need to wonder about a different wheel size and descend into these comments)? I adapted the wheel size to match the given frame size and repaired some typos and improved the typography. I kindly ask you to approve of the edit. It'd help me as a reference, too.
    – user69411
    Apr 25, 2023 at 0:16

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