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I am trying to wrap my head around the benefit I may get out of small changes regarding my transmission ratio.

Here is the premise:

  • 11-42 cassette (Shimano M7000)
  • 36-26 crankset (Shimano MT600)

I found that I generally don‘t use the lowest gears much - if at all - as the hills around here are more like bumps in the landscape.

That led me to wondering if maybe even small tweaks, like switching to a cassette with less teeth in the lowest gear as well a crank with more teeth would even be recognizable.

To summarize: Would changing above mentioned cassette and crank to

  • 11-40 cassette and
  • 38-28 crankset

even matter?

I am very interested in your experiences and thoughts about such small changes.

Supplementary question: would that change lead to compatibility issues?

Thanks!

  • 1
    I have done a similar swap upping a 42 tooth big ring for a 44. For me there was a notable difference. The area I ride has a long slight downhill section where the 44t/11t gearing combo helps. But I still need the 22t/36t set up for the steepest parts So to answer your question of it be perceptible for me it is. As to the cost effectiveness I did it as part of replacing worn parts. – mikes Jun 9 at 20:29
  • This may help you getting a feeling for the various gear ratios: ritzelrechner.de – mkrieger1 Jun 10 at 12:09
4

To start with, forget the math of the gear calculators. You can use those later....

If you are spinning out - is you cadence at 90-100 when spun out? If not, leave the chain rings and work on spinning technique. Changing the chain rings will help only for the times you are spinning out. If you spinning out for a only a short percentage of the time, it may be best to accept it and use the time to perfect spinning fast and smooth. Keep in mind an increase the size of the chain ring comes at the cost of larger speed jumps between gears.

If you are finding the jumps between gears are too large (i.e. can't get the right gear for the speed so 'hunt' for a comfortable gear), reducing the size of the largest cog will reduce the size of jumps between the larger cogs- exactly how far it goes depends on the specific cog sizes used in the cassettes. Ideally you want a cassette size that gives you the lowest gear you use on its largest cog.

Head out on ride that represents a high speed day you regularly have (e.g. a tail wind on a long down hill), pay attention to the high speed sections - how much are you spinning out and how much would you benefit by going 5% faster (36->38 is about 5%) keeping in mind that 5% faster needs much more than 5% effort.

Now focus on your slow speed - e.g. hill climb into a head wind - what is the lowest gear are you using? Select a cassette with the largest cog the same size as the lowest gear you you want. You may want to have a bit larger so you have another gear or two spare.

If you think you will increase the chain rings as well as change cassette, you may want a bit lower again (26->28 is about 8%), this is where you may want to reach for the gear inch calculators discussed in other questions..

Overall the cost of dumping a good cassette and chain rings for 2 tooth differences is likely to be disappointing, but if replacing due wear, certainly worth while.

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  • +1, but "reducing the size of the largest cog will reduce the size of each jump" - unfortunately not "each" but usually the last few :) – Zeus Jun 10 at 0:55
  • @Zeus : Good point - have edited answer. – mattnz Jun 10 at 1:57
  • Selecting a cassette with the largest cog the same as used on the ride could well be impossible when there are just two choices 11-40 and 11-42. I argue the difference is quite small. Also the jumps are not too big, even on a 38 with an 11 speed RD. I ride an 8-speed RD gravel bike and I only lack gears between on the road, not off. – Vladimir F Jun 10 at 7:05
  • @Vladimir F - Shimano 11 speed cassettes come in a wide range of sizes well beyond 11-40 and 11-42 of the M7000 SLX range. Op could even install a non- Shimano brand if he desired and the world would not end. – mattnz Jun 10 at 9:31
  • @mattnz cassettes do, but the the rear derailleur does not (officially) support them in 2x11. – Vladimir F Jun 10 at 10:58
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I would say that changing the crankset by 2 teeth is not worth the money it costs. At least try to only change the chainrings first.

Cassettes are much cheaper so it is more natural to start there. However, your current derailleur has the minimum size of the largest cog 40, exactly as you proposed. It won't do much. So thinkink about also increasing the chainrings is natural.

You can calculate the difference using a gear calculator like http://gears.mtbcrosscountry.com If you keep the the smallest cog 11T, which you have to, only larger chainrings can enable you higher speed in flat sections and downhill parts where you control the speed by your power. The denser cassette can only help you to have smaller jumps between sprockets. But with 11-speeds you don't have too large jumps and off-road you don't need such finer ratios as road racer like.

So in the end the chainrings or, indeed, the whole crankset may be be a better investment.

This is your current setup http://gears.mtbcrosscountry.com/#29/2.10I1931I1370

With 28-38 you would get http://gears.mtbcrosscountry.com/#29/2.10I1542I1370

As you can see, your maximum speed at 80 rpm cadence would increase from 35.9 to 37.9 km/h. That means you could keep your cadence lower at higher speed if you want, not that it would be any easier to go high speed.

Changing the cassette to 11-40 does only a very marginal change and I would only do that when having to buy a new one.

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  • Thanks Vladimir, from your experience would you consider it worth it to upgrade the crankset? I see, that the difference in max speed isn‘t that much on paper but I struggle to imagine if it ‚feels‘ more suited for straight tracks rather than climbs. – Xylose Jun 9 at 14:01
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    @Xylose it really is individual. I think it does make a difference. Try to go for individual chainrings, look for something like bike.shimano.com/en-SG/product/service-upgradeparts/slx-m7000/… (change according to your exact cranks model). – Vladimir F Jun 9 at 14:05
  • thanks for the tip, I‘ll look into my chainring-only upgrade options. – Xylose Jun 9 at 14:08
  • You may find out that they are not officially supported for MT600-2. They still could work well but may be a topic for someone else to answer or for a different question or for your LBS staff. They should be both 96 bcd and the same bolt pattern but I do not have a personal experience and there could be a difference I am missing. – Vladimir F Jun 9 at 14:10
  • If that‘s the case I‘d really consider upgrading the crankset altogether (something I‘ve not done before - that‘s what makes it so interesting :) ) – Xylose Jun 9 at 14:13
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Changing the chainrings simply changes how fast or slow you can pedal. A 5.5% larger chainring (e.g. changing from 36 to 38 teeth) allows you to keep pedalling at a 5.5% higher speed. Of course this assumes that you are limited by how fast you can spin the pedals (and not by your fitness or road/trail conditions).

Going for a cassette with a narrower gear range reduces gear steps. This is generally desirable because you can pick exactly the right gear for the current circumstances. In a mountain bike it can be less of a problem because conditions usually change all the time. But when you are riding on flat terrain for an hour and one gear is just a bit too easy while the next one is just a bit too hard it’s annoying and less efficient.

If you compare the 11–40 cassette with the 11–42 cassette you can see that the steps between the larger cogs decrease. Where you previously had a 17% step from 24 to 28 teeth you now have a 13% step from 24 to 27 teeth. Of course at the same time the slowest speed you can go has increased from ~5.8km/h to ~6.05km/h because your largest cog is smaller.

https://ritzelrechner.de/?GR=DERS&KB=26&RZ=11,13,15,17,19,21,24,27,31,35,40&UF=2215&TF=90&SL=2.6&UN=KMH&DV=teeth&GR2=DERS&KB2=26&RZ2=11,13,15,17,19,21,24,28,32,37,42&UF2=2215

11–40 on the top, 11–42 on the bottom. With a single 26 teeth chainring: ritzelrechner.de

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The change in the lowest gear would be from 26/42 = 13/21 = 0.619 to 28/40 = 7/10 = 0.7. That is a relative change by 13%. That's noticeable, but it's not much. It's like losing a single gear on a finely stepped transmission. The effect on your gear stepping will be very slight, and I'd wager not noticeable.

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