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I have a Cannondale Topstone 3 with 9 speed Sora Rear 11-34 Front 46/30

I was wondering if I could fit a 11-36 cassette to help with hill climbing. I'm not at all technical with specs so any advice would be fantastic.

Mark
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    Fitting a 36t cassette can help, but I wouldn't assume the gain to be significant. I would rather advice to keep your current one and replace it by 36T when it's worn. What kind of pedals are you using? flat or clipless/automatic? – Rеnаud Feb 24 '22 at 13:48
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    Also, another point, for reference: with 9 speed components, you also have more flexibility as you can also use MTB/trekking components: you could for instance use a triple chainring from the trekking range (44/32/22), but then you would need to change the crankset, front derailleur and one of the brifters. That will be more expensive, but that will give you a range that no gravel transmission can match. – Rеnаud Feb 24 '22 at 14:02
  • Changing from 34t cassette to 36t only makes it 5.9% easier. Noticeable but not world changing. – Michael Feb 24 '22 at 14:03
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    "only 5.9% easier" is still quite significant and may be all that's necessary. It's a noticeable difference when riding, at the very least. – Noise Feb 25 '22 at 08:27

2 Answers2

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The rear derailleur you have is nominally only able to clear up to a 34t large cog. What this means is that if you put the 11-36 on, even with the b-tension screw all the way in so that the derailleur is dropped as low as possible, you will likely find it still grinds against the 36t in the lowest gear.

Sometimes that can be cheated acceptably by replacing the b-tension screw with a longer one or inverting the one you have. Even when this works, the down side is that it makes the shifting a little laggy everywhere else. When it doesn't work, it's usually because the angle the screw is hitting the dropout at gets too extreme for it to be solid against it.

However, there are compatible 9-speed mountain rear derailleurs, for example any of the 9-speed Deore, SLX, or XT models that are made to clear a 36t. The XT-level RD-M772 is probably the easiest to get of those. What you could do is get the cassette, try it with what you have, and have a fallback plan of upgrading to RD-M772 if hacking your Sora RD is unsatisfactory. If you did that you also get a better overall quality part which could have some up side in performance and durability. With the big 16t gap up front you will need the SGS (long cage) versions of those derailleurs.

If you go to the 11-36, you must replace or at least lengthen the chain no matter what you do, so that things won't break if you accidentally shift into large/large. Unless the chain you have is very fresh it probably makes more sense to just replace it at the same time as the new cassette.

Nathan Knutson
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The main problem is that officially the Shimano Sora RD-R3000-GS rear derailleur’s maximum sprocket size is 34t. However, Shimano specs tend to be conservative, so exceeding them by 5.8% with the 36t sprocket is probably going to be fine.

The derailleur’s capacity is 43. You need 41, so you are close but still within spec. (46-30) + (36-11) = 41.

My main concern would be that the gear jumps are even bigger on the 11–36 cassette which I would find quite annoying. Edit: On a 12–36 the jumps are smaller, if you don’t need a fast gear that much it might be an option.

Unfortunately I don’t think you can use smaller chainrings on the crankset.

Michael
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  • Only 2 teeth would need to be added on the entire range of the cassette. For 9 speed 11-34 you might have something like 11-13-15-17-20-23-26-30-34, whereas 11-36 would be something like 11-13-15-18-21-24-28-32-36. So the jumps are all 2 then 3 then 4 as you move up the cassette, just with slightly different jumps. I don't think most people will notice that much. It really depends where you spend the majority of your time. If you will often be switching between 15 and 18 in cruising speed then you might have a problem, but the difference between 15-17 and 15-18 jump is pretty minimal. – Kibbee Feb 24 '22 at 19:22
  • @Kibbee: A 18% gear jump is already huge. Imagine you are pedaling on the 20t sprocket but there is slightly too little resistance and you are already doing 102rpm cadence. You switch to the 17t sprocket. Your cadence suddenly drops to 84rpm. A 20% jump would drop you to 81.6rpm. It depends a lot on usage. For off-road or traveling bigger gear jumps probably won’t hurt that much. – Michael Feb 24 '22 at 19:41
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    I agree the jumps are substantial, but the difference between going to 81.6 vs 84 RPM isn't going to be a huge problem for most people. Also, you could get a 12-36 if you didn't mind sacrificing some top end speed and get 12-14-16-18-21-24-28-32-36 which actually has smaller jumps than the 11-34 while also providing an easier gear. – Kibbee Feb 24 '22 at 21:20
  • Thank you for all your advice. I do bike packing so I'm normally around 25kg including bike when fully loaded, so looking for help with these pesky Scottish hills. – Mark Feb 25 '22 at 13:52