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Ive got a 2018 Halfords Carrera Valour 18" 24 speed mountain bike which I use regularly. I cant afford to splash out on a new bike so was planning to do some basic budget upgrades to help with the hills as the old age is killings the fitness.

What I was planning is to replace the standard 42-32-22 front chainring with a single 32tooth 104BCD ring and new 170mm crank arms. I very rarely use the outer chainring so not bothered for speed. Along with this, swap out the rear 8 speed 12-32T cassette with an 11-40T. That should give me the lower gearing for the climbs without loosing too much for level and downhill pedaling.

What Im unsure about is the wide jump between the lower gears. Would this be a real issue or would I be better going for a 9 or 10 speed cassette to fill in the gaps and change the rear shifter to a 10 speed one.

Thanks in advance.

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I looks like an 8-speed 11-40T cassette would likely have pretty big jumps (which is what you intuited): e.g. 11-13-16-20-24-28-32-40T or 11-13-15-18-22-28-34-40. Those jumps range from approximately 15% to over 25% each, which could feel like a lot. (In addition, the gaps aren't very even; the first has a 20% - 14% - 25% sequence, which will be jarring, while the second has a 22% - 27% - 21% sequence.)

On the other hand, to get a better and more even range you'd need to go to a 10-speed cassette which would mean you have to change your shifter too. That would probably double the cost of the upgrade, not even allowing for the cost of a new chain.

Given the replacement cost for your bike is £335.00, spending £43 for a new crank and chainring, plus £27 for a new cassette, about the same for a new shifter, £46 for a derailleur, £20 for a new chain, plus probably a new cable... (The M4100 shifter is compatible with the M6000 derailleur based on this question.) It adds up to half the price of a new bike pretty fast. At that point you have to consider if it's worth sinking that much money into an old bike instead of buying one that better suits you. (You might have some luck looking at used bikes, I don't know what the supply is like these days.)

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    I’m currently repairing an old bike and it’s astonishing (and kind of sad) how quickly it becomes economically nonviable to replace a few components, even if you do all the work yourself.
    – Michael
    Jun 20, 2023 at 6:11
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Your proposed change will make your lowest gear harder and will not help you achieve your stated goal of making riding up hills easier.

Your current smallest gear is a 22/32 which is significantly smaller than the smallest gear after the change 32/40.

Having a small extra chainring on the front is extremely useful when our fitness decreases with age. It's literally called a granny ring!

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