Changing bike chainring or cassette

Hello, I have a TX400. We're heading to the Andes this spring, and I wanted to see about changing my cassette to switch from an 11-35 to an 11-42 so I can tackle the big climbs more easily. So far, I've only found discussions from cyclists who switched from a 48-36-26 chainring to a 44-32-22. Has anyone kept the original chainring and just changed to a larger sprocket?

Hi, To know if the rear derailleur can work properly with an 11-42 cassette, you need to check its capacity. The capacity of a derailleur is expressed in number of teeth. It’s manufacturer data.

Next, you need to determine the required capacity for the planned drivetrain. The required capacity is calculated as follows: (Number of teeth on the large chainring - number of teeth on the small chainring) + (number of teeth on the largest rear cog - number of teeth on the smallest rear cog)

In your case, (48 - 26) + (42 - 11). That’s 22 + 31. So, 53.

Your rear derailleur must therefore have a capacity of at least 53 teeth.

If that’s not the case, you’ll need to either change the chainrings (while keeping the same tooth difference between the small and large chainring) or find a derailleur with that capacity.

So, it might be a question of rear derailleur capacity that’s why you’re not finding any feedback on changing the cassette.

I’m not sure a 11-42 cassette can be adapted to a triple chainring setup. It’s really designed for double or single chainrings. With a small 22-tooth chainring, you can get some really short gears—even with a 34-tooth cog—which’ll let you tackle just about any climb

You should specify exactly (brand, model, and reference) what drivetrain is currently installed on your bike: front and rear derailleurs, cassette, and crankset.

You’ll find all the info you could need on this well-known site.

https://www.sheldonbrown.com/

Especially about gearing:

https://www.sheldonbrown.com/bicycleGears.html

For touring with heavy luggage, you’ll want a mountain-bike drivetrain: - 3 chainrings, usually 22/32/42 or 44 - 8 sprockets, 11–34, or a custom 13–34 (the sweet spot according to some)

Why 8 sprockets? Because on tour you need a tough chain. A 7/8-speed chain is the most durable option.

A top brand for touring is KMC.

https://www.decathlon.fr/p/chaine-8-vitesses-kmc-e8-s-118-maillons-renforcee-adaptee-pour-e-bike/_/R-p-343944?mc=8773397

Back in the day I found a Shimano groupset at Decathlon and asked them to install it for me.

It seems to me that the goal isn't to change the drivetrain but the cassette—replacing an 11-35 with an 11-42.

"Has anyone kept the original chainring and just switched to a larger sprocket?"

It seems to me the question is broader.

It seems possible for a Shimano GRX 600 groupset: "I have an 11-speed GRX 600 groupset where I replaced the 30-tooth chainring with a 28-tooth one. I also swapped the cassette for an 11-speed Shimano 11/42."

Hi there, After some research, the TX 400 is normally equipped with a Shimano Deore XT RD-T8000 long-cage rear derailleur. This derailleur accepts cassettes where the smallest sprocket must have 11 teeth. The largest sprocket should have between 32 and 36 teeth. So, it's impossible to fit an 11-42 cassette. Regarding the chainring, the difference between the large and small chainring shouldn't exceed 22 teeth. So, replacing the original chainring with a 44-32-22 chainring is possible (44-22 = 22). The derailleur's capacity is 47. PS: Shimano's automatic site translator clearly isn't up to scratch 😄, but it's the numbers that count.

Hi Claude, I installed an 11-34 with an 11-42 but on a bike equipped with a double chainring (50-34). However, on my touring bike Vélo de Ville, after a trip to Peru, I replaced my small 26 chainring with a 22—just the small chainring, I didn’t change the other three. Happy riding.

Hi, What’s the model of your rear derailleur?

Hello, What’s the model of your rear derailleur?

Hi, I had a short-cage Shimano 105 derailleur that I swapped out for another Shimano, but a LONG-cage one. I don’t remember the exact model (I’ll check when I’m back home if you want the precise one). Guy

10 or 11 speed? Are the shifters also Shimano 105?

Hi Wegg, It’s an 8-speed cassette and the shifters are original 105. The bike is a Decathlon Cobra 720 from last century 😄. Guy

Hi Wegg Here’s my ride with the 11-42, Shimano Sora 8-speed long-cage derailleur.

Hi Guy,

Thanks for the photo. It’s clear that the older Shimano 8-speed groupsets allowed a lot more flexibility for playing with gear ratios.

Hi Canigou, In the Andes I had 3 chainrings (22 x 32 x 44), 9 sprockets (from 34 to 14) Deore XT. The smallest gear (22 x 34) moved me forward 1.32 m per pedal revolution: perfect for climbing with a load of around 50 kg (bike + panniers). AE

I recommend changing the chainring—it’s more effective and lets you use all the gears on the cassette.