Greatest strain

[motorbiking]

10 speed chain is much thinner.

7 speed cassette is 36mm
12 speed cassette is 40mm

 

[durhamplumber]

10 speed chain is much thinner.

7 speed cassette is 36mm
12 speed cassette is 40mm

Inch and a half thick chain???On a pedal bike?

 

[motorbiking]

This is the width of the cassette, i.e. a 12 speed gets nearly double the number of gears in around 10% more width, so the gears have to be more narrowly spaced.

 

[Brigadier]

This is the width of the cassette, i.e. a 12 speed gets nearly double the number of gears in around 10% more width, so the gears have to be more narrowly spaced.

And, because the frames are generally standard size, the wheel itself has to be made more narrow, to accommodate the wider cassette in the same - sized frame.
This makes the wheel a bit weaker.