What rear mech do you have, i.e. is it short, medium or long cage?
Pretty certain that no 10 speed Rival mech will take a 40t.
To stand a chance of getting an expander running you'd need to use x9 or similar, and even then frame geo might prevent it from working.
You'd then need a goatlink or similar if that's the case.
@Howard started
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What rear mech do you have, i.e. is it short, medium or long cage?