Upvote:3
The only consistent thing about carry-on baggage rules is that they are generally very inconsistent. They vary not just between airlines and cabins as you'd expect, but also from flight to flight and passenger to passenger depending on the circumstances.
Some airlines do not enforce weight restrictions at all. Some enforce them routinely - sometimes with that check being done at check-in, other times being done at the gate.
I'm not aware of any airline that lets you "trade" your checked baggage allowance for extra carry-on, however it's certainly possible that by not checking a bag you can avoid going to the check-in counter, which might avoid the need to have your bag weighed and might allow you to carry a heavier bag onto the flight. How successful this is likely to be will vary depending on any number of variables, so I don't know that I'd be relying on it!
Upvote:6
Not a chance. Carry on and checkin are different allocations and they are not interchangeable.
Usually for carryons, size is an issue for airlines. If everyone brings a lot of carryons, then overhead bins gets full and airlines will force us to gatecheck luggage. So, amount of carryons has to be limited.
Many airlines won't weigh carryons normally. But, if they see a particularly oversized or seemingly overweight bags, they will ask to weigh and checkin those.