Perhaps this may help
I2C protocol is 8 bits - usually.
To take advantage of both I2C and ASCII protocol your "data" should be represented as ASCII code AKA 7 bits.
For example numerical data "100" should be converted to ASCII code and transferred as hex 31 30 30 AKA three ASCII characters 1 0 0.
Since you do not transfer binary representation of your data as 8 bits word you have means to detect and even correct errors caused by noisy transmission media.
Never mind the "limits of data type " - immaterial trivia in this case.