minimal broadcasting frame length in a CSMA/CD protocol

i'm unsure about the following question, would appreciate your assistance with it:

in a CSMA/CD network with a cable length of L, and propagation speed T, with no need of repeaters(the signal is not decreasing): is it possible to decide the minimal length of broadcasting frame that can be broadcasted in the channel?

this is what i think: $$L_{min} = 2 * \frac{Max \ \ Length}{propagation \ \ speed} * RATE$$ however, we don't have the rate, so i don't see how it is possible to overcome this and calculate $$L_{min}$$

can it be represented just as a function of T and L? i don't see how, but would very much seeing how it is possible to represent $$L_{min}$$ using only T and L as defined(propagation speed and length of the cable).

thank you very much for helping