I guess it might help if you gave a little more info, such as....your truck, their truck, someone elses truck, contract driving, part time driving??... What I have found out over the years is a equal split usually works better for both.
Example: lets say you are going to team with someone in a fleet truck, owner pays for fuel and tolls, everything else come to the drivers, the total income to the drivers is split evenly between drivers.
If you are teaming with the owner of the truck your rate per mile should be lower b/c you will be paid for all miles the truck does in any given week and at least half of all the other income...detention, stop, haz-matect...
But everyone is different, my co-driver and I split everything 50/50 therefor at the end of the week our checks are the same and there is never a problem with someone making more than the other and it helps you split the work load evenly.....Hope my two cents help