Nelson,
Nothing to be concerned about. The Kuhmo run flat is a tried and true tire for the 1800. Be aware that it will behave differently in some situations like uneven ground and ruts in the road. Just think of a tire that is flat on the bottom and how it will behave when you run over uneven ground where one edge of the tire is on the ground and the other has nothing under it. It will push the bike to lean in the direction of the void. This is only a factor at slow speeds. Coming to a stop or moving slowly, at a stop sign, parking lot, gas station, etc. Just be aware of the behavior so you can plan ahead. Dont use the gas pump with uneven ground, avoid the rut in the road, park in a spot with flat ground, etc.
You will aslo notice some other stuff that you will like very much...
Better traction on wet roads, better handling on gravel, better braking ability, and the list goes on. You have undoubtedly already noticed that it has a very smooth ride and those little bumps you fell with a motorcycle tire are a thing of the past, and oh yes it is a run flat dont forget. So if you ever run over something that causes rapid trie defaltion you will not only be able to safley stop the bike, but you will also be able to drive it at zero air pressure at reduced speed for a limited distance to get it repaired or replaced. This has also been tested.
Don't be concerned about cornering. It is true that the car tire will corner a little differently than a round motorcycle tire, but if you keep kuhmo on you will find that it grips the road just a good as a motorcycle tire. Some say better.
Also be aware that tire pressure will be different in the kuhmo than you are used to with a motorcycle tire. Many run the kuhmo at 32 psi, but changing the pressure as little as 2 psi either way will change the way it handles. Experiment a little and you will find what is best for you.
If you want more info about running a car tire on the 1800 look into the GL1800Riders Forum under the sub forum Darksiders. You can ask questions there and find a wealth of information on the subject.