I’m looking for a cyclometer that will allow me to switch between training/racing wheels/tires and not have to mess with the computer.
Can anyone recommend a multi-bike/tire computer?
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Unless you are switching from 25s to 19s, I doubt you’d see much difference. That said, Most Cateyes support multiple bikes. You still have to hit some button combo to switch it, but it’s usually not too tough. I use my Polar S710i with multiple bikes. It has different wheel sizes and also settings for the presence of the cadence sensor. Most only support 2 bikes.
Thanks for the reply.
I’m switching from 23’s to 20’s. Do you think a single bike computer would be fine?
Probably good enough for government work. 
If you want the computer to be as accurate as possible, you’ll want to do a roll out test anyway. You can do it for both combos and see what the difference is. If you’re talking 2098 vs. 2102 you’ll be fine setting it to 2100 (or however your particular computer works). A few mm is going to make much of a difference.
BTW: Roll out test: pump tires to normal pressure. Start with valve stem at Bottom Dead Center. Mark floor where valve is. WHILE SITTING ON BIKE, roll forward one complete revolution of the wheel. Mark floor where the valve is now. Measure distance traveled (between marks).
I use a Vetta V100HR on both of my bikes (tri and road) and just switch it from on to the other. no problem with the switch just snap off the computer and snap back on. I use 23’s on my tri bike and 20’s on my road, just make sure you enter the set up correctly then you never have to worry about it.
the vetta has everything piece of candy included and I love that it is wireless