reel specs

Question
QUESTION: How do you determine the maximum # test line that can be spooled on a reel?
Specifically, I am interested in buying a Medium Heavy rod and a reel to go with it. I would like to be able to fish 20# test. If the reel says: line capacity - 170/12 (Daiwa-X Super Tuned Casting Reel), does this mean that it won't work; or does it just mean that it can hold 170 yards of 12# but could work just holding less 20#?

ANSWER: Hi Larry, and thanks for your question. It will work fine, but as you guessed will hold less line. I do this all the time,by the way,as my hands are small so I prefer a smaller framed reel.

---------- FOLLOW-UP ----------

QUESTION: Thank you for answering my question. As a follow up, does that mean that the reel is not limited by the weight of the line at all? In other words, if a person wanted to put 50# on, he could but would only be able to get a very small amount 50# spooled.
Also, what is meant by the spec they give 170/12. Is it just a middle of the road figure, from which a person can then determine the yardage of any weight line he might want to spool?
Finally, have you use the reel I mentioned? If so, what were/are your impressions?

Answer
Hi Larry, thanks for this question too.
In my opinion this is true to an extent. Reels,like everything mechanical,are built to design limits and it would be possible at some point to exceed those limits. When that happened things would break,or gears would strip. In today's world I think those limits are pretty high as designers have to expect that someone is going to spool up with some mighty high-test braid, which they don't list a capacity for at all.
The 170/12 spec assumes that most 12# test is going to be about the same diameter and with that size line you should get 170 yards ofline on the reel when spooled properly.
I have not used this reel.