Tub to Shower Conversion

[shamrock_94]

From reading on this and other boards, I see that in order to to convert a tub/shower to a shower I must replace the 1.5" waste line with a 2" waste line. I understand this is code, but can anyone explain the rationale? I don't see the difference between using a tub/shower and a shower. If I take a shower in a tub/shower or a shower stall, the water use would be the same. What gives?
thanks in advance.

[Lancaster]

A shower needs to drain faster than a tub.Tub has a lot more capacity than a shower does,will take much longer to flood and overflow.

[Bob NH]

A shower has less storage capacity before it runs over. A 1.5" drain in a shower will probably work fine if the drain is good. It is even less of a problem if you have the 2.5 GPM limit of modern showers.

The codes are made to deal with worst cases. It could be a problem if you installed one of those multihead body wash things that use 10 to 12 gallons per minute of water from 4 or 5 heads.

If you can get it past the inspector, you can probably get by with the 1.5" drain. If you are doing the plumbing yourself, you can deal with it as you wish.