Yeah, my stock brake lines were 1/4" OD, but...
1/4" OD brake lines are .194" ID, which works out to have a cross section area of .0295 square inches.
3/16" OD brake lines are .132" ID, which works out to have a cross section area of .0136 square inches.
Since I will be running two lines to the rear brakes now, it works out to be .0273 (.0136 * 2) versus .0295, which is only about 7.5% smaller than a single 1/4" OD line. I do not think it will be an issue.
Side note:
I never noticed just how big the dual rear wheel cylinders were until I pulled them out and sat them next to the single front cylinder:
[img]
http://img412.imageshack.us/img412/6191/mastersmalllh8.jpg[/img]
They are huge!