25-75 where did u get that from?
The triceps accounts for approximately 60 percent of the upper arm's muscle mass.
wikipedia 
that's for average men I don't know about the growth potential of each muscle
Well i didnt actually google it, just a rough estimate, ive always heard that tris make up about 3/4 your arm. Was just trying to make a point, hes asking how to get "big arms". Below is just a quick article.
Big, muscular arms don't come overnight. You have to work your biceps and your triceps.
In fact, if you want big arms, working your triceps is more important than your biceps. In your upper arm, there are two major muscle groups - the biceps and the triceps. The biceps are comprised of two parts, while the triceps are comprised of three. As such, the triceps takes up more upper arm space than do the biceps.
Even bodybuilders who already feel as if they have nicely developed triceps should not neglect direct triceps exercise in favor of extra biceps work, because improving triceps thickness by 1-2 inches will immediately result in an apparent biceps size increase, a fact that many bodybuilders do not realize. Many seek to achieve a specific arm size, but since approximately 66 percent of the upper arm is occupied by the triceps muscle, logically, the triceps actually becomes far more critical than the biceps in reaching this goal, despite many referring to this as a "biceps" measurement (nobody seeks to learn the size of a bodybuilder's triceps, when this in fact is a more significant factor comprising upper arm muscle mass). There is no effective way of measuring the biceps without also accounting for triceps thickness, and although this should seem obvious, there are many bodybuilders who do not realize that building massive triceps also provides an illusion of bigger, thicker, more impressive biceps muscles.
Therefore, if having big arms is your goal, then it makes sense to spend more of your time working your triceps. In fact, you should spend at least one third more time on your triceps than on your biceps.