Very Short Spell Failure Change, mostly for gishes

[Phosphate]

Reduce spell failure by x% where x is double your dex mod.

[Techwarrior]

I'm not seeing how this is enough.
To discount the spell failure for leather armor I need a 20 dex.
To discount the spell failure for a chain shirt, which is what I need to not need to cast mage armor, I need a dex of 30.
I'd much prefer to find a way to snag armored mage. It'd get me a lot farther. Maybe a PrC that gives Armored Mage.

[J.Gellert]

You can just remove arcane spell failure altogether, and have a clean conscience. It's not that important to the game.

[Nighthawk_986]

You can just remove arcane spell failure altogether, and have a clean conscience. It's not that important to the game.

I would have to dispute that a slight bit actually. I don't know about you guys, but when I play a mage, I make sure that Dex is the stat I dump my 2nd highest roll into so I have at least a little AC without the need to cast. However, if there wasn't Arcane Spell Failure, I wouldn't have to worry about doing that. I would instead wear Heavy Armor and use that 2nd highest roll on a different stat entirely (more than likely Con. for Concentration checks, a higher Fort., and more HP.)

[Xechon]

This is not gamebreaking, but removing the armor check penalty definitely is. Do not give casters more power/hp.

True, it doesn't reduce entire armors well, but that doesn't strike me as the point. It's supposed to reduce the chance of failure, letting casters take a risk of losing a few spell slots, but gaining a bit of protection. Overall, nice idea.

Might you consider limiting it by the armour's max dex bonus, for obvious reasons?

[tarkisflux]

I agree that the base reduction is pretty low. By mid levels, you get better mileage out of casting a 1st level spell each day than you do by putting on leather armor, and you have enough slots to afford it. I don't see this as enough to convince casters to change their tactics in general.

So consider me in the "needs more / consider outright elimination" category. You could probably dump ASF for armor with which you were proficient, if you didn't want to dump it entirely. Then the wizard who wants to wear heavy armor has to pick up a few feats or multiclass, which is at least a cost for the ability. Since there are lots of "you don't suffer ASF with these armors (that you also happen to be proficient with)" class abilities in the game at this point, it's really not that outlandish either. There are other things you could do to make it more expensive as well (make it a feat, make it an Alternate Class Feature taking in place of specialization, whatever) if you wanted to, but I don't think they're particularly necessary.