Rules Junkies: 2d10 vs d20

[AeroDm]

One of the great things about D&D are those moments when a nat 20 comes up when it was really needed and everything works out. Yet in a regular combat of 4 on 4 you are expecting a nat20 to come up every other round or so. Likewise, it has always bothered me that an 8 strength character could break something that an 18 strength character failed at because of the variance of the die.

I have always liked the idea of using 2d10 because while it still allows for a great deal of variacne, it tightens the curve a great deal. You can expect, with some accuracy, values to fall between 7 and 13, meaning the individual plusses are more important than the d20 roll.

The obvious problems are that many combat will drag out as they need a 15+ to hit and this is actually hard to accomplish, but assuming this is known ahead of time it shouldn't be too big an issue.

What are the less obvious problems that can't be seen at first blush? Has anyone tried 2d10 and if so what were the results?

 

[dvvega]

Using any dice combinations other than 1d20 do lead to reduced criticals and failures.

Your natural 1 becomes a 2, your natural 20 is 2 10s.

You favour the skill over the random die roll as well. Which is a good thing, as long as you set new guidelines for automatic failures and critical ranges.

As for the 8 strength vs 18 strength, 20 is not a guaranteed success. It never is with skill checks. So an 8 strength rolling 20 is a 19, which is the BARE MINIMUM 18 strength can get on a d20 roll.

During combat, a natural 20 is just a lucky blow so strength doesn't matter there.

 

[Diirk]

As for the 8 strength vs 18 strength, 20 is not a guaranteed success. It never is with skill checks. So an 8 strength rolling 20 is a 19, which is the BARE MINIMUM 18 strength can get on a d20 roll.

Huh? Wouldn't the bare minimum on a strength check for an 18 str character be 5 ? (1 + str mod of 4)

 

[iblis]

From memory, I think Unearthed Arcana has optional rules for using 3d6 instead of d20, for all kinds of things. Have you got UA?

Of course, using that variant, you'd end up even further down the same path.

 

[Turanil]

Using 2d10 would be somewhat more realistic, in that statistically an average result (of action) would occur most of the time.

My suggestion is this: don't change anything except that 2d10 instead of d20. But then, don't supress d20 entirely. Let players choose to use either method. 2d10 could be used in most cases, but sometimes, usually in emergency situations, a character is willing to act spontaneously, do unusual things to try get an edge, has some adrenalin surge, etc. In such cases let them use the d20. The difference: critical success come very rarely with 2d10, but critical failures never come with 2d10 (you cannot roll 1). On the other hand, critical successes come more often with d20, but critical failures (roll of 1) are also possible. In the latter case, add the houserule that something determined freely by the GM happens when rolling a 1 (combat: loose weapon, hit oneself, etc.; repair: totally destroy the thing instead of repairing it; etc.).

Just my 2d10 of course, err... I mean: just my 2 cents.

 

[-Eä-]

Note also that the mean result is 11 with 2d10, while it is 10.5 with 1d20

 

[Greatwyrm]

Taking 20 on skill checks becomes more attractive. Taking 10 (especially if you can do it as some kind of class ability) is much less attractive.

 

[Tonguez]

while it is 10.5 with 1d20

No thats the median - I know its common, but 1d20 doesn't have a meaningful mean because every number has equal probability

 

[RandomUsernamehmimo71]

I've seen this argument a few times. What it basically comes down to is that 2d10, or, by extension 3d6, is better for opposed roles.

For a normal role, to hit a DC, all you are doing is skewing the probabilities toward the middle numbers. While this may seem like your goal, mathmatically, you can achieve the same results by simply raising the DC.
I know it seems counter-productive, but all 2d10/3d6 does in those instances it make it difficult to calculate the percentage of the time when someone will achieve a desired result.

When you have a opposed role, however, it gets more interesting, because both rolls are biased toward the middle, so skillpoints, BAB, etc count for more. The non-roll value becomes more importaint.

Outside of opposed rolls, there's not a whole lot of point, though, unless you mean it as a quick-and-dirty way of raising every DC in the book, automatically.

-Colin

 

[Malin Genie]

No thats the median - I know its common, but 1d20 doesn't have a meaningful mean because every number has equal probability

The mean for a discrete numerical distribution is

Sum(x.p(x)) where p(x) is the probablility of result x occurring.

Why would each of the p(x) being equal (i.e. 0.05) not allow for a 'meaningful' mean ??

Malin "sad for the lack of statistical education in our youth" Genie