D20 vs D100 for a Sci-fi Game?

[Soft Serve]

For a lightcore Sci-Fi game how do you feel on D20 vs D100?

The only arguement I've seen was all about probability, but I'm wondering how you guys feel on how it effects Attributes and Skills and the like.

[TAROT]

Is Lightcore a setting? When I Google, all I get is fibreoptics.

I don't understand what dice have to do with genre/setting.

[Soft Serve]

Lightcore being the opposite of Hardcore.

As in Traveller to me is a Hardcore Sci-Fi setting because it's super in tune with the mathmatical aspects of the game. Like how fast your ship goes after however long of acceleration and the entire construction and creation process is very complex. (not that it's bad, but it's not what I want.)

Lightcore being I would only ever try to figure that out if I absolutely had too.

[Webhead]

Which game systems are you considering using?

[Soft Serve]

I'm not. I want to make my own.

[Webhead]

Ah, I see. In that case, I think it's entirely based on your familiarity with such systems. If you know d20-based systems really well and can thus manipulate, extrapolate and gauge the "feel" of such a system, I would go that direction. Likewise for percentile systems.

[Richard Littles]

I'd say neither and use a 3d6 based system since both d20 and d100 are linear die rolls. Characters will fail more often using a linear system then with a bell curve system.

[outrider]

I agree with richard. It depends on what you are trying to accomplish. A bell curve will give more reliable results than a linear system.

[Soft Serve]

Bell Curve?

I know the average of D6 rolls is like 3.5, but if that's the case wouldn't a D100's average be about 50-50.5 or so? In which case...what's the difference?

[Richard Littles]

Bell Curve?

I know the average of D6 rolls is like 3.5, but if that's the case wouldn't a D100's average be about 50-50.5 or so? In which case...what's the difference?

A bell curve is the probabilities of hitting a specific total on 3d6 (or other multiple dice). For example, to roll an 11 is a 62.5% probability since there are three dice in play and the odds are in your favor that you will end up getting an 11 as a total 62.5% of the time since 11 is the mean for distribution. A roll of 3 and 18 sits at the extreme ends of the distribution of die rolls and occupy a .46% chance of a person rolling 3 1's or 3 6's. This means that on average a character's skills etc... will work reliably with a small percentage chance of them getting a critical failure or success. Positive modifiers are used sparingly because a single +1 can represent anywhere between 6%-16% chance on 3d6.

For a d20, each side of the die has an equal chance of showing up which is a flat 5%. Thus, the die rolls are very wild in their distribution where you will get critical failures, critical successes, normal failures, and normal successes equally. This leads to skills and other character abilities to be very unreliable. This is why d20 based systems use a lot of positive modifiers to boost the character's probabilities up to 63% because without them it's a very frustrating thing to sit through miss, miss, miss, miss, hit, miss, hit, hit, miss, etc.... A modifier in d20 is a flat 5% and at higher levels of the game there is the modifiers being outrageous like a +5 sword etc... The sword grants a +25% chance to hit itself.

The d100 has a 1% chance for any side to show up. It is far more granular in the distribution over d20, but it suffers from the same fickleness with probability regarding successes and failures as d20. Like the d20, depending upon how the system is written can pile on a lot of modifiers to give a character a reasonable chance to perform anything successful.

In Dark Heresy, a starting character will have on average a 30% in skills and they would routinely fail their rolls if there wasn't a rule in the book that said that all rolls for standard tasks are doubled. What this means is that for a standard task, a character's roll is 60% or less instead of 30% or less. For easier tasks the skill roll is multiplied repeatedly for each step it becomes easier.

If you were to compare starting characters between Dark Heresy, D&D, Fantasy Hero, and GURPS Fantasy you will find that the first level characters in D&D and Dark Heresy are totally incompetent in what they can do since the base chance of success is right around 30%. Contrast this a 75 point character in GURPS Fantasy and Fantasy Hero, the characters are totally competent in what they can do due to their base chance of success is at 62.5% for an 11 or less roll. Most characters in Fantasy Hero and GURPS Fantasy have at start a 13 or less roll in most skills which means they will be successful 83.8% of the time. Keep in mind that this is for standard tasks without any difficulty.

[Soft Serve]

Then why is that preferred? It seems like after you become successful at something there's no real need to roll for it since there is such a small window for error.

[Law Dog]

I'd say neither and use a 3d6 based system since both d20 and d100 are linear die rolls. Characters will fail more often using a linear system then with a bell curve system.

Depends on the system and how high the stats/checks are.

You can represent the same % chance of success or failure in both systems. A 10 or less 3d6, an 11 or more 3d6 and a 50% over or under are all essentially the same rolls.

[templeorder]

D20 goes in jumps of 5% probability. Its easy to conceptualize. D100 has varying adaptations. These can be linear or random in progression. Only Star Frontiers used a more interesting approach which had a learning curve i really liked. In the end, its matters most about flavor and which system suits best. I find D20 does not suit me. I really only play my own Incarna system any more, but i play sci-fi, western, fantasy - all genres. I prefer d100 for the flavor. And D100 tend too to use less dice (tend, not all) - i prefer less dice.

[Dytrrnikl]

Maybe it's due to my experiences with FASA Star Trek, d100 system, I am a fan of percentile systems and opposed rolls for ALL Sci-fi light- or hard- core. Although after reading Rich Littles support for 3d6, I'm inclined to agre with him. I do prefer more lethal games though as well, as it is not uncommon for player's in my games to have at least two characters, sometimes three throuhgout the course of a campaign.

[Soft Serve]

Maybe it's due to my experiences with FASA Star Trek, d100 system, I am a fan of percentile systems and opposed rolls for ALL Sci-fi light- or hard- core. Although after reading Rich Littles support for 3d6, I'm inclined to agre with him. I do prefer more lethal games though as well, as it is not uncommon for player's in my games to have at least two characters, sometimes three throuhgout the course of a campaign.

Same on about everything you said. I haven't tried 3D6 yet so if I find it's either too difficult or someone talks me out of it I think I'll try it on.