Deceleration Drift


Rules Questions


So... I am driving my alchemical steam device. It moves forward five feet as an acceleration action, from a stop. That's great.

Next turn, since I only wanted to move forward five feet... it goes forward TWENTY FEET as I try to stop! AHHHHH! *crash*

Why do I have to be an expert to have even a 50% chance to dock my corvus?

I'm guessing this is not RAI?


Got a link to the specs of this vehicle?


According to the deceleration maneuver this is true of ANY vehicle, as far as I can tell.

Also, we don't appear to be able to five-foot-step as a vehicle, either. Attacks of opportunity for all!


Purplefixer wrote:

According to the deceleration maneuver this is true of ANY vehicle, as far as I can tell.

Also, we don't appear to be able to five-foot-step as a vehicle, either. Attacks of opportunity for all!

I don't think objects provoke attacks of opportunity, so it'd only provoke when you bullrush or overrun with the vechile.


This still doesn't adress the question of why, when I accelerate five feet from a dead stop, that I drift forward up to twenty feet more when trying to stop the vehicle. This is true of an alchemical sky dragon and of a chariot.


Should there be a 'nudging' maneuver added? Or should the game limit the amount of drift to half acceleration? Or half the previous speed?


A case for applying common sense when the rules don't do so. The actual vehicle rules are intended for intense driving under combat conditions, not parking your care. You probably shouldn't be applying those rules outside of combat.


Even in combat, 20 feet of drift is SIGNIFICANT. I ease my chariot forward and end up running into the barn wall while trying to line up a shot with the hobgoblin enforcer. This is conducive to neither barn nor chariot safety.


As I said, it is for combat speeds, much faster than 5 feet/turn. For example in really life I can sprint fast enough that it can take me 20 feet or more come to a stop. A chariot moving at speed will take much more because of higher mass and velocity.


Isn't that what deceleration each turn is about? If I'm going 60 with an acceleration of 20, it takes me one, two, three turns to come to a complete stop, 18 seconds, a tremendously long time.

Yet if I accelerate 5 feet from a dead stop, the next turn I drift 5-20. There's no rule covering this other than that, which makes no sense.


Any other thoughts on this phenomenon? Errata?


My thought is you should have not chosen to drive an alchemically powered vehicle.

PRD wrote:
Alchemical: Rarely, an alchemical engine may propel a vehicle. Powered by steam or more volatile gases and reagents, a vehicle with an alchemical engine requires either a Knowledge (arcana) or Craft (alchemy) check to be driven. The base DC to drive an alchemical vehicle is 10 higher than normal. Alchemical engines can be extremely powerful, with the ability to propel vehicles hundreds of times their size. They can also be very fickle when driven by creatures uninitiated in the secrets of alchemy.

(emphasis mine)

A more.... normal vehicle would have a DC of only 5 to stop out of combat or 20 in combat. This seems to be completely as intended.


Their complaint happens regardless of the vehicle they drive. This is why you should always open your rules post by posting the relevant rules.

Deceleration wrote:
Decelerate (standard action): With a successful driving check, the vehicle's current speed decreases by a rate up to its acceleration (in 5-foot increments; minimum 5 feet). On a failed check, the vehicle does not decelerate. Either way, the vehicle can move forward diagonally. If deceleration reduces a vehicle's speed to 0, some amount of inertia will continue to move the vehicle forward. The vehicle moves forward (either directly forward or forward diagonally) 1d4 × 5 feet before coming to a complete stop. Having the Expert Driver feat reduces this distance by 10 feet (minimum 0 feet).

So without Expert Driver you always drift at least 5 feet. With it... you still have 50/50 odds of moving at least 5 feet.

And, unfortunately, this looks like part of the basic design of the rules.

Acceleration/Deceleration wrote:
Vehicles must accelerate to reach their maximum speed. Each round, with the proper driving action and a successful check, the driver can increase the vehicle's movement by its rate of acceleration, as long that value is no greater than the vehicle's maximum speed. Vehicles must decelerate to slow down and are hard to stop at an exact point.


Bob's on board.

Do you believe it's the intention to cause the vehicle to lurch forward up to twenty feet during a basic shift of position?

Do you think Renaissance chauffeurs spent a lot of time backing up laboriously to get the coach into the right place?

I'm hoping for some Dev feedback on this. It's not quite as jarring as pirates dropping dead from lethal rashers of Rum, but it seems like a significant oversight in the rules of the system.


These are just quick add on rules. Pathfinder can't be all things, and one of the things it isn't is ChariotWars (assume game idea though) and as such the rules are brief, quick and dirty. Meant to give you enough to make it work, but not necessary provide a full simulation.

It is pretty simple to use some common sense, like deceleration won't cause it to move faster than it was before decelerating and that the maximum inertia won't be more than 5' less than then previous speed. I doubt they will make any official rules changes to such a minor part of the rules, but most people and groups can probably handle this without any particular difficulty.


We're all pretty much agreed that the lurch is silly, though? No dissenters?


Oh yes, absolutely. But the rules are full of all kinds of weirdness like this. I mean, you can stop a horse on a dime, why does attaching it to the front of a cart suddenly stop you from doing the same thing? On the flip side, you can accelerate your rowboat to top speed in a single round (using the S&S rowboat). Apparently the oars are rocket powered (or it's just really slow). Anyone standing next to a wall towards the front of the ship when you hit something with the ship (sudden stop) takes 1d6 for the impact, 1d6 for not being able to move through the wall, and has a chance of outright killing lower level sailors... from tapping the pier coming in.

The rules are an abstraction, in this case apparently everything has to coast in like a boat. Or presumably you don't yell "Whoa" at the horses fast enough and overshoot your mark a little when stopping.

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