As per the rules on page 247 of the Core Rule Book it seams that the first four metres of a running start do not bring anything in comparison to a standing horizontal leap. Is this intended? Any ideas?

Could be an error. There is a difference in test difficulty in the Rogue Trader core book, which makes more sense. I haven't checked Black Crusade, Only War has the same version as DH2.

Rogue Trader version:

I see it as a minimum requirement to "activate" and is needed to get the later bonus.

For every four additional metres beyond the first four that the character runs before making the leap, he receives a +10 bonus to his Agility test (to a maximum of +30).

But yeah, no real difference as far as I can see.

Still, you would expect that a 4 meter sprint before jumping has more effect than just jumping while standing still.

Exactly!

To me it seams it would make more sense to handle it like in the jump case. If you try to leap without running you just have a basic width, let's say SB/2 m, without the possibility to extend this with DoS on a test. That would be 1.5m for an average character.

Still, you would expect that a 4 meter sprint before jumping has more effect than just jumping while standing still.

Hmm, I don't know. A "4m sprint" is only about 4 good strides for a short person and only 3 or maybe even 2 for a longshanks; not much of a run-up in the grand scheme of things.

At first, I agreed with you; 4m seemed plenty long enough a run-up, but on consideration, I'm not so sure. Is it long enough to give a bonus over a standing start? That's the question.

I've no statistical data on jumping ¹ , but personally, I'm happy to let the rule stand as it is. The difference between success and failure is pretty significant in this case (for an average dude (Ag/Str 31) it's the difference between up to 5m and 1.5m; as Strength or Acrobatics gets higher, that difference only increases), so handing out bonuses on this one seems like a big deal.

Note also that a bonus to this check also increases the potential distance you can jump and factor that into whether you think a couple of steps run-up will have an impact.

Let's plug in a couple of numbers; a starting character with Strength and Agility 30 and Rank 2 Acrobatics does some jumping:

Standing start/up to 8m run-up: 40% of success, <5.5m covered on success, 1.5m on failure

8m-12m run-up: 50%, <6m

12m-16m run-up: 60%, <6.5m

16m+ run-up: 70%, <7m

The first recognised long-jump world record in 1912 was 7.61m. It's improved somewhat since then, but our starting character with average stats and a little focus on Acrobatics is nearly there himself. The current standing long-jump record is 3.73m and the rules allow Mr.Average-stats beat that by a solid meter and a half! We're not exactly looking at an infallible system here...

A little bit of digging reveals that 12 to 22 strides is an optimal "approach" for an olympic long-jump, depending on experience. Assuming an average "sprint-stride" is about a meter, it seems the 4m increment of bonuses that the rulebook suggests, might be about right.

I'm not saying a 4m run-up shouldn't give a bonus necessarily, just to consider whether it really should .

1 - OK, so I looked up some stats later on as I wrote this reply...sue me ;D

Thank you for your in-depth explanation. I actually did not take the rules for Acrobatics into account. After reading your reply, I now think that the rules for running jumps are fine but the standing jump distance should be somehow shortened. What do you think?

I'm personally happy to let the rules lie as they are, but that's just because I'm not a big fan of house-rules (they rarely tend to pan out the way whoever invented them intends).

Having said that, the standing jump rules probably could use significant curtailment. Changing the basic distance on a success to half Strength bonus, with half-meter increments for each DoS above one should be fine. Call it one-quarter SB on a failure, maybe. Round up to nearest half-meter, maybe?

That means an average dude, on a standing jump, can jump up to around the 3m mark on a good success, but still gets to cover 1m if he fails (and let's face it, you can trip 1m without even trying to cover a distance). To put any more of a crimp on it than that would really make PC's seem a bit pathetic and they are, after all, supposed to be the stars of the show (even if it is the grim darkness of the far future!).