Fibresand, is what I was thinking of.
Gareth, every racecourse in the world has standard times for its distances. Whether you run on so-called dirt, sand, Fibresand, Tapeta, StrathAyr, Equibase, Polytrack, mixed polymers, turf (and then - which turf? Rye, downland, digitarius, Florida, blue grass mix, etc., all giving a different cushion and needing different watering management). We do have the same surfaces - Del Mar has Polytrack, so it's the same as Lingfield's surface! Yes, there are some 'dirt' tracks extant in the USA - I didn't deny there were. We don't have 'dirt' in the UK - but no-one runs on actual dirt, because that would be totally rock-hard in summer and a bottomless pit in the rain. It's still a managed sand-based surface, so it's not unlike Fibresand. And while you may think that turf is turf, it isn't. You're no more running on a 'same' surface if your track is covered in a bare four inches of topsoil, like Brighton, with downland grasses on the high ridges and rye grass in the straight, and growing a Kentucky Blue mix with a deep topsoil in the USA. They don't give the same feel to the jockey and they don't provide the same cushion to the horse - yet for the purposes of argument, they're all called 'turf', because they're made of little green shoots and not out of a non-grass surface. Thus, the difference in timings over the same distances - and taking into account the landscape features mentioned by Shadow Leader, of course, which slow times down at such courses. You're not going to go as fast around Chester's endless turns, for example, tiring the near-side lead of the horses, as you will on a straight course, where they can change leads, rest their leading leg, and gain a speed boost.
Ergo, a jockey knowing those standard timings will know how to work his horse's run in tune with course differentials: if XYZ track, turf, very flat, never softer than Good, has a certain reading for its mile, and ABC track, being turf, turning, and generally Soft to Good, has a slower standard timing for its mile - he's going to ride according to the standard times and adjust his style of riding to the quirks of ABC, isn't he?
Thus, if you simply take a course's standard times for its distances, figure in your own horse's times at work (and allow for the quirks of your gallops or the course you're sending him to), then your jockey certainly has to know what pace he's going to be doing to match or exceed the optimum pace for the race. Hell's teeth - if they don't, then let's send them out with enormous stopwatches attached to their wrists like cross-country riders do in eventing!
Shadz: uh, thanks for that! Was twitting over this post for so long, missed your own input! Yes, really 'orrible gritty stuff, I believe. But, while we're talking about the remaining 'dirt' tracks in the USA, while we know they're not real dirt like dirt roads, just what exactly are they? They look like a kind of sand mix to me, because they get as sloppy as a beach when the tide's coming in. Did you ever visit the US and see what they were comprised of? Or maybe Jinnyj did? Be interested to know.