I'm rusty at physics but I'll try to do the best I can here. I'm going to try to talk about inline skating, pacing and friction.

Inline skates usually have 4 or 5 wheels on each skate. Each wheel contains ball bearings which let it spin with a minimum amount of friction. These bearings are greased or oiled to minimize friction. There is, however, still friction there -- and it gets worse as the ball bearings age and wear out with use and the lubricant wears out or is contaminated by dirt.

The other friction occurs where the skates meet the road. You'll notice that skating on a smooth surface is much easier than a rough one and takes less effort. This is the road on wheel friction working against you.

You, of course, are pushing against these two forces of friction with kinetic energy released by muscles in your legs. Skating is not a completely forward force -- it has a little bit of side to side lateral rocking motion involved to it. So the total force excerted by a person is broken down into forward and side to side forces. Any energy used for side to side motion is energy wasted in the fight against friction but nevertheless useful for things like balance and the fluidity/ease of the skating motion.

So we have three forces involved: the force of friction of the road, the force of friction of the ball bearings in the skate's wheels and the forward force of the person that is skating forward.

To have sustained movement on inline skates a person has to constantly fight against the two opposing forces to maintain speed because those forces will work to decelerate him. The person has to excert more force to get up to speed from zero velocity (rest) but once at a pace speed he only has to excert enough force to beat friction in order to maintain the speed.

So there's seems to be a certain maximum efficient speed (call it MES) that can be reached where a person is exerting the minimum amount of effort to beat friction but still maintain a high speed. The MES is of course dependent on the level of the two forces of friction: the road and the bearings. There are a lot of other factors too, like how the skate it put together and lubricants, which affect energy transfer.

The road you have no control over, but you do have control over how much friction occurs on the ball bearings because the faster you go the more friction is subjected to them. So from this you can say that there's a maximum efficient speed for the bearings themselves, which is directly proportional to your MES.

People tend to think that this is due largely in part to the quality of the bearings: a lot of inline skate bearings are manufactured based on the ABEC scale. The higher the rating, the more expensive the bearings. Apparently bearing quality has little to do with speed -- it is more a factor of choice of bearing lubricant and the fit of the skate components. Of course a more expensive wheel may have a better lubricant as well, to compliment a higher ABEC number.

So the trick to pacing yourself is this: try to max out the efficiency of the bearings as much as possible. For me this is much less than the speed that I could be skating at but if I did go faster I'd just be wasting energy fighting the increased friction of the bearings. This increased friction only decelerates me quicker and tires me out. There's a certain point where if you want to go faster you'll have to buy a higher quality bearing or skate (or just get stronger and have more stamina to constantly fight the losing battle against the increased friction).

Speedskaters sometimes use skates with more wheels. Do more wheels increase speed? More wheels could improve the skater's balance but they could also get in the way of a stride. Speedskaters tend to be leaned over more with a lower center of gravity so they already have a balance advantage over most people. Though speedskaters (on road or ice) seem to use a much different and longer stride than, say, hockey players or recreational skaters.

From a physics point of view more wheels means more friction, right?. Well, not really. The friction is partly a function of the load weight on each wheel (downward force of gravity). If you have more wheels then the weight of the person is more distributed and the downward force on each wheel is less. So this actually decreases the friction experienced on each wheel. This is especially true for the road friction but maybe also marginally true for the bearing friction, where gravity has less of an impact.

Another way for skaters to be more efficient is to concentrate on skating technique. Like I said above, a lot of exerted energy is "wasted" on lateral motion. This motion is never used in the fight against friction but if it were you would surely go faster with less fatigue. So an improved technique that translated a larger percentage of the exerted energy into forward force would also help.

Personally I try to use a longer stride and keep the lead skate (the skate not pushing) as straight ahead as possible to lessen side to side motion. As your balance improves with practise you can take longer strides (balancing on one skate essentially) and have less lateral motion. A good way to practise this is to purposely balance on one skate for few metres, especially while leaning forward as in a normal stride.

Incidentally, this whole discussion could also be easily used with ice skating. The only difference is that ice skating just has the one force of friction between the skate blade and the ice and that opposing force is much less than road or bearing friction. Of course that all depends on the quality of the ice. :)

So that's my rather long intepretation. If you made it this far, any thoughts?