On an extended descent, a good braking technique you can use with rim brakes in order to keep the rims cool is to adopt the same technique you'd use on a tandem without a drag brake: you brake for six seconds with the front brake, then let off and let the bike roll for six seconds, then apply the rear brake for six seconds, then let the bike roll for another six, then repeat. This heats each rim for six seconds, then lets it cool for 18 seconds. It's a good idea to have dual pivot brakes front and rear; with their greater leverage than the older single-pivot sidepulls sidepulls, there will be less strain on your hands. And the bike will actually slow down with just the rear brake activated.

Of course, if the descent is REALLY steep, you'll just have to use both brakes to stay on top of the descent. Use constant pressure on the rear brake, and as soon as the rear wheel starts to skid, ease off on the FRONT brake. This will put more weight on the rear tire and stop the skid. Apply the front again and repeat as necessary. On a hot day and a long, step descent, it's worth it to stop and check the heat on the rims (touch it with the part of your hand covered by glove - I always wear full-finger gloves because that's what I wore on the track). Not so much an issue if you use a mechaincal disk brake, but I don't like encumbering my fixie with all that extra gear. I like to be able to remove the brakes and swap handlebar/stem assemblies and be able to use my fixie at the velodrome!

The pedaling technique of just staying ahead of the crank is called "floating the pedals" in track racing. On a descent, you don't want the pedals to be pushing your feet, nor do you want to be applying any back pressure; this is bad for your legs. I don't even use a lock ring to hold the sprocket, I think they are more dangerous than they're worth. I'd rather have the rear sprocket unthread on a descent than to have the chain get trapped and have the rear wheel lock up because the sprocket won't unthread. I raced track for 35 years and never used a lock ring and never had any problems. As long as you tighten the sprocket with a chain tool, it will stay on as long as you don't do a stupid skid stop. Not using a lock ring lets you use the older threaded road hubs. Back in the 60's and early 70's, the threaded rear hubs were spaced for 120mm dropouts, the same as on track bikes. (I also use 126mm threaded road hubs, but I respace the axle so that the hub is centered for a 120mm dropout. This minimizes dish and I only need a 2mm spacer inside the sprocket to get a perfect chain line.

(Off-topic note: rear axles were fine when dropouts were 120mm. As soon as they went to 6-speed freewheels on 126mm dropouts, axles started to break on the freewheel side. This is one reason they invented cassettes, so that they could put the bearings closer to the right dropout. This is why it's best to use a real track bike (drilled for a rear brake and using a road fork) as the basis of a road fixie, because you want to use a centered 120mm rear hub.)

Descending is easier on shorter cranks. I'm 6'1" and I use 165mm cranks on the road fixie, same as on the track. The shorter cranks are an advantage, as having your feet closer to the center of the circle means your feet are travelling slower (linear velocity) for any given crank rpm (angular velocity). Note that if you switch from 170mm cranks to 165's, you will need to RAISE your saddle 5mm, as your saddle height should be in relation to the lowest position of your pedal, NOT to the center of the bottom bracket spindle.

And one more thing: a perfect chain line is absolutely critical. If the chain is not dead straight, then as soon as it starts to stretch, it will be prone to falling off, usually when you are spinning fast downhill. So you need to dial in the chain line, and you need to use a 1/8" chain. The reason you do NOT use a 3/32 chain is because these are designed to be flex laterally in order to accommodate weird chainlines. 1/8" chains are designed to run straight, with very little lateral flex. So as long as you've got a straight chainline, the 1/8" cain will be more likely to stay on, even where there's too much slack.

And speaking of slack, if you race track, you want to adjust the chain so that it is as loose as possible without falling off. This minimizes friction and lets you go faster. On the road fixie, it's a trade-off. Too loose and the chain is likely to fall off. Too tight, and you are crushing the bearings in your rear hub and bottom bracket (that's what that "popping" noise is). So be very careful with your chain tension.

Luis