After over 10 years of obtuse obscurantism that had decreed that the Hour Record had to "get back" to Eddy Merckx (49,431 km / h in 1972) and his bike, instantly erasing the performances that came after his attempt, from great athletes such as Moser, Obree, Boardman, Indurain , Rominger and Boardman again in 1996, the "pundits" at UCI decided in 2014 to retrace their steps, allowing the use of aerodynamic bikes again, in line with those authorized for pursuit racing on track. 

The previous decision had in fact castrated every interest in this fascinating challenge, with only Chris Boardman (49,441 km/h in 2000) and an admirable Ondrey Sosenka (49,700 km/h in 2005) making serious attempts, which eventually resulted in them doing better than Eddy Merckx. 
This however showed how utterly RIDICULOUS the UCI's demand to compare performance that were decades away was, although achieved with similar bikes: a result that showed Sosenka to be stronger than Merckx is at odds, to say the least, with the palmares of the two riders... 

The back track decision of the UCI has immediately reignited the interest in the Record, with several athletes having (successfully) tried, or announcing attempts in the near future. 

The UCI has canceled the performances achieved in the 80's and 90's, although obtained according to the UCI rules from back then. 
Even though Obree's (51,596 km/h in 1993 and 52,713 km/h in 1994) and Boardman's (56,375 km h in 1996) aerodynamic positions would no longer be legal today and Indurain's (53,040 km/h in 1994) profile of the frame was also unauthorized according to today's standards, one cannot help but wonder why Boardman's performance in 1993 (52,270 km/h) has been struck out. 
His position on the bike and the Corima frame are in fact no different from that adopted by Voigt and Brandle in their successful attempts in the last months, and even the wheels (both 28") would be admitted today. 
Tony Rominger (53,832 km/h and 55.291Km/h in 1994) used a steel frame that would be embarrassing if compared to today's standards, but his front wheel was 26", with a 28" on the rear, and this is not allowed by current UCI's regulations, even though the fact that a smaller front wheel can give an advantage is yet to prove (in fact, even back then many track top athletes, including Boardman, chose 28" wheels in the front too). 
Even Francesco Moser (50,808 km/h and 51,151 km/h in 1984) had used a front 26" wheel, but his frame and the position on the handlebars were much less aerodynamic than those accepted today: in particular the "triathlon position" (now allowed) enables a speed increase of 1-2 km/h compared to the famous "cow-horns handlebar" position that he adopted. 

- TRACK LENGTH - 

Back in the 80's we were convinced that longest tracks were the fastest, and that long straights could favor the speed of the cyclist. 
As a matter of fact, it is truly the exact opposite. 
The banked curves allow the center of gravity of the rider to travel a shorter distance than the measurement line followed by the wheels: in substance, the mass of the cyclist "cuts" the curves, saving about 2-3 meters per lap, depending on the velodrome. 
In fact, the longer the curves compared to the straights, the faster the track. 
This explains for example why Rominger gained 600m/h at the Manchester Velodrome over that in Bordeaux: both are 250m long, but the English one has longer curves than the French. 
As a matter of fact, the UCI even then had forbidden the use of tracks shorter than 250m for Hour Record attempts. 
Thus it is a bit surprising that the current Hour Record set by Mathias Brandle (51,852 km/h on October 30th 2014) has been achieved on the velodrome in Aigle (headquarters of the UCI), which measures only 200m and therefore provides an "illicit" advantage over longer tracks. 

- MUSIC during the Attempt - 

In the past, the regulation was forbidding the diffusion of music during the attempts and the use of all types of earphones was not admitted either, because it was believed (rightly so...) that the athlete could take advantage of this. 
I remember that Francesco Moser, during one of his several attempts at sea level (Stuttgart 50,644 km/h in 1988) was approached by an individual who promised great advantages (1-2 km/h, according to him...) if Francesco had chosen to listen to the music that he advised, during the effort: of course it all came to nothing, because the regulation expressly forbade it. 
Jens Voigt during his successful attempt on the 18th of September 2014 (51,115 km/h) was "accompanied" by music personally selected by him and played out loud in the velodrome in Grenchen...