Wind resistance. I remember an old Popular Mechanics issue that showed a bicycle rider behind a train, riding on boards that filled in the area between the tracks, at speeds over 100 mph.

 

This explains a lot of it:

https://en.wikipedia.org/wiki/Cycling_records#History_of_motor-paced_records

"Fred Rompelberg from Maastricht, Netherlands is the current holder of the motor-paced speed world record cycling with 268.831 km/h (166.9 mph) since 1995.[1] He used a special bicycle behind a dragster of the Strasburg Drag Racing Team at the Bonneville Salt Flats."

https://tandemgeek.wordpress.com/2011/06/05/a-note-from-larry-black-classic-rendezvous-weekend/

Here is a guy that made 127MPH:
"José Meiffret (1913-1983, born Boulouris, France) was a cyclist who set a world motor-paced speed record of 204.73 km/h (127.243 mi/h) behind a Mercedes-Benz 300SL on the German Autobahn on July 19, 1962 [1] at Freiburg Germany. This record was set on a bicycle setup with a 130-tooth chainring, weighing 20 kg and equipped with wooden rims.[2]"

I was in awe of him as a child..

http://cycling.ahands.org/bicycling/datewithdeath.html

Here is a picture of his bicycle (website is in French)

http://speedman.over-blog.com/pages/Un_velo_dexception_-2256004.html

This was not his first attempt. In the past he didn't do so well...

http://www.britishpathe.com/video/motor-paced-cycle-speed-attempt-ends-disaster

Women used to do it too:

http://www.britishpathe.com/video/feminine-pictorialities-no-34-going-the-pace

I did a bit of this for 4 man team training in the 80's. It is very hard...

 

Here is an Attempt behind a Porsche 935 - notice the Roller in case the bike tire got too close to the car

 

All of that info looks good. The idea of "racing" behind an assist vehicle seems odd to me. Who should get the credit for the win? The rider or the pace vehicle driver?

 

To me it's both! Being the driver is not easy and if something goes wrong with your driving the results can be unpleasant.

 

Here is a picture of his bicycle (website is in French)

http://speedman.over-blog.com/pages/Un_velo_dexception_-2256004.html
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Wow. I'd hate to get my pants caught in that chain

 

Now you know how Junior Johnson discovered drafting in nascar.

 

they probably did it because someone wanted to show off their shiny new motorized bikes and paid the promoters to let them run at the front of the pack...

in the end, when looking for reasons for things like this, just follow the money..

 

Err.. no.

It is how fast can I go on a bicycle. That's what it's about from a riders perspective. Do you have the skill and the balls to do it? Nothing to do with money.

Is there someone looking at the rider and thinking "I could make a buck off this!"? Yes, of course there is.