Which Tour de France cyclists are on a good day and which ones are desperately fighting the gears in the grupetto a kilometre behind the leaders?
Normally, this sort of precious information is guesswork even to expert cycling commentators and journalists who rely on race radio broadcasts and the same confusing TV feeds as everyone else to build a picture of how each of the 21 stages is unfolding.
But from the 2015 edition, which kicks off this Saturday, this is about to change for anyone watching the world's most extreme sports event dressed up to look like a countryside cycle jaunt, including the millions of devoted bike fans around the globe.
For the first time in the history of the Tour de France - and possibly sport itself - fans following the race on TV or the Internet will be able to track the performance of the 198 competitors in real time using data fed to a website from a GPS sensor fitted under competitors' saddles.
The result of a tie-up between the company that owns and runs the Tour de France, the ASO, and data services firm Dimension Data, the GPS tracker conveys data such as a rider's speed, their proximity other competitors and, of course, their exact position on the road.
Normally such intimate data would be the preserve of teams, which also have access to private biological data such as heart-rate and power output which won't be part of the feed.
It's a once unimaginable step up for fans, indeed the entire cycling industry, and might come to be seen as a nuisance for the riders themselves, most of whom would rather that their bad day in the mountains trailing the contenders wasn't so publically visible to the entire Internet.
"The technology will allow cycling fans to follow the race in ways they've never been able to before," commented Dimension Data executive chairman, Jeremy Ord, employing under-statement.
"Until now it was difficult to understand what was happening outside of what could be shown on the live television coverage. The ability to follow riders, get accurate information about which riders are in a group, and see real time speed are just some of the innovations that will be realised through this solution.
"During the duration of the three week race, we'll be rolling out a range of new capabilities, including a beta live tracking website."
Building the analytics platform to process all of this data in real time had been demanding, he said.
According to the firm, the 198 riders will generate 42,000 heo-spatial points and 75 million GPS readings for a website expected to be viewed by 17 million visitors at a rate of 2,000 page requests per second to the company's cloud data centres.
Fans and journalists alike will also get access to a historical view of each rider's performance over the three-week Tour the better to settle arguments about who has been pulling their weight, sometimes literally - or not.
Big data has been used for some time to analyse the basic sporting performance in sports such as football but this has never been offered to the public in real time with no mediation.
Cycling is probably the most complex sport ever conceived when it comes to understanding what is going on. Tour de France stages often exceed 200 kilometres each, across high mountains, through bad weather, with even the race cameras mounted on motorbikes and helicopters getting only a letterbox view on the action.
"This top notch technological development will enable a better analysis of the race, highlight the race tactics, and also show how essential in this sport is each rider's role within his team," said Tour de France director, Christian Prudhomme, who has always been keen to promote innovations to expand cycling's horizons beyond narrow tradition.
"It will now be possible to understand how to prepare for a sprint finish in the last few kilometres of a stage, feel the wind's impact on the rider's speed, and so much more. Our efforts combined with those of Dimension Data will permanently change the way we follow cycling and the Tour de France."
The technology behind the new system had a test run-out on the bike of 2014 Tour de France winner Vincenzo Nibali at the recent warm-up competition, the Critrium du Dauphin.
"We analysed one cyclist cycling at an astounding 104 kilometres per hour," noted Dimension Data's Ord, a reference to the dangerous downhill speeds riders often attain in an effort to keep up. "This type of data has not been available in the past."
Dimension Data will publish the Tour de France website link later this week but in the meantime fans have to make do with a lovely video advertising what's coming.
What would 1950's Italian icon of global cycling Fausto Coppi have thought about all of this? Most likely he'd have rejoiced loudly as long as the system said arch rival Gino Bartali was behind him.
This story, "As big data hits the Tour de France, cycling will never be the same again" was originally published by Techworld.com.