Here, courtesy of Cycling Weekly, external, is the course profile.

As you can see it get seriously lumpy and bumpy in the latter stages with a 9km climb to be negotiated on three separate laps.

The action is starting to simmer with a couple of riders testing the pace at the front, checking behind them to see if there is any enthusiasm for an early break.

Image source, Cycling Weekly

Britain's Ashley McKenzie is in action in the judo from 14:00 BST.

The 27-year-old won Commonwealth gold in the men's -60kg in 2014, but will come up against strong opposition for Olympic honours - including world number one Kim Won-jin of South Korea.

Image source, Reuters

Image source, Getty Images

They've got the big guns out for this one. Literally.

The men's road race starts at Forte de Copacabana, where there is an armed turret with two guns pointed skywards (it's on that concrete slab at the end of the peninsula on the photo above).

From there it's 237.5km of glorious coastline, with some not so glorious climbs and descents.

At the end of the outward stretch, the riders will do four laps of Circuito Grumari, with each lap including a 1.2km climb and a 2.1km climb.

They'll then head back along the coast and, just before they return to the finish at Copacabana, there will be two and a bit laps of Circuito Vista Chinesa - which means three slogs up an 8.9km climb and a steep ascent.

We are in full Olympic swing now. Water polo, handball, rowing, fencing, table tennis... Take your pick.  

If only there was one handy page with links out to all the live streams available to watch...

Image source, .

Kate Lloyd: Have watched approximately five minutes of #bbcrio2016 and am now completely hooked. Come on Team GB.

Nicola Fletcher: Well I need to get the Rio rowing location on my travel to-do list, serious wow factor!

Harry Tough: Gold today for Froome would cement him in British sporting greatness. (If he wasn't a great already)

UCI president Brian Cookson drops the flag to set the peloton on their 237.4km way.

Great Britain and Kazakhstan are at the front as their pedal away from Copacabana.

Luke Reddy
BBC Sport in Rio

All over for Jen McIntosh and it's barely started.

A total score of 415.9 was needed to reach the final of the women's 50m air rifle. That would have given her the top eight place needed but 414.7 is good enough for 15th.

She's chatting to coaches and looks frustrated more than disappointed.

China's Du Li topped qualifying.

Image source, Getty Images

Australia's Melissa Tapper is competing in the table tennis competition right now. Some of you will be familiar with Tapper's story - she was born with Erb's palsy (nerve damage) in her right arm. Despite this, however, she has become the first athlete from Australia to compete in both the Olympics and Paralympics.

Fancy some Tapper trivia? Well, she has a tattoo of a star on her left wrist and the names 'Jack & Ann' on her right foot to commemorate her grandparents.

Watch Melissa in action against Brazil's Caroline Kumahara via the schedule page (here).

Chris Boardman
Olympic cycling champion on BBC TV

It's the hardest Olympic race I've seen, it is brutal. Particularly the two 4km climbs, then a 6km descent under the jungle canopy that is treacherous. There's a huge drop-off on both sides of the road, and it'll define how this race plays out.

The mistake the British team made in London was to put everything behind Mark Cavendish when they couldn't control the race. Here they've got some fantastic individuals. But to win it you've got to be quick over the hills and on the descent, and in a sprint to the finish, too.

Image source, Getty Images

Who are GB's rivals for this one then?

Well, you can rule out the sprinters from this one - the course finish is preceded by three laps of a pretty tasty looking undulating circuit, so you won't see any of the big-name sprinters in teams.

Instead, it's one for the grinders and sluggers.

All-rounders who have a reputation for doing well in the Classics - Europe's top one-day races - are the ones to look out for.

The 2014 Tour de France winner Vincenzo Nibali of Italy is considered the favourite.

Spain's Alejandro Valverde and Belgium's Greg van Avermaet could also be worth keeping an eye on.

Ed FitzGerald: Not sure why everyone is touting Chris Froome for gold. Stage racer supreme maybe. But hardly a one-day specialist or bunch sprinter.

Rob Hayles
Former GB cyclist on BBC TV

The Olympic road race is very hilly, with some really severe gradients. Riders like Chris Froome usually revel in the mountains - that's where he earns his victories in the Tour de France. 

But the variables are so huge here. Each squad has got five riders instead of the teams of nine you see in the Tour, and that makes it much harder to control the race. 

Froome's climbing ability is suited to this, but his time-trialing ability gives him an even better chance of gold on Thursday. 

Image source, Getty Images

Froome, Geraint Thomas, Ian Stannard, Adam Yates and Steve Cummings go from 13:30 BST.

The water gets a bit bouncier in the middle of the race because of the wind. On a normal rowing course, the inside lane is only 5-10m from the banks but on open water like at Lagoa Rodrigo de Freitas it has a lot more distance to build up strength. It is blowing across the course and the conditions look very rough and choppy.

Sir Steve Redgrave
Five-time Olympic rowing champion on BBC TV

The sidewash is awful to row in. When they get out into the middle of the lake and into the wind, it is getting really choppy.

Ondrej Synek, the Czech silver medalist from the past two Games, wins heat five, but gives a doleful shake of the head as he crosses the line.

It is a hard grind out there in choppy conditions.

James Cracknell
Double Olympic Rowing gold medalist

The British fans were all on their feet to cheer Alan Campbell and he has not disappointed. When I spoke to him the other day, he said he was here for one medal – gold. He knows he can perform on the big stage but he has to build some confidence after a couple of indifferent years. 

Sir Steve Redgrave
Five-time Olympic rowing champion on BBC TV

I think Alan Campbell will be happy with that. He looked very smooth and very strong. He has got a lot of races in the next few days so he has got to pace himself, but it was a decent start.

Great Britain's Jennifer McIntosh has failed to make the top eight shooters who will contest the women's 10 air rifle final.

She finishes 15th in 414.7, a best ever result for Britain in the event.