And in further troubling Lotus news, Romain Grosjean is heard on the radio asking if the vibrating he feels when he brakes is "normal"?

I'd say only if your brakes are made of strong cheese, Romain.

Lots of tinkering going on with Pastor Maldonado's Lotus. It may be gearbox related - if that gets changed he'll incur a penalty. I'm not sure Lotus can afford many gearboxes...

There are 45 minutes of first practice remaining - here are the top five:

1. Nico Rosberg

2. Daniil Kyvat

3. Daniel Ricciardo

4. Carlos Sainz

5. Lewis Hamilton

Andrew Benson
Chief F1 writer in Austin

“For some reason, Red Bull have been a bit coy about which spec of Renault engine they will run here this weekend. Renault have brought an upgrade, using 11 of their 12 remaining tokens, but the team claim it is worth about only 0.15secs a lap and therefore, as Daniel Ricciardo said on Thursday, ‘probably not worth’ the grid penalty, especially on the track on which they expect to be most competitive of the remaining four.

"BBC Sport can reveal that Red Bull will run the old spec on Friday and almost certainly for the rest of the weekend, although that has not been officially confirmed by the team yet.”     

Nico Rosberg has shed another second off his leading time, as he registers a 1:53.989. 

We're wet and wild in Austin, Texas this weekend. We want your memories of F1 in the rain - use #bbcf1 on Twitter to get involved.

Valtteri Bottas almost takes out his whole Williams team with a slight misjudgment. The Finn overshoots the mark as he comes into the pits and causes a few engineers to wake up as they dive out the way. "Sorry for that," Bottas says on the radio as he sheepishly makes his way back on to the track.

Image source, F1.com

Lewis Hamilton is on the board and is fourth, 0.591secs behind team-mate Nico Rosberg. Between them are Daniil Kyvat and Daniel Ricciardo.

Image source, Rex Features

Ferrari have told Kimi Raikkonen to take it easy on the brakes. "We might have a problem," they tell the Finn - if only this race was in Houston...

It's a proud day for Alexander Rossi as he he takes to the track in his home GP. The Manor driver has the slowest lap of the nine drivers to register a time so far - but he's done it in this awesome-cool star-spangled car.

Andrew Benson
Chief F1 writer in Austin

“As expected, Fernando Alonso will have exclusive use of an upgraded Honda engine here in America this weekend - the one he used in Friday practice in Russia, where he took the grid penalty for it. But don’t get your hopes up - insiders say the improvement is marginal at best.

"‘From the cockpit it is difficult to feel this kind of difference,’ Alonso said, ‘but the data shows the improvement on the engine is as expected. This is good news because there is a little bit of a different concept on how the engine is built'.

“Production schedules mean that Jenson Button will not get his version of the engine until a subsequent race (Honda has not confirmed which one as yet). ‘I’m hoping it’s a really good upgrade,’ he said. ‘I hope he’s really quick and annihilates me all weekend! It’s unusual to say that.’ It was a clever and cute thing to say in the circumstances.”

Nico Rosberg has registered the quickest lap at 1:55.102 as a few times start to appear on the board. Five other drivers have completed a lap as the track looks to dry off a tad - Kimi Raikkonen, Jenson Button, Marcus Ericsson, Sebastian Vettel and Raffaele Marciello.

Image source, Getty Images

Rain can mean many things. Drama, excitement or, if it's really bad, total boredom.

Do you prefer grands prix when it's wet and wild? Or do you like a fair fight on a dry track?

What are your most memorable races in the rain?

What are the worst driving conditions you've ever had to deal with (feel free to send us a photo)?

Get in touch on any of these using #bbcf1 on Twitter.

Only Marcus Ericsson has registered a complete lap (2:01.702) - he mentioned that the home straight has a few unexpected bumps. Felipe Massa has complained of the odd river here and there on the track.

Mercedes may be eyeing up a run out - and it will be with the intermediates.

Andrew Benson
Chief F1 writer in Austin

“The latest development in the increasingly ridiculous saga over Red Bull’s future engine supply is that the former champions have now approached Honda about next year.

"It’s somewhat ironic that a team who claimed they would pull out of F1 if they did not get a competitive engine is now going cap in hand to troubled Honda. But leaving that aside for now, the reality is that McLaren have a contractual veto over any decision of Honda to supply a second team and it is highly unlikely they would want Red Bull to have one.

"Insiders say the most likely resolution for 2016 is that Red Bull use an unbranded Renault engine. Beyond that, sources say Red Bull is recruiting a lot of engine engineers with a view to building at least part of their own engine in the future. Some believe they are planning to buy an internal combustion engine from Renault - or Cosworth - and put their own hybrid system around it.”

Pastor Maldonado's Lotus has barely got on the track and it's having problems. He tells his team there is something wrong with the gear box and he'll be heading back to the pits to get it looked at, which is a shame, as I was looking forward to what the eccentric Venezuelan might get up to in the wet.

Ericsson is joined on track by both of the Ferraris, who will be keen to give that new engine a run out. And now the numbers on the circuit are starting to swell.

"It's not too bad," Ericsson says of the track on the team radio.