Renault's upgraded F1 engine to wait until Brazilian Grand Prix

The French manufacturer has made an upgraded power unit available to customers Red Bull and Toro Rosso from this weekend's race in the United States.

Renault has used what was described as a "significant" amount of the 12 tokens it had available on the new system.

Toro Rosso has opted not to run the unit for the remainder of the current season as it is expected to return to Ferrari power next year, using a 2015-spec unit.

As for Red Bull, Daniel Ricciardo made clear on Thursday the risk of running the new engine for this weekend's Austin race was "probably not worth taking".

At a track where Red Bull is expected to be strong, taking a 10-place grid penalty would outweigh the performance advantages of the upgrade, which is understood to be worth only around 0.15 seconds per lap.

The forecast for wet weather for the majority of the weekend also counts against Red Bull, limiting the prospect of gathering meaningful data.

At next weekend's Mexican Grand Prix, the altitude of the Autodromo Hermanos Rodriguez - at two kilometres above sea level - also counts against Renault.

It means Brazil represents a more logical step for the upgraded engine's introduction.

That gives Renault two races - with only the season-ending event in Abu Dhabi to follow - to gather as much information as possible and provide a platform ahead of its planned return as a works team in 2016, with its takeover of Lotus still in the pipeline.