Bourdais and Renger van der Zande currently sit sixth in the standings with two races to go, having scored a single victory in their #01 Chip Ganassi Racing Cadillac V-Series.R at Laguna Seca in May.
The Frenchman noted that the change in tyre compounds that began three races ago at Watkins Glen had adversely impacted Cadillac's form, having finished no higher than fourth since the six-hour race.
“We can see that some cars use the tyres better than others depending on the conditions,” Bourdais said.
“We’ve been using the harder tyre from Michelin ever since Watkins Glen and it’s definitely flipped the order a little bit.
“The Cadillacs were a bit happier on softer compounds, taking better care of the tyres.
“Now that it’s the harder tyre through the summer and it’s going to hold true at Indy, it has been harder for us to extract the most out of it and others have been able to kind of pop up in terms of performance.
“It’s interesting to see the evolution track to track and circumstances after another. I think it’s all very close.
“The BoP [Balance of Performance] has worked well. It’s been good racing and we’ve seen a lot of different winners.”
Source: Autosport