The smaller rim size was under consideration largely as part of ongoing efforts by the FIA to reduce the overall weight of the 2026 cars.
However, the change was opposed by Pirelli both for reasons of practicality and because of the potential marketing impact.
F1 switched from 13 to 18 inches in 2022, mirroring the trend of the wider car industry, and a reduction is seen as a backwards step in terms of both the image of the sport and technology transfer.
A new size would also require major changes to Pirelli's production process, which would have to be undertaken in time to launch a full test programme with F1 mule cars in 2025.
It would also create an additional challenge for the teams on top of everything else that they will have to deal with heading into the new era.
The 2026 regulations were discussed by teams and the FIA at a recent meeting of the technical advisory committee.
While the outcome has not been announced officially, it was agreed to stick with 18-inch rims, but with a slightly different tyre size and shape.
"We are close to the final version of the sizes," Pirelli F1 boss Mario Isola told Motorsport.com.
"Obviously when you design the wheel, you have to consider all the package, brakes, wheel, suspension, tyre, so I believe we are close to the final sizes.
"We have to change because the new car is different, and in any case, we have to design a smaller tyre.
"The discussion is between 16 and 18-inch tyres. And our preference is to stay on 18-inch tyres. And I believe that there are valid reasons to stay on 18-inch, with smaller tyres, but still the same rim.
"That's what we are discussing, just a bit smaller diameter, a slightly lower profile and slightly narrower tyre."
Isola downplayed the likely weight saving from a switch to 16 inches.
"There is an element that is weight," he said. "And clearly that affects all the package, and also the wheels. The difference between 16 and 18 and a narrow 18 is not huge. So the weight element is there.
"But it's not the only element. There is an element of performance. Because obviously if you were to go to 16-inch tyres, much smaller, the risk of overheating is much higher. A smaller diameter means that you disperse the heat in a different way.
"And so there are many elements that if we wanted to design a tyre that is in line with drivers' expectations. For performance, the 18-inch tyre is better than the 16."
