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 Autosport.
"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.
Source: Autosport