UPDATE: Goodyear has been working with NASCAR on plans to introduce a new tire in the Monster Energy NASCAR Cup Series in 2021. Instead of the 15-inch tires currently used, the targeted size of the new tire is 18 inches and coincide with the introduction of the Generation-7 vehicle.
The impetus behind the change, according to Goodyear’s Director or Racing Greg Stucker, is to help make the cars look more like the ones a customer would drive off the showroom floor.
"There are not a lot of vehicles out there that run 15-inch wheels," Stucker said. "Everything is from 17 (inches) on up, so that’s really the driving factor to try to make it a bit more relevant to what’s on the street today."
For now, Stucker said the goal is to outfit the Monster Energy Series cars with the new tires, and no plans are being made yet for NASCAR’s other national series.
— NASCAR.com —
UPDATE – 8-14-2019: Goodyear’s Greg Stucker announced on SiriusXM NASCAR Wednesday morning that 18 inch rims will be run next season.
— Bagman (@TheMikeBagley) August 14, 2019
ORIGINAL POST 7-13-2019: After decades of using 15-inch diameter tires, NASCAR and Goodyear definitely will increase tire size diameter – probably to 18-inches – beginning in 2021 when the new Generation 7 Cup Series racecar is put into use, Kickin’ the Tires has confirmed.
"It is not just a tire change, it is the overall Gen 7 package that everybody is working on for 2021," said Greg Stucker, Goodyear’s Director of Racing. "Part of the whole idea is to try to update the cars somewhat, make it a little bit more relevant to what you see on the street these days. So, I think there will be probably some more differentiation among manufacturers, the car itself will be totally different from a performance perspective.
And one of the things we are looking at is to go with a larger diameter tire, a larger wheel diameter. We have been running 15-inch (tires) here in NASCAR for a lot of years now. If you look at cars on the street, you don’t see too many 15-inch wheel diameters anymore. So, we are looking at larger wheel diameters and our target is 18-inch."
Stucker explained there is a lot still to determine on exactly how it will affect racing on the track but with a wider tire, there will be an increased contact patch between the tire and the track. Currently, the contact patch is about half the size of a sheet of copy paper. Any increase would give drivers more grip but, according to Stucker, it won’t necessarily increase heat build-up in the tire as the tire compound has yet to be finalized and would change from track-to-track like it does now.
A spokesperson for NASCAR stopped short of giving specifics other than to confirm the work being done, "Indeed, there is development work underway on an 18" set-up."
See much more at Kickin the Tires.