What Are These For?

[bob darcey]

I have (2) 10" wide 13" wheels from a mid-70's GRD. Both wheels have (3) 5/16"-24 threaded holes at 120 degrees, with surface plates rivited on. What are they for and how should I plug them? Baffled.

[J Leonard]

Bolts go in them to keep the tires from becoming unseated. Although they look further away from the bead than my Dymags.

[johnhafkenschiel]

I have (2) 10" wide 13" wheels from a mid-70's GRD. Both wheels have (3) 5/16"-24 threaded holes at 120 degrees, with surface plates rivited on. What are they for and how should I plug them? Baffled.

You have an old school GRD (they made them 1971 to 1975. There was an issue with F2 and F3 and Atlantic cars with the tire beads walking toward the drop center. This equipment is called 'safety studs'. This hardware was the solution. After installing the tire on the rim, the 5/16"-24 bolts with silicone gasket gel on the threads are inserted into the rim hardware to seal the assembly and are threaded subflush into the wheel inner surface. The installer then seats the beads. After that the bolts are screwed down thru the cast mag rim. Set to recommended tire pressure and spray test for air leaks. The bolts you select should stand proud of the inner surface after tightening down enough to prevent the tire bead from walking down to the drop center. My 1972 Brabham BT38 has these both on the 14" rear wheels and the 10" fronts.
You can read a more professional discussion of this subject on page 108-109 in "Prepare to Win" by Carroll Smith

[bob darcey]

Excellent, John, thank you. The Smith write-up is helpful as well.

[tstrong]

Excellent, John, thank you. The Smith write-up is helpful as well.

Yes Bob as mentioned above all my GRD Atlantic wheels had these safety studs. We used 5/16 button head Allen’s with dowty seal washers to seal. ALWAYS back them out before you take the wheels to have tires change. An installer will certainly forget to back them out at some point even with explicit instruction and rip a big hole in your wheel. Ask me how I know!!! Todd

[Jerry Kehoe]

These bolts or screws were required in many series for awhile until the rims had the safety beads. Always were a pain as Tod was right in that you had to make sure they were not in the way of the tire busters!