Thanks very much for pcd size of 5.25" so I can do some calculations.
This really has cleared 2 long terms unknowns' for my new hill climb car design.
For GT40 people here the attachment may be helpful for you as well.
Working from the weight on a rear tire under acceleration it's possible to work out the maximum traction available and this is critical, not HP etc.
Using standard power and weight info from this thread, the attached calc's show that G5 7/16" bolts will fail quickly with tire mu = 1.5.
From the Metalistik catalog it's also clear the individual wheel torque is more than double the max stated for this part, so that explains the repetitive failures.
Imho doughnuts are fantastic in principal for torsional flexibility which minimizes shock loading along the whole power train, and from the data in this thread I can figure out the correct size for long life of rubber, bolts and tripod.
Thank you all for the rich information on this thread.
Cheers
John