Technical Wheel Stud Question

[fearless]

Right, I want a wheel stud conversion, and it seems they have a tendency to vary in price and apparent quality/strengh massively.

There seems to be an awful lot of contradicting info out there but the below I found, and seems to make sense to my half mechanical mind

8.8 grade bolts are 800MPa ultimate tensile strength (the first 8) and have a proof strength of 80% of UTS, that is, 640MPa (the second 8).

10.9 grade bolts are 1000MPa UTS (the 10) and a proof strength of 90% of UTS, 900MPa (the 9).

Whilst 10.9's are therefore stronger, they are less ductile which is an issue in a failure scenario. 8.8's are nicer in the sense that they have higher plastic strain energy, or in simpleton terms: will tend to deform rather than snap.

8.8 are more than sufficient for a car application in terms of strength and for the reasons mentioned above are more desirable than 10.9's. However, this applies to applications where one expects to fail the joint and you require some level of fail safe by having the joint take up energy in plastically deforming.

In either case, people would torque tighten either wheel bolt the same in both cases. This bolt preload will result in a very modest tensile load in the bolt for which an 8.8 bolt will have ample reserve. If one doesn't torque tighten a 10.9 bolt any higher than an 8.8 there is no benefit in using a higher spec bolt.

The load through the wheel is taken out through the friction at the joint, since wheels don't have a spigot. So as above, you can only get more load capability through the joint by torque'ing it up more. For a car wheel application there is absolutely no benefit in employing a 10.9.'

So simple question, is it really worth going for a 10.9 high tensile rolled thread stud kit, over a normal looking 8.8 cut thread kit?

From the varying reports I can find, wheel bolts are 8.8 anyway, so is it nesaccery to go to some carlos fandango kit?

many thanks for your thoughts.