Sprogs, There is no denial 630 is quite a high spec martensitic stainless steel. As with most stainless steel fasteners, galling/cold welding of the threads could be problematic (like you will find it hard to undo the bolts later) although the fact that the hub is a diissimilar material goes along away. Designing threaded parts you have to consider not the strongest material to use. The success of a bolt is the amount of pre-load to 'stretch' it when tightening compared with the load that it has to hold. With a high UTS steel, you may not 'stretch' the bolt sufficiently and the joint will undo itself. Don't want that for wheel nuts! And then to achieve the pre-load you may find you have to torque upto ridiculous values that may damage the hub thread. Given the load is not constant but more oscillating, shear and tensile all at the same time I still say its better to put up with the rusting chrome.
It's going to be really very hard to design a bolt that's as good as a conventional 8.8 bolt. How did you verify that your custom design meets its design requirement? An obvious drawback is that a machined thread will never be as strong as a cold rolled thread. A good read on this subject is Carroll Smith's excellent book on nuts and bolts. Its far more scientific than any layman would ever imagine.
Also you calcs are a bit simplistic. 210hp from a bike engine is not a good basis for comparison. There is of course no such thing as BHP, it is merely and expression of torque at a given speed. (see
http://www.epi-eng.com/piston_engine_technology/power_and_torque.htm for an explanation)
Now a 210bhp will produce less than 100ft/lbs of torque in all likelyhood given the high rpm at which the max power is generated. (Exactly why an F355 produces so much less torque than a 4200GT). It is torque which becomes the baseline of the oscillating, shear and tensile stresses, as well as the weight of the vehicle and the suspension loads introduced.
A race bike with rider probably weighs in at less than 250kgs. So the load pwe wheel is 125kgs. On a 3200GT at GVW this is going to be around 4 x that figure.
The torque of the 3200GT is 5+ times that of the bike. So drive induced loads could well be 5 x that of the bike. Given the car has an LSD, we have to assume all the torque can be directed to one wheel.
So the car has 5 wheel bolts vs the bikes one.
I would not mind betting the bike bolts is of larger CSA, so it can take more load.
So the bottom line is that the bike bolt has to deal with less than 20% of the load, its probably thicker. Race bikes (and their components) are built/lifed to last one race only.
Parisien,
in answer to your question, hydrogen embrittlement of the studs occurs during plating for corrosion protection. Most studs are black steel for this reason, but will rust. Improper plating can take the temper out of steel. Have a read of this:
http://www.fera.org.uk/pdf/Fera activity listing - hydrogen - march 06.pdf
The jury is out on whether de-embrittlement can be successful if performed any significant time after the plating. Electroplaters will more than likely not de-embrittle unless you specifically request.
there' is a reason why i ask