in theory.. and as you are screwing a steel bolt into a steel hub..
the shank length should be 12mm longer than original ..
with the threaded length the same as original..
therefore the new bolt would be overall.. 12mm longer than original..
the important thing is that the number of threads and "engaged threads" is the same as, or as close as possible to the original.
if you were to use a bolt with a short shank and long thread, it would place more of the threaded portion of the bolt within the spacer or wheel, stress raiser.. weak spot.. not good.
In fact that's why we moved from the old wheel studs to wheel bolts.. bolts with a shank are stronger under both shear and tensile load..
the number of engaged threads required is calculated from the bolt diameter/pitch and the material it is screwed into ..
if you are screwing a steel bolt into an aluminium alloy "hubcentric" spacer, without steel inserts, the number of "engaged" threads needs to be double that of steel.
there are other issues like differing expansion coefficients, bolt length/stretch etc..
however that won't apply to you.. as you are only using 12mm spacers.. the steel bolts screw directly into the original steel hub.
hope that isn't too confusing..
Gettin' to old for this sh*t
Last edited by seadart; 21-02-14 at 09:40.