Quote:
Originally Posted by Big Windy
tom, i think what swamp is saying (and I agree with him) is, where do you get 20mm from? how do you know that this is the threshold? is there actual evidence that shows that certain added stresses exist beyond 20mm?
the point is that a lot of people (including myself) will say that you are good with less than 10mm, or 15mm, or even 20mm, but that is not from actual experience or evidence, rather from common practice. 20mm could be a totally arbitrary number for all we know...it would be nice to have some real data, but i think there are simply too many variables.
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Thanks, I thought I was being clear but that made it 100% clear.
Quote:
Originally Posted by tom @ eas
This is why extended lugs are necessary. A minimum of 6-7 turns is a good indicator of a firmly seated fastener.
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Not quite. A much prefered and more generic engineering rule of thumb is 1 diameter of the fastener length to be into the base material. For a 12 x 1.5 mm fastener this means 8 turns (12/1.5 = 8). I would not go with as little as 6 turns on this thread size. That is only 6x1.5mm = 9mm, or 75% of the diameter engaged.
As a side note the when under tension loads (NOT side loads) the first 2-3 threads of almost any fastener and the material it mates with will hold the vast majority of the load. This is due to the elongation of the entire fastener. The threads past those simply become a loose fit. However, when you want to consider side loads, resistance to stripping and other load conditions the rule of thumb above comes into play.
Quote:
Originally Posted by tom @ eas
Spacers are even a common mod of Ferraris that see track duty to increase track width.
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Good point. Further evidence that in general spacers are fine.
Quote:
Originally Posted by tom @ eas
On another note, H&R offers a particularly wide spacer (30mm) for X5s which allow the lugs to thread into the spacer itself (DRA Series), and no reports of damage since the models were introduced back in 2000, clocking quite a bit of miles to date.
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Now X5s don't typically generate M3 type cornering loads, but at grip limit the loads will be large. This also reinforces my point that 20 mm is a totally aribitrary upper limit.