Spacers: what size???
10-31-2006, 01:07 PM
#31
Weathergirl
Rennlist Member
Rennlist Member
Regarding stress on the threads and studs, interesting comment here:
http://forums.pelicanparts.com/showt...37#post2670337
http://forums.pelicanparts.com/showt...37#post2670337
...Realistically - let's be serious, a SINGLE 1/2" grade 8 fastener can carry something like 15,000 to 20,000lbs axial load (don't quote me too hard on that as that is from memory and might be off but close enough for discussion) and 60% of that in shear. Then use 5 of them to hold only one of 4 wheels on. So you put a car through 2gs of load (say 6000 for a heavy racecar - and a car that I want if it is pulling 2gs), say the rear drive wheel carries ALL of the load which isn't realistic, add in some engine torque for shear, and maybe you end up with a combined axial squared/shear cubed ratiod loading of 10,000lbs (because this car is badass!). One stud can take all of that load.
So five with only 6 threads will probably last forever.
So five with only 6 threads will probably last forever.
10-31-2006, 01:34 PM
#32
Originally Posted by RallyJon
Really? What's the rationale for that? Is the issue how many threads are needed to support 90 ft-lbs of torque without stripping.
H&R says for M14 x 1.50 you need 7.5 turns for safety. Tirerack says the same thing.
H&R says for M14 x 1.50 you need 7.5 turns for safety. Tirerack says the same thing.
10-31-2006, 01:37 PM
#33
Weathergirl
Rennlist Member
Rennlist Member
Right. The tricky part is finding out where the edge is, so as to determine when you're close to it vs. when you're nowhere near the edge, but worrying that you might be and spending time, money and effort increasing an already ample safety margin.
10-31-2006, 02:57 PM
#35
Weathergirl
Rennlist Member
Rennlist Member
13.5 vs 14mm would be a wash, but 7.5 turns is only 11.25mm, which is a pretty significant difference. I understand that the oft-quoted "full engagement" is to ensure that the threads won't fail before the bolt/stud itself, a standard that is meaningless here.
The only issue in this specific case is the amount of thread required to support and maintain 90 ft-lbs of torque. Nobody ever addresses that. Likely, if you put 90ft-lbs on a single thread, it will fail. How about two threads? Three? Seven?
Also, I'd like to see a distinction between aluminum and steel nuts. If an aluminum nut can hold perfectly safely with 7.5 threads, a steel one can probably has the same holding power with 4 threads.
The only issue in this specific case is the amount of thread required to support and maintain 90 ft-lbs of torque. Nobody ever addresses that. Likely, if you put 90ft-lbs on a single thread, it will fail. How about two threads? Three? Seven?
Also, I'd like to see a distinction between aluminum and steel nuts. If an aluminum nut can hold perfectly safely with 7.5 threads, a steel one can probably has the same holding power with 4 threads.
11-01-2006, 10:25 PM
#36
Rennlist Member
Thread Starter
Just wanted to post a thanks to everyone who contributed. I'm going with 7mm in the rear and although I have bought 14mm for the front (thanks Jim), I'm going to have them machined to either 10mm or 12mm. As for studs, the slip-on spacers I bought come with longer studs and I will use Bill's numbers as a reference to check them when they arrive.
