12-09-2011, 03:38 PM
No, no I could not just look and guess. I did have to measure. And I did.
Here is the process: as the imaginary circle diameter cannot be measured directly with a five bolt pattern (it can with a 4 or 6 bolt pattern) I used a digital vernier to mesure the distance between two alternate bolt centers: not adjacent, skip one and go to the second bolt. THis is the largest distance that can be actually measured on this setup.
Now here is the calculation, for those who like to peek at a little bit of trigonometry.
a) a triangle is formed with summits a,b,c opposing sides A,B,C : summits a and b are the center of alternate bolts, and the third is the center of the hub. The angle formed at the center with the radius (between sideA and side B) going to each alternate nut is 2/5 of a circle, hence 144 degrees.
b) A and B, the two radius, are the alleged half diameter of the bolt circle, namely either 114.3/2 or 115/2
c) the length of the third side, the distance between the center of alternate bolts, is calculated with the equation C = sqr(A*A + B*B -2*A*B*cos(c))
..you can do it with the scientific calculator or use triangle calculators on the net.
Based on alleged bolt circles, we should have
C = 108.706 mm for 114.3mm (4.5in) bolt circle or 57.15mm radius
C = 109.3715 mm for 115mm bolt circle or 57.5mm radius
I trained the digital vernier with measurements using alternatively inside and outside measurement prongs to alleviate visual illusions when measureing from the stud centers. I also measured outside of the studs, and inside of the studs and averaging the 2 readings for the center..
inside measurement www.avigex.ca/xport/ver5s.jpg
outside measurement www.avigex.ca/xport/ver2s.jpg
I took tens and tens of measurements to extract an average reading from the sum of all readings thus taking care of over and under measurements. Measurements were consistent within a very small margin of variation . Measurements were conducted on both front and rear hubs on the car, and on three other hubs on the bench, two front and one rear ( taken off the car for bearing hum, a classic on the TS) .
So here is the punch. Measurements fell consistently within 107.9 and 108.9, most near to 108.6 with a few exceptions over 109, thus giving an average of 108.65, very near to 108.7 that would correspond to 4.5 in bolt circle. I extended the vernier to 109.3 and in that condition, the prongs of the vernier fell ostensibly outside the center of the studs. So conversely, the 115mm convenience label would turn out to be even less than 114.3, as tested on seven GM wheel hubs that GM labels as 115 One of the hubs on the table, though, visibly from a different manufacturer, was just a little over all the others and provided an average (of ten readings) at 109.077mm, hence between 108,7 and 109.37, and corresponds to almost midway between 114.3 and 115.
Bottom line: none of the measurements, even if we isolate the highest readings, prove the 115 label. "GM proprietary" 115 label IS actually closer to standard 4.5in 114.3mm.
WIth that number of takes, the residual error in measurement is dramatically small....another book on statistics would have to be opened here....The only way these measurements could have been significantly false would have to involve a faulty digital vernier but do not have any doubts.....I will go to that length and test another vernier agaisnt mine. Any discrepancy WILL be reported.......
12-11-2011, 11:59 AM
NEW FINDINGS: doubt is the base for science.....so Well....yes...case revisited...new conclusions....
With results from the bench hub taking distance from "on car" mesurements, (see previous), doubts on my alleged conclusions started to install. Remember that initial measurements "on car" were tentatively using the apparent stud centers.... and these seemed to come smaller than following "on the bench" measurements once I found the discarded hubs....I must conclude that visual illusion was part of the game.
Bench measurements were easier to control...so I discarded all other measurements and started again with all the hubs I had..more than I had found initially....I happened to have six "scrap " hubs (3 used in first takes, then found three more, including 2 rear for Intrepid ) and in fact ....
.. 1 of the first 3 front hubs came from my son's Intrepid.... They are almost identical, except for the way the three bolts hold them to the car strut: on one car, the threads belong to the strut, on the other, the hub unit has the threads....I think that I was mislead ... forgive me if I mislead you.
I paid extra attention to clean the studs with power wire brush so no foreign particle could interfere .
After separation of the two types... I made separate new measurements "by type" .....and the difference really appeared. And....it was easy to stack together the two types, stud against stud....and even visually, there, one directly against the other, there was a difference....small yes, but visible.....(PHOTO COMING) SO I confess, first mistake was to try to pinpoint stud centers on the car.....the other was I had the two types mixed on the bench, having forgotten that at one time, my son had his Intrepid hubs changed in my garage....
ahhh...so my GM dealer goofed in 1993....with obvious "no consequence" though.....as 500gpx suggested...
WHy in the hell did GM go to 115.....when 4.5in 114.3 is almost the norm all over the place, specially the Japanese, Camry, Sonata.... Suzuki....... ahhh... anyway....
....OK now.....let's talk about theories for climate changes.........