914 four bolt pattern Options

[lmcchesney]

I have not found a complete source of accurate information on this topic.
The 914 is listed as having a 108mm four bolt pattern. What measures 108mm?
The offset of my empi's are about 100mm. Is this the true specs?
I have read else where that offset is a incorrect term. My use of offset is the distance from the inner surface of the wheel to the edge of the wheel rim projected down to the center line. Is this correct?
Wheels are measured as 15 x 6.5. How do you measure the with of the rim? Is it from outer (curb surface) to outer or within the bead to bead? If you were to place your ruler on the rims, from what point to what point would you measure?
What bolt dia and length and thread patern are standard? Ebay has a set of bolts that are 2 3/8" or 60mm in length and 1 1/2 inch or 36mm thead length. This allows about 50mm engaged inside the rotor hubs. What length should the bolts be inside the rotor hubs to be safely secured?
Thanks,
L. MCChesney

[Dave_Darling]

Yes, it's 4x130mm. Measure from one bolt center to the opposite bolt center. (Works because we've got an even number of bolts.) You can also measure from the inside edge of the one to the outside edge of the other. Don't know where you picked up 108mm...

Offset, as mentioned, is the distance from the rim's centerline to the mounting pad where the rim sits against the hub. Backspacing is the distance from the plane of the inner lip of the rim to that of the mounting pad. (Note that you can calculate offset from backspacing if you know the rim width and can estimate the thickness of the rim lip.)

Rim width is bead-to-bead, so you'd put your ruler inside the rim, where the tire goes. (Easier to use a set of calipers with "inside" measuring jaws.) If you measure outside-to-outside, you will get results that are "about" a half-inch too large.

For alloy wheels, you need the long lug bolts. I recall they've got about 40mm worth of threads, but it doesn't all wind up on the inside of the hub.

Very few companies currently make wheels with the 4x130 bolt pattern. Fewer make ones with a 914-friendly backspacing, which is about 4.5".

--DD