Buggin_74 wrote:...Anything in 4x100 is going to need narrow coil springs at its a pattern not really made with offsets more than et35.
you wont find any that clear stock springs...
4x100 rims with less backspace than typically found on a FWD car are out there, but they are the exception. And the whole point of the exercise is to move the tire contact patch inboard to reduce the scrub radius, so if you're going to the trouble to change bolt patterns you may as well plan on some smaller-O.D. coil springs.
An offset "more than et35" would have even more backspace, exacerbating the scrub radius problem..."ET" comes from the German
einpresstiefe, meaning insertion depth and is a measurement of the displacement of the lugbolt plane from the centerline of the rim. Any positive ET number indicates that the lugbolt plane is closer to the outside of the rim than to the inside (more backspace than frontspace), and almost all stock wheels for any make of car are positive offset. A rim with a negative ET would be like the "reverse" rims of the `50s and `60s where the center of the rim was cut out and turned around to give less backspace/more frontspace in order to widen the trackwidth.
ET numbers are expressed in millimeters by convention, while backspace is given in inches. Backspace also is measured from the lugbolt plane to the outside of the lip of the rim, which is typically ~½" more than to the area where the tire bead sits (the latter is how rim widths are measured).
Take the case of the stock 4" ET40 rim for example. Its center is half of 4", plus about ½", from the outside of the lip "in" from the dirty side of the rim. The 40mm positive offset tells us how much further in the lugbolt plane is.
1" = 25.4mm so 40mm = Approx 1.57"
Add them up to get the backspace measurement. 2 + ½ + 1.57 = just over 4".
A stock Type III/Karmann-Ghia 4½" ET46 rim will just
barely fit on a 1302 with stock springs if the tire is skinny enough. Its backspace is ~4.5". The 5½" ET34 Sports Rim is ~4.6", and it won't fit - obviously neither would the 914/4 5½" ET40.
A stock May`72-up Type I 4½" ET41 rim will fit (backspace of ~4.3"); the early ET26 Sports rim was designed for the 1302, so it fits too. Backspace is ~4.25". With either of these rims you get about ¼" or so of clearance between the inner sidewall and the coil spring, depending upon the tire.
Say that you got some 6½x15" ET33 BBS 4x100 rims like these:
http://i1051.photobucket.com/albums/s42 ... M00046.jpg
Their backspace would be just over 5" (3.25" + 33mm + ½") so they obviously won't work with the stock springs unless you added some spacers about 5/8" thick - and that would defeat the purpose of going to all this trouble. But if you fit coil springs which were 1½" smaller in O.D. you'd gain 3/4" of sidewall clearance, enough to work. The inside sidewall would be ~1" further inboard than stock, while the outer sidewall would be 1½" further outboard, so the scrub radius would be greater than stock but only by about ¼".
The smaller the O.D. of the spring, the larger an ET number you could run to tuck the tires in even further and reduce the scrub radius.
Ideally you want at least ¼" of sidewall clearance on the "light" (front) end of the car and at least ½" at the rear. More would be better, but most of the time that'll be enough for you to realize that a tire is going down and get to the side of the road before the sidewall gets damaged as the tire bulges from underinflation.
One last pitch for the Porsche 5x130 pattern - 6x15" "Cookie Cutters" or Fuchs would look bitchin' on that `71 IMO (the latter would be more period-correct, but either would look better to me than some ricer wheel with 8 holes in it). Say you got some in common ET35 or 36, the backspace is ~4.9" and the scrub radius would actually be a little better than stock. There's a wide variety of Porsche wheel styles from which to choose if you ever go to a larger tire, and most are around ET50 or so which means all it takes to use them is the appropriate width spacer.
