Hello, I have seen an attractive ad for a set of Dodge Charger Police Steel Wheels 18x7,5" with 245/45-18 and I reckon they would suit my big white whale nicely. A slooow Pro Touring build process is starting up! The wheel offset is 18 mm and with a 20 mm thick bolt pattern conversion spacer the new offset is -2. Is that even remotely possible on a stock '69 Skylark? The rear is problably no issue, there is enough of room now with my 235/60-15 on what I believe is a 0 offset wheel (15x7"). 245/45-18 has a 15 mm bigger diameter. I would like to go a lot bigger in the rear later on, like 255/55.
Most Buick rally 15x7 wheels have a 3/8" offset. That would be about 9.5 mm positive offset. Your new setup would move 235 tires out about 1/2" (11.5mm), and out 21.5mm (7/8") with the 245's. Tire clearance to the outer fender will be getting tight, especially with wider tires.... do you have over 1.5" clearance now? Ideally, you want wheels with positive offset to move the tires inward.
A dead end, maybe. The weight of these wheels may also change my mind (30+ pounds). Another option is to go for gen V Camaro steel wheels. Just as heavy of course, but bolt pattern is correct for starters and they have a 38 mm offset. But they don't come with the cool chrome caps ...
Do you know the difference between back spacing and offset? Back spacing is so much easier to measure, and deal with. All you need to know is that on a 70-72 Skylark/GS, a 7" wide wheel needs 4 3/8" back space to center the wheel in the wheel well. An 8" wide wheel, needs 4 1/2". A 10" wheel need 5 1/2-5 5/8" of back spacing. On a 68-69, things are considerably tighter. That same 8" wheel needs 5" of back space. Not sure if a 10" wheel will work.
That doesn't sound easier!p:grin: For your examples for the 1970-72, you can just say preferred offset is zero, or up to 3/8" positive. That will cover all wheel widths. The thing I don't like about the 'backspace' term is that it can be misleading. For example, a steel 15x7 Buick wheel actually measures 8" wide edge-edge. And that 8" is what the 4-3/8" backspace is referenced to....not the 7" that one would think a 15x7 is. I don't know if all wheel manufactures measure backspace the same way....does it depend on the thickness of the rims outer edge? Does a steel wheel have the same edge thickness as a cast aluminum wheel? Do some manufactures measure backspace from the tire mounting edge and not the outside rim edge? Those could be variances between manufactures that lead to purchasing the wrong wheels. Or is there a 'standard' all manufacturers adhere to? Offset is offset and won't vary between manufactures or measurement technique. 'Backspace vs offset' may be a 'USA vs the world' situation where the USA measures backspace, and the rest of the wold measures offset. Offset seems to the more popular standard on foreign and new USA cars.
Walt, this video covers it all, http://www.youtube.com/watch?v=2K1lUlv9ZOA I was just concerned that the OP knew the difference. I can't tell you how many people use the two terms interchangeably and think they are the same thing. You want to talk about getting into trouble when ordering wheels, that's one sure way to do it. Another is mixing up English and Metric measurements. Use one or the other I say. You can easily calculate offset from back space, and visa-versa, but everyone should know the difference.
I know the difference between backspace and offset, don't worry I measured my 7x15" Torq Thrust 2 wheels: 95 mm backspace. Total width of wheel is 8 or 7,5? If 8 then my current setup has the sam front spacing as the Dodge wheels with conversion spacer. Only need to fit the slightly bigger and wider tires, about 15-20 mm left outwards in the front wheel housings today. Hmm, seems possible after all.
