It was suggested I post a portion of my latest part of my project journal that deals with tire/wheel choice. I wanted to get some actual measurements of my car to be certain of my rim and tire choice. I was burned by the FAQ on the 8.5" rim w/3.75" backspace fits the wheelwell post. That might work on a Monza but definitely not an early Vega. So I decided to build a test rig to get some measurements of the sweep of some tire/wheel choices I wanted:
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I decided to build a rig to measure how big I could go for tire size. This should also help others for tire size. I've removed the inner gusset that would technically interfere with the widest tire. Here's another pix of that:
As you can see I've flattened that gusset out. Here's a pic of my rig. For the sake of outlining the factors I've got 28-spline S10 axles in a Monza housing. I'm retrofitting '04 Malibu Maxx rear discs. They are 0.3" thick at the flange. I pushed the rear axle way up into the well. I figured out I could use as large as 245/45 R17. The specs on that tire are: 9.6" sect. width, 8.7" tread width, and 25.7" dia. That would come really close to the full extent of the well. 245/40 R17 worked out as well: 9.8" sect. width, 8.7" tread width, and 24.7" dia. With these tires the width is right at the extreme with 1/2" to spare at the rear and about 1/4" from my rolled wheel well rim. I may go with 235/40 R17 just to be safe: 9.5" sect. width, 8.4" tread width, 24.4" dia. The more I think about it the first one is the best choice though. It's got good section width, clearance to spare, and extra tread width. The only thing is the overall dia. It's an extra inch, raising the ride height 1/2". Hmm. Anyway here's my pix. In order to fit these tires in here with even clearance I worked out that I would need 4.2" backspace. Looks like if I get the Torqlite 8x17 0-offset that should work out to needing a 0.3" spacer. I figured I could get an extra couple rear rotors and have the flange cut off then use it as a spacer!
Hopefully this will help others make the right choice for them. I think it's pretty important to get the right measurements for your actual car. I think we are dealing with some inconsistencies based on what axles we are using or modifications we've made. Good luck everybody.