Summerfun

Guys,
I have a question and would like some thoughts from the collective.
Question A)) is the question but I threw a few more in in case someone was bored and felt like sharing some valuable information and ideas

Take a C3 (74 for that matter) and install
1) 2" offset trailing arms
2) shorter spring (not necessary for 18" wheels)
3) offset sway bar

Considering that there is 11" space between the chassis and the inner lip of the rear fender.

A)) Where does the face of the hub sit in relation to the chassis and fender. I understand that C3's have little variances within the same year. Is it exactly in the middle or closer to the fender? I know I can go and measure it but I was wondering what the factory numbers were for interest sake. Presumably it is right in the middle as I have read that as much as 5,5" backspacing can be had with above mods.

I'm trying to calculate a half inch ballpark area of where the offset of a 9,5" or 10" rim of 18" diameter can be to maximize available space.

B)) I presume that a 10" rim (which is really 11" wide lip to lip) with a tire on that will naturally be wider again than 11" will not be able to tuck inside the fender. That's another discussion which you are welcome to run with. A 9.5" rim is pretty much in the same ball park as the 10" rim as far as the rubber on it is concerned.

C)) What effect, if any ,will a little negative camber have on getting a 10" rim/tire to clear under driving conditions?

D)) I don't believe I can tuck either of the above inside the fender even with the mods as the numbers just don't add. In that case it would probably look better to have the rim/tire come to the outer edge of the fender or just a little to the outside of it at most. If the fender is 3/4" thick I can go with a maximum width tire (rim less obviously) of 11,5" or it will rub the chassis after mods.

E)) Effect of tire flex during driving conditions and considerations regarding this in deciding how far the rim/tire combo has to sit from the chassis at rest? This probably has some relation to C)) above

Thanks

3JsVette

I think about the widest wheel and tire combination you're going to get on the rear of a C3 is a 285/40-18 mounted on a 10" wide wheel with 5.5" of backspace. More than 5.5" of backspace and the frame not the trailing arm becomes the limiting factor. You also need a little luck to fit a max combination on any of these cars as the ride height, wear and tear, damage and build quality can also steal just a little bit of the room that you thought you had. It seems no one has a problem with a 275/40-18 tire on a 9.5" wheel with 5" of backspace. Also if you have 11" of room you can't use all of it because you should have a minimum of a 1/2" clearence between the wheel/tire and/or body/suspension. There is a tool that can mount a tire and be adjusted to what ever wheel dimension you want to check for clearence. You can simulate what ever wheel diameter, width, and backspace you like to test fit. IMCO though I always feel the best way is to try someone's combination that works to see if it works on your car and you can see if there is any additional room to go bigger. I usually suggest to do a search using "17s" or "18s" as there is hours of reading on this but based on your post it sounds like you have already done the research. Do you have a particular wheel/tire combination in mind?

Summerfun

I'm going to have to go with what I know works......BMW Replica TT chrome 5x120, 9,5" wide front ad rear with 25mm offset using 1" spacers all around. Maybe lose the rear spacers after mods in post #1

That is until decide to pull the trigger on Josh's fender flare kit that he is selling on Ebay, same as here..http://forums.corvetteforum.com/1581563798-post147.html

gcusmano74

The factory setup has an wheel offset of zero. If you change it by much, you will be changing the way the tires load the wheel bearings. This will likely shorten the useful life of the bearings somewhat, depending on how the car is driven.

3JsVette

Well no. It doesn't. The factory wheel is 8" wide and the backspace is 4". Yeah I know can't I count? A 8" wheel is actually 9" wide. The width is measured from bead to bead not edge to edge. So for the factory wheel to have 0 offset the backspace would have to 4.5".
That's why it's always easier to use backspace when these wheel dimension questions come up.