There’s not a lot of information out there if you are running SN95 axles on a fox! Finding the correct offset is an ordeal. After reading thousands (yes that many) of posts on various websites, I still have no definitive answer. People leave out important variables, don’t know their offsets – it’s a jungle out there. The fronts are relatively easy since 0.120″ isn’t that big of a deal. So I set out to figure this out on my own. Hopefully this post will help answer some questions. Now for a warning: These cars are old, tolerances aren’t really all that tight and there’s a lot of variables still with even the type of tire you’ll be using. So do your own math to double check, don’t just rely on this thread.
First some basic information:
- The SN95 spindles will increase your track width by 0.120″ (3.1mm) per side.
- The SN95 axles are a 0.78″ (19.8mm) wider per side.
- 1999 factory GT wheels are 17×8″ with 30mm offset.
- 2014 factory GT wheels are 18×8″ with 40mm offset.
- Stock 4 lug stuff is mostly 15×7″ wheels with 20mm offset.
Let’s start with the basics because if you have an 8” wide wheel with 30mm offset and another 30mm offset wheel but 9.5″ wide, it will be a very different fit due to the centerline of the wheel.
Offset: If you lower the offset, the wheel will move outward, or end up sticking past your fenders with more chance of rear fender lip rub. If you increase the offset, the wheel will be closer to the inner fender wall, or risk rubbing to the strut, tailpipe or frame on the back.
Backspace: This is the distance from the inside edge of the wheel to its mounting pad. The backspace is half the wheel’s width plus offset, plus 1/2″ Adding backspace, brings the wheel closer to the inside running the risk of rubbing on the suspension parts. And less backspace pushes the wheel out. This website has an offset to backspace converter: http://www.weldwheels.com/ccwheel/faqs/converter/
Going to fox-length Axles?
It’s not “that” bad of a job and I was seriously contemplating it. You basically need Ford Ranger driver side axles (example: 1992 3.0L V6 7.5″ rear-end), some North Car Racing brackets and possibly an adaptor for the axle hub for your discs to sit correctly. The job would probably only take a few beers to do. Anyway, just a thought! You could run 9 to 10″ wheels with 20 to 25mm offset (do a search, lots of info for that setup).
First thing I wanted to do was make a scale sized illustration, for that I needed to measure things, a straight edge, some beer and a measuring tape is all you need. [Note: make sure it’s flat with the mounting surface on the disc]
Looking at the smallest space for measuring the space between the rotor and inner fender wall.
Now to figure out how much space there is between the rotor surface (mounting surface) and fender lip.
Here’s the resulting illustration, first one is with the 1999 GT wheels, second is with the 2014 GT wheels with the FWD offset of 40mm. If you want to play around with a pretty elaborate calculator, this is the best one I’ve found so far: https://www.wheel-size.com/calc/
Below are pics with both the starfish (8″ wide and 30mm offset) compared to the 18×8 2014 GT Premium wheels (40mm offset). You will notice the 2014 wheels are more tucked inside the fenders. These are on my 87 notchback with SN95 axles and spindles.
Checking out wheel size options
I really like the look of the 1999GT wheels and how it sits relative to the fenders. It’s not too tucked in, or too ridiculously outward like a farm tractor. So, I’m using the starfish wheels as reference – or I should say a goal for how the wheels sit.
I like to visualise things so I made a jig out of cardboard, fridge magnet and a straight edge. It’s not the perfect tool (the right one holds your tire and allows you seriously configure things properly) but with some redneck engineering, beer and few cuss words, you can get an idea.
You can make your own cardboard, just remember to add a half-inch on each side for the lip/tire to give some “wiggle-room” – Not an exact science but sure beats spending countless days exhausting google’s resources.
My findings, using this rig, are:
- 8″ wheel needs around 30-40mm offset
- 8.5″ wheel is around 30-35mm offset
- 9″ wheel is around 30 to 40mm offset
- 9.5″ wheel needs anywhere from 42 to 50mm offset
- 10″ wheel is around 50 to 55mm offset (looks close to the inner fender too)
I’m going with a 8.5″ wheel with 35mm offset, I tried that wheel with a 245 sized tire, see pic below. I like how this sits, my car is normally lower than this – it’s lifted at the sub-frame connector, but even at ride-height, this offset would be pretty “driveable”.
This is the end result with my new 18×8.5″ (35mm offset) wheels on my Sn95 axle’d fox! I still have to get an alignment up front as you can see but I think this sits very well now! I’m very happy with this look, now I need to finish all the body work (wet sand, get hood and bumper cover painted)…
At this ride height, I will have to roll the fenders, maybe lift the height a little.
I really hope this is helpful and that it inspires you to do your own math for finding wheels. Feel free to comment below if something is awfully wrong here, also if you have pics and want to share your setup, please use this form: http://featureyour.foxstang.com/?page_id=149 if we have enough submissions, I can create a searchable database for others to use.
Next year, I will go with fox length axles, I already ordered the brackets and my plan is to go 10″ or wider wheels, even if I have to cut and weld stuff to get it done 😀 That will be another blog post. So stay tuned and thanks for reading – also please share! Here’s a video to go with this post: