No matter what, your speedometer will never be 100% accurate. So, the question is ROUGHLY how much will it be off.
Go to tirerack, and you can see some EXAMPLE tire diameters. I believe they also have a tire size calculator.
The EXACT model and year of the tire along with the EXACT rim and the EXACT tire pressure are just
some of the factors involved in the actual tire diameter.
ALSO, unless you use 100% the EXACT tire (impossible to get now) and rim on a Fox, there is almost a 100% chance of interference issues.
There are at least THREE major changes that effect wheel clearance between 85 and 93. For an 86, you have the tightest.
ALSO, gee, opps, SORRY, I ******FORGOT****** to mention something
SUPER MINOR like I rolled the fender lips, put more caster, used spacers, pushed the LIVING F******* OUT OF THE FENDERS, and if I go over a bump greater than 0.0000001", then the tire will scrape.
DUH!! Is that important???
So, IMHO, take ANY tire or lowering advice in the forums for what it's worth - pretty much worthless.
Hey, you're on a tight budget. If you want to waste your money on doing stuff because people pretty much NEVER mention
SUPER MINOR stuff like ......., that's your choice.
Also, do a Google search for tire size calculator. There are now many websites that have javascripts to do the calculations.
But, again, realize that tire diameters are like pant sizes IN REALITY THERE IS NO SUCH THING AS "A STANDARD". But, for a specific "size", they are often close. Also, like pants, there are MANY "RICER" tires out there with a "245" spec that are in reality thinner than a typical "215"! So, BFD if someone is running "305's", you need to know the tire MODEL AND YEAR (yes, many of the the same model varies sizes over the years).
Good Luck!
Four Eyes Rule!