Will a 1990 Chevy Celebrity tire fit 1986 s10 pickup?

No, a 1990 Chevy Celebrity tire will likely not fit a 1986 S10 pickup. While both are GM vehicles, they have different wheel sizes and likely different bolt patterns. The tire size itself might be similar *in terms of overall diameter*, but the wheel's bolt pattern and center bore (the hole in the center of the wheel) will almost certainly be incompatible. Trying to force a mismatched tire and wheel onto a vehicle can be dangerous.