Well,after talking with two tire stores,who were no help at all because they couldn't mindlessly punch it up on the computer,I'm going to rely on the guys that know how to get things done....our list members.

I have a 85 GT and I'm finishing up a 4.9 conversion....
I'm going with 16x7 wheels with 38 mm offset front and rear..... I need some opinions on what tire size would be appropriate.
What I'm aiming for is a wide tire in back and just a little bit narrower in front...sorta give it that old school muscle car look.
I also want a tire tall enough to fill in the fender wells without hitting anything though.
I need to decide on a set of tires this weekend because I'm having my chip burnt for the computer and tire size is required info....

[This message has been edited by MadProfessor8138 (edited 03-26-2016).]

Stock tire size: 215/60R15

Tire width: 215 mm/ 25.4 mm/inch = 8.5"
Tire side wall height above and below rim: 215 mm x .60 = 129 mm = 5.1"

Tire height: (5.1" x2) + 15" rim dia = 25.2" overall stock tire height.

Use the above to calculate your ideal tire height and width.

For general comparison between tire size options within the same rim size use the following rule to keep roughly the same height and change the width: Whatever you do to the first number in increments of 10, do the opposite to the second number in increments of 5; 205/65R15, 215/60R15, 225/55/R15, 235/50R15, etc.

A 225/55R16 is a start at 25.7" tall and 8.9" wide. From there a 235/50 or, 55.

Good luck and don't over do it with the tire size by getting to far away from stock tire height, it can affect offline performance and fuel economy efficiency threshold (taller tires = reduced fuel efficiency in town and potentially better economy on the hwy)

[This message has been edited by Joseph Upson (edited 03-26-2016).]

I use 16/205/55 in front , 16/245/50 in the back .I have had bigger tires in front and the steering becomes high effort and just gives the car a ponderous feel for lack of a better word .The difference in size eliminates snap throttle oversteer , and you just dont need a really big tire in the front because it is not carrying that much weight .Stock widths for the 15" tires on GT models from 86 on was 205 front 215 rear .Not really enough to help snap throttle oversteer but pretty adventurous by GM to do that as different tire sizes front to back was a rarity in 1986 , except on exotic cars .

wftb.........So,am I doing the math correctly here?
You're saying that you run a taller tire in the front and a shorter tire in the rear?
Why is that?

[This message has been edited by MadProfessor8138 (edited 03-30-2016).]

The rear tires being much wider have a taller sidewall than the fronts .I had a set of 40 profile in the front that I did not like at all because with my 11" brakes it took almost nothing to lock them up .My tire dealer recommended the 55 profile fronts and they really look right on the car and work really well .

wftb.....okay,I just ran the numbers on the tire sizes you gave....seems pretty good.
My only question though : I'm going to use a 16x7 rim with a 38mm offset....my car is a stock 85 GT and I'm wondering if there will be any clearance issues with the suspension.

I have an 85 SE V6 that has been modded; I have exactly the same size wheels- I went with 205/55s in front and 225/55s in back- slight difference in diameter...The fronts are tight on the wheels for good steering feel and quick reactions, while the rears are slightly softer, yet wider for power application. These tire sizes are on a number of common vehicles so they have a good chance of continued production and a wide choice of performance tires... I was using General G-Max AS-03s which were very good(And light), but I just switched to BFG G-force comp-2 A/Ss, which are substantially heavier(2lbs up front and 4 in back). I can't post a pic, but if you want PM me and I can email you a pic- the car looks like it was designed with these size wheels/tires in mind....

[This message has been edited by cvxjet (edited 03-31-2016).]

I run 16X7 rims as well but i don't know the offset .Picked them off tire racks recommended fiero wheels .I dont have any clearance issues but I have coilovers all around . I doubt that you will have a problem in the front , but the worst that might happen is you will need to go to coilovers in the back .Kits are readily available . and for now anyway there is still a big selection of tires in the 16" size .

[This message has been edited by wftb (edited 03-31-2016).]