Drag radial on a 71GTO
 

Looking for what size drag radials those are,running on a 71GTO, I have 15x8 centerline wheels with a 3 1/2 backspace, Hodgkins 1.5 inch lowering springs on the rear, and 1 inch lower on the front.. the front wheel sixe is 15x3 centerline with a 28 in tall tire or the morose 29.1 tire have both choice..

But looking for maximum size DR I can run on the rear

Thank you Tom

Rear tire Drag radial on a 71 GTO
 

Looking for what size drag radials those are,running on a 71GTO, I have 15x8 centerline wheels with a 3 1/2 backspace, Hodgkins 1.5 inch lowering springs on the rear, and 1 inch lower on the front.. the front wheel sixe is 15x3 centerline with a 28 in tall tire or the moroso 29.1

But looking for maximum size DR I can run on the rear

Thank you Tom

A week and no one responded?

The 3-1/2" backspace is what limits you. Most of our GTO's like right about 5" backspacing to center the wheel in the opening, and you are 1-1/2" towards the outside of the fenderwell. What size tire are you currently running and what is the clearance between sidewall and the inner fender lip? If you get really serious you will need to replace your rims with a set with more backspacing.

For what it's worth, I have 9" W x 17" diameter Year One aluminum Rally II wheels on the 65 GTO. They come with 5" backspacing. The largest tire I have so far is a 275/40/17. Regardless of what you wind up with, I want to suggest that you try Toyo Proxes TQ drag radials especially if you don't want to have to park when it rains. Unlike the Nitto 555R drag radials that are death traps on a wet road, the Toyo Proxes TQ drag radials are far safer in the rain, and do a good job with traction.

Now I might argue the point on the Nitto 555's. The Mickey Thompson's and BFG's were truly frightening in even light rain, but I've been stuck in several rain storms and the Nitto's didn't cause any problems and did well. I haven't tried the Toyo's so can't say how they compare to the Nitto's.

Thinking about going to a 17" rim on the '65 Catalina Safari and will look into the Toyo's.

I will elaborate my reasons for no Nitto 555R and why I like the Toyo Proxes TQ drag radials. I had a pair of 295/40/16 Nitto 555R drag radials on the rear of my 89 Conquest TSi 4 cyl turbo. 5 speed manual transmission. Great tread on the tires, which may have been 4 months old or so. I was on a well maintained Interstate, doing 70. Rain starts coming down, light to moderate, and I slowed to 60. After about 5-10 minutes like that the rear slid out, no warning, and nothing visible on the road to cause it. I wound up in the grass, not having gone far enough to cross and hit oncoming traffic. If I would have gone off the right side, I may have been in the trees, and not here to post this.
The Toyos have an asymmetrical tread with enough voids to channel water out. DEFINITELY a better dual purpose tire. The only place I would ever run 555R Nittos again is at the track, but the Toyos are so good I don't see going back to Nittos unless they had a particular size I wanted and only at the track.

I got caught in a downpour while going cross country in Missouri with a brand new set of BFG TA Radials I installed in SoCal just before the trip and it was a handful keeping the car between the lines and going straight. Sometimes it's the storm and not the tire. Here's photos of the Toyo and three versions of the Nitto 555. I run the 555R but I see that they also now have a 55RII that has a little less tread, and finally a 555 that looks to be a nice sticky street tire.

Anyway, none of this answers the question of what sized tire, but waiting to see what Adecco is now running and the clearance to the wheelwell molding.

Drag radials,
 

If I were you I go 15x10, 5.5" back spacing, Mickey Thompson 295-55-15's, should fit with no problems.

I run a 275/60/15 MT pro drag radial on the rear of my 71.... 8” rim with a 5” backspace. No need for a larger tire.

I have tried larger tires with mixed results...rubbing on the inner wheel wells and exhaust pipe. Mostly on a hard launch.

My car is not jacked up so your mileage may vary some