# Largest tire for a 1966 GTO



## JohnPaul (5 mo ago)

i have a 1966 GTO stock suspension. And I would like to keep it that way. I would like to get 17 inch wheels. I want to put the best offset wheel along with the widest and tallest tire possible. I see 4.5 offset is common, but I think I can go further in and be able to put a large and wide tire on. Any suggestions on wheel offset and tire size?


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## Baaad65 (Aug 29, 2019)

Some 17" American Racing wheels have a 5.47 or 12mm offset. Go to tiresize.com they have a lot of good tools and visualizers so does American Racing.


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## lust4speed (Jul 5, 2019)

You need between 5" and 5-1/4" of backspace to center the wheel. Anything less than 5" will place the wheel too far to the outside and you will have to reduce width by going to a small sized tire.

To utilize the widest rim you need to tap in the inner part of the wheel well tin so that the vertical sheet metal is slightly inward of the frame rail, and trim the outer fender lip and stainless molding. The best trimming method is to relocate the molding screws to the outside of the existing holes by about 3/8". After marking and drilling the new holes remove the molding and mark your cut line between the old screw holes. Use a cutoff wheel and cut between holes. If you are unfamiliar with using a cutoff wheel this would be a good time to visit your local body shop and have them make the cuts because this part gets really messy. This will insure that if the tire does touch, it will only rub on the frame rail or the rounded part of the inner fender well about 2" up from the molding. If you make a cut greater than where the existing screw holes are located you run the risk of separating the pinch welds holding the inner fender in place to the quarter panel.

I have custom 15" steel rims on the '67 GTO by Wheel Vintiques, but did go to an off-the-shelf 17" Torque Thrust II by American Racing for my '65 Catalina Safari. The strange thing is American Racing wants $329 for a 17" rim with 5.01" backspacing but the price jumped up to $573 for the same wheel with either 5.25 or 5.50 backspacing. While I could have used the additional backspacing, the extra $500 plus tax for the pair wasn't worth it to me.

I kept to an 8" rim because the 10" spread the 275/60R15 tire a little to much on the GTO. When you go from an 8" wide rim to 10" you are already the proper distance from the frame and the additional width of the rim/tire all goes to the outside. Have read that a 245/60R15 is the largest tire on a 10" rim and the 8" just works better all the way around. This is with the car at stock ride height and jacking the rear up would get you by with the wrong combination, but the era of a massively jacked up rearend has passed. Also figure that a 275mm width is 10.8" wide mounted on an 8" rim and 11.5" wide on a 10". Maximum width with the above trimming gives you 12" and the 275 tire on an 8" rim allows for a half inch of inner and outer clearance and that doesn't rub. While I usually run a slight California Rake with the rear about 1" taller than the front, I can let the airbags down and don't have any rubbing. Here's a photo of the GTO sitting level with 275/60R15 Nitto drag radials.


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## Sick467 (Oct 29, 2019)

lust4speed said:


> You need between 5" and 5-1/4" of backspace to center the wheel. Anything less than 5" will place the wheel too far to the outside and you will have to reduce width by going to a small sized tire.
> 
> To utilize the widest rim you need to tap in the inner part of the wheel well tin so that the vertical sheet metal is slightly inward of the frame rail, and trim the outer fender lip and stainless molding. The best trimming method is to relocate the molding screws to the outside of the existing holes by about 3/8". After marking and drilling the new holes remove the molding and mark your cut line between the old screw holes. Use a cutoff wheel and cut between holes. If you are unfamiliar with using a cutoff wheel this would be a good time to visit your local body shop and have them make the cuts because this part gets really messy. This will insure that if the tire does touch, it will only rub on the frame rail or the rounded part of the inner fender well about 2" up from the molding. If you make a cut greater than where the existing screw holes are located you run the risk of separating the pinch welds holding the inner fender in place to the quarter panel.
> 
> ...


Thanks for the advice on packing a larger tire back there @lust4speed! It appears to me that the upper centered section of the inner wheel well is already narrower than my frame. I measured where the piece of masking tape is in the following picture from inner well to inner well, it was 46-3/4"...










My frame above the axle is at 47"... (it just dawned on me...you can't tub these cars without changing the frame...hmmm?)










I am thinking that the only areas of concern are the areas between the clips in this picture (between the wooden clothes pins towards the front and between the metal ones at the rear...










Does that sound right? If so, that should be pretty easy to do. It's a bit hard to know for sure since my car is off the frame.

With respect to the 8" wide rim versus the 10" wide rim. If I were to have a custom 12 bolt made for my car and could specify the actual width (wheel mounting surface to wheel mounting surface), would there be an advantage to going with a 10" wide rim for a fuzz more tire width? OR, do the same measurements you stated above still apply?

One more, do you have the same tires and wheels all the around? If so, any love-taping or lip trimming that had to be done to the fronts?

Thanks for posting! And, I love your car. Ironically, my intentions are to produce a very similar look as yours. Tyrol Blue, plain black rims with caps, slight rake, but I won't be doing a vinyl top.


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## RMTZ67 (Mar 12, 2011)

I have 255/40/17 and 225/40/17 on 8" wheels w/ 4,5 offset and that's about max. 245 in the rear is possibly safer.


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## LiplessSoul (4 mo ago)

JohnPaul said:


> i have a 1966 GTO stock suspension. And I would like to keep it that way. I would like to get 17 inch wheels. I want to put the best offset wheel along with the widest and tallest tire possible. I see 4.5 offset is common, but I think I can go further in and be able to put a large and wide tire on. Any suggestions on wheel offset and tire size?


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## LiplessSoul (4 mo ago)

JohnPaul,
This is my first time on this forum. I'm sorry that I am piggybacking on to your question. I will probably need the answer to your question in about a year. My question is... who knows who has a full WS, WT or WV 389 to sell to me. I need the engine done or undone for my 66' Convertible GTO 
I am just out of Philadelphia. Sorry for your inconvenience and grateful for any of your help.


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## Sick467 (Oct 29, 2019)

After de-gooing parts of my rear wheel wells, I have found that the pinch welds that join the wheel wells to the trunk floor rusted through pretty bad in places...I am considering removing the pinch welds altogether and replacing with pieces of angled sheet metal welded in. This would eliminate the common interference points with larger tires and be as easy as rebuilding the pinch weld lips. There are a few places I will be watchful of...the areas where the short trunk bracing meets the wheel well and the long brace that runs side-to-side under the package tray.

Anybody see anything wrong with that?


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## Sick467 (Oct 29, 2019)

I have finished up my wheel well mods and did not see the need to add the angled sheet metal. I ended up welding the floor pan behind the rear seat & the trunk panels to the inner wheel well from the inside, trimming the majority of the pinch weld off from underneath (leaving a 1/4 to 3/8"), and welding a bead along the newly cut edge, basically joining the two welds into a thick one. This process was done all the way from the lower leading sections where the wheel well met the panel behind the rear seat, up and over the panel under the package tray, and back down tpast the lower rear body bount bracket. After some test pounding of the new seam (where the pinch weld was), it proved to be much more solid than when it was just the pinch weld. Here's some photos of the progress and results...

I welded both sides (inside and underneath) indicated by the red lines...










Here are some finished angles...






























My pinch welds were swiss cheese in places and I wanted to gain all the room I could for wide tires...these two reasons were all it took to help make the decision.


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