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Deputy Director, Region 3 PA (west)
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Considering the large number of tire / wheel fitment questions asked about 5th Gen Caminos, I decided to incorporate a number replies I had posted over the years into a single post in the effort to share my experiences over the years with fitting larger tires to my ‘87.
In 1978, when the new “A” body (later to be designated “G” body) cars were introduced, GM departed from tradition and moved the tires more outboard of the chassis than in previous models. It actually resulted in a large scale front wheel bearing recall in 1978, when a number of bearings failed due to the increased load. I mention this fact because it relates to the difficulty 5th gen owners often have in trying to fit a larger wheel and tire combination. Many other production and aftermarket wheels are designed with positive offset, meaning the hub mounting surface is outboard of the centerline of the wheel. Too much positive offset moves the tire inboard and causes clearance issues with frame rails and suspension parts.
This drawing explains the common terms used.



So what does this have to do with fitting tires to your El Camino?
I’ve been fortunate to have a good friend in the tire business, which gave me access to different wheel and tire sizes, so my ’87 is loaded with as much rubber as will comfortably fit in the wheelwells. Hopefully you can use the info I provide to find a good-fitting set of tires for yours.

Subject vehicle: 1987 El Camino Conquista
Ride height (distance from the wheel opening lip to the ground at the wheel center)
Front: 24 1/8” Rear 23 5/8”
Front tires: BFG T/A 235/60-15, 26.1” diameter , 9 ¾” section width
Front wheels: GM Corvette Rallys, 15 X 8”, 4” backspacing

Comments: I’m pushing the envelope with this combination. No clearance issues with suspension and no rubbing on the frame rails or the left inner fender. Slight rubbing on the right side has worn a slot in the plastic inner fender at the top of the wheel opening about 3” inboard of the fender lip when wheels are turned hard left. I also tried the same tire with a 15 X 7” wheel with 4 ¼” backspacing. The bead lip of the wheel contacted the upper control arm on both sides. A little bending of the upper control arm lip solved that issue, but the tire tread rubbed the frame rail before the wheels could be turned to full lock, effectively limiting my steering travel. Therefore, I consider 4 ¼” BS wheels to be unacceptable for my use. With a shorter or narrower tire, 4 ¼” may work.

Rear Tires: BFG T/A 275/60-15, 28 ½” diameter, 11” section width.
Rear wheels: GM Corvette Rallys, 15 X 8”, 4” backspacing

Comments: Again, I’m pushing the limits of clearance. There is 1/8” clearance between the tire outside sidewall and the lip of the wheel opening. When heavily loaded, a severe bump causes the sidewall to lightly rub. A little grinding or trimming could fix the problem, but since it’s so rare that the truck is loaded, I haven’t made the effort. Also on severe bump, the tread surface of the tire contacts a few ridges at the back of the inner fender. Contact is so light that the undercoat is rubbed clean, but no damage to either metal or rubber. Clearance between the inner tire sidewall and frame rail with a 4” BS wheel is ½” left side, 3/8” right.
Originally the rear wiring harness was located on the outside of the left side frame rail. Relocating it to the top of the frame rail moved it out of harm’s way. Given that my suspension links are stock rubber, a little “give’ is necessary, so I feel I’ve reached the limits in tire size.

Conclusion:
What I’ve posted here are my measurements on my near-stock’87 Camino. As the man says, your mileage may vary. 70’s and 80’s vehicles often have side-to-side dimensional variations, and things like specific ride heights, condition of body mounts and suspension bushings can also affect your results. Also, there’s an unrecognized and unpublished measurement that affects tire fit. For want of a better term, let’s call it “mounted tire backspacing” or "MTBS", a measurement between the hub mounting surface of the wheel and the widest point of the tire sidewall, which would be about 5¼” on my rears.
Most folks today are going for 16-20 inch wheels with 35 to 50 series tires, which have less sidewall bulge than my 15’s, so a 4½” BS, 9” to 9 1/2” wide wheel with a more straight-sidewall tire may fit fine, since the “MTBS" may very well be the same as my combination.
Two other points I’d like to address with folks inexperienced at radical tire and wheel changes. First, in order to maintain the original vehicle design parameters, I encourage you when replacing tires, to select a tire with an equal or greater load capacity than the O.E.M 205/75-14 tire, which was 1532 lb. capacity. I don’t care how large your wheels are or how wide your tires are. IMO, if you’re running a tire with less load capacity than the original issue tire, you’re flirting with danger. Secondly, wheel spacers are sometimes a necessary evil, but avoid them whenever possible. If you find spacers are necessary, use the absolute thinnest ones possible and make certain you have enough exposed thread on the wheel studs to engage the entire threaded portion of a lug nut.
Tires and wheels are an expensive modification. Before you write the check, spend some time on the tire and wheel mfr’s websites and know the dimensions of your proposed combination. Using my dimensions as a reference, you should be able to determine with reasonable certainty whether or not your combination will work.
I hope I haven’t bored you to sleep. Considering the high number of “will these fit?” posts on ECC, if my advice can help someone buy the right tire / wheel combination the first time, it was a worthwhile investment of my time.

Comments, replies and constructive criticism are welcome.

Bill
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Hello, could you take a look at this post? I'm new to this forum and you seem pretty knowledgeable. Any help would be appreciated. Thanks!


PS: sorry to bombard you, I should have posted here first instead of on your profile page.
 
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