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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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Deputy Director Region 6 - Supporting Member
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Thanks Billy! PM sent to acauth1 regarding placement as an article. Hoping you, or someone, can do a similar piece for the other gens.

:beer:
 

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Nice post billy,should be a sticky. A couple more notes when trying for maximum tire size, as stated` my' , I have noted some front ends like `mine' are shifted slightly to one side,ie, onebetter, one worse. Also note that some tires such as bfg radial ta's tend to have a hint more width than stated size. If you really want to be the man, do a proper modification for that fat rubber. Your smile will thank you.
 

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i have an 87 thats stock and put 17x8 boyb coddington magnetos under it with a 4in back spacing and it looks good and dosnt rub ever but you have about and eighth inch between the tire and the framerail in the back. i also put low profile tires on it but cant think the size off the top of my head
 

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Thanks for all the time and effort your put in it will be a great help to us newbies:You_Rock:
 

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Awesome thread! I will be adding my wheel combination to this thread as well. With 20x10's in the back (1 1/2 adapter), I have about 1/2" from the tire to the frame rail in the rear....Can't remember off the top of my head the actual tire dimensions though.

Aloha'z and great job!
 

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Wow thats some good info. This is what i've been looking for. I just have 1 question is -19mm to much offset I've been looking for an answer to that and havent had much luck thanks
 

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I have two questions, and I am setting all pride aside because I know they are stupid questions. 1: How much does backspacing affect the fit of the wheel to the car. 2: What is the bolt pattern for my '80 elkie.
 

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Deputy Director, Region 3 PA (west)
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Discussion Starter · #9 ·
No problem. As I said in my post, if I can help someone get the right tire and wheel combination the first time, the effort in composing my post was all worthwhile.
1) Backspacing is the critical element in positioning the tires relative to the vehicle center line. Too far outboard and you have interference with fender lips or inner fenders. Too far inboard and you have interference with suspension components or frame rails. 5th gens were originally designed to accommodate a 205/75 X14 tire. When we upgrade to larger tires and/or wheels, carefully positioning the tire in the wheelwell becomes a critical consideration.
2) The bolt pattern is 5 bolts on a 4.75 inch bolt circle.

Bill
 

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Here are two sites that I've found to be very helpful. If you know your original factory supplied tire and wheel sizes, you can easily compare that with any proposed tire and/or wheel sizes that you're considering..............Ken


http://www.rimsntires.com/specs.jsp?item=Wheel-Tire size comparer&sw1=225&ar1=60&bd1=15&rw1=7.0&et1=10&sw2=235&ar2=50&bd2=17&rw2=8.0&et2=11&text1=Old Front&text2=New Front

http://www.rimsntires.com/specs.jsp?item=Wheel-Tire size comparer&sw1=245&ar1=60&bd1=15&rw1=7.0&et1=10&sw2=255&ar2=45&bd2=17&rw2=8.0&et2=11&text1=Old Rear&text2=New Rear
 

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No problem. As I said in my post, if I can help someone get the right tire and wheel combination the first time, the effort in composing my post was all worthwhile.
1) Backspacing is the critical element in positioning the tires relative to the vehicle center line. Too far outboard and you have interference with fender lips or inner fenders. Too far inboard and you have interference with suspension components or frame rails. 5th gens were originally designed to accommodate a 205/75 X14 tire. When we upgrade to larger tires and/or wheels, carefully positioning the tire in the wheelwell becomes a critical consideration.
2) The bolt pattern is 5 bolts on a 4.75 inch bolt circle.

Bill
Another question, how much play do I have with the offset? A buddy told me to mention to yall that my goal is not restoration, but rather performance without butcherring the body of the car. I'm not sure if that makes a difference.

Sent from my PH44100 using AutoGuide.com App
 

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Deputy Director, Region 3 PA (west)
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Discussion Starter · #12 ·
Another question, how much play do I have with the offset? A buddy told me to mention to yall that my goal is not restoration, but rather performance without butcherring the body of the car. I'm not sure if that makes a difference.

Sent from my PH44100 using AutoGuide.com App
Read my post again thoroughly and you'll have the clearances that I measured on my truck, but 1/8" to 1/4" is about all the flex you have. I'm with you as far as performance.
I've spent all my adult life involved in autocrossing or oval track racing, so I'm all about fitting as much rubber as possible and there isn't any spare room in my wheelwells with the tire and wheel combo I'm running now.

Bill
 

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Deputy Director Region 6 - Supporting Member
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Without reviewing the complete GREAT article that BillyJack has assembled for all.....I think the offset variance is 0 to -20.

I am happy to see that members are reviewing this to help with their choices. It scares me thinking of what some might try with spacers and longer studs and such. This article was created for what WILL fit without adaptations.

If anyone out there has the ability to write up something similar for the other gens, I at least would love to see it happen!

Thanks...Randy :beer:
 

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I have 15X7 235/60-R15 on the Front and 15X8.5 255/60-R15 on the back. One of my fronts has come up with a crack and needs to replaced. Is there a advantage to the smaller width on front other than stance? Would like to run 15X8.5's on the front so i can rotate my Tires? Thanks Bud
 

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Deputy Director, Region 3 PA (west)
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Discussion Starter · #16 ·
As I said in my original post, 235/60 on 8' wheel / 4" BS is pushing the clearance envelope. At stock height, I just don't see a 255/60 on 8.5 fitting without problems. Of course if you already have a pair on the rear, you can do a trial fit yourself. Bolt them on and work the steering from lock to lock. Then jack up one side and cycle the steering again from lock to lock. If it seems OK, then take it for a ride, trying to load the front suspension at each front corner separately. I'm a former Autocrosser and semi-retired Circle Track wrench, so I'm all about having the widest wheel and as much rubber as possible on the front. But without serious tweaking of fender lips and inner wheelhouses, I think my combo is at or very close to the limit on a 5th Gen.
If you do elect to swap your rears to the front for a trial fit, please post a report of your findings in this forum so it will add to our database.

Bill
 

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Thank You Bill, Will do the swap to make sure. That was what i wanted to do before i do buy. Will be wanting to put Mickey Thompson Sportsman S/T Radials on if it all fits. The combo i have Know there was no prblem on the front but did have to put spacers and Longer Studs on the rear for the 8.5's Will give a Follow up It may take a week before i can get to it. Thanks Bud
 

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85 ss seeks iroc wheels and what else is needed?

Hi..can anyone pls help me with the shopping list that I'll need?
1: 1987 iroc 5 spoke "1 line" 16 x 8 wheels.
2: what lug nuts are needed? are they diferent btwn the rear stamped wheels being put on the front and the front stamped wheels being put on the rear?
3: what size spacers are needed on the rear?
thx everyone!
pls also send the info to: [email protected]:You_Rock:
 

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Excellent thread indeed! Just what I was looking for. Why isn't this thread a sticky??? Thanks for the post and the link via the Region 6 forum.
 
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