'78-'87 Tire / Wheel fitment guide - El Camino Central Forum : Chevrolet El Camino Forums
El Camino Central Forum : Chevrolet El Camino Forums
 
Ground Up
User Name
Password

Reply
 
Thread Tools Display Modes
  #1  
Old 06-21-2011, 05:35 AM
BillyJack's Avatar
BillyJack BillyJack is offline
Deputy Director, Region 3 PA (west)
Master Wrench
 
Join Date: Feb 2009
Name: Bill
Location: Pittsburgh Area
Year: 1987
Model: Conquista
Region: 3 (DE,NJ,PA)
NECOA #: 13628
Posts: 1,555
BillyJack has a reputation beyond reputeBillyJack has a reputation beyond repute
Garage
Default '78-'87 Tire / Wheel fitment guide

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 ” 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 ” 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 ” BS wheels to be unacceptable for my use. With a shorter or narrower tire, 4 ” may work.

Rear Tires: BFG T/A 275/60-15, 28 ” 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 ” 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 5” 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 4” 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

Last edited by kenrogers1; 06-23-2011 at 10:41 AM.
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Smilies
Options

Register Now

In order to be able to post messages on the El Camino Central Forum : Chevrolet El Camino Forums forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in



Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
'78-'87 Tire / Wheel fitment guide - Read before buying! BillyJack Wheels & Tires 68 12-15-2018 11:34 AM
wheel fitment ? thundercat2 Body Restoration 3 02-14-2009 03:49 PM
wheel fitment stevenbg9 Wheels & Tires 0 03-02-2008 11:52 AM
70 ElCamino Tire Fitment Mr. Duece General BS Topics 7 10-14-2005 10:24 AM
ZQ-8 Wheel Fitment?!? 83Eldog General BS Topics 0 04-26-2004 12:44 PM

All times are GMT -7. The time now is 05:19 PM.
Powered by vBulletin® Version 3.8.8
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Logos and trademarks on this site are property of their respective owners. Comments are property of their posters, the rest 2001-2009 by me


 

Garage Plus vBulletin Plugins by Drive Thru Online, Inc.