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Discussion Starter · #42 ·
Read the "sticky" at the beginning of this sub-forum and you'll have your answer. As long as your Rallys are the typical 4" backspace, you should be fine with 225's.
Bill
 

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1980 Elky

I have just bought a 1980 and it came with what appear to be Olds wheels. I have bought 15x7 front and 15x8 rear rally wheels. The rears have a 4.25 backspace. Does anyone think I'll have any problems with a 255/70-15 tire?? Any chance on a 275/60 fitting?
 

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Discussion Starter · #44 ·
The 70 series tires should clear OK. A 275/60 will be really close to the frame with a 4.25 BS wheel. As mentioned in my "sticky", I've got 3/8" to 1/2" clearance with a 275/60 on my 4" BS Rallys. Depending on the tire's contour, it may work or you may need up to a 1/4" spacer.

Bill
 

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Discussion Starter · #45 ·
I just looked at my "sticky" in this subforum and noticed two errors. First, the diagram of common terms has disappeared, So here's a re-post:

Also, the height numbers on my '87 are incorrect:
Here's what it should read:
Subject vehicle: 1987 El Camino Conquista
Ride height (distance from the wheel opening lip to the ground at the wheel center)
Front: 25 3/4” Rear 27 1/2”
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

I'll get in touch with Ken and see if I can re-open the edit window.

Bill
 

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Fitting 17 inch rims:
I hope I'm posting this in the right place. I was able to fit 17 inch wheels on the front and back of my 82 El Camino 305 engine, stock suspension. Here's what I learned.

Front wheels
I special ordered 17 x 8 inch wheels for the front. I had ordered them with 4.5 inch backspacing because I thought I had measured correctly, but I did not. The tires were 245/45r17. With a wheel spacer (metal plate made to fit between the hub and the wheel to make better clearance) about 1/4 inch in width, the tire rubbed slightly on the rear side of the upper control arm and on the edge of the sway bar linkage (on the driver side control arm and passenger side sway bar linkage when the wheels were turned for a lefthand turn, and on the passenger side control arm and driverside sway bar linkage on a riighthand turn). Even with the spacer, I had ordered a wheel with too much backspacing. Like the advice stated previously, on the front wheels, 4 inch backspacing is the maximum you can use without rubbing issues.

How I fixed the problem:
I used a wheel adapter (similar to a wheel spacer, but uses its own set of studs to secure the wheel, ie - wheel attaches to adapter, adapter attaches to hub) I did a lot of research on many different forums (classic car, 4x4, autocross, and any other that would test the limit of wheel performance), and found that you CAN use wheel adapters safely, but they MUST be installed correctly or your wheel WILL fall off which can result in a seriuos accident and your car getting a lot of damage.
Using a wheel adapter requires the following:
-Hub stud length cannot exceed the width of the adapter
Meaning if you hub's studs are one inch from the hub to the end of the stud, then you cannot use an adapter 1 inch or thinner. This will result in your wheel being torqued unevenly against your hub's studs rather than evenly and safely against the flat surface of the adapter. There was a man on a forum that ignored this rule, it placed the weight of the car on the studs, the studs snapped off while driving, and his wheel buckled under the car.
-Get "Hub-Centric" wheel adapters
"Hub-Centric" adapters place the weight of the car on the hub, rather than placing it on the studs, by using a center bore that fits snug over your hub. Using a "lug-centric" adapter will wear your studs down and strip them out, resulting in weak studs, and, of course, your wheel falling off.
-Use proper torque specifications, don't guess.
There was a corvette guy that didn't torque his lugnuts down properly and when he went to touch the lugnuts, the studs fell off in his hands, which sucks, cause he then had to remove the studs, put new ones in (which is not fun) and start all over.
-Order good qaulity Adapters
Some grades of cheap aluminum will not hold the force of your wheel on hard turns. They can cave or warp. I would recomend billet aluminum or high grade aluminum adapters with STEEL studs. Aluminum studs (you can laugh, but they are out there) will deffinitely snap off.
-Use Acorn style, open lugnuts
Acorn (tapered at the bottom) lugnuts ensure a proper fit by centering the the stud in the hole. Flat lugnuts will not. Again, some guy used his Ford Expedition lugnuts (which are flat on the bottom and notorious for being unsafe, thay had many recalls in the 90's because of this) cause he was too lazy to go out and buy the proper ones, his will spun in an oval and . . . you guessed it, his wheel buckled under the car on the highway.
Open lugnuts allow the stud's threads to engage all the way, and some drag strips will allow you to use spacers and adapters ONLY if you have open lugnuts (so they can see that the threads are engaged), if you have lugnuts with a cap, the studs could stop at the cap, and when you torque the lugnuts down, they may torque without actually pressing the wheel against the adapter or hub, so you may think it's on all the way, but it's not.
-Do quality checks often
In some cases, there is something unforeseen, make sure you catch the problem before you accidently destroy your car and have to start all over anyway. Better safe then sorry.

If you follow these rules without exception, you should be safe. If you ignore any one of these rules, there are many examples that will prove that your wheel WILL FALL OFF!!! There's your warning.
 

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Rear Wheels
I actually used 17 x 10 inch wheels with 4.5 inch backspacing. After the 315/35zr17 tires were added, there was about 1/2 inch of space between the tire and inner fender, which leaves some, but not much, room for play when your wheels hit a bump. I also installed a rear disc brake kit that pushes the rear shocks further away from the tires, but the stock drums fit as well. The only exception is that I had to roll the rear fender lip, then re-install the chrome trim and roll that as well. I also use stock style air shocks and El Camino cargo springs.
Summery: 17 x 10 inch wheels are wide, but will fit given that
-Your car is not lowered dramatically
-You roll you outer fender lip.
-You don't go with too large of a tire (ie. a drag tire). Radials should be fine.
-Do not exceed 4.5 inch backspacing.
-Remember that ofsett is different than backspacing.
-Measure 5 times, order once.


Hope this helps. If I find any problems or upcomings, I'll add them later. :secret:
 

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Discussion Starter · #48 ·
Thank you for your comprehensive post. When I wrote my original guide, I could only speak authoritatively about the 15 inchers I had experimented with. Your post addresses some issues that certainly will be of value to members in the future.

Bill
 

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Hi and thanks for the great post. I just picked up a 1981 Caballero that has Buick rims on it. I am going to put on Speedway Rally style rims and needed a proper starting point for tire size.Your information helped.Thanks again.
 

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Bill thanks for starting this out with some really great information,

You know I have the dimensions pretty much figured out except for two things

1. The backspacing!
2. The offset!

A lot of the manufacturers show the backspace but I am not seeing the offset and I am unclear about how these two figures may effect each other and the wheel location once in the wheel opening? If I can't get the offset figure how can I be sure what the correct backspacing should be?

I also was wondering what those two figure are on the stock wheels?

When it comes to my stock wheel/tire size it appears I have a lot more room/clearance between the outsides of the wheel/tire then for the inside. My stock rear tires comes closer to the frame rails then any other place?

Thanks again,

spoony
 

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Discussion Starter · #51 ·
Since the diagram has mysteriously disappeared from my original post (thanks, photobucket!), here it is again:


Offset is the measurement of the wheel mounting flange with respect to the centerline. I.E. "deep dish" wheels have negative offset, while typical wheels for front-wheel drive vehicles have the mounting flange more toward the outside of the car (positive offset).

Bill
 

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Discussion Starter · #52 ·
Bill thanks for starting this out with some really great information,

You know I have the dimensions pretty much figured out except for two things

1. The backspacing!
2. The offset!

A lot of the manufacturers show the backspace but I am not seeing the offset and I am unclear about how these two figures may effect each other and the wheel location once in the wheel opening? If I can't get the offset figure how can I be sure what the correct backspacing should be?

I also was wondering what those two figure are on the stock wheels?

When it comes to my stock wheel/tire size it appears I have a lot more room/clearance between the outsides of the wheel/tire then for the inside. My stock rear tires comes closer to the frame rails then any other place?

Thanks again,

spoony
Long ago, offset was the only spec published by the wheel mfrs. When cars got smaller while wheels and tires got larger, some wise man determined that backspace may be a more relevant measurement to use when attempting to upsize wheels.
By definition, backspacing is the distance between the wheel hub mounting flange and the inboard edge of the wheel. If you were to place a bare wheel on the ground with the outboard face down, lay a straightedge across the back (inboard) edge of the wheel and measure the depth to the wheel center mounting flange, that's the backspacing.
IIRC a stock 5th gen has a 6" wide wheel with 3" backspacing.

Bill
 

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I have 18x8.5 with a -6 offset 4.5" back spacing will a 255x45x18 tire fit and not rub? I know a 245x45x18 should fit. Need to know so I have the wheel wells with as much tire for the look with no adapters.:dontknow:
 

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It's been a long time since I've been on. My wife and I just had our first child and work has been eating up all my free time. But I did find some information that should be useful.

These are the dimensions and notes for my 82 El Camino. Hopefully I'll find time soon to post some pictures that will help. The information below was found on tirerack.com, I believe. Online tire stores will usually have the dimensions of the tires somewhere on their website to help you determine fitment. The actual width of the tires is what you will want to know before you buy, different brands may have the same tire size and rating, but completely different tread widths.

Rear:

Sumitomo 315/35 R 17 35Z

Width of tire: 12.6 inches
Diameter of tire: 25.7 inches
Revolutions per mile: 808
Weight: 28 lbs
Max Load: 1433 lbs
Max psi: 44 psi
Tread Depth: 9/32"


*Side note* These are the tires I have on my 82 El Camino (wheel tubs are the same for 78-87 models). With my wheel dimensions listed previously in this post, they will rub on the inside (on the frame rail) with stock or lowered suspension while turning on hard corners, or stiff suspension and the pickup bed loaded down with any load. My car has new cargo springs (AKA variable rate springs) and oem-style shocks (you know, those horrible air shocks that always leak air and need filled up every three days or so) and these tires would rub on hard cornering.
I fixed this problem by installing Hotchkis sway bars on the front and rear to keep the car from "leaning" on hard turns. I also had to ROLL THE REAR FENDERS to get them to clear properly on hard bumps. I would assume a 24.5 inch wide tire or smaller would work better. I just like wide tires that have a "donut" bulge around the rim.
What you need to make these work:

  1. Roll rear fenders
  2. Good springs
  3. Good shocks
  4. Aftermarket sway bar


Front:


Sumitomo HTR A/S PO1 245/45-17


Width: 9.6 inches
Diameter: 25.8 inches
Revolutions per mile: 808

Weight: 25 lbs
Max load: 1521 lbs
Max psi: 51 psi
Tread Depth: 10/32


Front tires fit fine if you follow the wheel fitment info previously in this post. Hope this info helps.
 

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Ray7007, to answer your question, I think that your size will fit easily on the rear (see if you can find the actually tire width from the manufacturer of your tire, a google search or phone call should help, be as specific as possible ex: instead of 315/35 r 17, search for Sumitomo 315/35 R 17 HTR 35Z, each letter and number has a designation that helps determine the function and characteristics of the tire).
But I am 100% certain your wheels will not fit on the front without a hub-centric spacer properly installed. With that backspacing, your wheels or tires or both will rub. I tried with 4.5" backspacing and drove on them anyway, and etched a nice little chunk out of my control arm and damaged the lip of my brand new rims. 4 inch backspacing is the absolute most you can get away with on the front. And I would not go with a tire with more than 9.6 inches of width, even then, it may still rub, mine rubs on the fender molding and I need to roll the fender.
I know that may not be what you want to hear, but trust me, it's better to stay within those dimensions than tear up brand new wheels and tires and not be able to resell them all scratched up.
 

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Discussion Starter · #56 ·
Thanks for the updates.
Additions to this thread with updated data for additional tire and wheel sizes is always appreciated.

Bill
 

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American Torque Thrust II

My plan is to put a set of classic Torque Thrust II on my 84 Elco I would like to go 15x7 up front and 15x8 in rear what confuses me is the back spacing I don't want to get the wrong wheel PLEASE help!
 

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Discussion Starter · #59 ·
The first "sticky" post in this thread should have answered your question, but I'll repeat. For an 8 inch wheel in the rear, go with 4" BS. You have a bit more flex using 7 inchers up front. Anything in the 3 1/2 to 4 inch range will work in the front.

bill
 

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'78

Hey guys. I have a continuing question on this. I have a '78, which already had 15x8 corvette wheels when I bought it 9 years ago. Measuring several times it looks to be 2.5-3 inch backspace. Hopefully I'm measuring at the right point. I put a tape measure through the wheels from farmost points then subtracted 1/2 inch for the lips. The offset I got is from the outer edge of the wheel to the face of the wheel where the lugs are. Also I do not know the BOLT PATTERN I have t know. The wheels got messed up by a moron tire place putting new tires on them so its time for a new set anyway. I've been looking at the AMERICAN RACING wheels. Anyone have a good experience wit these? Id love to see before I buy them and have the accurate bolt pattern of course. Can anyone help? Thanks guys!!! I haven't seen several of you in Florida for awhile due to other life problems but want to get back to it!!! Have a great one!
 
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