Subject:General Wheel/Tire Fitment and Suspension Guide.


Since these questions arise quite often, we have decided to put together just a general overview of the basic suspension and wheel upgrades owners of 78-88 G-bodies commonly make. We have tried to outline the most common wheels sizes, and as such, anything over 17" diameter and 9" width will not be discussed.

Disclaimer: No guarantee of fitment is made or implied. Each car is different, and you should take the time to carefully measure YOUR car to make sure the chosen wheel will fit without interference. As the title says, this is only a general fitment guide. Also, the owner, administration, staff, membership nor anyone else affiliated with www.montecarloss.com assume no legal liablity implied or otherwise for the content in this guide. Use at your own risk!

Wheels & Tires

The stock 4th Generation Monte Carlo SS wheel is 15 x 7", a 5 on 4 3/4" bolt pattern, and 3.75" backspacing. The SS was outfitted with
215/65-R15 tires from the factory. The following are recommended backspacings for a variety of wheel sizes, followed by the recommended range of tire sizes according to www.tirerack.com in italics, overall height of the tire in parentheses. Realize that the overall height of the tire will have an effect on speedometer and mileage readings. See The Tire Size Calculator to determine the percentage error of your speedometer with non-stock sized tires.

Follow this link for John Bzdel's excellent diagram explaining the various terms commonly used in tire/wheel discussion.

Click here for a great tire math website.

-Thank you to Larry (whitess) (Added 2/18/04)

Please note: Rubbing or other interference problems may occur with non-stock wheels/tires, especially extremely wide tires. This problem can usually be remedied with the use of a steering box with shorter stops, either the XH F-body box or other aftermarket boxes.

<blockquote>

For 15" wheels:

<blockquote>
15 x 7": 3.5 - 4.0" B.S.

• 215/65-R15 (26.0")
• 225/60-R15 (25.6")
• 235/60-R15 (26.1")
• 245/60-R15 (26.6")

15 x 8": 3.5 - 4.0" B.S.

• 225/60-R15 (25.6")
• 235/60-R15 (26.1")
• 245/60-R15 (26.6")
• 255/60-R15 (27.1")
• 265/50-R15 (25.5")
• 275/50-R15 (25.9")

15 x 9": 4.0 - 4.5" B.S.

• 255/60-R15 (27.1")
• 265/50-R15 (25.5")
• 275/50-R15 (25.9")

</blockquote>

For 16" wheels:
<blockquote>
16 x 8": 3.75 - 4.0" B.S.

• 225/60-R15 (24.9")
• 245/50-R15 (25.7")
• 255/50-R15 (26.1")
• 265/50-R15 (26.5")

16 x 9": 4.0 - 4.5" B.S.

• 255/50-R15 (26.1")
• 265/50-R15 (26.5")

</blockquote>

For 17" wheels:
<blockquote>

17 x 8": 3.75 - 4.0" B.S.

• 235/40-R17 (25.3")
• 245/40-R17 (24.7")
• 245/45-R17 (25.6")
• 255/45-R17 (26.1")

17 x 9": ~4.5" B.S.

• 255/45-R17 (26.1")
• 265/40-R17 (25.3")
• 275/40-R17 (25.7")

</blockquote>

</blockquote>

Springs and Shocks

This is only a partial listing of available springs and shocks available for the G-body. We have tried to gather part numbers for the most
commonly used spring/shock combos. Most part numbers taken from www.jegs.com . Part numbers may vary by vendor. Check before you order to ensure that you have ordered the correct spring or shock for your application.
<blockquote>
Springs:

• Eibach - 363-3803-140</font>
• Hotchkis - 515-1902F & 515-1902K (1" drop)</font></font>
• Edelbrock - 350-5230
• Moog - See Jeff Davidson's Moog Spring Chart for part
  
  numbers as well as exhaustive specs.

Shocks:

• Bilstein - B36-0949 (F) & B46-0929 (R)</font>
• Edelbrock IAS - 350-3377 (F) & 350-3477 (R)</font></font>
• Belltech Nitro Drop - 146-7012 (F) & 146-7517 (R)
• KYB - KG4513 (F) & KG5548 (F) - Thanks to Zack (ZMonte85)
• Monroe Sensa Trac - MNR 5840 (F) & MNR 5802 (R)
• Competition Engineering - ???

</blockquote>

Brakes

By far, the most popular major suspension upgrade is the "Big Brake Swap." This swap consists of either Global West, Hotchkis, or UB Machine upper control arms, spindles and calipers from a '77-'96 B-body, 1LE or comparable rotors, B-body master/booster or G-body dual diaphragm booster, and assorted hardware. For an excellent write up on the 12" Brake Swap, reference one of the following links:
<blockquote>

• J. Matthew Daugherty's write-up .
• Steve Parker's write-up .
• Anthony Kiska's write-up with pictures.
• Car Craft's article here . - Thanks to L. Garcia (82caballero)
• C5 Calipers/Rotors . - Thanks to L. Garcia (82caballero)
• Another C5 conversion . - Thanks to L. Garcia (82 caballero)

</blockquote>

Frame Braces

As you may well know, the stock G frame isn't very rigid. Simple, but extremely effective, handling mods is the addition of frame bracing. Some have chosen to fabricate their own, and various braces can be pulled from Pontiac Grand Prixs. Marcus, an authorized vendor on this site, makes very nice custom bars for the G chassis. Contact him for more information.

Here are some words from Larry (whitess) concerning some of the braces on his car. (Added 2/18/04)

For other information not contained in this guide, see the Suspension Technical Section on this site. There are many excellent links detailing specific chassis components and modifications for the G-body.


Q & A:
<blockquote>
It has been measured to be about 3/8" per side. It is slightly noticable, but will not cause problems unless your current wheels are extremely tight-fitting.

If you measure from inside lip to inside lip (where the tire comes in contact with the rim), it should be 7", assuming they are stock

4.5" backspacing should be just fine.
</blockquote>
General Comments:
<blockquote>
This is a great idea, Scott. We will work on this list soon. Anybody with anything to contribute to this idea, please do so
</blockquote>

Okay guys, in an effort to put together an exhaustive FAQ for the basic suspension/wheel/tire questions often asked here, we have started this "guide." Please realize it is in its infancy, and anything and everything any of you can contribute will be added. Please keep replies on topic and only to contribute to the guide.

Also, we realize that 275 is not the widest tire that has ever been put on a G-body. I know several people here are running 295s, and I'm sure somebody out there has a 3-- tire in the stock wheel wells. But that is severly streching the limitations of the fenders, and we do not recommend it.

If you disagree with anything posted here, by all means voice your opinions and it will be discussed.

Again, post any and all part numbers or other useful links you have and we'll add it.

Thanks again,
Brandon

Alright, errors have been corrected and it's been updated, I think Sorry for the long delay in updating this thing.

We've given credit to those who have contributed part numbers and links. (Thank you )

Also, I added a "Q&A" and "General Comments" section because I felt bad for just deleting everybody's posts.

Any comments/questions/corrections you have, let us hear 'em.

Also, Phil (phil240) or anyone, do you have the C.E. shock part numbers?

Thanks again,

Brandon

Under the KYB shocks, you have an F for the rear shocks, the second number. Just thought I'd point it out so it doesn't confuse anyone.

This was definetly a good idea!

"the recommended range of tire sizes according to [url= http://www.tirerack.com"]http://www.tirerack.com"[/url]

Are the sizes listed recomendations from tirerack or are they tried and true sizes known to work on our Montes? Also, It would be nice to differentiat between the front and the rear. In other words...Front, range of tire sizes,BS,rim size etc and the same for the rear.

on the stock aluminum wheels for 86-88 ss's is there
supposed to be more torque used to keep these wheels
on these cars.in other words should i use a air impact gun on these wheels or can i just use my four
way lug wrench.thanks for any help.

^^^ just make sure that you tighten them equally. ive never torqued my wheels, but i always triple check to make sure theyre equally tight.

never use an impact, and always torque them. They call for 85, but I run 100 in the rears. They can be sensitive and warp rotors if over torqued.

Are you sure about this?

Why would a 235/40 be taller than a 245/40?
It is my understanding that the 40 means that the profile of the tire is 40% of the 235mm or 245mm respectively. Is this incorrect?

To figure a tires diameter, here is the method.

Lets use 275/40/17 for an example.
275 is the metric cross section width of the tire.
40 is the heighth of the tire from the rim to the OD. This is a percentage of the tire width.
17, of course is the rim diameter.

So for this tire we take 275/25.4 to get the english width of 10.8". 40% of that is 4.3". So the diameter of this tire is 17" + 4.3" + 4.3" = 25.6".

I get so tired of hearing people say that they have 50 series tires, "they are wide!", wider than my 40 series tires. Not necessarily, depending on what the first number is. My 275/40/17 & 245/45/17 tires are about the same diameter.

Scot

I think thats a typo it would seem to me 40% pf 245 would be more than 40% of 235...and you can use an impact if you have the special torque sockets that are meant for bolting up wheels

good, thats exactly how I understood it. thanks


my thoughts exactly. The only reason I ask is because I am looking into a set of 17X8's or 17X9's and I wanted a taller profile in the rear, which SHOULD result in a taller tire.

Also... will a 17X9 fit in the rear without modification? I will already be modifying the inner fenders on the front because I want to lower it more than they will allow

So how bout them 17X9's?

Will they fit without notching the frame rails or any other mods?

I currently have 17X9.5" Centerlines in the back with 275/40/17 tires. It is close but they clear.

Scot

what backspacing are you running?

Just wanted to let everyone know that I managed to shove a set of 295/50/15's on the rear of my car with an 8" wide rim and they fit PERFECT. The were about 1/4" from the frame rails and right under the fender lip. Didnt stick out at all. And the car has belltech rear springs, so its lower than stock. I can get the back spacing off of them for anyone that is interested.

Would f-body spindles(70-78) with a 2" drop still be fine for the big brake swap? I was looking into the possibilities and found these and a coil over setup that is designed to replace stock GM parts which would allow you to adjust ride height. Would that be too much?

on my 87ss im looking for 2in drop in front and rear..have 5660 springs, wheels looking to use
16x8 or 17x8 will i still have to use drop spindles???/

i learned today that 275/60/r15s will fit on an 8" rim.

these are 255/70r15s on my stock rims(rear only)they are not very wide.i have lift springs in the rear and i mounted the spring seats higher than stock when we built the ford 9 inch.the only close spot i had was near my 3 inch exhaust but it has never hit even with a full carload of people.im very happy with this setup.ive had these on for a few months now and i do all kinds of driving.

Lower it.

never!

For those that are also young and stupid......
295/50/15's will fit on a stock 87-88 15x7 wheel just fine with stock suspension and a 5/16" spacer, and it is safe as I have just went on a trip to Texas and back with absolutely no trouble at all, which was 1400 miles round trip.

I'm not so young, but maybe stupid. Do you think a set of 275/60/r15's will fit under the car? I'm gonna try since I just bought a new set of four for $190. I got a suspicion I'll only be using two of them if any.

^ 275's work fine on the rear. I have them on stock 86' Rims(I know dangerous, I didnt put them on)

John B has 275's up front!