What is the biggest tire and rim width that anyone here has run on a 66 bonneville or catalina? I am thinking of having some custom made american racing salt flat specials made in 16x8's Will these fit?

The light at the end of your tunnel is just a freight train coming your way - Metallica

What is the biggest tire and rim width that anyone here has run on a 66 bonneville or catalina? I am thinking of having some custom made american racing salt flat specials made in 16x8's Will these fit?

The light at the end of your tunnel is just a freight train coming your way - Metallica

These are the wheels. I will put on the spinners as well. Should be unique as I have not seen these around anywhere. I am hoping that I can get the 16x8's to work.

The light at the end of your tunnel is just a freight train coming your way - Metallica

Be careful at the rear. The very top half of the well opening where the skirt meets dosen't give much clearance. You also have to remember that the shock mount is pretty close to the wheel too. I dunno about an 8" width. Id stay safe and go 7". You need as much backspace as possible. As big as those cars are, there isn't much room for wheels under there. Keep in mind they had a 14x6 from the factory as a standard wheel.



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I know this is a late reply, but I just recently registered!
I have a 65 GP, very similar to your 66 in this respect. Just shipped two 15 x 7 Rally II to Stockton Wheel to have them widened to 15 x 8, with 5.500" custom backspacing. These wheels will then be fitted with P285/70R15, which will have a section width just a hair over 11", and a diameter of 30". The car currently has 265/70R15, but I want a wider look than that.

Minor trimming on the inside of the fender skirts, rolling the wheel opening lip, and removal of the factory fender skirt latch and striker plate is mandatory. I now use spring-loaded 1/4" steel pins to hold my skirts in place thru the wheel opening lip, they are out of sight, of course, and a little difficult to reach. Also, lower shock mount must be relocated.. I drilled a new 1/2" hole for the shock stud that is about 1" futher inside on the lower control arm bracket than the original...it does cause the lower shock mount to not point straight backwards anymore, but it looks fine.
Also, as was already mentioned, it is difficult to imossible to fit a wide tire between the brake drum and wheel opening lip when installing \removing tire...this can be overcome by unbolting the lower shock mount to allow further axle drop.

5.500" backspacing combined with an OVERALL rim width of 9.00" (a 15 x 8 rim is 9" wide overall) plus one inch of tire sidewall bulge past the rim equals 11.00"..and the above mods should leave 12.250" between frame rail and wheel opening. There will be only .625" clearance between tire sidewall to frame, and tire sidewall to wheel opening. Poly busings in the rearend control arms will then help minimize tire rubbing. I beleive this is as max tire as you can get before major surgery on the frame is necessary. Will try to update this topic with pics once I get my rims back from Stockton.

Since I should be getting my new pair of Stockton Wheel modified 15 x 8 Rally IIs soon, here are some "before" shots of the car...it currently has 15 x 7 Rally II all around, with 225\70R15 on front, 255\70R15 rear. The new rear tire will be 285\70R15. Note the 1.5" gap between frame rail and inner sidewall, and the relocated lower shock mount, to clear the new rims when they get here. Also note tight clearance between outer sidewall to fender skirt...factory fender skirt latches had to removed to prevent rubbing, replaced them with two 1/4" steel linch pins through the wheel lip and skirt, their positions are at roughly 2 and 10 o'clock, viewed from side of car. A little hard to reach with those big tires in the way!

Rear-side view.

Very nice Mike. Glad to finally see a picture. Ed

Got the new pair of 15 x 8" 5.500" backspacing rims yesterday! Here is a test fit pic from last night...note the lower shock modification for clearance. Hope to get the rims painted tomorrow, new P285\70 tires next, then will post the "AFTER" pics.

1.5" clearance on either side, without tires. She's gonna be tight.

OK, you can get off the edge of your seats now...here are the AFTER pics! 285\70R15...I had to do some minor trimming on the fender skirts for clearance, but that was all part of the plan to fit the widest rear tires possible on the GP.

Very tight fit. Rear suspension must be allowed to drop as far as possible to allow room to slip the tire between brake drum and quarter panel. I love the look, but as I expected these taller tires are making the 3.23 gears feel like 3.08s....time to start looking for some 3.42 or 3.55s!

Side view, a little dark.

Very cool looking car!
I'm putting together a 65 GP myself. The body is still off the frame and I'm starting to put the chassis together. I really like the rake your car sits with. Are your springs replaced with stock units or did you use different springs to adjust the ride height? I've been debating what springs to get. Heavy duty (a/c springs) for better handling, station wagon springs for the rear, etc...
There's only a one inch difference in your front to rear tire diameter and I wouldn't expect that to create that much of a rake.

My car has 8-lugs on it but that may change after seeing yours. It sure has an aggresive stance that looks good.

The front and rear springs are 2 year old heavy duty units from Espo, but once installed, the car still sat mostly level, and to me was jsut too low in the rear...and I do not care for the low riding look with a factory fullsize. (The center cap on rear wheel was halfway hidden behind the fenderskirt, and it just looked bad.)

So I stretched the rear springs out by chaining the pair between a large tree and a tractor. The stretching made the springs gain about 3-4" in height unloaded, and once reinstalled (quite a task), lifted the rearend about 1.5". Then the taller 285\70 tires shown have lifted it a bit more. Ride quality is unaffected by the spring stretching. The pictures seem to make the rake look like more than it really is in person.

Another angle, rake is not quite as steep as the picture makes it look...I took the photo from a low position to show the tire tread width more.

Ponchodriven, I measured the front and rear tires for height, with air pressure set at 32psi in all four. The very center of front wheels are at 12.50" off the ground, the rears are at 14.25"...so rear tires are 1.75" taller in radius (3.5" diameter) than the fronts.

Dude, that's my car! I bought from bigcountry, who still doesn't know I'm a Metallica fan too, back in February. I don't have good close pic of the rears, but here is the best photo I have of the wheels.
Fastboy
http://a6.cpimg.com/image/90/57/2969...-028001E0-.jpg

WHERE DID YOU BUY THOSE RIMS AND DID THEY FIT RIGHT OUT OF THE BOX

The 15 x7 Rally II rims came off a 70's Grandville or Bonneville, not really sure since I bought them second-hand. They were brown and silver before sandblasting. Repainted them myself. 5" lug bolt pattern.

The front rims, with 225\70 tires on them, fit just fine...no rubbing at all.

The rear two...shipped them to Stockton Wheel in CA. to have them widened 1" (to 15 x 8 with custom backspacing of 5.50"). They fit fine but are very tight on clearance using 285\70 tires. You will have to do all the modifications on rear of car that I listed earlier in this topic to use the same rim\tire combo...assuming you have a mid-60's B-body.

Thanks. Looks great

Rim fitment
 

Let me first start off by saying thanks to "arowhed" and everyone else for the great information listed in this post. My question is this.... I have a 1966 Grand Prix and I believe that in 1966 the rear axle was lengthened by approximately 3/4 of inch on either side... How does this affect the rim recommendations? Also, there is a difference between back spacing and offset, so what is the offset of the wheels when the rim has 5.50 inch of backspacing. I am trying to figure out how much clearance is in the front so I don't have to cut off the factory fender skirt attachments... Any help is greatly appreciated. Thanks. :confused: :D

Bump
 

Bump...

measure your diff backing plate to backing plate just under the chock mounts and i'll do the same for my 65.

while you're at it measure the center of the shock bolt to center of shock bolt also. i curious if they relocated them at the same time.

mike

65 and 66 are exactly the same rears and axles. I have both rears and they have the same measurements.

As far as I know the 66 B body Pontiac rearend is exactly the same as 65...axles shafts from 65-70 B body are fully interchangeable..I have 1968 Catalina shafts in my 65 housing right now. Rearend width is 65.50" inches brake drum face to brake drum face.
Lower shock bolt mount location unchanged as well, at least between 1965 to 66.

I believe backspacing and offset are confusing terms, so to clarify, if you take my modified rear rims, without a tire on them, and lay them face down on floor, set a 3' or longer straight edge across back side edge, and measure down from it to the point where rims will contact brake drum, that distance is 5.50" .....and if ya measure down to the ground through one of the spoke holes, that is exactly 9". (which means a 15 x 8" rim is actually 9" wide overall, and 8" wide bead to bead)
What I di was cut most of the "ring" off a pair of 15 x 7 Rally II, leaving only the centers, shipped them to Stockton told them to put 15 x 8 rings on them with 5.50" backspacing. They shipped them back, in bare steel, for $100 each, plus shipping. Really, from the outside of the wheel, they still look like stock 15 x 7, as far as "depth"...because even though the rims were widened 1 extra inch, it is all to the inside, therefore adding 1 extra inch to the backspacing as well.

If you modify your rims like I did mine, there is NO WAY you can retain the factory fender skirt latches. Even stock 15 x 7 Rally II will rub the tire sidewalls on the latches.

with the info that's been provided in this thread about b/spacing and mods required to get wider wheels on these cars i'm going to stick this thread here and copy it to the suspension forum.

i think it'll save a lot of questions in the future.

mike

great sticky!

so 8 is the widest..

but what about tallest wheels capable?..
:confused:

65-66 B body wheelwell will accommodate a little over 30" tall tire before ya start rubbing the wheel opening towards front of car. So whatever wheel diameter\tire size combo you want to run, max tire diameter is still gonna be around 30" tall.

As for wheel height specifically, I've only experience with the stock 15" x 7 and custom 15 x 8 Rally II, but....I would bet a very low profile (short sidewall) tire on a 17 or 18" rim would allow the rim width to grow to 9", due to much less tire sidewall bulge beyond the rim's width, that low profile tires usually have. Also, with a taller rim, the lower shock mount\bracket will fall INSIDE the rim's inner diameter, which may make moving it unneccessary??

For test fitting, anybody got access to a 17(or 18, 19?) x 9 rim with around 6.500" backspace and 5 x 5" bolt pattern?

For what it's worth
 

Okay, here is what I have and it's no where near conclusive, as I am still working on it. I have a 20x8.5 (9.5 inch total width) rim. I have a 66 GP and the offset of the rim is +14mm (approx. 1/2 inch). I figure that the backspacing is approx. 5.25 inches with this setup. The rim has a 255/50 R20 tire on it currently (which doesn't buldge that much). With this setup I have 1/16 inch in the front by the wheel well and 1 15/16 on the rear to the frame rail (car is not being driven, I am going through it and making it mine). The shock tower is not an issue as there is plenty of clearance with this size rim.

I also have a 65 Full-size posi rear that is going into the GP. From articles I have read the 65 full-size axle is 3/4 inch shorter on either side, although all the mounting is in the exact same place for 1966. The way to tell it is a 65 compared to a 66 is to stick two fingers in between the backing plate and the lower control arm (?). If two fingers fit it is a 1966 rear, if they don't it is from a 1965. I am hoping this is true because I am looking forward to the rim being recessed 3/4 of an inch to give me more of a centerline. If the rim is recessed the 3/4 of an inch then I calculate I can get a 285 on the rear, but (and this is a BIG but) I will have a little over half an inch on the backside of clearance and a little under 1/2 inch of clearance on the front. If I stick with a 275 tire I will have over 1/2 inch on the front and the rear with this combination. The tire would be a 275/45 or 275/50 R20.

Sorry to be long-winded but I truly love this site and it has provided me with an exceptional amount of information that until now I have not really been able to contribute much to.

Does anyone know how much clearance should be maintained on the outside and inside at a minimum? I am planning on using Poly bushings to limit the amount of axle travel. My friend, who knows Pontiac's pretty well, said to leave atleast 1/2 inch on either side.

If anyone wants I can post some pictures, just tell me what you want to see pictures of.

Thanks.

Larry "Kid Skid"

Again, pretty sure there are NO differences between 65 and 66 fullsize rears. 65-70 B body all use the same bolt-in axle shafts (9783561, same part for Right or Left side), differentials\ring and pinion gears(within three different ratio series), brake drums, backing plates, etc. I have a Hollander Interchange manual that confirms this. Can you show us this article you mentioned that supposedly outlines differences, becasue I am quite curious to see it.

Now....Rear axle HOUSINGS are different between the following year groups among B body: 65-67, 68, 69-70, I think the main difference being coil spring perch size, not anything to do with axle shaft length.

kidskid is describing the differences in "a" body axles.

my hollanders states the same thing ase arowhed's.

i actually have a 69 impala 2dr i'm considering cannabalizing for my /gp to have disc brakes and a 12 bolt. per hollanders it'll work.

mike

Told you I was a newbie... :)
 

I'll check the axle that I got that I think is shorter. Are there some numbers or something that I can look for that would identify the axle? I am pretty sure when I bought the axle it was advertised as a full-size 65 axle. If it is the same length I am going to have to re-think my wheels... :) If nothing else I am having a blast with the old pontiac... it's been in my family 41 years... thanks for the info and I will post what I find. I will also look for the article I found, probably confused what I read... wouldn't be the first time with pontiac stuff.

Update
 

I checked the axle late last night (early this morning at 2 a.m.) because I couldn't wait. Arowhed and Mike Nixon both are right, the axles are the exact same length. There is one very important difference though... the 65 is a posi unit! :) That's probably what I bought it for, although I would love for it to be shorter because now my wheels won't fit right! :noidea: I guess I am going to have to go back the drawing board and find some wheels that measure up! :) Thanks for the help to both of you and I will post pics when I can figure out what to do next... :D

you could have the axle you have narrowed, but the wheel's will probably be cheaper.

i guess i'm spoiled with that stuff as moser engineering is located about 8 miles from me.

mike

Mr Nixon..living only 8 miles from Moser, eh? VERY interesting! Do you get a "locals" discount??
Kidskid, from what you described above, looks like your gonna need a wheel with at least another 1" of backspacing. Post some pics of the front and rear clearance as is, if possible.

on the discount, i have no clue as i run my stuff thru my business.

i do know local stuff gets priority on the job list!

and yes it's handy.

mike

What is the minium amount of space to leave between the wheel well and the tire and the frame and the tire? Where can I get poly bushing kits for a full-size 66 pontiac? Arowhed, I believe that you left aporoximately 1/2 inch on either side of your wheels, is that enough space? Have you had any rub issues? I believe that you used poly bushings, did you also use boxed arms? Thanks.

Sorry for late reply, holidays ya know! Rear control arm bushings are from Competition Engineering, the kit is availble through Ames Performance.
I have 1/2" inch inner sidewall to frame and outer sidewall to whel well, but that required wheelwell sheetmetal modifications and removal of factory fender skirt latch assemebly, as well as some trimming on the fenderskirts.
1/2" is not really enough, as I do still get very occasional rubbing, but is is very slight..not enough to damage the tire. 3/4" to 1" would be ideal but I was willing to cut it extra close.
I don't have boxed control arms on the car right now but do have a pair waiting to be installed...not really all that necessary unless you a have very healthy engine and steep rear gear.

arowhed, you wouldn't happen to have the competition eng part #'s for that bushing kit handy would you?

i want poly-graphite bushings for mine when i upgrade the suspension on mine.

mike

Mike, the 65/66 fullsize cars use the same rear bushings as the GTOs use, so the poly bushing are no problem for the rear, but I've yet to find anyone who supplies poly bushings for the front.
Bob

6t5 thanks for the info.

i'll have to do some digging i thought i saw a kit for the poly front bushings somewhere.

mike

I looked at a 65 Cat the other day. It is the one on collector car trader the beige one on airbags. It was a pretty car. I believe he was running weld evo 18X8 wheels with 245/40/18's on it. It cleared even when it dropped down. I did not see any surgery to the wheelhouse at all. I did not drive it but I did not see any scrubbing on the tires.

Here is another question. How big of a 14 in tire can you buy now? I want to run eight lugs on my car and really want a redline tire.

hitman, i'd run the repro 15" rims on the 8 lugs just for the tire size selection.

i'm not sure what the largest 70 is but you can still buy a 245 60 r14 which is too wide for these cars.

mike

Cooper Tire still makes and sells a 225/75/14 "Trendsetter SE" tire, it's 27.3" tall. They also sell it under the Mastercraft IV all season brand name. Here's a pix of it on an 8 Lug wheel.

I think I was where the repro 8 lugs were about 190.00 a pop. Is that corrrect? I assume that did not include everything you needed.

for the pricing on the drums check postings in this forum and the new parts forum by dm_fan.

mike

I am about to put a rear sway bar and 15" rally II's under my 65 2+2. Dedhead or Mike, do you guys think I can fit 245 60 15's under there?

Let me put that another way. A 245 tire is about 9.65" wide, maybe 11 inches with the bulge? With a 60 percent aspect ratio, the sidewalls should be 5.78" tall each. So add the 15" wheel and I have a tire/wheel that is about 26.6" tall. Does this fit according to you guys' experience? I can and will go to my local tire store once I am rolling again, but I am trying to plan and therefore budget before I get back to work on it. Thanks for any insight.
Barry

Wait. I guess I skipped over Mikes post of 1/7/07. Even with the taller wheel, I guess 245's won't fit.