17x11 fit 2nd gen firebird

[stangs400]

hey all, ive been doing a ton of research on wheels for my 71 firebird. Ive narrowed it down to either a set o boss 18x8 and 18x9.5, or Torque thrust II 17x9 and 17x11. The only question I have is, the 17x11s ive looked at are 7.75" backspacing and +45mm offset. I talked to NOT A TA, who has The 14 car on here, he is currently running 17x11 with I believe 6.75'' backspacing. I just dont know his offset, or if the wheels Im looking at would fit. Thanks.

[cheapthrillz]

Offset and Backspacing are both the same measurement (kinda)..... Backspace is measured in inches from the inner most part of the wheel to the mounting face. Offset is measured in mm from the centerline of the wheel to the mounting surface. You can calculate the offset of an 11 inch wide wheel with a 6.75 inch bs.

Half of 11 is 5.5, so 6.75 minus 5.5 is 1.25 inches which is a +31.75 mm offset.

Here is a visual aid:



Hope this helps!

[tazzz25906112]

For an 11" rim with a 315X35X17"most people are running 5.75" backspace..... This allows the tire to just squeak under there and you'll have to roll the lip a little and modify the rear seat belt hump (in Camaro's anyways)....

This is a max combo and I truly believe if you try running a 6.75" b.S. you will find your rim square n the middle of the spring pack.... Measure twice order once my friend cause this stuff has a way of biting you (ask me how I know that ;-) LOL)

[NOT A TA]

Like Albert says, Measure and then measure again! Early 2nd gen birds have a different wheelwell configuration than Camaros and later birds. So don't adopt what works for them, also you have no seatbelt bump to worry about. I tried my wheels from The 14 Car on my 74 Camaro and they wouldn't fit.

[WS6]

John where was the interference with your wheels on the camaro? Just curious. I find it remarkable how different these cars are from one another even though they are the same platform.

[a73formula]

on my 73 formula I ran the ttII's in 17x11 with 6" bs and no problems with anything. I think 5.75 bs will put the lip to far outside the quarter lip.

[mc84_zz4]

Here is the best wheel calculator I have used:
http://www.rimsntires.com/rt_specs.jsp

[NOT A TA]

OK, as we know, EVERY CAR IS DIFFERENT. Even cars of the same year and model have slight variances due to the inconsistancies of manufacturing at the time these cars were originally built so anyone considering pushing the limits of the stock wheelwells should measure, measure, measure, as Albert said.

My current wheels are 11's with a 6.75 backspace but that may not work on someone elses car, everything is very close. I did not have any rubbing issues (unmodified wheelwells or fender lips) until I got to be a better driver on track and then started getting a slight rub if I hit the angled curbing hard on corners at full boogie. Experienced track drivers behind me told me they could see the rear movement that caused the rub. The 315 35 tires touch the inner fenderwell just above the shock and the (non rolled) fender lips on both sides due to movement of the rear when combined with compression of the suspension. It's very slight but a bit disconcerting if I'm hauling butt on a track. My fear is that the rub might cause just enough braking action at some point to cause a spin if I'm driving at the limit (mine or the cars). Panhard bars etc. were recommended but I haven't done anything because it only occured on track and only under certain extreme conditions, plus I'm putting narrower wheels on. No rubbing issues on the street ever.

I'm switching my wheel/tire combo very soon and will be running 18 X 10 Rushforths all around with 285/295 Yokohama AO 48's. Backspacing yet to be determined until after installing the new Baer brakes. It will be interesting to see the difference going from 275/315 to 285/295 since the car felt very good on track the way it was. Turn in should be a bit better but the rear may want to drift out under power on corner exit with the narrower rear tires, I'll go easy and feel it out the first few track sessions.

The suspension, weight of the car, and payloads it will carry as well as the intended use of the car will determine rubbing issues. The famous seatbelt bulge was started in 73 I think to allow for the retractor mechanism for the rear seatbelts. To max out wheelwells with the bulge the retractors need to be removed and the bulge persuaded with a BFH.

70 birds came with Pontiac 8.2" 10 bolt rears as well as 12 bolt Chevys and I believe starting in 71 8.5" 10 bolt chevy style rears were used as well as some 12 bolt Chevy units. Some of the rears used over the years in Birds and Camaros may be slightly wider/narrower than other ones? I originally decided to use the 11's after seeing the Hotchkis F-71 Camaro and talking with the tech guys there. They had used 11's and I wanted to try so I measured, remeasured and measured again, over and over for two years before getting the courage to order non returnable custom made wheels that were a real stretch for my budget at the time.

After thinking about when I tried the 11's on my 74 Camaro it really has no relevance since it had a 12 bolt from who knows where in it. Below is a couple pics that kind of show how tight the 11" 315 combo is on an early bird. I've run the wheels on a '70 8.2 Pontiac rear, a 70 8.2 Chevy rear and a '76 Corporate (Chevy) 8.5 all of which were 10 bolts. The positioning of the wheels in the wheelwell is the same on all three. The tire just lines up with the edge of the body and there's minimal clearance to the springs.

Pic from many years ago when I was putting the suspension and wheels on. Yes, I cleaned and painted the tank.



How much wider are they really you might ask. Here's a 255 60 on a 7" rallye wheel behind the 11" wheel. 11's are BIG!



Pic I took yesterday while out and about. You can see I have room for suspension travel before contacting the lip. You can not tuck a 315 and slam the car in the weeds with stock wheelwells. Gotta touch up that paint on the door lock, gets scratched up unlocking the car at the supermarket. LOL Yes, I drive it around town for errands all the time!



Tire just lines up with the body at the beltline, if I had any less than 6.75 backspace they'd be sticking out.

[JRouche]

No thats some MEAT! Looks good. Side pipes???? Well, the car looks good. JR

[Skip Fix]

I can tell you even a 225/70 on a TA 8" snowflake wouldn't fit the front end of my 79 Camaro. Wheel openings are way different.

[NOT A TA]

I can tell you even a 225/70 on a TA 8" snowflake wouldn't fit the front end of my 79 Camaro. Wheel openings are way different.

Was it a 3rd gen snowflake? They have different backspacing.

[srh3trinity]

John,
What setup (specs) are you going to go with next. I realize you are going with 18 x 10 Rushforths, but I was curious about the backspacing. Are you hoping to tuck things in a little more? Are you making a compromise on the front end with turning radius or are you really able to accomodate 285's up front?

[NOT A TA]

The turning radius is already compromised by the 275's I've been running the past 6-7 years. The tires will just touch the fat swaybar at full lock. Knowing they'll hit, I just don't turn that tight. I will install steering stops when I put the 285's on to make sure that if I'm sliding on track and crank the wheel to full lock to try and control the slide a tire doesn't skid from hitting the swaybar.

The new brakes, wheels, and tires combo is a result of being very lucky to have won the Performance Therapy photo contest where I won the Baer Brakes, Yokohama tires, and Rushforth wheels that are going on the car. Todd at Baer said the brakes should be going out soon and after I install them I'll measure for the backspacing. The wheel size/tire size is a result of what I won in the contest. After reviewing the wheel size choices available from Jay and the tire sizes available from Yokohama in the AO48 DOT-R tires I run, the 285/295 on 10" all around seems like the best match up for track use. Going up to 18" hoops allows some serious stoppers from Baer.

I'm not going to try to tuck them. A 285 on the front will have to be out where the current tires are and then there's no point to trying to move the rears inward.

Here's the tires waiting to be installed!

[carbuff]

John,

Do you by chance have any more pics of your car that you could share? I don't think I've seen a real build thread on your car, just a few pics here and there. I LOVE this picture. Would love to see a few more from various sides, and particularly under the hood if you have them.

THANX!

[POS71RS]

John, I gotta say... that car is absolutely BEAUTIFUL... I love the early 2nd gen Birds!
I'm astounded that there's so much difference between them and the Camaros though! I would have sworn they used the same inner wheel wells, etc. But that offset wouldn't work in a Camaro I'm sure. I'm running 315/35/17s on 5.75" and there's really no room for growth.. and the fact that there's no seat belt hump in the Birds at all just leaves me confused... and I don't think retractable rear seatbelts were an option on the 71 Camaros either... but yet they have the humps there.
I may have not needed to flatten the humps on mine, I just did it for giggles.

PS, your car just made me finally want sidepipes... I've never been a huge fan... but that looks fantastic! I want them bad now! Are those the evasive Hookers?

[LeighP]

My 71 Firebird does not have the seat belt humps.
John, I'm still blown away you can fit that much tyre under those rears without touching the fender lips.....

[aronhk_md]

I think one of the keys to John's backspacing may be the height of the car as he said. 6.75" backspacing on the rears might be fine at that ride height, and some compression cornering, but any lower and he'd begin to make contact with the inner wheel wells...and of course maybe the fender lips as well.

John.....what springs are you using in the rear....are they a stock type?

My car came to me with the 335/60/15 tires on a centerline style wheel with about 5.5" backspacing as pictured in my signature. The tires just stick out of the wheel well openings, and its been no issue because the car sits high. That'll change as I try to lower it and get 18" wheels under it.

Its one reason I'm really leaning toward a set of those Summit Legend/Vision 18" wheels. At about $600 a set I can use them a year or two and then find a buyer probably at $450....which spells minimum outlay for now and minimum loss down the line....while improving the handling from 15" wheels set up in a skinny/fat tire config. In a year or two the rear will hopefully get a minitub, new stronger rear with a triangulated 4 link setup or maybe a 3 link....need to see what the best is. So it makes no sense to buy expensive wheels only to have to find a buyer later.

[a73formula]

6" bs was perfect on my car, that extra .75" would have put the tires into my shocks but my tires line up exactly the same on the outside and I had no seatbelt hump on mine in 73 so maybe mines an earlier car or something not sure on that. Love you car. I just picked up a 75 t/a, we'll see what ends up on that

[SS1156]

No thats some MEAT! Looks good. Side pipes???? Well, the car looks good. JR

What kind of tires are these? How well do they work? I like the tread pattern and was thinking they should be decent in the wet as well.

[NOT A TA]

John,

Do you by chance have any more pics of your car that you could share? I don't think I've seen a real build thread on your car, just a few pics here and there. I LOVE this picture. Would love to see a few more from various sides, and particularly under the hood if you have them.

THANX!

Do I have pics!!! LOL... Ya dating back to the early 90's! ahaha There was no real "build" just an evolution of sorts as I fixed it up over the past couple decades. I'll PM ya a link to my bucket accts. of the picture stuff since the world went digital. Someday maybe I'll write a history thread since the project started before there was a WWW. Sorry I didn't see your post back when you posted.

POS71RS: I think most of the Camaro-Firebird difference is the shape of the outer fender being flared on the bird. As for the sidepipes I don't know what they are. The front and back halves don't even match really. I used adapters machined out of aluminum because the front part is smaller diameter than the rear sections (you can see in the side shot). I got them in a "everything in the garage" buy from a bud that was moving far away back in the 80's and they were new in boxes. I figured no one had ever used them because they didn't fit together so I made the adapters. I do have a set of NOS HOOKER side exit headers and the sidepipes to match I'm probably going to install pretty soon.

Leigh: Since I added a couple hundred lbs of roll cage they just very lightly touch if I hit the curbing really hard on a road track at full tilt. Same with the inner fender by the shock. just a very light touch under the hardest cornering punishment. On the street they never touch. If I switched to Global West rear shackels it would probably limit the movement enough to prevent the inner touch but since I'm going with narrower tires that won't be necessary.

Aron: Correct! I didn't try to slam my car by cutting springs and using blocks etc. The suspension is Hotchkis springs and sways with Bilsteins. Global west Del-A-Lums in stock control arms. No Herb Adams mod. I don't have a budget for fancy stuff and spend my money on track days and wear items. Plus I don't want to be in the car too deep since there's always the risk of balling it up on track and having to walk away. Most of the car was built with used or inexpensive parts and I did almost everything but weld the cage myself. So if I total it on track I could probably part it out and get most of my money back unless it burns. Sooo... I have 2 fire systems.

A73formula: Ya, if there's no hump it must be an early car or maybe they went with the retractable in 74 but I thought 73's got them. The 75 has different rear fenders I believe so it might be tough to get more than a 285-295 on 10" under it.

SS1156: The tires in the pic are Yokohama AO32's which are a DOT R tire with a treadwear rating of 60. They are amazing when warmed up on a dry track and fair on a wet track but not like a regular tire. I put 2 wheels off twice at Palm Beach International the last time I was on a wet track. They don't make the AO32 tire anymore and the new ones are the AO48's shown in other pic above. I get them in the harder compound for heavier cars being used on full size tracks. Lighter cars get a softer compound. I had to replace the front AO32's at Sebring the day after the pic above was taken and the rears are due now too, so getting a full set from Yokohama made my day!

I'll post up a project thread when I get started with my upgrades. The Baer brakes arrived the other day and they are KILLER! 14" slotted rotors with their 6P calipers in the new Nickle plating. So it's time to get started so I can measure for backspacing with the new brakes to give Jay for the new Rushforth wheels.

Here's the new brakes on spindles. They're as big as the wheels the car left the factory with!