tilstad

Im getting new rims, and wonder what the original backspacing is on the 16x8 formula rims. Do I have to use the different backspacing on front and rear on my new set, as on the formula ones?

I am getting the TT II's in 16x8, but dont know what the backspacing I have at the moment is.

But have anyone tried the same spacing on both tires? What happens then? Does it hurt drivability or handling?

Imo it looks kind of silly with the wider stance up front, but I guess it's like that for a reason.

First choise would be original backspacing, second would be a backspacing which made it having a wider stance out back or at least the same as on the front, but at the same time only using the original 245/50-16 tires all around.

I wouldnt choose the second if that in any way screws up the handling on the car. It would be too expensive to get another set of rims after that.

So in short, original backspacing, or custom backspacing?
And in both cases; what backspacing?

I appreciate any comment on this subject.

Thanks
Kjetil

DJP87Z28

For the info you want, why not try the company you are planning on buying your new wheels from. They should be able to give it to you and if they can not I would not be purchasing the wheels from them.

tilstad

Well, I guess you have a point there. But the thing is I got a feeling they gave me a price way too low, because one of them got a little angry when he heard the price I got, and it was less than half of the most expensive dealers.

I just thought it would be kinda wise to do a "fast in - fast out" before they change their mind. Not to annoy them unnesseseraly..

Even so, it would be a bit safer if I could certify that thay chose the right ones...

DJP87Z28

Good thinking. You will not be saving any money if the wheels do not fit. Also be leary of some low ball pricing, and is your source any good???

tilstad

The source is good, its the biggest parts dealer in my country, and they are accredited by most amcar guys where I live.

It's also my most local shop, and they have been around since the sixties.

But one thing that they probably can not answer, is the part about original or custom backspacing. That's why I asked the question here.

Kjetil

DJP87Z28

Ok, try a search on this site and there should be the info you need. Good luck.

tilstad

Now I have been sitting here for about five hours reading through lots of post after searching for "backspacing"

But incredible enough, I still havent found an ansver to this!

It's way too late to go on with this, I need an answer now, or I have to wait another week to get the rims and be able to drive the car again.

The "Do a search" frase one often gets, doesn't really always work out when all the posts you search trough only says the same thing...SEARCH!

Not ONE of all the post I read trough either linked to the answer or anwered the seemingly easy question of what the original backspacing was.

Guess that about sums it up..

DJP87Z28

Try this web site. it uses the iroc wheels as examples for backspacing and offset.www.skulte.com

tilstad

Maybe Im just too tired, its 3 am here now, and I really just need to get to sleep.

But I cant see that they even mention what the original backspacing is on my 16x8 formula rims. As far as I know, there would be a different bs on the rims thay sell, and the one I got, and I am not getting them, I am getting some 16x8 ones...No to hell with it, Im just about done with this crap, I'll buy a used original one + a weekation to Greece instead!

REDZ28

I guess no one knows the answer to this guys question. Truly amazing with all the so called experts on this board!

tilstad

This is almost insane....

I sent a mail to Summit, and thought "shurely, they must know the answer to this since they sell them..."

Here is their reply;

"Response (Damon) - 05/25/2003 01:29 PM
Hi there. I do not have any information that tells me what will fit properly on your application. You will need to measure to determine what will work. If you are not certain what to measure, you might want to check out some of the Thunderbird message boards online, and you might find someone who knows what will work. I hope that gets you started. Thanks ."

GREAT!! Another board! Yeah RIGHT!

z 28 jari

iTrader: (1)

I think your backspacing at 16x8 original wheels is at rear 123mm(16mm offset)and front bs is 110mm(0mm offset).

Jari

Anth's Iroc

I believe the fronts have a 4 1/2 inch backspace and the backs are 5 inch.Thats what I used on my iroc when i put my centerlines on......

LilJayV10

iTrader: (5)

I have no advice on what the correct backspacing is and I am amazed that no one knows, i am almost tempted to go out and measure it myself. It is a good thing that you are checking it, I see so many white trash(sorry if i am not politically correct) 3rd gen's driving around with the wrong back spacing that makes them look like crap but think they are the shizzle.

ok, i'm done.

Jason

tilstad

Lol, well I don't see many thirdgens where I'm at, but I think I see what your meaning. You think about people having the wheel all out to the fenderlip, yet beeng quite narrow? Kinda like just spacing them outwards?

I actually found me some BMW wheels today, used, and I loaned a pair home to try them on. Those were way over what I had in mind tho', being that they where 19x11,5 at the rear, and 19x 9 at the front and 275/30-19 tyres. Looks kinda like all wheel and just with a little duct tape on them...But the funniest thing is that they acually fitted. Didn't expect that. Havent tried the front ones yet tho.

LilJayV10

iTrader: (5)

I have heard that BMW wheels will fit and have the correct backspacing, who would have thought.

z 28 jari

iTrader: (1)

Yeah,they fit,but you should use centering rims between hub and wheel.I had bmw 8,5X17 wheels at my -85 z-28.Wheels have been there 3 years,no problems.

Jari

tilstad

What do you mean by "centering rims"?

z 28 jari

iTrader: (1)

Centering rim is thin machined rim that goes between wheel centerhole and hub(at bmw wheels this centerhole is approx. 74mm and thirdgen hub is 70.6mm).You can made that rim steel or aluminium.Mine is done by aluminium.

Jari

tilstad

Okey, I see. Havent heard of those before, but I think I see the advantage. Do you fear that if you didn't have them that you would easily put on your wheels a little wrong, so they would be uneven when they rotate? The ones I tried on todau where like that, but they where like that with the original pontiac rim too. Think I have bent the rear axle or something when I hit a curb a couple of weeks ago.

But the wheels I found looked absolutely awsom. But them "Falken" tires, they are kinda ripoff. Said 275/30-19 on them, but I measured them with a regular measuring stick, and they werent wider than 235. My original 245x16 were actually wider. Good thing it sat Yokohama on the rears, they measured 300, but were supposed to be 275 too.

z 28 jari

iTrader: (1)

I think there is a possibility that wheels can go wrong position if you don't put those centering rims between wheel and hub(120mm vs.120,65mm).My original z-28 7x15 wheel centers exsatly to hub.Isn't it so, that hub centers wheel and bolt's keep it in place.

tilstad

It would seem that it would be better, but on the rear there arent any center sticking out at all. You may be right on this, I have actually never thought of it, but if it is so, where can I get me those? Or do I have to have a machine shop make them?

z 28 jari

iTrader: (1)

Yeah,someone who has turning machine can do them(at machine shop forexample).Do you have drumbrakes at rear?.At my Z have diskbrakes at rear and they have about 1cm wide "centering area".

Jari

tilstad

I have drumbrakes. Looks like there is going to be a fair bit of machining to get those bmw wheels onto the car. Already I have to get the center of the wheel bored up a tad, and perhaps mill down the spindle a little.

How about lugnuts? I thought of milling them to get the correct angle on the wheels. Or could they be bought so they'd fit? The wheels i tried on came with bolts, guess converting to bolts would not be any easier..

z 28 jari

iTrader: (1)

I think there is asymmetrical wheelnuts at wheelshops.Maybe those help.And bolt threads are 12x1.5mm.

SpeedCat86

Sorry I'm late, but here's some info that should help.

Backspacing / Wheel offset:

Jari was right. On an 8" wide wheel, the backspacing for the front wheels will be 4" (0 offset) The backspacing for the rears will be 4.5" or 4.75" depending on the wheel manufacturer.

Tilstad, you mentioned that you thought the front track is wider than the rear track. This is not true. On an F-body fitted with 15x7 or smaller stock wheels, the rear is actually wider than the front. When the cars were equipped with 16x8 wheels, the rear wheels needed deeper backspacing to maintain the same track width as the front wheels, and still leave adequate fender clearance.

Most of us who have fitted aftermarket wheels, like the Torq-Thrust II's, get all 4 wheels with the front backspacing (0 offset) This allows you to be able to put any wheel on any corner of the car, so that you can rotate the tires without removing them from the rims. The rear tires will be about 1/2 inch wider on each side, but they do not stick out past the wheel well edge.


'Centering Rings'
Some cars, usually European and Japanese makes, use a 'hub-centric' wheel design, which means that the wheel hub is used to locate the wheel, and the lugnuts simply hold it on. Aftermarket wheels for these cars usually require a spacer or 'centering ring' to positively locate the wheels.
Most American cars (older models, and almost all trucks) have 'lug-centric' wheels, which means that the lugs and lug nuts locate the wheel to the hub, as well as hold it on. That's why most lug nuts have tapered faces, which fit against a tapered 'seat' on the wheel.

If the BMW wheels are a hub-centric design, they will take some work to fit on the Camaro/Firebird, which uses lug-centric wheels

tilstad

Ok, but how do one tell if a wheel is hub centric? The bolt holes are not any bigger than the bolts, and it have a conical seat where the nuts goes. I'm sorry for having to ask this, but what does "tapered" mean?