Wheel Question - Page 2 - Vintage Mustang Forums
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post #16 of 29 (permalink) Old 12-03-2018, 04:08 PM
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It's just the wrong backspace. It's not the wheel width is what I am saying. You have the same physical space under the fender as I do.

I spent a fair bit of time measuring clearance front and rear and comparing it to a wheel I already had with a known backspace to work out the correct backspace and width that could fit. These cars have such limited space under the fenders, that if you have a lowered car and want bigger wheels, you have to do your research or you run the risk of wheels just not fitting.
All things being equal a 17x8" wheel with 4.75" of backspacing is still going to stick out .25" further than a 17x7" wheel with 4" of backspacing. My 17x7" wheels with 4" of backspacing barely fit right now with a 215/45/17 tire. I tried a 225/45/17 tire and it rubbed on the fenders quite badly when turning the wheel and I didn't want to have any rubbing issues. I initially wanted to use 17x8" wheels all around and bought some 17x8's with a 4.75" backspacing and they stuck out of the wheel well by about a half inch. No way those were going to fit with a decent sized tire on them. I'm sure the aftermarket, made overseas fenders probably don't help and likely aren't the same size as the originals but in my case, this is about the biggest tire/wheel combo I could go with up front without rubbing like crazy.

Last edited by MUSTANG65FBK; 12-03-2018 at 04:17 PM.
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post #17 of 29 (permalink) Old 12-03-2018, 04:17 PM
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this is about the biggest tire/wheel combo I could go with up front without rubbing like crazy.
The biggest in the backspace you had. It's just not the right backspace for your setup.

So with your 17x7 4"bp wheels, an 8" with a 5" backspace would have the same fender clearance.
So if you want to go 8", you need 5"bp minimum, and by the sound of it, a 5.25" would fit better.

Last edited by hus65; 12-03-2018 at 04:22 PM.
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post #18 of 29 (permalink) Old 12-03-2018, 04:25 PM
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The biggest in the backspace you had. It's just not the right backspace for your setup.

So with your 17x7 4"bp wheels, an 8" with a 5" backspace would have the same fender clearance.
So if you want to go 8", you need 5"bp minimum, and by the sound of it, a 5.25" would fit better.
But you just said earlier that a 4.75" backspace would've worked? Also, the wheels that I wanted to use didn't come with a 5"-5.25" backspace. Finally... I didn't want to have issues with the inside of the wheel lip rubbing against the UCA's or anything else.
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post #19 of 29 (permalink) Old 12-03-2018, 04:26 PM
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Although you would not think it possible, there is some variation in how
backspacing is measured. A certain wheel company in Australia (the
name of which I will not mention) screwed up the construction of a set of
$1400 three-piece 16x8 rims for my '66 GT way back in the 80's.......
that's why I mention this. (photo of stupidly expensive rim at the bottom)

The true backspace measurement is from the mounting pad of the rim to the
very back "face" of the rim.
Measuring to the tire bead seating area is a sure way to cause problems but
I have seen it done more than once.

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Last edited by GT289; 12-03-2018 at 04:32 PM.
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post #20 of 29 (permalink) Old 12-03-2018, 04:47 PM
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Quote:
Originally Posted by hus65 View Post
The biggest in the backspace you had. It's just not the right backspace for your setup.

So with your 17x7 4"bp wheels, an 8" with a 5" backspace would have the same fender clearance.
So if you want to go 8", you need 5"bp minimum, and by the sound of it, a 5.25" would fit better.
But you just said earlier that a 4.75" backspace would've worked? Also, the wheels that I wanted to use didn't come with a 5"-5.25" backspace. Finally... I didn't want to have issues with the inside of the wheel lip rubbing against the UCA's or anything else.
Yeah on a stock setup they do. You said your setup pushes the wheel out further, so you need more backspace.
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post #21 of 29 (permalink) Old 12-03-2018, 04:59 PM
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Yeah on a stock setup they do. You said your setup pushes the wheel out further, so you need more backspace.
"It makes no sense to say if you have a different setup like a granada, that 8's won't fit." I'm so confused, this was your comment from earlier.
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post #22 of 29 (permalink) Old 12-03-2018, 05:34 PM
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Ok, I'm going to combine my posts into one post to try and make it more clear.

The width of the wheel you can fit has nothing to do with the hub, and where the hub sits. It has to do with how much space you have under the fender, including the UCA clearance and clearance when going lock to lock.

On a 65/66, and an 8" wheel in a 17 or larger size WILL fit the front. There's is enough space between the fender and the UCA to do this. An 8" wheel will also fit the rear, no dramas. Plenty of space between the fender and front inner wheel well for that.

Once you work out what size wheel you can fit, then you work out what backspace or offset you need. That is based on where you're hub sits. If you hub sits closer to the fender, you need more BP. If it sits further in, you need less BP. Same as when guys shorten their rear end to get more dish on the wheels. Same size wheel as before, but less backspace.

For you vehicle, if the front hub was stock a 17x8 with a 4.75bp would fit (assuming the wheel BP is correct as mentioned above by GT289). You said your granada setup(which I dont know much about) has pushed the hub out further towards the fenders. This means you need more backspace on your wheels. So the 17x8 4.75bp that would have fit, now needs to be 17x8 5"bp for eg.
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post #23 of 29 (permalink) Old 12-03-2018, 06:54 PM Thread Starter
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Fellas, no need to argue. I'll just put a rear sway bar on, and it will be all good.
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post #24 of 29 (permalink) Old 12-04-2018, 01:39 AM
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Ok, I'm going to combine my posts into one post to try and make it more clear.

The width of the wheel you can fit has nothing to do with the hub, and where the hub sits. It has to do with how much space you have under the fender, including the UCA clearance and clearance when going lock to lock.

On a 65/66, and an 8" wheel in a 17 or larger size WILL fit the front. There's is enough space between the fender and the UCA to do this. An 8" wheel will also fit the rear, no dramas. Plenty of space between the fender and front inner wheel well for that.

Once you work out what size wheel you can fit, then you work out what backspace or offset you need. That is based on where you're hub sits. If you hub sits closer to the fender, you need more BP. If it sits further in, you need less BP. Same as when guys shorten their rear end to get more dish on the wheels. Same size wheel as before, but less backspace.

For you vehicle, if the front hub was stock a 17x8 with a 4.75bp would fit (assuming the wheel BP is correct as mentioned above by GT289). You said your granada setup(which I dont know much about) has pushed the hub out further towards the fenders. This means you need more backspace on your wheels. So the 17x8 4.75bp that would have fit, now needs to be 17x8 5"bp for eg.
The hub actually does have some impact on what size of wheel can be used as disc brakes, not just Granada style disc brakes, are going to push the wheel out further than a drum brake will. Also, not all wheel manufacturers are going to have multiple different sizes in backspacing to be able to accommodate all different widths of wheels. Like in my particular case... the 17x8" wheels that I wanted to go with were only available in a 4.5" backspace so I had to use a 17x7" wheel instead because of clearance issues. Not trying to argue, just don't want someone to spend hundreds of dollars on tires and wheels because they heard something online and then it doesn't fit for them.

My advice would be that since our cars are all slightly different, to take your car to a local tire shop and have them measure it, or if you can do it yourself that works too, that way you're not guessing when buying wheels and tires that can be hundreds, if not thousands of dollars. I had this issue of buying the wrong backspacing on my wheels with the first set as I was told that they would fit. Luckily I was able to sell them locally for the same price as I purchased them for and didn't lose any money on the deal. The second time I drove the car up to Les Schwab and had someone there measure everything up so I didn't have the same issue again.
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post #25 of 29 (permalink) Old 12-04-2018, 01:41 AM
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Fellas, no need to argue. I'll just put a rear sway bar on, and it will be all good.
I've got the rear 3/4" sway bar that I took off my 65 fastback sitting in storage somewhere in the attic. If you pay the shipping and make it worth my while, I'll gladly ship it to you.
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post #26 of 29 (permalink) Old 12-04-2018, 02:57 AM
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The hub actually does have some impact on what size of wheel can be used as disc brakes, not just Granada style disc brakes, are going to push the wheel out further than a drum brake will.
.
Look there was never an argument, I'm just trying to explain a concept and maybe the way I'm saying it isn't easy to understand, as the above comment is not true, and was spoken above in detail in the post above. It doesn't matter if the disc brakes or granada brakes or whatever have moved the hub out in terms of what width wheel will fit. Not one bit. It just means you need a different backspace to what would fit a factory setup.

And no, not all wheel manufacturers have the right backspace, in fact most don't. It just means you can use those wheels. You can't go around saying an 8" wheel won't fit, because it will. You just might not be able to use an 8" because you want a particular type of wheel that only comes in a certain offset that won't work.

It's been well documented for a long time that 17x8 in 4.75 will fit a stock setup quite nicely. If you have changed the hub setup, then it sucks to learn the hard way, but the standard fitments no longer apply.

And also, not all disc brake setups push the wheel further out. Only a few do and most of them will tell you about it. I have a 14" Brembo setup on the front of mine without changing the hub offset
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post #27 of 29 (permalink) Old 12-04-2018, 04:22 PM
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And no, not all wheel manufacturers have the right backspace, in fact most don't. It just means you can use those wheels. You can't go around saying an 8" wheel won't fit, because it will. You just might not be able to use an 8" because you want a particular type of wheel that only comes in a certain offset that won't work.
Lol that's exactly what I just said in my last post.... "Also, not all wheel manufacturers are going to have multiple different sizes in backspacing to be able to accommodate all different widths of wheels. Like in my particular case... the 17x8" wheels that I wanted to go with were only available in a 4.5" backspace so I had to use a 17x7" wheel instead because of clearance issues." That's why I'm saying that not all 17x8" wheels are going to fit on the front of a 65/66 car, sometimes they won't fit even with the 4.75" backspacing that everyone recommends, my car in particular is one of those that wouldn't fit even with a 4.75" backspace wheel.
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post #28 of 29 (permalink) Old 12-04-2018, 05:26 PM
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Fellas, no need to argue. I'll just put a rear sway bar on, and it will be all good.
That's a whole nother can O worms ,
Like I said I have Granada's with 17x8x4.75 with 225/45/17 and a ton of room
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post #29 of 29 (permalink) Old 12-04-2018, 05:50 PM
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