Wheel and tire spacing.
#1
Hello all.  I am buying new rims and rubber for my 71 mach 1.  

What tire size do most people use for the front and back?

I am buying aftermarket rims - what offset and backspacing do I need in order for it not to rub?

Thanks!  Jon
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#2
What kind of rims are you after?  Old school, modern (larger diameter), deep-dish, more 'flush-mount' (less deep-dish), etc.?  

What kind of tires?  Low-profile, staggered (wide rears, narrower fronts), stockish (pizza-cutters), etc.?

Rims & tires definitely make a huge difference.  Here's mine during restoration with the stock size 14x6 steel wheels and factory 'sport' hubcaps and 195/70R14 'pizza-cutter' stock-ish sized tires:

[Image: attachment.php?aid=12593]

And here we are about an hour later with the Cragars and Cobras:

   


15x8 (front) & 15x10 (rear) rims, with 245/60R15 and 295/50R15 tires, respectively.

Rims & tires definitely go a LONG way toward the appearance of the car.
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#3
It looks like Mister 4x4 probably answered your question and provided a good example of works on his car.   Personally, I would prefer a 15x8 wheel on the rear and 15x7 on the front if you are looking to run a wider tire on the back and a narrower tire on the front.  If you are going with the same size tire on all four corners I would stay with 15x7 wheel if you are going with a 60 series or a 15x6 for a 70 series tires.

Depending on the tire size you choose will determine the backspacing you will need.  Keep in mind, if you installed aftermarket front disc brakes on your car you may have to go with a 15 inch wheel opposed to a 14 inch wheel for caliper clearance.  Generally speaking larger the tire size  the deeper the backspace you will need.  For example, with a 4.5 inch backspace the wheel will set closer to the rear springs than a 4 inch backspace. So if you put a larger tires on the back of you car you want a deeper backspace so the tire does not rub on the lip of the quarter panel.  I ran into an issue with the backspacing on my 66 Mustang because I installed 1 inch lowering springs in the back.  I needed a deeper backspace to prevent the tire from rubbing on the lip of the quarter panel.  At that time I purchased 15x7 Torq-Thrust wheels and if my memory serves me correctly they came with 3.75 or 4 inch backspace.  I need another 1/4 to 1/2 inch backspacing for clearance to make them work.  I ended up changing the wheels to the Magnum 500's that had a deeper backspace.  

In addition to backspacing, if you get a tire that is too tall in the front you can run into clearance issues with your front fenders. Do some homework before buying your wheels and tires especially if you are buying them online because they can be difficult to return if they were installed. Sometime you are better off going to a local tire shop and have them guarantee fitment and clearance.

Here is a link to a tire chart.  I find this helpful when comparing tire sizes.

https://tiresize.com/calculator/
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#4
As the guy's have said there are a lot of size, and width options that will work. Take a look at your standard wheels, make a few measurements. of them, to get a basic idea what clearances you have when they are installed on your car. This will give you the basic measurements, to start with. If your standard wheels / tires are to close to the fender lip, add some to the backspacing when you order new wheels, but be sure you have enough room on the backside to do this, as the clearance between the spring, and wheel / tire will change, by the amount of backspacing you added. There is quite a bit of room in the Mach1's wheel well. and with a lot of measuring, you can come up with a set of wheels / tires that fit, and look great. Everyone has a little different perspective, on what the perfect look is. So do some "homework" and you'll come up with a good solution. One thing that came to mind, was the Eastwood Company. (Eastwood.com) Makes a fender lip roller, which attaches to the axle and allows you to safely roll the inner lip without damaging the fender, or the paint, unless you try to get crazy with it. I've seen it gain 3/4 to an inch of extra clearance, when done correctly.   Hope it helps. 

JTS
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#5
(08-24-2019, 10:14 AM)Mister 4x4 Wrote: What kind of rims are you after?  

Hey Mister 4x4.  These are the rims I was looking at. https://www.carid.com/american-racing-wh...44571.html



They are supposed to be a "garunteed fit" for a 71 mustang.


Attached Files Image(s)
   
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#6
(08-25-2019, 11:50 PM)Mustangmike Wrote: It looks like Mister 4x4 probably answered your question and provided a good example of works on his car.   Personally, I would prefer a 15x8 wheel on the rear and 15x7 on the front if you are looking to run a wider tire on the back and a narrower tire on the front.  If you are going with the same size tire on all four corners I would stay with 15x7 wheel if you are going with a 60 series or a 15x6 for a 70 series tires.

Depending on the tire size you choose will determine the backspacing you will need.  Keep in mind, if you installed aftermarket front disc brakes on your car you may have to go with a 15 inch wheel opposed to a 14 inch wheel for caliper clearance.  Generally speaking larger the tire size  the deeper the backspace you will need.  For example, with a 4.5 inch backspace the wheel will set closer to the rear springs than a 4 inch backspace. So if you put a larger tires on the back of you car you want a deeper backspace so the tire does not rub on the lip of the quarter panel.  I ran into an issue with the backspacing on my 66 Mustang because I installed 1 inch lowering springs in the back.  I needed a deeper backspace to prevent the tire from rubbing on the lip of the quarter panel.  At that time I purchased 15x7 Torq-Thrust wheels and if my memory serves me correctly they came with 3.75 or 4 inch backspace.  I need another 1/4 to 1/2 inch backspacing for clearance to make them work.  I ended up changing the wheels to the Magnum 500's that had a deeper backspace.  

In addition to backspacing, if you get a tire that is too tall in the front you can run into clearance issues with your front fenders. Do some homework before buying your wheels and tires especially if you are buying them online because they can be difficult to return if they were installed.  Sometime you are better off going to a local tire shop and have them guarantee fitment and clearance.

Here is a link to a tire chart.  I find this helpful when comparing tire sizes.

https://tiresize.com/calculator/

Thanks for the info.  I think its just stock brakes so I should be all good.  Yeah I've looked at some sites that give "guaranteed fits" for 71 mustangs, so I might get rims from them.  Im hoping for wider back rims, skinnier front rims, and probably the same backspace as the stock rims that are currently on the car.  (They are not in good shape so they need replacing).
Reply
#7
(08-26-2019, 02:05 AM)JTS71 Mach1 Wrote: As the guy's have said there are a lot of size, and width options that will work. Take a look at your standard wheels, make a few measurements. of them, to get a basic idea what clearances you have when they are installed on your car. This will give you the basic measurements, to start with. If your standard wheels / tires are to close to the fender lip, add some to the backspacing when you order new wheels, but be sure you have enough room on the backside to do this, as the clearance between the spring, and wheel / tire will change, by the amount of backspacing you added. There is quite a bit of room in the Mach1's wheel well. and with a lot of measuring, you can come up with a set of wheels / tires that fit, and look great. Everyone has a little different perspective, on what the perfect look is. So do some "homework" and you'll come up with a good solution. One thing that came to mind, was the Eastwood Company. (Eastwood.com) Makes a fender lip roller, which attaches to the axle and allows you to safely roll the inner lip without damaging the fender, or the paint, unless you try to get crazy with it. I've seen it gain 3/4 to an inch of extra clearance, when done correctly.   Hope it helps. 

JTS
Hey JTS.  Thanks for replying.  I don't think my standard tired are too close to the fender, so I should be all good there.  You have a valid point- there is quite a bit of room.  
I'm probably gonna take a good look at the current measurements and get something close to that.  I've seen there are websites that have guaranteed fits for 71 mustangs, so hopefully if i order some from them, they will fit like they say.   

Thanks.  -Jon
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#8
What size are you going for?  15" diameter, 7-8" width, and 60-series tires will be a good size.  As I mentioned, ones up front on mine are 15x8 with 245/60R15s.  It's a good overall size, and will work great front and back.

If you're going for larger diameters (16, 17, or 18"), you'll need to adjust the 'aspect ratio' (or sidewall series) to compensate for the overall wheel diameter, which could have an effect on your gearing and speedometer readings.  The tire width (in millimeters) will have an effect on the sidewall aspect ratio - the wider the tire, the taller the sidewall, unless you drop the aspect ratio number.

27" overall diameter is what you're shooting for to keep everything working without having to compensate by changing rear differential gears and the speedometer gear.
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#9
(08-26-2019, 11:46 AM)Mister 4x4 Wrote: What size are you going for?  15" diameter, 7-8" width, and 60-series tires will be a good size.  As I mentioned, ones up front on mine are 15x8 with 245/60R15s.  It's a good overall size, and will work great front and back.

If you're going for larger diameters (16, 17, or 18"), you'll need to adjust the 'aspect ratio' (or sidewall series) to compensate for the overall wheel diameter, which could have an effect on your gearing and speedometer readings.  The tire width (in millimeters) will have an effect on the sidewall aspect ratio - the wider the tire, the taller the sidewall, unless you drop the aspect ratio number.

27" overall diameter is what you're shooting for to keep everything working without having to compensate by changing rear differential gears and the speedometer gear.

Hey.  I'm looking at 15 diameter, hopefully 8 at the back, and 7 at the front.  My question now is offset!  You said you have 10 inch on the back, and 8 on the front.  whats your offset for each?  If I have 15"/8inch tires, what should my offset be?  How much room do I have to play with?

Thanks man.  -Jonner B
Reply
#10
The 8" wheels will probably come with 4" or less, and the 7" with 3.5" or less.  My 15x10s originally came with 4.25" of backspacing, but they stuck out about an inch too far, so I custom ordered a set with 5.25" backspacing, and they're just about right (less 'deep dish' look though, which is a bummer).

Standard backspacing on those rims should be just fine.  Can't wait to see it all come together!
Reply


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