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Test fitting a 315 on my 66

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My build has the DSE mini tubs with the Crites leaf spring relocation kit installed. The DSE site claims a 315/35R17 or a 315/18R30 should fit. I do not have the exact tire but a buddy just happen to buy a 315 20 inch tire. I borrowed it to see how it would fit with the DSE mini tubs. The lip is rolled and in the pictures there is 3/4 inch between the backside of the tire and the inner tub. Since I do not have my suspension yet I do not know for sure how far up the 315 will sit. I plan on dropping the car 2 inches. I think I just may end up running a 305 to be safe. That will give me another .400" of tire clearance with the 3/4" I have on the inside.

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Discussion Starter · #3 ·
I don’t have it mounted in a rim plus the tire I was using is a 20 inch. But from I can tell it will depend on how low the car is. I think with my set up and stock height it would clear with no issues. But I want it two inches lower so it looks like it will be very tight with the car lowered. So much so I think a panhard bar would be needed to keep the axle centered.
 

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Discussion Starter · #4 ·
I already posted these pictures in my build thread but thought I should update this old post in case anyone searches for this type of fitment.

I bought two used 315/35 17 tires which is one of the sizes DSE claims fit their mini tub kit. Happy to say I think they should fit.
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Discussion Starter · #5 ·
A little measuring and my tightest point is 13 inches. That would leave .400 of clearance or .200 clearance on the inside and outside. A 305 would give me a total of .500 more for clearance. Think I’ll go with a 10 inch wide rear rim. The amount of offset I will need may allow me to run a later model mustang rim with no custom offsets.

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Like any other size, there's a lot of variation in the width of 305's and 315's between manufacturers. The 315 AR-1's I run on my firebird now are nearly a full inch wider than the R888's they replaced. I'd check clearance before mounting your new tires in case you need to change brands.
 

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Discussion Starter · #7 ·
Like any other size, there's a lot of variation in the width of 305's and 315's between manufacturers. The 315 AR-1's I run on my firebird now are nearly a full inch wider than the R888's they replaced. I'd check clearance before mounting your new tires in case you need to change brands.
Not set on any brand. These were cheap enough to buy just for mock up. If they fit they may only be burn out tires.
 

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If its a 20 inch tire I wouldn't trust any measurement you get off of it....just because its 315 doesn't mean a thing, sidewall and diameter play into how a tire fits as well. You have to break down and actually buy the wheels and tires you plan on using to test fit....no other way to avoid unpleasant surprises down the road.
 

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RTM, do you mind telling me how wide of rear axle you went with in order to get the 4.25 backspacing requirement? I'm dealing with my falcon, but just compiling numbers before I place my order for a new 9". I don't think I'll be able to use my current 9", because it stepsmdown twice from the center section.
 

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RTM, do you mind telling me how wide of rear axle you went with in order to get the 4.25 backspacing requirement? I'm dealing with my falcon, but just compiling numbers before I place my order for a new 9". I don't think I'll be able to use my current 9", because it stepsmdown twice from the center section.
Mine stepped down twice as well, I was able to use it...but modification of the watts-link weld bracket and bolt-on bracket are required.
 

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Discussion Starter · #11 ·
If its a 20 inch tire I wouldn't trust any measurement you get off of it....just because its 315 doesn't mean a thing, sidewall and diameter play into how a tire fits as well. You have to break down and actually buy the wheels and tires you plan on using to test fit....no other way to avoid unpleasant surprises down the road.
That was the very first tire I tried because a friend had a set. The tires I bought used are the correct 17 inch tires that DSE said would fit.
 

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Discussion Starter · #12 ·
RTM, do you mind telling me how wide of rear axle you went with in order to get the 4.25 backspacing requirement? I'm dealing with my falcon, but just compiling numbers before I place my order for a new 9". I don't think I'll be able to use my current 9", because it stepsmdown twice from the center section.
My axle is the early 57-59 housing and the step down is pretty small plus my bracket for the WATTS link is mostly on the larger diameter of the axle tube. The axle is 52.25 housing flange to housing flange.

I'm not sure if you mean 4.25 wheel back spacing or something else? If you do mean the wheel back spacing then I can not help you because I have mini tubs and the SoT axle link bars are moved inboard to make room for the 315 tire. My back spacing will be close to 7 inches, give or take some. So nothing on my car will relate to a stock mustang tire set up.

Speedway motors has their tire fitment tool back in stock so I ordered it.
 

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My axle is the early 57-59 housing and the step down is pretty small plus my bracket for the WATTS link is mostly on the larger diameter of the axle tube. The axle is 52.25 housing flange to housing flange.

I'm not sure if you mean 4.25 wheel back spacing or something else? If you do mean the wheel back spacing then I can not help you because I have mini tubs and the SoT axle link bars are moved inboard to make room for the 315 tire. My back spacing will be close to 7 inches, give or take some. So nothing on my car will relate to a stock mustang tire set up.

Speedway motors has their tire fitment tool back in stock so I ordered it.
All this info helps... your axle measures around 57.25", accounting for a 2.5" distance from axle flange to housing flange. Im also installing DSE mini tubs, and SOT 3-link coulover kit, but since it is a Mustang kit going in a Falcon, I have a lot of unknowns to deal with. I'll do the tubs first. Then decide if my current axle will work for me. I have your original install thread saved, so I can use it for reference. Thanks..
 

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Discussion Starter · #14 ·
Bought the tire figment tool and it looks like I can fit the 315 tire. The pictures show it setup with a 10.5 rim width with 7 back spacing.
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