#1  
Old 06-06-2021, 10:39 PM
DM3 DM3 is offline
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Default New wheels and tire sizes, thoughts.....

So I am looking to replace the temp 18" wheels I bought.


Currently the front wheels rub on the subframe, but just barely.


Here is what I am currently running:


Front: Ridler 18x8, 4.5 BS, 215/45 R18, Dia. 25.6, Width: 8.5

Rear: Ridler 18x8, 4.5 BS, 275/40 R18, Dia. 26.7, Width: 10.8


Here are my options:


Front: 17x7, 4 BS, 215/50 R17, Dia. 25.5, Width 8.5

or

17x7, 4 BS, 225/50 R17, Dia. 25.9, Width 8.9

or

same I am running now with a 1/4" spacer so it does not rub


Rears: same I am running now, no issues, plenty of room

or

18x9.5, 5 BS, 295/35 R18, Dia. 26.1, Width 11.6



Front, if I run 17's, I get an extra 1/2 inch the wheels move outward because of the back spacing, the 215 tires will not rub, the 225 tires would be really close. If I go with the 18x8 in the front and 215 tire, I would need a 1/4" spacer to move out the wheel enough it would not rub. I was told spacers are not a good option.


Rear, I can run what I have now, I like the look, but if I go to the 18x9.5, the wheel/tire will move in about an inch and will stick out past the wheel well edge by an inch, and the tire will be 1/2 inch smaller in diameter and almost an inch wider.


Please share your thoughts, comments or past experience.


Thanks

DM3
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  #2  
Old 06-07-2021, 07:36 AM
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amcmike amcmike is online now
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With that shallow of a backspace and narrow of a tire on the front, I'm surprised you're having rubbing on the subframe. My 245/45 on 17x8 with 5" backspacing barely touch at full lock. On our cars with disc brakes 4.75 to 4.8.125" backspace on a 8" wheel is usually ideal on the front and that's with a 245 tire. Are you sure it's rubbing on both sides? I wonder if you have a frame alignment issue.

For the rear, an 8" wheel is way to narrow to run a 275 (minimum is 9" wide). Reason I say this, is that super-narrow rim is probably changing the effective tire width a little bit (roughly .2mm per 1/2" as a general rule). So, your actually is probably like 10.2" wide on that narrow rim. In other words, when you get the correct width 9.5" on there the overall tire width will be like the 10.8" dimension. I'd probably see how the existing tire works on the 9.5" before trying to up-size. The other thing is a 295 would need about at least a 10" anyway. Again usually the ideal backspace is 5.5" with a 9.5" width rim on the rear. (P.S. I run a 17x9.5, 5.5 BS with 275/40s rear).

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  #3  
Old 06-07-2021, 11:31 AM
JLMounce JLMounce is offline
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The slight amount of rub you are seeing is a result of increasing your total wheel and tire package size. With an 18" wheel and 45 series tires, you're just about 27" with the current tire widths. The F-bodies were designed with 26" tall tire. in an 18" wheel package you really want a 35 series tire.

Are you leaving the stance of the car alone? If you have any plans to alter how it sits, do that BEFORE you go buying new wheels/tires. It will fundamentally alter where contact points will be in comparison to the wheel and tire combo.

The 67/68 cars become a bit easier with their round cut fender, but a soft spring can lead to hitting the top of the tire when extending the wheel package outward. Their total clearance inside the factory wheel houses tends to be about half an inch to an inch narrower than the 69 body work however.

235/45/17's on 17x8" wheels with a 0 offset all the way around seems to be a no fuss sweet spot that you don't have to worry much about. You may get a tiny amount of scrubbing in the front, especailly if it still has drums up there, but that only happens at full lock and is generally not a huge concern.

If you end up going taller, wider or both with the wheel and tire package, there's simply no way around the fact that you're going to have to measure and like amcmike hints at, you're going to end up with backspacing needs that are not commonly found in off the shelf wheels. The 17x8 and 17x9.5 wheels on my 69 end up at -7 and -8 offset respectively. the 275 section width tire on the 9.5" wheel in the rear is at the limit of what the stock wheel houses can realistically handle. There's "technically" enough room in my combo for a 17x10 and a 285 section width tire, but it already rubs the inner wheel house wall at high angle approaches to parking lots etc.

In general, I think if you get your overall tire diameter back to a nominal 26" you're going to be ahead whether you are going to a 17 or not. Choose the wheel size based on how much tire you like. If you like the more visable sidewall of the 40/45 series tire, choose the 17" wheel. If you like a smaller sidewall, stick with the 18" wheel.

For street tires in a non-competitive setting a basic plate type spacer to help position the wheel is not an issue, as long as it's not too big. I wouldn't go larger than 1/4". The only thing you may run into is that the shank on your studs may end up being a bit too short. Quick stud change to solve that. No real safety concern though. If you decided you wanted to put R compound tires all the way around and go compete in road course or auto-x, you would want to think about either upgraded studs, or a hubcentric spacer with integral studs.

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  #4  
Old 06-08-2021, 08:33 AM
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RocktimusPryme RocktimusPryme is offline
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It seems like not every car is the same. Mine only rubs on the passenger side, which is even stranger. I thought an alignment would fit it but it didnt. Its only at full turn, so Its not that big of a deal. I went to a 225 wide tire on a 17 and it still kisses the right frame member at full turn.

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  #5  
Old 06-08-2021, 03:12 PM
JLMounce JLMounce is offline
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It could still be alignment related. In a linkage system like that in a first gen, there's some variables at play that your basic alignment tech might not think to check which can cause one side to have more steer than the other.

The pitman arm can only be attached in 90 degree increments, so it's hard to mess up there, but take this scenario into account.

1. The steering box has aged and has some tolerance stack in it.
2. The steering linkage has aged and has some tolerance stack in it.

Think about what happens when you "center" the steering wheel to start the alignment. Many times this is either done with the car stationary, or at best over just a modest run up the alignment rack's runways. You can stack a lot of tolerance there and the wheel may appear to be on center. The alignment is performed and the toe is set at the tie rod sleeves. This car because of tolerance stack in one direction will likely drive straight, but may exhibit more turn to one side than the other because the system wasn't truly at zero.

Add in a worn out rag joint or an aftermarket steering wheel that is maybe a single spline off from center... I think you see where I'm going with this. Your basic alignment service tech at PepBoys isn't going to bother checking any of this. His job is to simply get the wheels in spec as the car sits on the rack.

This is now unrelated to the OP's original question, but it points to why keeping the steering system is good condition is so crucial to how these cars drive. It may speak to why there's a desire to move to a rack and pinion when data proves over and over that doing so in a stock sub-frame first gen actually makes handling worse.

What does happen though is steering gets a lot better. Not necessarily because rack and pinion is better, but because replacing what you had with a new rack, fixed all the old and worn out in the original system.

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  #6  
Old 06-09-2021, 11:05 PM
DM3 DM3 is offline
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Thanks for the info guys, I will let you know how it turns out when I pull the trigger.

DM3

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