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  1. #1

    Default Wheel clearance required

    Hi all,

    So I picked up a set of 17x9 245/45R17 Cobra R replicas this week and had a chance to mount them tonight. After measuring the clearance between the wheel and the front struts I only have 3.45 mm clearance.

    My question is what is a acceptable clearance I should be aiming for? I know a lot of people use the 8 mm spacers with similar setups. But I also would rather not have to replace my wheel studs. Right now I have 10.5 threads engaged without a spacer.

    Has anyone had a similar setup or experience that you could pass on? I recently changed my front spring isolators to prothane ones so my front end is sitting a little higher than I would like so that will be addressed

    Thanks in advance. Name:  20200111_200703.jpg
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  2. #2
    Moderator wraithracing's Avatar
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    The general rule of thumb on thread engagement that I am aware of it depth of engagement should equal the diameter of the stud. So you are just past the 1/2" of engagement if 10.5 threads.

    The 3.45mm of clearance is definitely tight and you will most likely see some rubbing of the tire on the strut during driving. Technically you could probably run an 1/8" hubcentric spacer and be fine, but ultimately that is your decision. Good Luck!
    ​Trey

    "I Don't build it hoping for your approval! I built it because it meets mine!"

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  3. #3

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    Thanks Trey,

    I have been considering going with a 1/4" to be safe but that would mean replacing my wheel studs. The only hubcentric that I can find are with Maximum Motorsports or CJ pony. They are a little more expensive than the universal ones that LMR sells but I like the fact that they won't move around.

    The studs I'm thinking I'll go with are the moroso 3".

  4. #4
    FEP Senior Member Patrick Olsen's Avatar
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    I don't see any problem with ~3.5mm of clearance to the strut. I'd run it as-is.
    '89 GT convertible - not a four-eye
    '82 Zephyr Z7 - future track car

  5. #5

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    Quote Originally Posted by Patrick Olsen View Post
    I don't see any problem with ~3.5mm of clearance to the strut. I'd run it as-is.
    Interesting.. you don't think ill have rubbing issues when turning or when the suspension moves up and down? I need to lower the front of my car a little bit since replacing the spring isolators it sits about a inch or so higher than the rear

  6. #6
    Moderator wraithracing's Avatar
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    You can always mark the inside of the tire with tire chalk or grease pencil. Take the car for a spin around the block and then pull the wheels back off to see if you had any rubbing. Obviously major rubbing you will most likely hear or notice thru the steering wheel, but the above method can help determine how much or how bad the rubbing is if not really noticeable otherwise. Good Luck!
    ​Trey

    "I Don't build it hoping for your approval! I built it because it meets mine!"

    "I've spent most of my money on Mustangs, racing, and women... the rest I just wasted."

    Mustangs Past: Too many to remember!
    Current Mustangs:
    1969 Mach 1
    1979 Pace Car now 5.0/5 speed
    1982 GT Stalled RestoModification
    1984 SVO Still Waiting Restoration
    1986 GT Under going Wide Body Conversion Currently

    Current Capris:
    1981 Capri Roller
    1981 Capri Black Magic Roller Basket Case
    1982 Capri RS 5.0/4spd T-top Full Restoration Stalled in TX
    1984 Capri RS T-top Roller
    1983-84 Gloy Racing Trans Am/IMSA Body Parts

  7. #7

    Default

    Thanks Trey,

    Thats a good idea ill give that a shot once things warm up a bit. Then if I have to install spacers ill probably only need small ones

    The rear seems to have good clearance but the only thing i dont like is how far in the tires sit but thats just cosmetics.

  8. #8
    FEP Senior Member Patrick Olsen's Avatar
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    Quote Originally Posted by Foureyedjoe View Post
    Interesting.. you don't think ill have rubbing issues when turning or when the suspension moves up and down?
    The wheel is bolted to the hub/rotor, which is mounted to the spindle, which is bolted to the strut. All of that stuff moves together, whether it be up/down when you hit a bump, or pivoting when you turn the steering wheel, so none of that movement changes the clearance between the tire and the body of the strut.

    The clearance will only change due to the sidewall of the tire flexing / deforming under load. But that's basically all happening at the contact patch, which is 180deg away from where you're concerned about strut/tire clearance. Here's one of my other cars seeing heavy cornering load at a track event. You can see how much the front and rear tires are being deformed at the ground, but if you look up at the top of the tires, the sidewall looks pretty much vertical, so clearance to the strut would not be changed much, if at all.


    So, I can't guarantee you'll have zero rub, but I'm pretty sure you'll have zero rub, or maybe very minor rub.

  9. #9

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    Quote Originally Posted by Patrick Olsen View Post
    The wheel is bolted to the hub/rotor, which is mounted to the spindle, which is bolted to the strut. All of that stuff moves together, whether it be up/down when you hit a bump, or pivoting when you turn the steering wheel, so none of that movement changes the clearance between the tire and the body of the strut.

    The clearance will only change due to the sidewall of the tire flexing / deforming under load. But that's basically all happening at the contact patch, which is 180deg away from where you're concerned about strut/tire clearance. Here's one of my other cars seeing heavy cornering load at a track event. You can see how much the front and rear tires are being deformed at the ground, but if you look up at the top of the tires, the sidewall looks pretty much vertical, so clearance to the strut would not be changed much, if at all.


    So, I can't guarantee you'll have zero rub, but I'm pretty sure you'll have zero rub, or maybe very minor rub.
    Perfect. Thanks for the info and feedback. I will run it as is and keep a eye on things but worst case I might need a 1/8th spacer. I still have to verify if there is any contact at full lock with the control arms but if there is Ill just install a rack limiting bushing. The tires came off of a 87GT and he didnt use any spacers. I know they use different spindles but I dont have any issues with the center caps being pushed out so fingers crossed ill be ok.

    Thanks again guys. This site is a awesome source

  10. #10

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    We do not manufacture 0.25" wheels spacers which are hubcentric. It is impossible to do with such a thin spacer.

    10.5 threads of engagement is fine. 6 threads ins the minimum that we recommend. If you installed 0.25" spacers, you would be at 5.5 threads engaged.

    The rule of having one diameter of threads engaged is a very conservative one. With 6 threads engaged on a 1/2" fastener with 20 tpi, the thread pullout strength is 95% of what it is with an infinite number of threads engaged. The first couple of threads take the vast majority of the load. The next couple of threads take a decent percentage of the load, the next threads only take a tiny amount of the stress, etc. It is very nonlinear, because the fastener stretches elastically like a spring.
    Jack Hidley
    Maximum Motorsports Tech Support

  11. #11
    FEP Super Member erratic50's Avatar
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    You could always loosen your strut bolts and allow some of the negative camber back out of the relationship between the strut and the spindle

    you would then need to adjust more negative camber into the strut mount at the top but the end result would be several MM of additional room at the strut for the rim and tire

    the other thing worth noting is that the 93 Cobra rotors on 87-93 V8 spindles are 4 lug but increase track width by 3/4 of an inch per side by spacing the wheel out away from the strut right at the hub/hat

    Also a 94-95 spindles would increase track width 1/8” but are 5 lug

    So there are many ways to solve this

    I had 17” tribar rims with 245/45/17 tire on 83 2.0 2WD ranger rotors and stock spindles for a while. The wheel and tire cleared the strut but the tire weights rubbed. Once the weights were moved this tight of clearance never made contact even while driving pretty aggressively

    So for what it’s worth, you probably won’t need spacers. You might but if you do it could suggest a lot of flex that should not be there at the spindle within the bearings

  12. #12

    Default

    Ya that makes sense. I put new brakes and bearings a couple months ago so I know they are good. I shouldn't have any play so I will try it without spacers and see how it is. Down the road I'll likely change to a 87-93 spindle but till then I will make what I have work

    Thanks

  13. #13

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    An issue I had when putting cobra fan blades in my 82 was the wheel barley clears the strut not the prob but when turning it would rub the Braided Brake line. And yess I lost brakes due to it burning thru that was not fun and prob lost some life in my tranny throwing it into first then park.. So make sure you have proper clearance from your brake hoses too due to the deeper offset.




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  14. #14
    FEP Super Member erratic50's Avatar
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    Yikes

    That is a very good point.

    Actual Cobra rims for the 93 are designed for a 3/4" taller rotor hat than the normal 87-93. That changes the wheel offset/backspacing conversation and whats necessary for those wheels to fit properly on a 79-93 standard Mustang with 4 lugs entirely.

    The choice there is spacers required or replicate what was used on the Cobra or don't run actual Cobra rims.

    Usually any 93 Cobra street car style rim on a regular foxbody is an imitation. You have to change brake rotors to on that is 93 Cobra street car version only which adds expense. The rear is a little easier to come by in 4 lug at the required width. Rear axles and brake brackets can come from a Thunderbird. Turbo Coupe has disc just like the Cobra. The others should have the length/style axles needed and brackets in order drum brakes still.

    Most of the imposters around are not actually directional like the real 93 Cobra street car 4 lug wheels were.

  15. #15

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    Quote Originally Posted by erratic50 View Post
    Yikes

    That is a very good point.

    Actual Cobra rims for the 93 are designed for a 3/4" taller rotor hat than the normal 87-93. That changes the wheel offset/backspacing conversation and whats necessary for those wheels to fit properly on a 79-93 standard Mustang with 4 lugs entirely.

    The choice there is spacers required or replicate what was used on the Cobra or don't run actual Cobra rims.

    Usually any 93 Cobra street car style rim on a regular foxbody is an imitation. You have to change brake rotors to on that is 93 Cobra street car version only which adds expense. The rear is a little easier to come by in 4 lug at the required width. Rear axles and brake brackets can come from a Thunderbird. Turbo Coupe has disc just like the Cobra. The others should have the length/style axles needed and brackets in order drum brakes still.

    Most of the imposters around are not actually directional like the real 93 Cobra street car 4 lug wheels were.
    Yeah it was night when I checked and only looked for basic rubbing spots.

    I personally will not be worried about the “tucked in” look due to swap soon. And I will clean up, powder coat and sell the fans cuz they are og.

    But longer studs and wheel adapters was going to be my route just to avoid those rotor prices.


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  16. #16

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    I'll definitely check brake line clearance and control arms. That would be Scary. To be clear my rims are 95 Cobra r replicas not 93 Cobra

  17. #17

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    Quote Originally Posted by Foureyedjoe View Post
    I'll definitely check brake line clearance and control arms. That would be Scary. To be clear my rims are 95 Cobra r replicas not 93 Cobra
    Ahh sorry I knew from the pics but it may just be your rims are wider then. I too have a pinky finger gap between the shock so I assumed they had the safe offset as the fans.




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  18. #18

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    No prob here are the specs of my rims for anyone interested in comparing
    Diameter 17"
    Width 9"
    Lugs 4
    Offset +20 mm.
    Backspacing 5.71 in.
    Bolt Circle 4.25 in

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