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Thread: Wheel Center Bore

  1. #1
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    Wheel Center Bore

    I ordered some wheels and they called to ask what the center bore is. I can't really seem to find it anywhere but in another thread someone thought it was 70.5. I wanted to ask in a thread about this specifically to make sure I don't have wheels made for the car that don't fit. Can anyone confirm for me what center bore I will need? Thanks.

  2. #2
    Cobra Doc
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    Subscribing as I would like to know the same as well. Also, what the bolt pattern is.

  3. #3
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    Bolt pattern is 5x114.3 aka 5x4.5

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    Senior Member edwardb's Avatar
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    Factory Five rear wheels measure 2.78 inches center bore. That's with a decent Mitutoyo digital caliper, so should be reasonably accurate. That converts to 70.612 millimeters. So the 70.5 number appears to be correct.
    Last edited by edwardb; 07-18-2019 at 04:36 PM.
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    FFR Maven Logan's Avatar
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    Note that the 70.5 mm figure is for an S550 Mustang (2015+) specification. This center bore will be what you need for the REAR of any FFR model using the S550 IRS. I intent to take a measurement of the FFR provided FRONT hubs when I get home in a couple hours, to close the loop on this. They’re certainly not larger, so 70.5 mm on all 4 wheels will still physically fit and work. In fact, I expect them to be the same so that they can sell wheels that fit front or rear interchangeably.

    There has been some internet chatter about whether the S550 is 70.3 or 70.5, but it is the latter. If you have a wheel with a 70.3 mm center bore, it will “fit” itself with brute force when you torque the lug nuts (150 lb-ft spec on the S550). But the proper bore size should be 70.5 mm.
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  8. #6
    Senior Member edwardb's Avatar
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    Just took off a front wheel and measured it. Exactly the same as the rear wheel I measured in post #4.
    Build 1: Mk3 Roadster #5125. Sold 11/08/2014. Build 2: Mk4 Roadster #7750. Sold 04/10/2017. Build Thread
    Build 3: Mk4 Roadster 20th Anniversary #8674. Sold 09/07/2020. Build Thread and Video. Build 4: Gen 3 Type 65 Coupe #59. Gen 3 Coyote. Legal 03/04/2020. Build Thread and Video
    Build 5: 35 Hot Rod Truck #138. LS3 and 4L65E auto. Rcvd 01/05/2021. Legal 04/20/2023. Build Thread. Sold 11/9/2023.

  9. #7
    FFR Maven Logan's Avatar
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    Question = answered!

    Thanks Paul! Hopefully the OP can rest easy with this confirmation, and move forward with his wheel purchase. You’re measuring the center bore of the wheel, which is fine, but run the caliper onto the OD of the hub too just for curiosities sake. Your measurement of 70.612 confirms that it fits over the hub, but not how much clearance exists between them at the interface. For example, some guys use wheels with center bores of 72mm+ and take up the excess gap with small rings. Not ideal, but those things do exist for a niche purpose.
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  10. #8
    Senior Member edwardb's Avatar
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    Quote Originally Posted by Logan View Post
    Question = answered!

    Thanks Paul! Hopefully the OP can rest easy with this confirmation, and move forward with his wheel purchase. You’re measuring the center bore of the wheel, which is fine, but run the caliper onto the OD of the hub too just for curiosities sake. Your measurement of 70.612 confirms that it fits over the hub, but not how much clearance exists between them at the interface. For example, some guys use wheels with center bores of 72mm+ and take up the excess gap with small rings. Not ideal, but those things do exist for a niche purpose.
    I put both back on and would prefer not to take apart again. Just looked up the Eibach 90.4.25.010.3 wheel spacers I used in the back. They are listed as 70.5 mm. Based on what I measured in the wheels, that would be a difference of .1 mm, or about .004 inches. I would guess they're not quite that tight. But pretty snug on both front and back. They need to lined up to slide into place. Certainly no alignment rings or whatever required.
    Build 1: Mk3 Roadster #5125. Sold 11/08/2014. Build 2: Mk4 Roadster #7750. Sold 04/10/2017. Build Thread
    Build 3: Mk4 Roadster 20th Anniversary #8674. Sold 09/07/2020. Build Thread and Video. Build 4: Gen 3 Type 65 Coupe #59. Gen 3 Coyote. Legal 03/04/2020. Build Thread and Video
    Build 5: 35 Hot Rod Truck #138. LS3 and 4L65E auto. Rcvd 01/05/2021. Legal 04/20/2023. Build Thread. Sold 11/9/2023.

  11. #9
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    Thank you both. When I spoke with them we put in the order for 70.6mm. I am guessing I am okay to leave that order as is and don't need to change it to 70.5. I'm no expert on this but I am guessing too big is okay and only too small is where problems arise.

  12. #10
    FFR Maven Logan's Avatar
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    To put this into perspective, a standard sheet of A4 printer paper is 0.05mm thick. So the difference between your spec of 70.6 and the machined diameter of the hub is barely the thickness of 2 sheets of paper total, or simply 1 sheet of paper all the way around (radius vs diameter). At this level you’ll be just fine. You couldn’t physically fit a hub-centering ring in there even if you wanted to, and this doesn’t need to be a press fit. If you had 1+ mm of difference on the radius it could be an issue, but I’d say you’re right on with your 70.6 mm. In fact, it will allow a nice fitup without having to wrestle the thing on and off, even if some gunk buildup was present.

    Congrats on ordering wheels! Now get the tire decision made so you can mount them up when they arrive!
    Logan's Gen 3 Coupe-R Build
    Ordered 4/23/19 | Delivered 6/29/19 | First Start 8/1/20 | First Drive 9/20/20

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