Wheel backspacing

Discussion in 'Suspension, Steering, Brake & Wheel Topics' started by Elliott Taylor, Nov 24, 2020.

  1. Z-Life

    Z-Life Nasty Member

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    Would someone with some experience and knowledge comment on fitment of these wheels for second gen, and what would/could be the largest tires on the back and front, I'd like the tallest & widest possible.

    https://www.ebay.com/itm/Staggered-Ridler-695-Front-18x8-Rear-18x9-5-5x4-75-0mm-Grey-Wheels-Rims/303434868460?fits=Year:1979|Model:Camaro|Submodel:Z28|Engine+-+Liter_Display:5.7L|Make:Chevrolet|Trim:Z28+Coupe+2-Door|Engine:5.7L+350Cu.+In.+V8+GAS+OHV+Naturally+Aspirated&epid=888702842&hash=item46a620a6ec:g:Yn0AAOSwKP5eE2Kn

    BRAND: Ridler
    STYLE: 695
    SIZE: Front:18x8,Rear:18x9.5
    BOLT PATTERN: 5x4.75"
    OFFSET: Front:+0mm,Rear:+6mm
    HUB BORE: 83.82
    BACKSPACING: Front:4.5",Rear:5.5"
    FINISH: Grey
    CONDITION: Brand New
    QUANTITY: 4 Wheels
    PART NUMBER: 695-8861G-695-8961G
     
  2. 8pack

    8pack Veteran Member Lifetime Gold Member

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    I would not go with less than 4.5" BS (factory) unless you like that look with the tires pushed out of the fenders.

    With 17 or 18" wheels If you go with wider than stock wheels (7") you also will potentially run into the tires rubbing the inner fender up front and the rear fender lip.

    If you are going with bigger wheels and tires all my research indicates 5" BS up front with an 8" wheel is safe and up to 5.5" depending on your suspension set up. Some people successfully run a 9" wheel up front with those BS options. 245/40/17 is the "safe" tire size choice.

    On the rear 5.5"-5.75" BS depending on your e-brake set up with 275/40/18. 18x9.5" wheel.

    Now, no matter what anyone tells you there is no perfect answer. It all depends on what your suspension set up is, ride height etc. For most of our cars the rear end is usually offset to one side or the other which affects rear wheel clearance. Not everybody's 1"drop or 2" inch drop is the "same". For example, lots of people say the 2" drop hotchkiss or custom works springs fit perfectly. On my car I needed at least a 1/2" spacer to get the right height and tire clearance. On my rear I don't think I can go anymore than 5.75" and I think only 5.5" with an 18x9.5" wheel because I am running Transam rear discs and the wheel will hit the e-brake cable/bracket. People will tell you they are running 315s with a 10" wheel and 6" BS no problem. I believe what they say, but something must be wildly different from my set up for that to work.

    You need to take actual measurements. You can go with the "safe" recommendations here and probably not have an issue, but anything more extreme without detailed measurements and you are rolling the dice on some very pricy purchases.

    Good luck!
     
    $ Mike 70 Z-28 likes this.
  3. EasyZ

    EasyZ Member Gold Member

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    Do you have any pictures you can send of your Z with the 18’s
     
  4. dave@ztech

    [email protected] Veteran Member Lifetime Gold Member

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    Pictures coming soon, need to get a couple of other items taken care of first
     
  5. Ben Barron

    Ben Barron New Member

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    All good advice. Especially 8packs. I'll just add on my car, stock up front except Hotchkis springs. With a 17x8 4.5 BS, a 245/45/17 will not work. I have to run a 245/40/17. Like 8pack says, every setup/car is a little different.
     
  6. JUNKYARD AUTOCROSSER

    JUNKYARD AUTOCROSSER Member

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    As a autocrosser for 40 years + I was always trying to get the most tire under my stock fenders. I've learned a lot thru trial and error , and suffered thru bent fenders , damaged wheels, and damaged control arms. This is what I am running today. I run 275x35x18 on 18x10 wheels up front with 6" backspacing. I rolled the front fenders and minimally trimmed the inner fenders. I run a stock subframe with 1979 spindles and rotors. I am also using global west upper and lower control arms which provide extra clearance for backspacing as well. All bets are off if you are using aftermarket spindles, and rotors because the offsets may be different from stock. In the rear, I run 315x30x18 on 18x11 wheels with 6" back space. I run finned aluminum drum brakes/ leaf springs with stock offsets. There is light rubbing/polishing on the inner body during autocrossing due to the lateral distortion on the tire when max cornering. I took a small hand sledge and beat on the inner body a bit. Nothing drastic, about 10 minutes a side, but it did reduce the rubbing. There is no rubbing during normal driving. I also trimmed the inside of the rear fenders. No issues with shock clearance. Again , all bets are off if you are running aftermarket rear disk brakes as the offset may be different from stock. I have accumulated a wealth of data over the years experimenting with different wheels and tires. My car is lowered about 2" front and rear. I also bevieve that my tires are maxed out to fit under stock fenders. Questions are welcome.
     
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  7. mid77z28

    mid77z28 Veteran Member

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  8. mid77z28

    mid77z28 Veteran Member

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    Gerald,
    Over the years autocrossing your car,How many different wheel & tire combos did you have on your car?And do you recall what size epsilon wheels did the guldstrand camaro have back in the 80s?Love the look and stance of that car.
     
  9. JUNKYARD AUTOCROSSER

    JUNKYARD AUTOCROSSER Member

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    Almost too many different combos too remember. SCCA rules required max 8-1/2 wide wheels. So I also ran Epsilon wheels 15x8.5 . The offeset for the front was 5-1/2 and the rear was 5 ( not sure, my memory is fading) . Maybe it was 5 in the front and 4-1/2 in the rear. the tire size was F60 front and G 60 rear. I believe the Guldstrand camaro was the same. After SCCA relaxed their wheel rules, I stepped up to Ronal racing wheels 16x10 front with 5-1/2 backspace with 255x50x16 . The rear was 16x10.5 with 5.5 backspace with 255x50x16 hoosier tires. The ronal wheels are super lite and I am looking to sell them. I also tried 15x11 with 5.5 backspace in the rear with 275x60x15 hoosiers. I ran this combo in the car craft article and also at the Nationals in Salina, Kansas, 1989. I stepped up to 17x11 wheels in front with 6" backspacing with 275x40x17 , and rear was 17x12 wheels in rear with 6" backspace and 315x35x17 tires. This combo damaged my fenders and stock control arms. For the super chevy challenge, I ran 9.5x17 wheel in front with 5.5 backspace and 275x40x17 tire. In the rear, I ran 17x11 with 6" backspace and 315x35x17 tire. Car came in 2nd place with Mary Pozzi driving. There are probably more combos, but This is all I can remember.
     
  10. JUNKYARD AUTOCROSSER

    JUNKYARD AUTOCROSSER Member

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    Please see my discussion below. take care and stay safe
     

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