72 Skylark 15x8 w/ 5.5 BS on rear

Discussion in 'The Hides' started by FoDoFoSho, Feb 21, 2022.

  1. FoDoFoSho

    FoDoFoSho Member

    I did a search, but didn't have much luck. Decided I'd just post and ask:

    I found a deal on a pair of 15x8 steel wheels and decided to pick them up before making sure they'd fit my needs. I like the look of a 275/60 in the rear, but didn't know if I'd need to run a smaller 255/60 to clear.

    Anyone have any experience with this much BS on a 15x8? Not sure if it matters or not but I plan to go with 4-wheel disc brake conversion in the near future also. I hear that can push the wheel outside some?

    Any help would be appreciated...and if I just need to sell these and pick up the more common BS wheel I guess I'll end up going that route.

    Thanks,
    C.J.
     

    Attached Files:

  2. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    For a 70-72 Skylark/GS, the best BS for an 8" wide wheel is 4.5-5". 5 .5" should be OK, that is the back spacing for a 10" wheel though.
     
  3. FoDoFoSho

    FoDoFoSho Member

    So I should be able to get away with a 275/60 with the 5.5 backspacing? Or I should just plan on mounting a 255?
     
  4. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    I don't like to guarantee anything. Like I said, 5.5" is the back spacing for a 10" wide wheel on a 70-72. The wheel should fit fine. Should be able to run a 275 tire, but you will have more room on the outside, and less on the inside.
     
  5. FoDoFoSho

    FoDoFoSho Member

    Gotcha. Thanks for the help Larry.
     
  6. Canadian GS 350

    Canadian GS 350 Well-Known Member

    84D31192-DBDC-4F78-A8AA-B69EA81308D0.jpeg 39A1FCC2-A201-40CD-93BE-2D1464F83085.jpeg 44B16E6F-AE78-4B0A-AC23-CA08682BF5D7.jpeg 34FB9AB0-9CF4-46BC-8B51-83994B6DE9E0.jpeg DF743695-DF1B-4BD1-BEF1-098E9C1BBDB5.jpeg A7E7FDB3-52D8-4CB9-A44E-8A11850D7E00.jpeg F7EC448E-94C0-4751-9AD7-6F715BC1D39E.jpeg 09CA6F77-B47F-4C1F-B04F-4B623217206A.jpeg Im running 15x8 rims with 5.5 inches of back space with a 275/50 Mickey Thompson drag radial. If rear end is well centered under body, no issue.
     
    avmechanic likes this.
  7. hugger

    hugger Well-Known Member

    I like using the 5.5bs over the 5i. Because it's easy to move the wheel out with a spacers to get perfect clearance,...can't move a wheel in without getting into a pile of work,...and keeps you from cutting up 1/4 panels
     
  8. rkammer

    rkammer Gold Level Contributor

    I have the Caruso 15 x 8 Ralleys with 4.5 in back spacing. They run The BFG Radial TA 295/50 x 15 Radial TAs just fine on the rear of my '70 so I decided to go with the MT ET street Radial SS drag radials in the 275/50 x 15 size. I like them because they are the same exact diameter as the Radial TAs and the same diameter as the front 245/60 TAs and they have an inch more tread as the 275/60s do. So, my speedometer and 3.42 gear ratio don't change and my GS maintains a lever stance. Now, lets see if they hook as good on the street and the track as the 275/60s do. Some of my Grand National friends with 10 and 11 second cars say they do. We'll see.
    IMG_8059.JPG
     
  9. sean Buick 76

    sean Buick 76 Buick Nut

    How are the 50 series tires wider than the 60 series? I’ve never heard of this.
     
  10. rkammer

    rkammer Gold Level Contributor

    That's almost always the case with a tire that is the same cross section measurement but has a lower profile. So, here are the measurements of the 275/60 vs the 275/50:

    275/60 - 28.2 tall, section width 11.1 inches, tread width 9.3 inches

    275/50 - 26.4 tall, section width 11.1 inches, tread width 10.2 inches

    Some folks maintain that the taller tire hooks better because the taller sidewall flexes better. I like the tire that's about the same diameter as the front tires and has more tread width. Also doesn't mess with my speedometer accuracy or my gear ratio. The turbo Regal and Grand National guys often use 50 & 40 series tires with success at the track too. They just have to be more precise with tire pressures.
     
    Last edited: Mar 29, 2022
    Mark Demko likes this.
  11. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    The 275/50R-15 is about 26" tall. That's about 1/2" shorter, so you will get a bit more gear out of it.

    The tread is a bit wider on the 50 series tire. It will have a wider, but shorter contact patch than the 60 series tire.
     
  12. rkammer

    rkammer Gold Level Contributor

    Larry, while several of the sites show the 275/50 x 15 MT Street SS to be only 26 or 26.1 inches tall, that's not the case. I went to the Summit and the Mickey Thompson site and they showed that size to be 26.4 tall which is about the same as the BFG Radial TA 245/60 x 15 (within 0.2 in.). I wanted to be sure so, I called Mickey Thompson and they confirmed that the 275/50 is 26.4 tall. When I got them home yesterday I stood them next to my front 245/60 front tires and they are just a tad taller without the weight of the car on them. Take a look.
    275_50 x 15 MTs (1).JPG 275_50 x 15 MTs (2).JPG 275_50 x 15 MTs (3).JPG
     
  13. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    Yes, I saw that. Must be more rubber on them because if you put a P275/50R-15 into a tire calculator, it comes up as 25.83" tall
     
  14. rkammer

    rkammer Gold Level Contributor

    Yes, that concerned me too. Glad the MT 275/50 is so close to that 26.5 ideal size for our cars. Here's another pic I just took with the MTs next to a spare BFG 295/50 x 15 I have which is what I run on the back of my GS. The spec on those is 26.6 in. tall. Look at that 295/50 next to the MT 275/50. Almost the same and the MT is actually a smidgen taller if you look at the bubble on the level. Just for reference, the MT has 6/32 tread depth and the Radial TA has 9/32 tread left out of 11/32 new. So, both tires new would be almost identical. Strange but true. Looks like Mickey T violated the P metric tire size rules, perhaps to our car's benefit.

    IMG_8068.JPG IMG_8069.JPG
     
    Mark Demko likes this.
  15. Buickless

    Buickless Well-Known Member

    Hi guys. Just doing some research and found this post. My question is what rear and front coil springs do you use in your cars. I will be adding a larger wheel and tire. And with my stock springs that can not happen. The car is a 70 Skylark currently 350 2 bbl. Thanks
     
  16. Canadian GS 350

    Canadian GS 350 Well-Known Member

    My 72 has stock springs as far as I know…….but she’s 50 years old, so who knows. I prefer stock ride heights, the 15x8 with 5.5 BS and 275 drag radial, no issues.
     

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