tire size question

Chassis, Suspension and wheels

  1. rcmaniac791

    rcmaniac791 Well-Known Member

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    So my tires are starting to show their age, and it's time to replace them. I'm currently running the stock size of 205/75/r15 on the stock 1984 M-body wheel of (I think) 15x7. IMO, there is not enough tire under the car, and I think it almost has the "pizza-cutter" look, especially in the back. Again, just my opinion. I'm going with the traditional BFG radial T/A with the white letters. I've been doing some research on different tire sizes and seeing what will work. This is what I found:

    For the front, I'm thinking 215/70/r15, and that should be just a little wider while allowing enough room for full lock-to-lock steering.

    The rear is where I have more questions. I'm leaning towards a 255/60/r15, and I took some measurements today and I'm pretty sure they will fit, but I don't want too much tire bulge on the sidewall. Does this seem like too much tire for the rear? I do like the fact that there will be more tire on the ground. Any input is welcome.
     
  2. Jonnyuma

    Jonnyuma Well-Known Member

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    235/60s and 255/60s on 15x7s.
    I haven't gotten down to measuring yet, but I was thinking of going to a 15x8 on the rear when I replace these chrome things. Backspacing will likely have to be custom. 2018-04-12 08.49.04.jpg If I have 4" of bs now (an educated guess), and add an inch of wheel width and split the difference with 4.5" of bs I think they'll tuck up nicely.... YMMV, but I think the dimensions are the same between the two body styles. 2018-04-30 00.21.26.jpg
     
    Last edited: Apr 30, 2018
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  3. 4speedjim

    4speedjim Well-Known Member

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    I just put Cooper 275/60-15 on the back of the J. Pretty sure a 295 will fit with stock 15x7 rims and no effort. Id guess 9 1/2" tread width. No noticeable trade off in power, rpm, top speed coming off @27.25 tall 215/70s. These are @ 29 - 29.25 in. They fit beautiful. I prefer the Remington's but the Coopers are made in USA, had no miles and where a very good deal. Not to imply the Remintons are foreign, I believe Coker makes them in Tn or Ky.
     
  4. Jonnyuma

    Jonnyuma Well-Known Member

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    Pics or it didn’t happen
     
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  5. Dr Lebaron

    Dr Lebaron Well-Known Member

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    I have 275/60/15 rears and 215's front.

    I had 245/60/15 on the back of a F/A and thought they were small.

    815leb2.jpg
     
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  6. Jonnyuma

    Jonnyuma Well-Known Member

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    What size and backspacing are your wheels? They look very tucked-in, not oversized at all. I'm guessing 15x7... ?
    I think I might rotate the 255s to the front (on 15x7s) and put 275s on the rear (15x8s w 4.5" of bs). That's the same size tires I had on my '69 300 hardtop... that thing was 20 feet long! A real land-yacht.

    I had 16x8s w 265/60 16 BFGs (no longer available... I got the last two in the country, but that's a different story) w custom 4 5/8" bs on the back of my Cordoba and still had to roll the fender lips... that's why so many questions.

    Eventually I'll have to get on the ground w a plumb-bob, straightedge, and a tape measure unless... you've already done that tedious job and are willing to share what you learned :rolleyes:
     
    Last edited: Apr 30, 2018
  7. 89.Fifth

    89.Fifth Well-Known Member

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    I tried 225 on the front in my 84 Fifth Avenue and they rubbed in tight corners. I have 215 now on my 89 and they do not rub.
     
  8. rcmaniac791

    rcmaniac791 Well-Known Member

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    Ok great. Thanks for the input everyone. I'm going to go with the 215/70/15 on the front and the 255/60/15 on the rear. Since the 255/60 is just about the same diameter as the stock 205/75 I know that it won't throw off my speedo.

    The other benefit is that since there is still some serviceable life in the current tires, I can put them on another project car that I'll be getting. So I get to kill 2 birds with one stone. Now all I have to do is make this all happen once the spring semester is over. only 2 more weeks...
     
  9. rcmaniac791

    rcmaniac791 Well-Known Member

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    Forgot to say that I'll post pictures once I get them installed. :cool:
     
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  10. Duke5A

    Duke5A Well-Known Member

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    Give some thought to going wider in the front. Staggering tires like that introduces understeer and it's more pronounced the greater difference in width between the front and the rear. 235-60-15 fits real nice upfront.
     
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  11. Duke5A

    Duke5A Well-Known Member

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    285's. :)

    IMG_0399.JPG
     
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  12. Jonnyuma

    Jonnyuma Well-Known Member

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    Are you still w a 15" rim, or did you go up?
    The tire looks like maybe a Nitto 555-series... ? I can't read the sidewall on my tiny phone screen.
     
  13. Duke5A

    Duke5A Well-Known Member

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    Nitto 555 285-18-40 on 9.5" wide rims. It just misses the lip of the wheel well and rubs a little on the inner fender when the back end squats. Probably the absolute max you can run without going to a smaller diameter tire and even then it won't get you much. Plenty of room between the rim and the spring though if you wanted to mini tub an F/J/M. Could probably get 325's under there.
     
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  14. 4speedjim

    4speedjim Well-Known Member

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    Back when rocks were soft and the wheel was first invented. It was an exciting time. I ran our used car dept. I put new rubber on everything I planned to retail. Matched sets of 4- 235/60-15s on all our 15" M&J trade in cars. Course there was no 16" 18" 24"+ anythings to choose from. 13"-15"s for cars and 16-16.5s for 3/4 & 1 tons. That was it for choices. The 235/60s or 70s on our cars helped them look eager, sturdy, ready. Black walls, blacked out wheels and poverty caps made for an intimidating menacing look. 5th Aves got white walls depending on appearance. With matched rubber and torsion bar suspensions, the cars carved exit ramps on high speed rails. Id double + 10 the posted exit speed and never chirp a tire. A little more speed and they'd scream for mercy. But you never lost your line, or confidence. Once body roll plants itself, locked in, you could pull near a G on whatever tires where on sale that month. You didn't make power, so you carved corners for entertainment I suppose. But, Nobody care about cornering or handling anymore. Have we DRIFTED away from handling...?
     
    Last edited: May 1, 2018
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  15. Jonnyuma

    Jonnyuma Well-Known Member

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    Wow... that's a lotta tire. If I could find aftermarket cop wheels (or similar) in +1 or 2 I'd gladly give em a go... I've got nuthin against larger diameter/lower profile rims and tires.

    Do you remember what your backspacing on the 9.5" wide rims is?
     
  16. Oldiron440

    Oldiron440 Well-Known Member

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    Drifted into dreamland, near 1G hahaha.
     
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  17. Dr Lebaron

    Dr Lebaron Well-Known Member

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    Rims are stock 15x7 4.5 backspace.

    Hears mine with a 80 Dip with the same size rears, but the Dip has 4 inch backspace
    Sept308.jpg
     
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  18. rcmaniac791

    rcmaniac791 Well-Known Member

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    So those of you who have run a 235/60 on the front with a stock steel rim haven't had any fitment issues?

    And will I notice a huge handling difference with running a 235 compared to the 215? Most of the driving I do is around town and highway. Not much carving corners for me.
     
    Last edited: May 1, 2018
  19. 89.Fifth

    89.Fifth Well-Known Member

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    Definite improvement from 205 to 215 but huge improvement from 205 to 225.
     
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  20. AJ/FormS

    AJ/FormS Well-Known Member

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    I love that car