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Tire Size Conversion

Discussion in 'Commercial Snow Removal' started by Sndun, Dec 1, 2001.

  1. Sndun

    Sndun Member
    Messages: 56

    I have a '98 Jeep Wrangler, 4.0, auto, with 30x9.5R15 tires on it now. I'm looking to purchase new winter tires but can't seem to get a straight answer on the sizing. I want to retain the 30" height and 15" rim size while trimming a little on the width. First, how much width reduction is recommended? Also, is there a way to cross reference sizes to "pick" the suitable one while also keeping load capacity in mind (it's also my daily driver to school)? I'm a little hesitant to state I recently purchased a new plow by the "s" name but compared to my last plow and vehicle, the Sno-Way is a heck of an upgrade for me so I'm actually proud of it. Thanks in advance.
     
  2. Kent Lawns

    Kent Lawns PlowSite.com Veteran
    Messages: 315

    30" diameter?

    245/75-15 gets you close or
    215/85-15 is the same height but narrower.

    The hard part is these sizes are rare.
     
  3. Sndun

    Sndun Member
    Messages: 56

    Availability is what I was afraid of. The company I plan on purchasing them from does not have those sizes in winter tires. They recommended 205/75R15 and 225/70R15. From what I saw the tire heights are 27" and 27.5" respectively with the latter being a P-Metric tire. :confused:
     
  4. DaveK

    DaveK Senior Member
    Messages: 420

    If your dealer has 225/75 it would seem that he would have 235/75 And it would closer to 30" and be narrower than the 225/70. If your dealer doesn't have it, try another dealer. That is a very common size.
     
  5. Kent Lawns

    Kent Lawns PlowSite.com Veteran
    Messages: 315

    A 235 is narrower than a 225?

    o...kay.

    Actually it's 10mm wider or about 1/2". 235/75-15 is however a very common size and about 28.5" diameter or so.
     
  6. DaveK

    DaveK Senior Member
    Messages: 420

    Well it has been awhile since I actually measured a tire.:) Speaking in relative terms yes. A 235 is taller than a 225 and a 75 is narrower than a 70. So a 235/75 is taller, and narrower (in relation to height) than a 225/70

    The actual width of the tread can also vary depending on the type of tread. Even on same size tires, a mud/snow will typically have a wider tread than an all season tire.

    I hope you didn't have to make a special trip to the tire store to measure them.:) And hope you measured two tires of the same brand and model.

    BTW, 10mm is about 3/8 inch rather than 1/2 inch. Unless of course you were rounding up to the nearest 1/2 inch. A 1/2 inch is about 13mm (12.7)
     
    Last edited: Dec 2, 2001
  7. MTCK

    MTCK Senior Member
    Messages: 346

    The "P" designation is for passenger car. I'm pretty sure you get more load capacity with a light truck, or LT tire. Load rating "C" and up shouldn't be hard to find, but those sizes mentioned above might be. Call around to a few places in your area until you get satisfaction.

    Marcus
     
  8. Kent Lawns

    Kent Lawns PlowSite.com Veteran
    Messages: 315

    No, I didn't measure them..lol

    225 is 225mm wide
    235 is 235mm wide

    ~Not too tough to figure out.

    70 or 75 is the percentage of height to width measured form the rim to the tread.
     
  9. MTCK

    MTCK Senior Member
    Messages: 346

    Yeah, Kent's right...... 235 is wider than a 225. 70 or 75 or whatever is your aspect ratio. Multiply your width say, 235 by your aspect ratio 75% and that will be the height of your sidewall. So, to get back to the point, get your aspect ratio higher for a taller tire.

    MT
     
  10. captjack

    captjack Member
    Messages: 53

    30-950r15 = 29.5 tall / section width=9.7
    LT235/75r15 = 29 tall / section width=9.3

    The width on the charts can be misleading.
    It is a measurement of the "section width" (bulge to bulge) on the sidewall.

    A p-metric light truck tire will usually have a narrower tread and it will usually appear somewhat rounded.

    A "LT" marked truck tire will usually have a wider tread area and a more squared off tread shoulder. This will make the tire look wider even when it's not.

    I would recomend you go with the LT 235/75r 15.
    It's about the same tire as the 30-950r15 less $20.

    I f you had 2 jeeps in a parking lot and 1 had 30/950r15 and 1 had the LT 235/75R15'S you would not be able to tell the difference with out looking at the sidewall.
    Good luck with your purchase,
    JACK

    NOTE-Measurements are from Goodyear Wrangler AT/S tires and may vary with different brands.
     
    Last edited: Dec 2, 2001
  11. DaveK

    DaveK Senior Member
    Messages: 420

    <iframe src=http://www.readyforawebsite.com/plowsite/tirecalc.html width=100% height=470></iframe>
     
    Last edited: Dec 3, 2001
  12. Sndun

    Sndun Member
    Messages: 56

    First, thanks to everyone who helped out with this.
    Davek, that "calculator" was very helpful.
    I ended up going with the 235/75R15 size. Found them for $381.50 mounted and balanced on new 15x7 rims and shipped to my door. If it ever snows, I'll find out if they were a good choice or not. Thanks again. :)
     
  13. DaveK

    DaveK Senior Member
    Messages: 420

    You need to share where you got them from. That is a very good price considering new rims, mounting, balancing and shipping.
     
  14. Sndun

    Sndun Member
    Messages: 56

    I ordered them from tirerack.com. I wasn't sure if I was able to say that so I left it out initially. I chose the Firestone WinterFire at $49 each. Hopefully it was a good choice but at that price I'll throw them in the trash and use my existing tires if they turn out to be that bad.