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Thread: Rim Width - Tire Width Equivalency Chart

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    Default Rim Width - Tire Width Equivalency Chart

    I'm looking to increase my contact patch and found the table in the link below helpful, so I thought I would pass it along. It is probably "no news" to most forum readers, but might help a few guys out.

    Cross reference table: Car tire tips - Pneus Online

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    http://www.trackhq.com/Banners/yellowsitesponsor.gif emilio700's Avatar
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    Quote Originally Posted by Loose Caboose View Post
    I'm looking to increase my contact patch and found the table in the link below helpful, so I thought I would pass it along. It is probably "no news" to most forum readers, but might help a few guys out.

    Cross reference table: Car tire tips - Pneus Online
    Except that it's not really correct.

    If grip is the priority, choose a wheel that is the same width as the tread (not casing).
    Last edited by emilio700; 09-15-2013 at 04:16 PM.
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    Thanks!

    Since casings are wider than tread, does this mean that tires that are wider than "ideal" in the referenced chart would be o.k.?

    Cross reference table: Car tire tips - Pneus Online
    Last edited by Loose Caboose; 09-15-2013 at 11:32 PM.

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    enjoys driving fast Jack Olsen's Avatar
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    In the case of the Nitto NT01, at least, the manufacturer's recommendations are very different from that chart.

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    Quote Originally Posted by Jack Olsen View Post
    In the case of the Nitto NT01, at least, the manufacturer's recommendations are very different from that chart.
    And neither are correct.
    Theseus: '94 Miata, NASA SU/TTU (in progress)
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    Quote Originally Posted by emilio700 View Post
    Except that it's not really correct.

    If grip is the priority, choose a wheel that is the same width as the tread (not casing).
    Im sort of tempted to disagree here.. but dont know if I want to open the can of worms. I think thats true in part.... but not the whole story.
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    Quote Originally Posted by gixxer_drew View Post
    Im sort of tempted to disagree here.. but dont know if I want to open the can of worms. I think thats true in part.... but not the whole story.
    A race engineer holding back on a technical explanation that almost nobody understands, but which is almost certainly correct. How refreshing . . .
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    Quote Originally Posted by Richard EVO View Post
    A race engineer holding back on a technical explanation that almost nobody understands, but which is almost certainly correct. How refreshing . . .
    I may be lacking certain skill at internet message-board chatting... but whenever I try to have these kind of conversations I end up regretting it so I just try to encourage people toward further research....

    The concept basically is you can try to work out the optimum rim width on a say a tire test rig... but in my mind is that even tire rig tests are steady state conditions and how the tire reaches its steady state is every bit as much about the dynamic handling behavior of the car as it is about ultimate "grip" (which I see as a four letter word). If you define it say as the peak lateral acceleration of the _car_ then having dynamic oversteer and understeer at any point in time can result in a lower total acceleration regardless of what the tire rig test tells is optimum grip level of the tire. In the old days they tuned balance by cranking up oversteer until peak lat G was achieved. What I mean to say is that among many other second order variables wheel width effects handling balance as well both dynamic and steady state. Steady state is easy, dynamic is what makes the best (and worst) handling cars. You dont get much "grip" when the car handles badly either.
    Last edited by gixxer_drew; 09-16-2013 at 10:08 PM.
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    Quote Originally Posted by gixxer_drew View Post
    I may be lacking certain skill at internet message-board chatting... but whenever I try to have these kind of conversations I end up regretting it so I just try to encourage people toward further research....

    The concept basically is you can try to work out the optimum rim width on a say a tire test rig... but in my mind is that even tire rig tests are steady state conditions and how the tire reaches its steady state is every bit as much about the dynamic handling behavior of the car as it is about ultimate "grip" (which I see as a four letter word). If you define it say as the peak lateral acceleration of the _car_ then having dynamic oversteer and understeer at any point in time can result in a lower total acceleration regardless of what the tire rig test tells is optimum grip level of the tire. In the old days they tuned balance by cranking up oversteer until peak lat G was achieved. The only two things you can do to change the *dynamic* behavior of the tire you are usually specified to use (or need to win) is the rim width and the pressure. Both are as much tied to the loading, springing, aero balance construction, CPLV, etc as they are to the dynamic behaviors relative to the load they carry. Peak force to slip angle is first order handling behavior and the others are all secondary save maybe aero on a high DF/weight ratio car (F1, etc). And you wont get any of that from the test rig data, which is already so far out there its just ballpark anyway. Build the car around the tire, and when you cant do that you have to change the tire and you have just a few tools. Otherwise its a patch up... which means you are taking away performance to find balance (or balance timing) and sometimes you think you find balance until that one condition happens and suddenly you remember it was a patch up job. The difference between the best handling cars and the ones that were remembered in history as bad handling I think is exactly that point. Im just trying to describe the forrest that I cant see because all these damn trees are in the way.
    Sheesh!

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    Quote Originally Posted by gixxer_drew View Post
    Im sort of tempted to disagree here.. but dont know if I want to open the can of worms. I think thats true in part.... but not the whole story.
    I feel your pain...lol
    That's not a Typo, I just can't spell no so well.

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    You really should have quit when I said we all appreciate someone smarter than us not making the point with a bullet. But you couldn't leave well enough alone. I have no idea what your latest post means . . . I guess ya'll engineers don't have a lot of "people skills" lol

    Quote Originally Posted by gixxer_drew View Post
    I may be lacking certain skill at internet message-board chatting... but whenever I try to have these kind of conversations I end up regretting it so I just try to encourage people toward further research....

    The concept basically is you can try to work out the optimum rim width on a say a tire test rig... but in my mind is that even tire rig tests are steady state conditions and how the tire reaches its steady state is every bit as much about the dynamic handling behavior of the car as it is about ultimate "grip" (which I see as a four letter word). If you define it say as the peak lateral acceleration of the _car_ then having dynamic oversteer and understeer at any point in time can result in a lower total acceleration regardless of what the tire rig test tells is optimum grip level of the tire. In the old days they tuned balance by cranking up oversteer until peak lat G was achieved. What I mean to say is that among many other second order variables wheel width effects handling balance as well both dynamic and steady state. Steady state is easy, dynamic is what makes the best (and worst) handling cars. You dont get much "grip" when the car handles badly either.
    Last edited by Richard EVO; 09-16-2013 at 11:32 PM.
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    Quote Originally Posted by Richard EVO View Post
    You really should have quit when I said we all appreciate someone smarter than us not making the point with a bullet. But you couldn't leave well enough alone. I have no idea what your latest post means . . . I guess ya'll engineers don't have a lot of "people skills" lol
    point taken
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    I think he said it depends on car setup and how it loads force on the tires. So.. Not just peak grip but an area under curve kind of deal. This is the first thing I read in the morning so you'll have to excuse me if I misunderstood.

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    A few things to keep in mind when making generic statements on tire and wheel sizing.

    Manufacturers are not held tightly to standards regarding sizing. One manufacturers 255/40/17 might be 10mm narrower tread but 10mm wider casing than another brand. Even within the same brand, two different models of tire in the same size
    might have different dimensions. Recommend rim widths as published by manufacturers are written by lawyers.

    The general rule still applies for those concerned with maximum grip from a high performance radial tire: Choose a wheel at least as wide as the actual tread.

    Case in point: The Hoosier 205/50/15 tires we race on have a 215mm wide tread and 240mm wide casing. What rim have we found them to be the fastest on? 228.6mm (9")
    Our 205 Toyo, Nitto and Maxxis tires are between 197-203mm tread. We run those on a 203.2mm wheel (8")
    This is not conjecture but back to back A/B testing, empirical knowledge.

    The lesson here is if you are looking for max grip, go measure the tread on the actual brand/model/size tire your are considering. Choose a wheel width that matches that tread width. Still doubts?
    Measure the tread and wheel widths on some high performance cars like the GT-R, Z06, 911, 458, etc. You'll find actual treads and wheel widths matched up.
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    Quote Originally Posted by Richard EVO View Post
    I have no idea what your latest post means . . .
    Come on, Richard. We all know you didn't even read it. TLDR, is that the acronym?

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    Quote Originally Posted by Richard EVO View Post
    You really should have quit when I said we all appreciate someone smarter than us not making the point with a bullet. But you couldn't leave well enough alone. I have no idea what your latest post means . . . I guess ya'll engineers don't have a lot of "people skills" lol
    I think he is just overestimating our intelligence. Something that is really hard not to do.

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    Quote Originally Posted by Loose Caboose View Post

    I think he is just overestimating our intelligence. Something that is really hard not to do.
    "No man ever lost money underestimating the intelligence of the American people." P.T. Barnum
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    Quoting carnies are we now?

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    Quote Originally Posted by cosmin View Post
    Quoting carnies are we now?
    Carnies? You just don't get it, dude . . .
    The deposed former Sheriff of trackHQ . . .

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    Phineas Taylor Barnum (July 5, 1810 April 7, 1891) was an American showman, businessman, scam artist and entertainer, remembered for promoting celebrated hoaxes and for founding the circus that became the Ringling Bros. and Barnum & Bailey Circus.[1]

    Sounds like a carny to me

    edit: and I'm just giving you a hard time. I completely agree with that quote.
    Last edited by cosmin; 09-17-2013 at 10:32 PM.

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