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  1. #1
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    HPF compares the effect of different sized wheels on the dyno

    Well all know lighter wheels are a good thing. But just how big is the difference? Well, as a car makes more power the effect is easier to see. HPF took a Stage 4 and tested it with a wide set of 19's and then the stock 19 inch M3 wheels. The effect is magnified on a more powerful car and at one point in the graph there is an over 60 whp difference between the heavier wheels and the skinnier, lighter stock wheels.

    Video is below
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    Video:


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    I have always found big wheels with flush setups just plain stupid if you are looking for performance.
    Click here to enlarge

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    Click here to enlarge Originally Posted by FR305 Click here to enlarge
    I have always found big wheels with flush setups just plain stupid if you are looking for performance.
    Well, he kind of needs them for traction.
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    Click here to enlarge Originally Posted by Sticky Click here to enlarge
    Well, he kind of needs them for traction.
    Not really. He could have more of a Full setup with a 18 wheel just as wide as the 20's but with a larger tire wall.

    for example:

    Click here to enlarge
    Last edited by 1cleanAMG; 12-24-2010 at 01:12 AM.
    Click here to enlarge

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    Click here to enlarge Originally Posted by FR305 Click here to enlarge
    Not really. He could have more of a Full setup with a 18 wheel just as wide as the 20's but with a larger tire wall.

    for example:

    http://ll.speedhunters.com/u/f/eagam...2/IMG_4551.JPG
    Oh, you mean same width but just not a "bling" ?

    They are 19's.
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    Click here to enlarge Originally Posted by Sticky Click here to enlarge
    Oh, you mean same width but just not a "bling" ?
    Exactly. Bling = Weight

    Click here to enlarge Originally Posted by Sticky Click here to enlarge
    They are 19's.
    He should have 17's Classic CCW's
    Click here to enlarge

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    $#@!.. im wanna put the 17's on now more than ever!!

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    European Car put wider wheels and more rubber on their Project Z4M. They got 13whp/10 ft.lbs gain over the OE wheel and tire set-up. The 18x10 Forgelines with upsized tires were 4 lbs lighter.

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    Click here to enlarge Originally Posted by FR305 Click here to enlarge
    He should have 17's Classic CCW's
    Perhaps, but he can also have more than one set of wheels. One for looks, one for the track.
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    This is how you do it right

    CCW Classics matte black centers with gloss black lips.

    Click here to enlarge

    Click here to enlarge
    Last edited by 1cleanAMG; 12-24-2010 at 01:45 AM.
    Click here to enlarge

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    Click here to enlarge Originally Posted by Sticky Click here to enlarge
    Perhaps, but he can also have more than one set of wheels. One for looks, one for the track.
    European Car kind of had opposite findings. Their upped tire size and wider wheels, gained HP/TQ.

    They attributed the gains to the lighter weight, not rolling diameter.

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    Ya, I guess, I know I will be running wheels for looks on the street and wheels for performance on the track.
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    Click here to enlarge Originally Posted by M3_WC Click here to enlarge
    European Car kind of had opposite findings. Their upped tire size and wider wheels, gained HP/TQ.

    They attributed the gains to the lighter weight, not rolling diameter.
    It is about the weight more than anything.

    The wheels here in the vid are both 19's.
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    Click here to enlarge Originally Posted by Sticky Click here to enlarge
    It is about the weight more than anything.

    The wheels here in the vid are both 19's.
    He says the ratio between the tire diameter and roller diameter change, that is what caused the difference in power readings. He is not really attributing it to weight, but rather the different rolling diameters.

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    Click here to enlarge Originally Posted by M3_WC Click here to enlarge
    He says the ratio between the tire diameter and roller diameter change, that is what caused the difference in power readings. He is not really attributing it to weight, but rather the different rolling diameters.
    That is true as well but the weight also is a factor.
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    Click here to enlarge Originally Posted by Sticky Click here to enlarge
    That is true as well but the weight also is a factor.
    Yeah I agree. I think it is the bigger factor actually.

    Here is some data from Europeancar's Project Z4M. They find the less rotational mass attributes to the bulk of the gains. As HPF seems to think the tire diameter is the main factor.
    http://blog.forgeline.com/tag/project-z4m/

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    Click here to enlarge Originally Posted by LostMarine Click here to enlarge
    $#@!.. im wanna put the 17's on now more than ever!!
    k1's ftw
    JB4LIFE

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    The rolling diameter is effectively changing the gearing and in this case making it taller, so the torque multiplication factor decreases with the bigger tire/wheel combo, and the weight is also a huge factor. This is a really cool video, though....I love it when shops test different things that we always talk about and put some hard numbers on them.

    I wonder if the difference is as great because the car here is making such big numbers. If it was a car making 400ish whp, the difference might have been much smaller.

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    Click here to enlarge Originally Posted by FR305 Click here to enlarge
    Not really. He could have more of a Full setup with a 18 wheel just as wide as the 20's but with a larger tire wall.

    for example:

    http://www.bimmerboost.com/images/im...10/12/1585.jpg

    Great point. I'm thinking about going with 16's when I go to the track this coming spring. The taller side wall helps a good bit. I wonder what the tq difference was with the tire/rim swap?
    Click here to enlargeClick here to enlarge

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    tires are pretty heavy too, i wonder what the difference would be from a 305-45-18 to a 305-30-20 would be...
    JB4LIFE

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    its not that difficult guys

    you want to minimize the amount of mass as you get further from the center of the wheel

    more mass further from the center = bad

    unfortunately we can't readily measure the difference between set ups, although total weight is a good indicator

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    Click here to enlarge Originally Posted by BASELINE Click here to enlarge
    I wonder if the difference is as great because the car here is making such big numbers. If it was a car making 400ish whp, the difference might have been much smaller.
    Definitely, the larger power accentuates the shift.
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    Click here to enlarge Originally Posted by mazdaspeed6 Click here to enlarge
    tires are pretty heavy too, i wonder what the difference would be from a 305-45-18 to a 305-30-20 would be...
    Pretty big... tirerack lists tire weights which is cool.
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    1 out of 1 members liked this post. Yes Reputation No
    The power increase has nothing to do with the tire diameter alone.

    When you change rear gear ratios on a car, does it make more power? No, it doesn't, the power output of the engine doesnt change nor does the power to the ground change, only the slope the power curve. Changing tire diameters is like changing rear gear ratio, assuming you neglect weight etc...

    The weight alone; also, does not attribute to the power loss. Physically, what is happening is the bigger wheel has more mass at the extremities of the rim. Meaning, the rim is heavier as you move from the center of the rim to the outside. This is called the moment of inertia.

    You can have two rims that weigh EXACTLY the same on a STATIC scale. And guess what, if one rim is a properly designed rim, it will be as light as possible towards the outside. If the poorly designed rim is heavy near the rim lip (or if you use a heavier tire), it will show you the exact same results as seen in this video because it has a greater moment of inertia despite the rims weighing the same.

    What people dont understand is that its not the weight of the rim, but the weight of the tire and ITS DIAMETER; the COMBINATION of weight distribution from center of rim to radius. A large heavy tire with a lot of circumferential mass will take a lot more torque to rotate than an identical relatively 'heavier' rim with a lighter tire.

    Weight alone is not the answer, diameter AND weight contribute to this phenomena.

    This is how rotating objects work, when something needs to be rotated it requires torque. Just like you can accelerate in a straight line, you can also accelerate in rotation, this is called angular acceleration.

    To get angular acceleration you need torque. The relationship between angular acceleration and torque is

    Angular acceleration = Torque / moment of inertia

    Doesnt that look familiar?

    Sort of like linear acceleration = Force / Mass

    Except for a rotating object we dont consider static mass, but moment of inertia, because static mass only doesnt tell you enough about how much rotational inertia an object has.

    I just needed to clarify some misinformation.

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