01-04-2021, 01:20 PM | #23 |
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Ha ha ha. I can see where this is going. Why would I go through that when there's a wealth of information on the internet supporting this? You can disagree adamantly but then I would simply lump you in with the flat earth crowd and move on.
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01-04-2021, 01:24 PM | #24 | |
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A tire's contact patch size is defined by the tire's structure, tread mold and inflation pressure. A lower profile tire does not automatically translate to more rubber on the road.
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01-04-2021, 01:25 PM | #25 |
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01-04-2021, 02:09 PM | #26 | |
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I’ve not calculated the exact resulting tire diameter between front and rear in all cars we mention here, I guess I trust Porsche here when they stated the larger contact patch without adding width and resulting added stability of the rear as their reason for staggering them...they usually don’t do things just because fashion. Last edited by solstice; 01-04-2021 at 02:24 PM.. |
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01-04-2021, 02:33 PM | #27 | |
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As opposed to what? If the staggered set up (according to BMW and Porsche) is the ideal set up, and the front diameter is 19 inches the 20 would be the preferred diameter of the rear. Likewise the M-Performance set up is 20/21. I |
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01-04-2021, 03:00 PM | #28 | |
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01-04-2021, 03:08 PM | #29 | |
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To be honest I’m not all that interested in the exact science behind this I’m more interested in the result. I’m getting impatient for quality reviews Last edited by solstice; 01-04-2021 at 03:13 PM.. |
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01-04-2021, 03:10 PM | #30 |
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01-04-2021, 03:11 PM | #31 | |
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In any case, it seems at least plausible to me that the car simply performed best with the different diameter wheels, so that's what they went with. That is to say, irrespective of the actual science behind the engineering, sometimes you test several different configurations and go with what works best. |
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01-04-2021, 03:25 PM | #32 | |
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01-04-2021, 03:28 PM | #33 |
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Blissfully ignorant.
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01-04-2021, 03:37 PM | #34 | ||
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G8x has equal front/rear tire diameters so that is irrelevant. |
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01-04-2021, 03:41 PM | #35 | |
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They wanted more contact patch and likely tried all options as wider wheels, more profile at the same wheel size and larger wheels and the best overall results were achieved with larger wheels. I don’t think the main target was a lower profile rear tire instead it was a larger contact patch. The sidewall was likely just tuned as a secondary parameter. For the G8X we haven’t gotten a detailed explanation to why it ended up were it did. Your guess is as good as any. I think mkoesel is close to the truth that this is more an empirical result of testing than a formula based decision. |
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01-04-2021, 03:41 PM | #36 | |
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Just shows how you can't rely on everything you hear, even if it seems from reliable sources...
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01-04-2021, 03:43 PM | #37 |
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I'm still gonna stick with they did it because it looks cool and has no ill effect on the car. Plus they can ramble on about improved turn in up front (presumably compared to a 20" front wheel). The G8x design is clearly about brash looks and 19" front/rear doesn't fit that theme.
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01-04-2021, 03:57 PM | #38 | |
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01-04-2021, 04:03 PM | #39 | |
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While we do not know the specifics of the G8X tire engineering, I did read up a lot about my M4cs, which also has staggered diameter rims.
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01-04-2021, 04:04 PM | #40 |
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Your own eyes is definitely the most reliable source
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01-04-2021, 04:06 PM | #41 |
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01-04-2021, 04:08 PM | #42 |
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False...
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01-04-2021, 04:10 PM | #43 |
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01-04-2021, 04:14 PM | #44 | |
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The increased contact patch from increasing diameter is minimal. Tire width is what actually effectively increases contact patch (and in turn the wheel width to accommodate the tire). But with an increased tire and wheel width, comes an increase in rubber, which increases tire deflection on load at a given tire pressure. This gives more grip but sacrifices responsiveness as CanAutM3 pointed out. To help balance this out, we can use a bigger diameter wheel to decrease the tire sidewall which will decrease deflection but maintain the contact patch. So no, WHEEL diameters do not increase contact patch, but they can allow for a wider tire without excessive tire sidewall. Additionally, having a larger overall diameter wheel/tire combo changes the overall driving ratio of the car. A larger tire means a higher potential speed. I don't know if the G80's rolling diameter will be more than the fronts because I am too lazy to look up the tire sizes, but that would be one potential reason for using a larger rear wheel. These arguments about the increased weight of larger rear wheels are kind of ironic given BMW increased the weight of the G80 by increasing its size, which isn't as correctable as new rims.
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