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02-25-2015, 10:06 AM | #67 | |
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I have driven cars before and seen what happens when the limiter is there - the car starts to shut down power and shudder. I have seen my M5 on this very Dyno at 155mph shut down in 5th before I got the remap done. On this same Dyno after being remapped it was doing 169mph in 5th. In 5th.. That was the Dyno speedometer measuring speed, not my cars. Dyno's measure true speed, the margin for error on a roller is less. EAS was used specifically to remove this type of argument. Most guys in SoCal know EAS and know their Dyno. This is a two wheel drive Dyno. Front wheels are on blocks and the speed is measured by the Dyno, not by the car.
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02-25-2015, 11:55 AM | #68 | ||
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02-25-2015, 06:24 PM | #69 | |
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02-26-2015, 10:36 AM | #70 | |
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The velocity of the surface of the tire equals the velocity of the car (not counting tire slippage/tires spinning). Tire diameter affects the rpm needed for the tire to achieve that velocity. A smaller diameter tire needs a higher rpm to reach the same velocity on the thread surface that a larger diameter tire has at a lower rpm (rpm of the wheel/tire). So, if the thread surface of a tire has a velocity of 150MPH, the car will also move at 150MPH (if there is no slip between tire and road surface). And that means that the rollers on a dyno also will represent the MPH the car travels at. And if you had two different cars with different diameter wheel/tire combos on the same dyno, you would see that the rpm of the wheels would be different at 150MPH (or any other speed). So changing tire diameter, deflated tires etc, affects the engine rpm needed to maintain the same speed (since diameter of the tire is affected). But the velocity of the tire (as shown in illustration below) equals the velocity the car is moving at (or the rollers reads). Last edited by Boss330; 02-26-2015 at 11:01 AM.. |
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02-26-2015, 10:45 AM | #71 | ||
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02-26-2015, 11:02 AM | #72 | ||
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Tangential speed is explained better here: http://en.wikipedia.org/wiki/Speed#Tangential_speed Quote:
Last edited by Boss330; 02-26-2015 at 11:13 AM.. |
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02-26-2015, 11:13 AM | #73 | |||
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02-26-2015, 11:24 AM | #74 | |
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In the example where you put smaller tire diameter tires on your car, what happens is that engine rpm increases since it needs to rotate the wheel at a higher rpm to maintain the same vehicle velocity. But even though the speedometer now reads higher, and the wheel (rotor) rpm is higher, the tangential speed of the tire is still 50MPH if the car moves at a true 50MPH (regardless of the speedo error increasing). You simply cannot have different vehicle speed and tangential speed of the tire. Unless you are doing a burnout or have tire slippage (which one in reality allways have to some extent). Tangential speed of the tire equals the speed of the car. And thus the roller speed is independent on wheel diameter on the car... What you are pointing out is that you need to know tire/wheel diameter if you want to CALCULATE tangential speed (or vehicle speed) based on rpm of the wheel. Here we allready know the tangential speed since that is measured by the rollers. If you want to calculate rotor speed from tangential speed, you would need tire diameter of course. Just think about it: If you have two tires rotating with a tangential speed of a steady 20MPH. One is 100mm and the other is 200mm diameter, so rpm of the wheels are obviously different. At what speed would they move if you put them on the ground and they still had a tangential speed of 20MPH... Last edited by Boss330; 02-26-2015 at 11:30 AM.. |
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02-26-2015, 11:59 AM | #75 | ||
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02-26-2015, 03:15 PM | #77 | |
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Tangential speed of the drum = tangential speed of the tire = theoretical speed of the car (since there allways is a degree of slip between tire and road/drum, - tangential speed of the drum/tire won't equal vehicle speed 100%, more like 99,99%) |
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02-26-2015, 04:07 PM | #80 |
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02-26-2015, 04:46 PM | #81 |
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02-26-2015, 08:13 PM | #83 |
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Nice!!
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02-26-2015, 11:40 PM | #84 |
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02-27-2015, 05:44 AM | #86 |
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02-27-2015, 08:51 AM | #88 |
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