08-19-2016, 05:26 PM | #1 |
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Semi slick tires for f20 M135i LCI?
Hi All,
I've been doing a lot of track days lately and I'm looking for semi-slick, or track oriented but still road legal, tires. My M135i has 245/35 R18 tires in the back, but from my research there are very few tire models in this size. What are you guys using? After the Michelin Pilot Super Sport that came with the car, I am now on a set of Federal 595RS-R. But they are not that much faster than the PSS and a lot less durable... I wanted to try the Michelin Pilot Sport Cup 2, but the closest size is 245/40, witch is 4% bigger in circumference. Is that too much, or is it ok if I go with this size? The speedometer/odometer gets its info from the front or rear tires? Cheers. |
08-22-2016, 03:25 AM | #4 |
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I imagine that the speedo drive will come from the gearbox (or perhaps the diff) so it is the rear tyres that will impact any change in the speedo accuracy.
There are tyre size calculator apps that will tell you the change in speedo accuracy. For example, a 245/35/18 to a 245/40/18 will mean the tyre diameter increases from 24.75" to 25.72". At 60mph the speedo will read 62.34mph. |
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08-22-2016, 04:35 AM | #5 |
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I think (also don't know for sure) the speedometer is based on DSC-sensors, where the computer estimates the actual vehicle speed based on rotation from all wheels, accelerometers and gyrometers.
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