Tire Fitment?
03-25-2007, 06:48 PM
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My Ride: 2007 530i, Black on Auburn, 6 Speed, Logic 7 Sound, Navigation, Sports Package, Dakota Leather
I purchased a set of wheels 18x8 front & 18x9 rear. I was wondering if I could fit 285/30/zr18 on the rear wheels without having to roll the fenders or make any modifications what so ever.
03-25-2007, 07:15 PM
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Originally Posted by nickcach' post='406898' date='Mar 26 2007, 10:48 AM
I purchased a set of wheels 18x8 front & 18x9 rear. I was wondering if I could fit 285/30/zr18 on the rear wheels without having to roll the fenders or make any modifications what so ever.
your car is only 530i not a 550i.It will be slow at lights and less MPG too
03-25-2007, 07:17 PM
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My Ride: 2007 530i, Black on Auburn, 6 Speed, Logic 7 Sound, Navigation, Sports Package, Dakota Leather
Originally Posted by pinguhk' post='406903' date='Mar 25 2007, 11:15 PM
why so big your car is only 530i not a 550i.
It will be slow at lights and less MPG too
your car is only 530i not a 550i.It will be slow at lights and less MPG too
For Autocross.
03-25-2007, 07:20 PM
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Originally Posted by nickcach' post='406898' date='Mar 25 2007, 07:48 PM
I purchased a set of wheels 18x8 front & 18x9 rear. I was wondering if I could fit 285/30/zr18 on the rear wheels without having to roll the fenders or make any modifications what so ever.
Now, let's calculate change in the wheel circumference since it affects speedometer and odometer. 2*(96.25 - 85.5) * PI = 67mm. Circumference of the 285/30 is 67mm shorter. Is is large or small difference? Let's find out.
275/35R18 rim diameter is 18 * 25.4 = 457.2mm. Add two heights of the tire and get total wheel diameter. Multiply diameter by PI (3.1415) and get total wheel circumference: (457.2 + 2*96.25 ) * PI = 2041mm.
The change is 67/2041 * 100 = 3%. This means with 285/30 your speedometer, odometer and MPG calculator will be 3% off. Smaller wheels makes more revolutions per mile so speedometer will be showing faster speed than the car actually is moving at. MPG will be higher since car will be thinking you traveled longer distance.
03-25-2007, 07:27 PM
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Originally Posted by uglybear' post='406909' date='Mar 26 2007, 11:20 AM
285/30 means tire is 285mm wide and 285*30% high. 285*0.3 = 85.5mm. Standard tire, I believe, is 275/35, which yields 275 * 0.35 = 96.25mm. So in fact, 285/30 is a smaller tire.
Now, let's calculate change in the wheel circumference since it affects speedometer and odometer. 2*(96.25 - 85.5) * PI = 67mm. Circumference of the 285/30 is 67mm shorter. Is is large or small difference? Let's find out.
275/35R18 rim diameter is 18 * 25.4 = 457.2mm. Add two heights of the tire and get total wheel diameter. Multiply diameter by PI (3.1415) and get total wheel circumference: (457.2 + 2*96.25 ) * PI = 2041mm.
The change is 67/2041 * 100 = 3%. This means with 285/30 your speedometer, odometer and MPG calculator will be 3% off. Smaller wheels makes more revolutions per mile so speedometer will be showing faster speed than the car actually is moving at. MPG will be higher since car will be thinking you traveled longer distance.
Now, let's calculate change in the wheel circumference since it affects speedometer and odometer. 2*(96.25 - 85.5) * PI = 67mm. Circumference of the 285/30 is 67mm shorter. Is is large or small difference? Let's find out.
275/35R18 rim diameter is 18 * 25.4 = 457.2mm. Add two heights of the tire and get total wheel diameter. Multiply diameter by PI (3.1415) and get total wheel circumference: (457.2 + 2*96.25 ) * PI = 2041mm.
The change is 67/2041 * 100 = 3%. This means with 285/30 your speedometer, odometer and MPG calculator will be 3% off. Smaller wheels makes more revolutions per mile so speedometer will be showing faster speed than the car actually is moving at. MPG will be higher since car will be thinking you traveled longer distance.
you work for a tire shop or make tires?
03-25-2007, 08:44 PM
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Originally Posted by pinguhk' post='406912' date='Mar 25 2007, 08:27 PM
thanks that is so calculation cool.
you work for a tire shop or make tires?
you work for a tire shop or make tires?
and since tires are part of the car, so I kind of wanted to know what those funny numbers on them meant 
Closest tire in 30 is 315/30R18
03-25-2007, 10:03 PM
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Originally Posted by uglybear' post='406951' date='Mar 26 2007, 05:44 AM
..I kind of wanted to know what those funny numbers on them meant...
http://www.carbibles.com/tyre_bible.html
Check out "A tyre size calculator".
There are also plenty of other "funny numbers" to keep
busy!ABC
03-26-2007, 04:41 AM
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Originally Posted by uglybear' post='406909' date='Mar 26 2007, 04:20 AM
285/30 means tire is 285mm wide and 285*30% high. 285*0.3 = 85.5mm. Standard tire, I believe, is 275/35, which yields 275 * 0.35 = 96.25mm. So in fact, 285/30 is a smaller tire.
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