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      10-01-2011, 09:30 AM   #1
Dukat
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Tread Depth Scanners

Tire Tread Scanners, The Next Wave in Enforcement Tech?

The capability to scan for this is cool, but is it that much of a problem to warrant such expensive tech being deployed?

Just when I was starting to enjoy our red light cameras which go off prematurely.

What do the #'s at the end of the tire spec mean? 245/45? I thought those were the size in mm, but when I convert 19"x8.5", they don't equal 245/45. My other guess is the 19"x8.5" is the size rim it fits on and 245/45mm is the size of the tire? If that's the case, why aren't both #'s in the same measurement system.. (all in inches or all in mm?)

2012 35i with SAP gets:
Double Spoke (Style 309) 19 x 8.5 light alloy wheels, 245/45 run-flat1 all-season tires2
35i without SAP gets:
Y Spoke (Style 308) 18 x 8.0 light alloy wheels, 245/50 run-flat1 all-season tires
28i without SAP gets:
Star Spoke (Style 306) 17 x 8.0 light alloy wheels, 245/55 run-flat1 all-season tires
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Last edited by Dukat; 10-01-2011 at 10:02 AM..
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      10-01-2011, 11:17 AM   #2
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Quote:
Originally Posted by Dukat View Post
Tire Tread Scanners, The Next Wave in Enforcement Tech?


What do the #'s at the end of the tire spec mean? 245/45? I thought those were the size in mm, but when I convert 19"x8.5", they don't equal 245/45. My other guess is the 19"x8.5" is the size rim it fits on and 245/45mm is the size of the tire? If that's the case, why aren't both #'s in the same measurement system.. (all in inches or all in mm?)...
The numbers on modern passenger vehicle tires represent the section width, the aspect ratio and the bead diameter.

A 245/45R19 tire has a maximum section width (the width of the tire carcass, not the tread) of 245 mm. It has an aspect ratio (the ratio of the section width to the section height of the rubber) of 45% of the width (245 * 0.45 = 110 mm) and a seated bead diameter of 19 inches.

The tires overall rolling diameter can be determined by adding the bead diameter to 2 * the section height, so a 245/45R19 is:

19 inches + (2* 110 mm (or 4.34 inches)) = 27.68 inches.

The mixture of English and metric dimensions is used for historic reasons dating back to the use of non-radial construction tires that were dimensioned in inches. When European radials became available they were specified in the metric dimensions, but used inch diameters to fit English or American wheels and the system has stayed with us ever since.

Race car tires are usually dimensioned in all-inch or all-metric dimensions.
You might see a race tire listed as: 28X10.3X15 which means it has an outside diameter of 28 inches, is 10.3 inches wide and fits on a 15 inch (bead diameter) wheel.

Last edited by Lotus7; 10-01-2011 at 11:23 AM..
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      10-01-2011, 11:34 AM   #3
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I'd never have guessed the 2nd number after the / was a percentage. So the greater the ratio#, the more 'low profile' the tire is?

That's for the great explanation Lotus!
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      10-01-2011, 12:03 PM   #4
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Quote:
Originally Posted by Dukat View Post
I'd never have guessed the 2nd number after the / was a percentage. So the greater the ratio#, the more 'low profile' the tire is?

That's for the great explanation Lotus!
The smaller the percentage, the lower the profile:

A 245/45R19 has a section height of 110.25 mm, while a 245/35R19 would only be 85.75 mm high.

That allows you to use a wide tire, but maintain the correct outside diameter by going to a lower aspect ratio;

A 275/40R19 gives 275*0.40 = 110mm or the same height (and therefore outside diameter) as the 245/45R19.
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      10-01-2011, 12:24 PM   #5
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I hope they do not take this further. I would much rather that the UK government invested in making our roads actually drivable, that in itself would increase road safety rather than trying to shaft us for us much as possible.. I wonder how much tyre wear is down to the state of the roads
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