OEM tire sidewall height questions
03-18-2010, 03:12 PM
#1
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OEM tire sidewall height questions
Anyone know why the OEM tires side wall height is 35 in the front and 30 in the rear? I know the height difference is very small, but I'm just wondering why they did that. Is it because of the weight of the engine?
03-18-2010, 03:39 PM
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a quarter mile at a time
Tire 101:
In any given tire size, there are 3 measurements given, tire section width in MM, the aspect ratio, and then the wheel diameter in inches. So for example: 235/35/19. The example tire is 235mm wide, has a tire sidewall height that is 35% of 235mm, and goes on a 19" wheel.
The reason the aspect ratio's are different front and rear on a C63 is because it has a staggered setup. The front and rear wheels are the same size (18"). The front tires are narrower than the rear tires however. Due to the added width of the rear tire, the ratio of that width must be smaller to maintain the same overall sidewall height.
In any given tire size, there are 3 measurements given, tire section width in MM, the aspect ratio, and then the wheel diameter in inches. So for example: 235/35/19. The example tire is 235mm wide, has a tire sidewall height that is 35% of 235mm, and goes on a 19" wheel.
The reason the aspect ratio's are different front and rear on a C63 is because it has a staggered setup. The front and rear wheels are the same size (18"). The front tires are narrower than the rear tires however. Due to the added width of the rear tire, the ratio of that width must be smaller to maintain the same overall sidewall height.
03-18-2010, 03:39 PM
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Ex: 255 X 0.35 = 89.25mm sidewall
235 X 0.40 = 94mm sidewall
in this example a 265/35/18 tire would have been closer to the 235/40/18 front tire, with a 92.75mm sidewall.
03-18-2010, 04:07 PM
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if you mean 40 front and 35 rear, the aspect ratio info is a % of the width of the tire. So to get 2 tires with a similar sidewall aspect, the larger tire must have a lower aspect ratio.
Ex: 255 X 0.35 = 89.25mm sidewall
235 X 0.40 = 94mm sidewall
in this example a 265/35/18 tire would have been closer to the 235/40/18 front tire, with a 92.75mm sidewall.
Ex: 255 X 0.35 = 89.25mm sidewall
235 X 0.40 = 94mm sidewall
in this example a 265/35/18 tire would have been closer to the 235/40/18 front tire, with a 92.75mm sidewall.
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03-19-2010, 02:46 AM
#8
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if you mean 40 front and 35 rear, the aspect ratio info is a % of the width of the tire. So to get 2 tires with a similar sidewall aspect, the larger tire must have a lower aspect ratio.
Ex: 255 X 0.35 = 89.25mm sidewall
235 X 0.40 = 94mm sidewall
in this example a 265/35/18 tire would have been closer to the 235/40/18 front tire, with a 92.75mm sidewall.
Ex: 255 X 0.35 = 89.25mm sidewall
235 X 0.40 = 94mm sidewall
in this example a 265/35/18 tire would have been closer to the 235/40/18 front tire, with a 92.75mm sidewall.
And if you want to stay true to the design and engineering of the car, find the detailed specs of the OE tires and then find tires that best resemble these specs.
For example, regardless of any of these numbers, you must match tire circumference to that of the OE. Every tire has a different value for revs per mile. OE for C63 is 827 front and 826 rear. If your replacement tire is a higher number for the drive (rear) tires, your car accelerates slightly faster, but your speedo and odo will read faster than your actual and vice versa.
I am often baffled by how people just change their tires to a wider one without considering the side effects. There is actually an aerodynamic disadvantage in going with wider tires while the actual traction does not improve based of the laws of physics.
Last edited by cyberorth; 03-19-2010 at 03:02 AM.
03-19-2010, 11:44 AM
#9
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Thread Starter
Guys, don't get too involved with these numbers. Every single tire has a different set of specs. these 'size' numbers do not give you exact values. Use them as guidelines. you can see the specs in the manufacturers' websites.
And if you want to stay true to the design and engineering of the car, find the detailed specs of the OE tires and then find tires that best resemble these specs.
For example, regardless of any of these numbers, you must match tire circumference to that of the OE. Every tire has a different value for revs per mile. OE for C63 is 827 front and 826 rear. If your replacement tire is a higher number for the drive (rear) tires, your car accelerates slightly faster, but your speedo and odo will read faster than your actual and vice versa.
I am often baffled by how people just change their tires to a wider one without considering the side effects. There is actually an aerodynamic disadvantage in going with wider tires while the actual traction does not improve based of the laws of physics.
And if you want to stay true to the design and engineering of the car, find the detailed specs of the OE tires and then find tires that best resemble these specs.
For example, regardless of any of these numbers, you must match tire circumference to that of the OE. Every tire has a different value for revs per mile. OE for C63 is 827 front and 826 rear. If your replacement tire is a higher number for the drive (rear) tires, your car accelerates slightly faster, but your speedo and odo will read faster than your actual and vice versa.
I am often baffled by how people just change their tires to a wider one without considering the side effects. There is actually an aerodynamic disadvantage in going with wider tires while the actual traction does not improve based of the laws of physics.
03-19-2010, 01:02 PM
#10
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Formula for calculating over all tire diameter
Formula for calculating over all tire diameter down to the xxxthousand.
Round up to the nearest hundred..sometire have more tread and some are wider than other.
Exemple size; 235/40/18
25.4mm=1"
235x.40x2/25.4+18=25.40"
Round up to the nearest hundred..sometire have more tread and some are wider than other.
Exemple size; 235/40/18
25.4mm=1"
235x.40x2/25.4+18=25.40"
Last edited by Peter_02AMG; 03-19-2010 at 01:05 PM.
03-22-2010, 03:36 AM
#11
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How can a larger tire improve acceleration besides adding traction? It should have the slight opposite with a taller rotating mass. I understand that the speedo will be off slightly, but the size should only be off by 1 or 2 MPH. The aerodynamic's of a tire that is only slightly wider or taller isn't close to the gains of increased braking, off the line traction, and increased corner speed.
Time to bust out the physics book...your traction argument may hold true only if you are comparing identical materials. Different tires have different friction coefficients. Wider doesn't automatically mean better traction.
My only valid reason for going wider is the looks...I have to be honest!
03-22-2010, 12:58 PM
#12
No, a larger number of revolution per mile means the tire is actually smaller in diameter.
Time to bust out the physics book...your traction argument may hold true only if you are comparing identical materials. Different tires have different friction coefficients. Wider doesn't automatically mean better traction.
My only valid reason for going wider is the looks...I have to be honest!
Time to bust out the physics book...your traction argument may hold true only if you are comparing identical materials. Different tires have different friction coefficients. Wider doesn't automatically mean better traction.
My only valid reason for going wider is the looks...I have to be honest!
