Question on Sidewall Sizes
03-13-2012, 01:11 AM
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E63
Question on Sidewall Sizes
I have a 2010 E63 and the tires that came from the factory had different sidewall heights (the fronts being 35 versus 30 in the rear). I was looking at a set of S65 wheels, but noticed the sidewall heights are the same (30/30).
Putting aside for the moment issues with offset and a taller aspect ratio that can affect gearing/speedometer readings, etc., are there issues with running the same sidewall heights front and rear? When I bought tires for the set of HREs I was running, I was told that I NEEDED to running a lower height in the back to avoid "issues." As I look for wheels to run while my HREs get repaired, I'd like to know how accurate that is so I can select wisely.
Many thanks for any guidance/input.
Putting aside for the moment issues with offset and a taller aspect ratio that can affect gearing/speedometer readings, etc., are there issues with running the same sidewall heights front and rear? When I bought tires for the set of HREs I was running, I was told that I NEEDED to running a lower height in the back to avoid "issues." As I look for wheels to run while my HREs get repaired, I'd like to know how accurate that is so I can select wisely.
Many thanks for any guidance/input.
03-29-2012, 12:34 PM
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Mercedes C230 Sport Sedan
Aspect Ratios
You need to pay attention to the overall height of the tire. If you have a 35 series tire on the front and a 30 series tire on the rear, the rear tire is probably wider than the front, and consequently, taller.
The manufacturer is going to have a specific number of revolutions per mile designed into the computer system for calculating transmission shift points, speedometer readings, and probably a host of other items. If you vary the height of the tire by more than about 3% from stock, the number of revolutions per mile will change enough to confuse the computer and cause the transmission to hunt for gears and provide inaccurate speedo readings. All of this you want to avoid.
I suggest you go to The Tire Rack's website and look up your original equipment tires, go to the specifications tab, and check the height of the tire. Then make sure the tires you want to run vary by no more than 3% of that figure.
The manufacturer is going to have a specific number of revolutions per mile designed into the computer system for calculating transmission shift points, speedometer readings, and probably a host of other items. If you vary the height of the tire by more than about 3% from stock, the number of revolutions per mile will change enough to confuse the computer and cause the transmission to hunt for gears and provide inaccurate speedo readings. All of this you want to avoid.
I suggest you go to The Tire Rack's website and look up your original equipment tires, go to the specifications tab, and check the height of the tire. Then make sure the tires you want to run vary by no more than 3% of that figure.
