My tires have my speedo off. Is there a way to fix it apart from new tires?

yardiewrx · 02-18-2020, 03:12 PM

I purchased a used 2015 with 19x9.5 and 19.10.5 Vorsteiner wheels. They are sporting 275x30 & 295's x 30's. Well I've taken it to work a few times and knew traffic wasn't going nearly as fast as the speedo was indicating so I checked it on my GPS and it's running about 5 mph faster than my true speed. Is there any fix to this apart from getting 35 series tires?

N1rve · 02-18-2020, 10:58 PM

Quote:

Originally Posted by yardiewrx

I purchased a used 2015 with 19x9.5 and 19.10.5 Vorsteiner wheels. They are sporting 275x30 & 295's x 30's. Well I've taken it to work a few times and knew traffic wasn't going nearly as fast as the speedo was indicating so I checked it on my GPS and it's running about 5 mph faster than my true speed. Is there any fix to this apart from getting 35 series tires?

You can either get your speedometer calibrated which is an expensive processes which I don't hear many people do, or actually just get proper fitting tires.

MineralWhiteF80 · 02-20-2020, 03:39 PM

All speedometers error on the fast side, typically in the 3% to 10% range depending on the manufacturer. Out of the 12 BMWs I have owned, I have seen they all read about 7% faster than your actual ground speed. So, if you are doing an indicated 100 mph, you are really probably going closer to 93 mph.

I believe it is against the law for an auto manufacturer to sell a car where the speedometer reads slower than the actual speed the car is traveling, so manufactures prevent that by making them read higher.

Also, cars that have 3 different wheel/tire size options from the factory all will affect ground speed differently. Many cars do not have the ability to tell the car which size wheels and tires are on it, so to cover all of the options, the fixed speedometer calibration will read high to take any variables into consideration. I know in my both of my 2018 model Porsches, you can scan through the gauge cluster and manually choose which size wheels and tires you have on the car with will reprogram the speedometer and tire pressure monitoring system to be more accurate to speed and appropriate tire pressures.

And if you like conspiracy theories, we can get into the one where car companies exaggerate the speedometer reading so that your car shows it has more miles on it than it actually has driven, which effectively shortens your warranty period by mileage. Or the more friendly theory, to make people think they are driving faster than they actually are which means the roads could be considered safer by everyone going slower than they think they are.

ibimmer954 · 02-20-2020, 06:52 PM

The speedo will be off by about 5% even with stock wheel and tire sizes. Don't worry about it. It's like that with all BMWs.

Computing 5% is easy. Take your speed, divide by 10 then divide by 2. So let's say you want to go 45. 45 -> 4 -> 2. So in order to go 45, your speedo must read 47 or 48. For 70: 70 -> 7 -> 3. So, actual 70 is 73 - 74.

02-18-2020, 03:12 PM	#1
yardiewrx New Member 0 Rep 10 Posts Drives: F80 M3 Join Date: Jan 2019 Location: Parkland, Fl iTrader: (0)	My tires have my speedo off. Is there a way to fix it apart from new tires? I purchased a used 2015 with 19x9.5 and 19.10.5 Vorsteiner wheels. They are sporting 275x30 & 295's x 30's. Well I've taken it to work a few times and knew traffic wasn't going nearly as fast as the speedo was indicating so I checked it on my GPS and it's running about 5 mph faster than my true speed. Is there any fix to this apart from getting 35 series tires?
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02-20-2020, 03:39 PM	#3
MineralWhiteF80 Dont listen to me 793 Rep 562 Posts Drives: F82, E92 M3, G30 M550i, E46 Join Date: Mar 2015 Location: Atlanta,Ga iTrader: (1)	All speedometers error on the fast side, typically in the 3% to 10% range depending on the manufacturer. Out of the 12 BMWs I have owned, I have seen they all read about 7% faster than your actual ground speed. So, if you are doing an indicated 100 mph, you are really probably going closer to 93 mph. I believe it is against the law for an auto manufacturer to sell a car where the speedometer reads slower than the actual speed the car is traveling, so manufactures prevent that by making them read higher. Also, cars that have 3 different wheel/tire size options from the factory all will affect ground speed differently. Many cars do not have the ability to tell the car which size wheels and tires are on it, so to cover all of the options, the fixed speedometer calibration will read high to take any variables into consideration. I know in my both of my 2018 model Porsches, you can scan through the gauge cluster and manually choose which size wheels and tires you have on the car with will reprogram the speedometer and tire pressure monitoring system to be more accurate to speed and appropriate tire pressures. And if you like conspiracy theories, we can get into the one where car companies exaggerate the speedometer reading so that your car shows it has more miles on it than it actually has driven, which effectively shortens your warranty period by mileage. Or the more friendly theory, to make people think they are driving faster than they actually are which means the roads could be considered safer by everyone going slower than they think they are.
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02-20-2020, 06:52 PM	#4
ibimmer954 Major 138 Rep 1,424 Posts Drives: '23 i4 M50, '15 M3, '18 911 Join Date: Jul 2007 Location: San Diego, California, USA iTrader: (0) Garage List 2015 BMW M3 [9.75] 2023 BMW i4 M50 [0.00] 2018 Porsche 911 C4S [0.00] 2019 BMW X4 M40i [0.00]	The speedo will be off by about 5% even with stock wheel and tire sizes. Don't worry about it. It's like that with all BMWs. Computing 5% is easy. Take your speed, divide by 10 then divide by 2. So let's say you want to go 45. 45 -> 4 -> 2. So in order to go 45, your speedo must read 47 or 48. For 70: 70 -> 7 -> 3. So, actual 70 is 73 - 74.
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