What is acceptable % error?
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What is acceptable % error?
When selecting tires for a car that are a different size then stock, there are several Tire Size Calculator sites that will compare the sizes for you. One of the factors that they compare are the differences in speedometer readings when a tire is a different diameter then stock. These are either a plus or minus reading. What is the greatest difference that is generally acceptable? What else is affected other then speedo and odometer readings?
AudiWorld Super User
Joined: Mar 2000
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From: Gainesville, FL
what size do you have now, and what are changing to?
Usually all plus one set ups are a little bit off, but not a big deal. Most go from a 16" rim with 205/55 tires (24.88 inches) to 17" with 225/45 tires (24.97 inches). If you are only off by a couple %, it should be fine. Remember, if the difference is 4%, that means you will only be off by 4mph at 100 mph, and only 2mph at 50mph.
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if you go with a smaller than normal size tire... you lose in terms of..
speedometer changes.. this would be a (-) and if you add it would become (+). What it all boils down to.. is changing the size of tires and wheels
and by doing this you must realize that this is progressive. so the faster you drive... with a larger tire.. the faster your car is actually going.. and your speedometer will be unable to match the speed. and vice versa for a smaller tire and wheel diameter.. the faster you go... the slower your car... your speedometer will probably show.. (ex.65 mph when your car is really going at 59)
and by doing this you must realize that this is progressive. so the faster you drive... with a larger tire.. the faster your car is actually going.. and your speedometer will be unable to match the speed. and vice versa for a smaller tire and wheel diameter.. the faster you go... the slower your car... your speedometer will probably show.. (ex.65 mph when your car is really going at 59)
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sort of depends...
Automatics seem to develop messed up shifting points when the tire diameter is different from stock. I have a manual A4 but our RAM is an auto and I went from 265/75x16 to 285/75x16 (which is a little under 4%) the shifting was clearly off under part throttle until we had the ECU recalibrated for the larger tires. Dodge RAM allows for that size change because the samebase vehicle can have a wide range of tire sizes from the factory, and larger aftermarket tires are pretty common. I am not sure if the A4 ECU allows an such recalibration...
Otherwise I would say <2% difference shouldnt be noticable other than some speedo error.
Otherwise I would say <2% difference shouldnt be noticable other than some speedo error.
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