OK so I took my car in to the dealership today to get the speedometer calibrated. These people are helpless. Their equipment can only change to factory-approved options. I'm calling around to speed shops to see if someone can do this.
A while ago I put 245/50 R16 tires on the car. The stock ones were 235/55's of course, and I have 3.42's. So I'm thinking that to calculate the new gear ratio I need to take the new tire size (245*.5 = 122.5) and the old tire size (235*.55 - 129.25) and then divide them (129.25/122.5 = 1.055) which means the new tires are making the speedometer 5.5% faster than it should be. So then, if I take 3.42*1.055 = 3.608 which would make my new gear ratio 3.61 to correct the speedometer. I have verified that the speedometer is indeed about 5% off by timing myself against mile markers.
So, can HP Tuners or the Hypertech programmer actually allow you to input a calculated gear ratio like this? Or does the car's computer only give you options to select from?
A while ago I put 245/50 R16 tires on the car. The stock ones were 235/55's of course, and I have 3.42's. So I'm thinking that to calculate the new gear ratio I need to take the new tire size (245*.5 = 122.5) and the old tire size (235*.55 - 129.25) and then divide them (129.25/122.5 = 1.055) which means the new tires are making the speedometer 5.5% faster than it should be. So then, if I take 3.42*1.055 = 3.608 which would make my new gear ratio 3.61 to correct the speedometer. I have verified that the speedometer is indeed about 5% off by timing myself against mile markers.
So, can HP Tuners or the Hypertech programmer actually allow you to input a calculated gear ratio like this? Or does the car's computer only give you options to select from?
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