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2005 gmc envoy_sle_xl
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Discussion Starter · #1 ·
Does anyone know what the highest change in tire size is before you have to reaclibrate the speedo? I'm looking to get some new tires for my stock 2005 rims. I want to possibly go a little bigger, but was wondering what people have gotten away with and not had to change any settings with the speedo?
 

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2007 gmc
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159 Posts
Does anyone know what the highest change in tire size is before you have to reaclibrate the speedo? I'm looking to get some new tires for my stock 2005 rims. I want to possibly go a little bigger, but was wondering what people have gotten away with and not had to change any settings with the speedo?
Up to you and what you want to deal with. I have a guy that increased tire height 7" and is dealing with the speedo being off for a while. I recalibrated his speedo but the ABS module was freaking out because of the drastic tire change. Currently looking for access to a GM Tech2 to adjust the ABS module then I will go back and recalibrate his speedo again. He is currently driving off a gps.
 

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2005 chevy trailblazer_ls
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916 Posts
Does anyone know what the highest change in tire size is before you have to reaclibrate the speedo? I'm looking to get some new tires for my stock 2005 rims. I want to possibly go a little bigger, but was wondering what people have gotten away with and not had to change any settings with the speedo?
I went from 245/70/16 to 245/75/16. Tire diameter increased one inch. The speedometer is off about 1.1 mph at 60 (speedo = 60, actual is 61.1). I calculated this over a one-hundred mile drive on an open road and confirmed it with my GPS.
 

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2005 gmc envoy_sle_xl
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Discussion Starter · #6 ·
that's not so bad only 1.1mph, if you have a gps then i'm sure it's fine since you have the speedometer on there, but my question is, how does a GPS speedo make a different measurment tehn your actual spedometer? Does it measure tire speed differently???
 

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2003 gmc envoy_slt
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7,190 Posts
A Global Position Sensor doesn't know if you even have wheels. It could be boat, plane, even walking. It gets the speed that the GPS unit is moving, on a global position, from satellite.
 

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2005 chevy trailblazer_ls
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that's not so bad only 1.1mph, if you have a gps then i'm sure it's fine since you have the speedometer on there, but my question is, how does a GPS speedo make a different measurment tehn your actual spedometer? Does it measure tire speed differently???
Actually, the GPS I use is not part of the vehicle. It's a Garmin nuvi 760. The unit receives a signal from at least four Satellites in low earth orbit. The position of the vehicle is constantly recalculated, giving direction of travel, speed, distance and elevation. This information is updated every second.
 

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:iagree:. At 100K miles actually driven, your odometer would read 110K. It's a personal decision wether this is accepable or not. I plan on getting a PCMForLess in a couple of months, I will have it calibrated for my tires.

An interesting observation I've had in the past couple of months is that rental cars seem to be set to read about 1% faster than actual speed. I've had three GM loaners (2009 TB, 2010 Caprice & 2009 Envoy) since June 1st and all three have been off the same amount. The vehicles all came from the same dealer/rental company. I wonder if they're trying to slow down the drivers and prevent accidents. :weird:
 

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2003 gmc envoy_slt
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:iagree:. At 100K miles actually driven, your odometer would read 110K. It's a personal decision wether this is accepable or not. I plan on getting a PCMForLess in a couple of months, I will have it calibrated for my tires.

An interesting observation I've had in the past couple of months is that rental cars seem to be set to read about 1% faster than actual speed. I've had three GM loaners (2009 TB, 2010 Caprice & 2009 Envoy) since June 1st and all three have been off the same amount. The vehicles all came from the same dealer/rental company. I wonder if they're trying to slow down the drivers and prevent accidents. :weird:
That's probably why. However if that was/is being done here in the states, they would be breaking federal laws on falsifying odometer readings.
 
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