Is this guy right?

[gmcman101]

I recently purchased a 97 gmc sierra 4x4 and the first this I noticed was the speedometer seemed to be reading a little faster than I was actually going. I took it to a chevy dealer to see if they could recalibrate the speedometer for me. After paying $35 dollars I was told I needed different size tires. The tires that are on it are 265/75/16 and they should be 245/75/16. Would this difference in size make the speedometer read 7-10 miles per hour faster? When I'm going 65 the speedometer reads close to 75. He also told me it could not be calibrated because of the year. It could only be done on newer vehicles. The vehicle also shuts down at about 98 so I'm really going around 88. Not that I drive this fast anyway but when your passing a long truck you kind of want to get around it asap.

[MT-2500]

It should be the other way around. Bigger tires should make speedometer show slower than you are going.
Is the odemeter off the same way to or just speedometer?
I would get a engine capable scanner on it and check the MPH reading in the scanner against speedometer reading.
Post back actual scanner mph reading verses speedometer reading.
MT.

[2000CAYukon]

I bought my 90 GMC K1500 Sierra new and it came with 265/75-16 tires. They are an optional size. Any GM dealer should know this.

Also, tire size is stored in the pcm and can be reflashed for tire size changes.

However, I think MT-2500 is on the right track. The dealer you went to either did not know how to reflash your 97 or they realized that something else is wrong and decided not to help you out.

The speed limiter can also be changed with reflashing; although, it should only be based on the speed rating of your tires.

//2000CAYukon

[gmcman101]

[quote=2000CAYukon]I bought my 90 GMC K1500 Sierra new and it came with 265/75-16 tires. They are an optional size. Any GM dealer should know this.

Also, tire size is stored in the pcm and can be reflashed for tire size changes.

However, I think MT-2500 is on the right track. The dealer you went to either did not know how to reflash your 97 or they realized that something else is wrong and decided not to help you out.

The speed limiter can also be changed with reflashing; although, it should only be based on the speed rating of your tires.

//2000CAYukon

The guy didn't mention anything about reflashing. Here is the actual diagnose'.
speedometer inaccurate at 60 mph 7 seconds off=9mph faster than actual speed-no programming available will need 245 x16 tires to correct.

[gmcman101]

[quote=gmcman101]

Originally Posted by 2000CAYukon

I bought my 90 GMC K1500 Sierra new and it came with 265/75-16 tires. They are an optional size. Any GM dealer should know this.

Also, tire size is stored in the pcm and can be reflashed for tire size changes.

However, I think MT-2500 is on the right track. The dealer you went to either did not know how to reflash your 97 or they realized that something else is wrong and decided not to help you out.

The speed limiter can also be changed with reflashing; although, it should only be based on the speed rating of your tires.

//2000CAYukon

The guy didn't mention anything about reflashing. Here is the actual diagnose'.
speedometer inaccurate at 60 mph 7 seconds off=9mph faster than actual speed-no programming available will need 245 x16 tires to correct.

I forgot to mention that the odometer seems to be accurate.

[gmcman101]

The guy didn't mention anything about reflashing. Here is the actual diagnose'.
speedometer inaccurate at 60 mph 7 seconds off=9mph faster than actual speed-no programming available will need 245 x16 tires to correct.
--------------------------------------------------------------------------------

I forgot to mention that the odometer seems to be accurate

[2000CAYukon]

96 and newer are OBD-II based and tire size/rear gear ratio is stored on the flash memory in the PCM. Re-programming (or re-flashing) is required to correct for tire size/gear ratio changes.

The question now is what tire size is programmed on your truck.

Here is Hypertech's website showing that they support Tire Size/Gear Changes for 97 GM Trucks

http://www.hypertech.com/gmfeaturechart.html

//2000CAYukon

[gmcman101]

Originally Posted by 2000CAYukon

96 and newer are OBD-II based and tire size/rear gear ratio is stored on the flash memory in the PCM. Re-programming (or re-flashing) is required to correct for tire size/gear ratio changes.

The question now is what tire size is programmed on your truck.

Here is Hypertech's website showing that they support Tire Size/Gear Changes for 97 GM Trucks

http://www.hypertech.com/gmfeaturechart.html

//2000CAYukon

Thanks, I'll take it to a different dealership and see what they can do. I appreciate your help.

[gmcman101]

Thanks, I'll take it to a different dealership and see what they can do. I appreciate your help.

[mikey531]

gmcman101 check this site out
http://www.1010tires.com/TireSizeCal...?action=submit

[WEF]

This is pricey but maybe cheaper than the dealer flashing plus the cost of a service call.... http://www.hypertech-inc.com/
I had one for my 95 (OBDII) Corvette mainly to adjust the speedo and turn on the cooling fans. I think it cost around $300. You can make a lot of performance type changes also but it's arguable if they are beneficial.

[gmcman101]

Originally Posted by WEF

This is pricey but maybe cheaper than the dealer flashing plus the cost of a service call.... http://www.hypertech-inc.com/
I had one for my 95 (OBDII) Corvette mainly to adjust the speedo and turn on the cooling fans. I think it cost around $300. You can make a lot of performance type changes also but it's arguable if they are beneficial.

Does the hypertech allow you to calibrate for large tires ? I called a dealership and the service guy said they can go as high as a 245-75-16. This really don't make much sense to me because some of these trucks came from the factory with 265-75-16. Could it be possible that the previous owner had large tires on it and when he got rid of it he didn't have the speedo recalibrated. According to the tire calculator the speedo should be reading a slower speed with the 265 then with the 245.

[gmcman101]

Originally Posted by WEF

This is pricey but maybe cheaper than the dealer flashing plus the cost of a service call.... http://www.hypertech-inc.com/
I had one for my 95 (OBDII) Corvette mainly to adjust the speedo and turn on the cooling fans. I think it cost around $300. You can make a lot of performance type changes also but it's arguable if they are beneficial.

Does the hypertech allow you to calibrate for large tires ? I called a dealership and the service guy said they can go as high as a 245-75-16. This really don't make much sense to me because some of these trucks came from the factory with 265-75-16. Could it be possible that the previous owner had large tires on it and when he got rid of it he didn't have the speedo recalibrated. According to the tire calculator the speedo should be reading a slower speed with the 265 then with the 245s. What else can it be, speed sensors?

[WEF]

That part of the Hypertech would probably be similar to the Vette. It will ask you the diameter of the tires and will have a number displayed that should be the stock diameter. You will then enter a higher number (in inches) to bring down the speedo reading. I used a Garmin handheld GPS to check the speed while I tried different entries until it read true.

If your engine is turning 2500 rpm with 265's and the truck is going a true 55 mph and then you put on the 245's, at the same rpm the truck will actually be going slower but the speedo will still read 55.

[gmcman101]

Originally Posted by WEF

That part of the Hypertech would probably be similar to the Vette. It will ask you the diameter of the tires and will have a number displayed that should be the stock diameter. You will then enter a higher number (in inches) to bring down the speedo reading. I used a Garmin handheld GPS to check the speed while I tried different entries until it read true.

If your engine is turning 2500 rpm with 265's and the truck is going a true 55 mph and then you put on the 245's, at the same rpm the truck will actually be going slower but the speedo will still read 55.

So do you think the hypertech power programer would be my best solution?