yea you can. we wont tell

 

Using cell phones and following the wife in the car, using cruise, the results are

38 MPH in the Blazer = 35 MPH
77 MPH in the Blazer = 70 MPH

Is there a difference in between truck and car tires, even though they are P235/70R15s? In other words, are truck tires (ATs)taller than car tires of the same size? The Blazer has car tires on it. Its a 99 LT 4x4. The tires on the Blazer matches the door sticker and RPO code. The RPO code doesn't specify car or truck tire.

 

now if you were REALLY Smart....
What is the air speed velocity of an unladen swallow?

[8D]

 

This would average out to be around a 9% difference in the speedometer if your measuring devices are accurate enough. Even if the vehicle were setup for 235/75R15 tires, that would only represent a ~3% difference to drop to 235/70R15. If someone had had the tire sized changed for 31" tires, then the difference dropping down to the 235/70R15 tires would be ~7%. ~10% for a correction factor to 32" tires and dropping back to 235/70R15

As far as the difference between a LT235/70R15 and a P235/70R15, no, ideally speaking, there is no difference as the number represent the width, aspect ratio, and the rim diameter. The difference is in the construction. An LT tire is generally much heavier in construction with more plies on both the tread and sidewall areas to handle higher loads. As a result, the LT tire may have a larger loaded diameter because one may be less likely to squat under load.

 

Thanks guys!!!!

 

Doesn't this also make the odometer incorrect such as make the odometer show more miles on the truck than what it really has??????

 

What are you talking about? Right now, if your speedometer is off, so is your odometer.

 

The point is, odo reflects more miles than what is actually on the truck. GM dealer service manual says replace the IP. I had forgotten about the speedo issue I had with an 04 Silverado Z71. IP was replaced and it fixed the issue.

 

You have two things at work here. Speedo is fast and ODO is climbing at a faster rate. Both of these could be caused by an improperly input tire diameter or gear ratio.