New truck tires question

[Bondo]

Re: New truck tires question

I just go out on the Intersate,+ Drive 60mph,+ See How Long It Takes..........Time It.....<br /><br />Is it a Mile a Minute, Or Not.......<br /><br />I Think that 235/80/16s are Stock,.......<br /><br />Your New tires Aren't Much Different,... in Diameter.......

 

[NathanY]

Re: New truck tires question

My 02 came stock with 245/75/R16 and now I have 265/75/R16's on it. I can tell you first hand there is no difference in the way that it drives, stops, or any difference in speedo. I have a GPS mounted on the dash and it is within 1 mph of speedo. Here is a pic of the truck with the 265's on it.<br /><br />

 

[Grant S]

Re: New truck tires question

I've done the same as you, I ran a tape measure around the circumference and noted the difference which in my case was less half an inch. If you go up a size in width, sometimes a size down in profile, from say 65 to 60 can bring the rolling circumference back within range.

 

[MrBill]

Re: New truck tires question

The second number 70 or 75 is not a measurement in inches, centimeters or milimeters...its the ratio of height to width, such as 70% as tall, as wide. The '70' has a lower profile, 50 or 60 would have an even lower profile. Somewhere, buried in this thread someone might have also mentioned this, sorry I didn't have time to read all after seeing one person mention that the second number was a mesurement in MM's.

 

[QC]

Re: New truck tires question

Grant S is right. Sometimes they will be close to equal, but absolutely tire size changes these things.<br /><br />The ABS thing is starting to make more sense to me now as the ECU would make a calculation based on what speed it should be going, if the calc speed and actual were dramatically different it could think there was slippage all of the time . . .<br /><br />Nate, I checked your tires with dollupers' calculator which illustrates this perfectly. You are 3.9% faster with the new tires at the same RPM. Your speedo now probably reads 1 mph slower than actual, it probaly read about 2 mph faster than actual before. I definitely trust your GPS waaay before I trust your speedo.

 

[dolluper]

Re: New truck tires question

If you really want to go crazy over this change your tire pressures it will also effect your speedo reading When I worked for the highways dept we recalibrated police car speedo's in the 70's, what a pain in the a$$ it was. We had a 2 mile test track and it was marked in feet before and after dead on. We would come back with the cal's and figger the right amount of teeth to change speedo gear in trannie. For a joke on other mec's doing this we would pump the tires up 10 lbs over after the run was complete and gear changed, then laugh are heads off when they went out to recheck it They always came back not right and the guy doing it was so pi$$ed It was mean but awful funny

 

[JamesCoste]

Re: New truck tires question

I'm a little worried about something. The truck rides smoothly; however, from about 37 mph to 41 mph the truck vibrates or "pulses" a little. I'm wondering if the ABS is activating causing the "pulse". At any other speed it is fine. I've only driven the truck with these new tires a couple days, so I'll give it time to see.<br /><br />I might take my truck by discount tires to let them test drive it and get their opinion. I'm surprised that they don't have an after market tuner that they use for customers who change tire sizes.

 

[JamesCoste]

Re: New truck tires question

Originally posted by Nate in AR:<br /> My 02 came stock with 245/75/R16 and now I have 265/75/R16's on it. I can tell you first hand there is no difference in the way that it drives, stops, or any difference in speedo. I have a GPS mounted on the dash and it is within 1 mph of speedo. Here is a pic of the truck with the 265's on it.<br /><br />

That is comforting to know. Thanks for posting. I noticed your truck is 4x4. I wonder if the stock tire is larger on it because it is 4x4. I should have looked, but I think my stock tire was 235.

 

[dolluper]

Re: New truck tires question

The 37 -41mph thing is probably the trannie haunting between lock-up OD going in and out ,when you increase speed it's ok it's locked in and it's smooth ,below say 35 it's smooth

 

[ae708]

Re: New truck tires question

If you don't have a GPS then drive a measured mile at a steady speed and divide the elapsed time in seconds into 3600 to get your true speed.

 

[JamesCoste]

Re: New truck tires question

Originally posted by dolluper:<br /> The 37 -41mph thing is probably the trannie haunting between lock-up OD going in and out ,when you increase speed it's ok it's locked in and it's smooth ,below say 35 it's smooth

Is that bad? Will that behavior tear up my trannie?

 

[JamesCoste]

Re: New truck tires question

Originally posted by ae708:<br /> If you don't have a GPS then drive a measured mile at a steady speed and divide the elapsed time in seconds into 3600 to get your true speed.

I was going to get my wife in her car and drive next to me. Once she sets her cruise control to 60, I'll record my speed, then 65, etc.

 

[QC]

Re: New truck tires question

How do you know that your wife's speedo is right?

 

[one more cast]

Re: New truck tires question

I put new tires on my '02 silverado last fall and was going to go with 265's and the tire guy at sams advised my against it. He said it could mess up to much stuff that was computer controlled. I don't know how much those guys really know about it but I stayed with the factory size.

 

[dolluper]

Re: New truck tires question

At 50,000 miles it's about time to change your trannie fuild and filter as just maintenance the haunting is pretty much normal for GM's at that speed you either go below or above offend hard in traffic to do it What happens is with the electrical pluses from the computer to the PWM [pluse width modulation] solinoid the torque convertor goes into lock-up mode then by backing off or speeding up the pluses are up and down it goes in lock-up and out of lock-up[haunting] If it gets real real bad the solinoid would be a good choice in checking,if in for a fuild change+filter it's easy to check and a good time to check it PWM sets code p1860 tcc solinoid sets p1864