Can we talk speedo calibration???

[Grumpy Bear]

1 hour ago, Mawz said:

Little bit of both I’d expect.

Tires will expand a little as they heat up, percentage error will grow to being noticeable as the speed goes up. 

Percentage error is fairly easy to check. If you’re seeing 1mph off at 60mph, flip to KM/H and see if you see 1KM/h at 60KM/H. If you do, your issue is primarily percentage and can be tuned out via calibration. If you don’t, it’s probably a mix of heat-induced growth and percentage error.

The resolution of the speedometer is higher in KM/H because the units are smaller and it’s limited to 1mph or 1KM/h as the minimum it can display.

 

Radial tires do not grow. Bias ply tires will grow. Is the OP using bias ply tires? 

 

Mickey Thompson Tires & Wheels – UNDISPUTED. ... Mickey Thompson slicks will grow approximately 1 to 1-1/2 @ 150mph (Note: Radial slicks do not grow).

 

https://www.motortrend.com/how-to/testing-mickey-thompson-et-street-ss-radials-2/

 

There was some concern that the 255 radials would grow with speed and come in contact with the front edge of the wheelwell opening, but the Mickey Thompson representatives told us the radial tires wouldn't grow at speed like our bias-ply slicks.

[mikeyk101]

8 hours ago, Grumpy Bear said:

 

Radial tires do not grow. Bias ply tires will grow. Is the OP using bias ply tires? 

 

Mickey Thompson Tires & Wheels – UNDISPUTED. ... Mickey Thompson slicks will grow approximately 1 to 1-1/2 @ 150mph (Note: Radial slicks do not grow).

 

https://www.motortrend.com/how-to/testing-mickey-thompson-et-street-ss-radials-2/

 

There was some concern that the 255 radials would grow with speed and come in contact with the front edge of the wheelwell opening, but the Mickey Thompson representatives told us the radial tires wouldn't grow at speed like our bias-ply slicks.

No, I have the radial tires. And now that you bring up the bias ply, you jogged my old brain and that is probably what I was thinking of. Getting older isn't for the weak...

[Grumpy Bear]

19 minutes ago, mikeyk101 said:

No, I have the radial tires. And now that you bring up the bias ply, you jogged my old brain and that is probably what I was thinking of. Getting older isn't for the weak...

I'm right there with ya partner.  

[mikeyk101]

I just wanted to add an update. I did end up bumping the pressure up on my tires. I am now running 40-41psi and actually like it. The speedo is still agreeing with the GPS speeds on Waze so that's good. I does feel a bit firmer and I seem to feel bumps and road defects a little bit more but not jarring. The biggest improvement though is in tracking while driving down the road. Before when I was running a lower pressure, it seemed to always want to wander a bit and I found myself constantly doing small corrections. Now, it just drives straight forwards with practically no effort. A much more positive feeling. 

 

Not real sure that much has changed on shifting but seems to be doing what it's supposed to. Mpg has increased as well. Not dramatic but I have noticed it and that was expected as it is now reporting actual mileage instead of less miles traveled over same distance. I had also done the trans thermostat pill flip some time ago which helped lower my transmission temps. It still seemed to be a bit higher than what others had experienced. A check on this today while running about 70mph down highway in 82⁰ temps had me in the 158-162⁰ range. It seems that this is just a bit more of a drop than before the speedo correction. Could be just my imagination, not sure. Either way, still much better than 190⁰+ I had before the pill flip. 

 

Still very happy with my 5+ year old truck and looking forward to many more years of enjoyment...