RC Speedometer Calibration Module issues

[romclean1]

Has anyone else had issues with using the Rough Country Speedometer Calibration module on a truck with Adaptive Cruise?  I just went to a larger tire and wanted to correct the speedometer reading. Driving at 30 it's off by 1 mph, at 40 its a bit more, at 60+ its closer to 3+ish or more.   The RC device (hypertech) does correct the calibration which is great, but when I turn on cruise things get weird.  If I'm truckin along at 65 on the highway and set cruise, the truck holds at 65 for few seconds and then accelerates to 69-71 and then pulls back and slows to 65.   Thats about the same amount the speedometer would have been off, + or - a mile or two.

 

RC support is was great and is looking into the issue, just curious if anyone else has had similar behavior especially if you have adaptive cruise.  The software has a specific entry for 2020 w/adaptive, which makes me think there is a difference in the programming.  

 

 

 

 

[romclean1]

Well it's been a week or more and no answers from Rough Country,  they've stopped replying to voicemails - disappointing.  I did try calling Hypertech who actually makes the module and they said RC had to provide support - but did give me a tip on changing settings by a fraction to "change up the math".  I was able to tweak settings to find a reasonable middle ground between speedometer calibration and cruise working, but what's the point if it's not 100% accurate -  so it's return/refund time.    I think this can probably work with the right update, but I'd recommend buying it from Hypertech vs RC, so you can skip the middleman and go directly to the manufacturer.

 

[TNAT4]

I had the same exact problem.  At first I thought it was my pedal commander interfering but when I took off the RC correction module the problem resolved.  I've not put it back on.  

[romclean1]

5 hours ago, TNAT4 said:

I had the same exact problem.  At first I thought it was my pedal commander interfering but when I took off the RC correction module the problem resolved.  I've not put it back on.  

So I think I’ve cracked it.  I modified the tire size to .2” difference and I’ve got speedometer reading maybe 1/2 mph faster than gps and adaptive cruise working with no issues at the right speed including following, slowing and then accelerating again all on it’s own smoothly. 
 

the software could use some polishing but overall this works.  

Edited December 22, 2020 by romclean1

[TNAT4]

1 minute ago, romclean1 said:

So I think I’ve cracked it.  I modified the tire size to .2” difference and I’ve got speedometer reading maybe 1/2 mph faster than gps and adaptive cruise working with no issues at the right speed including following, slowing and then accelerating again all on it’s own smoothly. 
 

the software could use some polishing but overall this works.  

So did you just do trial and error on tire size until it worked?  

[romclean1]

1 hour ago, TNAT4 said:

So did you just do trial and error on tire size until it worked?  

Yes, I only needed a fractional change in values to correct it.  I went from 275/60/R20 (32.9” in my particular case) to a larger 285/65/R20 (34.6” BFGs).  I changed that to 34.75” and I think it’s right on target.  (1.048 vs 1.054 or something like that) Speedometer is about 1/2 mph faster than actual speed, a tad over is better than a low reading in my book, cruise works as expected.  

[TNAT4]

Sounds good, I'll try again.  I had just given up on it.  

[romclean1]

Sounds good, I'll try again.  I had just given up on it.  

You can tell you hit the sweet spot when adaptive cruise is suddenly back to normal.


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[TNAT4]

12 hours ago, romclean1 said:

You can tell you hit the sweet spot when adaptive cruise is suddenly back to normal.


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I actually have 285/65/20 BFGs on my truck but I instead measured the tire size (they recommended that vs. entering the measurements).  We'll see how it goes