mikeyk101

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...

Interesting, and surprisingly that makes a lot of sense. I have heard about that before but didn't realize the correlation to the speedo error. Seems to me I have heard that happening with trailer tires as well. And I know it's a bit on extremes but you can see that happen with drag cars when they rev up to warm up the tires at the beginning of the run.

Well I broke down and ordered the Rough Country calibrator. I know the HP tuners were the recommended choice, I just decided to try the cheaper option first and figured I could always send it back if it didn't work. It came Saturday and I got a chance to play around with it. And I also discovered something interesting. So the truck came stock with 275/55R20 tires. Back in December like I mentioned, I switched out to 275/60R20 Falken Wildpeak AT3W tires. The specs for a 275/55R20 are listed as being 31.9" and the 275/60R20 are supposed to be 33" and Falken specifically says the Wildpeaks are supposed to be 33.1". I found out this is not the case. I run the tires right around 36-37psi. The OEM Goodyear Wrangler SRA tires also were max cold 51psi and I ran those at 35psi. With the 275/55 OEM, the speedo seemed to be correct but when I switched to the Falkens, the speedo was showing slower. So since both the Falkens and OEM Goodyears had max cold psi of 51, I figured they should be filled around the same. So playing with The RC calibrator, I first tried using the wheel size 33.0. I found that the speedo would now show me going faster than I was by a couple mph. So I then tried using 32.75. It still showed fast. I then tried 32.50 and it was better but still fast as I went at higher speeds. I decided to take a tape measure to one of the tires and I was surprised when it measured right at 32". I gave 32.25 a try as well and it was seemed to be right on but as speeds got around 60, it would be off by 1mph. So my final adjustment, I set the tire size at 32.0. This gave me the correct speed at both lower and higher speeds. So my speedo now gives me the correct speed and this was my original goal and I'm happy about that. But now I'm a bit confused. If the stock tire is supposed to be 31.9" and the Falkens are supposed to be 33.1", but in reality, the Falkens measure out at only 32", I don't understand why the speedo should have been off by several mph at higher speeds with the new tires. It makes me wonder what the actual height of the OEM sized tires were when running 35psi. I'm taking a wild guess that with original speedo calibration, it is calibrated for a shorter height than 31.9". How is the actual height of tires measured? Is it measured before a tire is mounted or is it measured after mounted on the rim at max psi? I'm guessing that when installed on truck and taken off jack, the weight of the truck will come into play and cause some loss in height but its interesting that a tire that is reported as being a 33.1" is actually just slightly more than an inch shorter. I'm wondering if I should try bumping the pressure up to maybe 44-45psi and re-measure the height. I'm just concerned that 1) this might be a rougher ride, and 2) I might end up wearing out the center of the tire too quickly. Thoughts???

Is your speedometer correct or does it read slower than you are traveling?

I only slightly increased from the 275/55R20 to 275/60R20 Falken Wildpeaks last December which I'm happy with. I dont know if I could justify regearing for that slight amount of increase. I really have no intention of doing a lift. I did do a 2" level and that has already caused me some grief while using a Equal-Izer weight distribution hitch for towing my camper. I did go through the setup and according to the directions and CAT scale weights, it was properly setup but I had too much sag in the rear. It would have been perfect if I didnt have the level, it was spot on but night driving, I was blinding oncoming traffic. Using AirLift 5000 bags, I corrected the problem. Because I plan on continuing to tow, doing a lift will cause even more problems. i'm set the way I want. I just need to get the Speedo recalibrated to match my true speed as it reads slower than I am going.

So over time, I've seen many threads about larger tires, lower mpg, trans issues, etc... And they all seem to link together. So you add larger tires, speedo reads slower as does odometer, causing you to think you have reduced mpg, and the trans will shift based on the oem tire/wheel combination which might no longer be ideal for current setup. And I wonder if this may also be causing some of the many trans issues I keep seeing. I see one solution that seems to work is to use the Rough Country Speedometer Calibrator 90009 which seems to handle reprogramming the speedo and odo, as well as correct shift points which would seem to make the trans work better. It is also said that it will help correct ESC problems that may occur because of modding. I have not been able to find very much info and would like to hear experiences from those that have used this calibrator. My main concern though would be that because of how it works, there will be traces of its use when linked up to a dealers diagnostic equipment. I saw that Rough Country does recommend that users use the calibrator to return the truck back to stock prior to bringing the truck in for service. And even going back to stock, it will still show that there has been some kind of modification done. I still have a couple years and about 60,000 miles left on my service plan. I guess I am being a bit of a wuss and am just concerned about something getting denied as a result of it. Is there a possibility that the dealer could perform some kind of recalibration? If not, I would still consider taking a gamble on the RC speedo calibrator. I know there are other tuners I could probably use that add a lot more choices but at a greater expense. I'm not really interested in getting that deep into tuning, just the speedo correction and trans shifting would be enough.

I will agree with others that the blind spot mirrors on the tow mirrors are a "HUGE" upgrade. The little circle on the stock driver's mirror is kind of a joke. The tow mirror blind spot mirrors are actually very usable, provide significantly more coverage, and make a big difference. The regular mirror is also much larger and easier to use. I feel way more comfortable and safe having tow mirrors attached. Oh, and when towing the 25' camper, they work a lot better. Even though mine didn't come with the complete "tow package", it came with a hitch receiver, a 4 and 7 pin hookup, as well as the locking rear differential with 3.42 gears. Since GM goes that far to provide a truck that is able to tow, I don't understand why the tow mirrors weren't installed at the factory. I can understand leaving the brake controller off as there are many aftermarket choices and the ability to do a plug and play install but no tow mirrors is a significant fail...

Youre on the right track. Because larger tires are on, the speedometer would need to be corrected in order to display your true speed. What you may not have noticed is that your speedometer will read a bit slower than the speed you are actually traveling. You can verify this by using the speed function on a portable GPS or something like Google Maps on your phone. So now you have to realize that you are traveling the same distances as before, using the same amount of gas, but your speedometer and odometer will be reading less miles traveled. Hence, you will see a reduction on your mpg. I would bet that you are still getting the same mpg as before, you are just using methods that are now in error. You either have to get your speedometer recalibrated or start using another method such as miles traveled as reported by a portable GPS to calculate your actual mpg.

When you check pressure in other tires, do they match on your hand held gauge?

Check with your dealer as there may be a recall. I had same thing on my 2016. Before I actually had a problem, while having one of the oil changes done, they did a software upgrade. Later, I had the problem anyway and they replaced the vacuum booster pump. @mjm-1957 has the correct answer.

I know this is an old thread but... I too feel my 2016 is rather sluggish starting off as well. I remember seeing a thread or 2 about turning off the stabilitrack. I will normally turn the stabilitrac off now because of that. Just last weekend, I was messing around trying to heat up my transmission to check the fluid level. I had the parking brake on and pressing hard down on the brake pedal with truck in gear. I noticed that rpms stayed low, maybe under 2k??? So I turned off the stabilitrac and pushed down on accelerator pedal and now it was trying to launch and much higher rpms. With stabilitrac off in traffic, I notice that it gets up and moves out much quicker. And this is without a tune.

Thats kind of what I was worried about. I'm really not interested in diving into all kinds of wiring in the cab. If that's the case, and you're probably right, the only choices I have are to just deal with it or to find a constant 12v supply and wire it up and a switch in the bed to activate the topper interior light. That would probably be the easier way to go.

A while back I swapped out the regular mirrors for some OEM tow mirrors as I have a camper trailer that I travel with. Thanks to the wiring harness I purchased from @pgamboa, it went pretty smooth. As part of the order, optional resistors were included that I could install to have the rear facing lights activate when in reverse. That wasn't a big deal for me so I didn't use them. I found out it's just as easy to hit the cargo light switch and they will stay on while reversing. On my setup, I also have a topper so the cargo lamp is pretty useless but the interior light for my topper is wired into the cargo light circuit via the bed lights. There are occasions where I'm out in the back country at night, I have to get something out of the bed. So I will activate the cargo lamps and get out. But as soon as I do, the rear facing mirror flood lights will kill my night vision. And same after coming from the bed back to driver's seat. TL;DR... So has anyone come up with a way to turn off the mirror flood lights so they don't always activate with cargo lamp switch? I do like them and they serve a purpose so I don't want to completely kill the feature. I just want to be able to have more control over it.

I will be heading down to the Smokey mountains tomorrow pulling my toyhauler travel trailer so I will be able to do some experimenting...

Turns out I had to change the value under Equation. After checking, I originally tried A*(9/5)-58 after reading it as a suggestion in a torque forum. That got me closer but values were still too low. I found another answer that said to use A*(9/5)-40. After changing to this, the Method 1 showed the same numbers for trans temp as the DIC. So looks like I am golden now. Here is screen shot showing temps after letting the OBD2 connect and just starting the truck...

So after you suggested this, I looked in the settings and found a "Manage extra PIDs/Sensors. Looking deeper, I did find some GM specific choices. When checking them, they were setup to display value in C⁰ and not F⁰. I did change the value to ⁰F but the readings still seem to be in Celsius still so I will have to do some more research on this. There were 3 different Transmission Temp choices listed, Method 1, Method 2, and Method 3. I added all 3. Method 1 and 2 both showed up but Method 3 was blank. Not sure why but I end up with different temps on each. At least I'm headed in the right direction. Thanks

So I was able to pick up an OBD2 splitter cable. I have both the Range AFM delete and the BAFX OBD2 reader with live sensor data. Both are urged in now and both seem to work. I am using the Torque Pro app for the sensor data. Surprisingly Trans temp option is not a sensor that the Torque Pro app can read. It does read the coolant temp and I can see how inaccurate the dash coolant gauge is now. It goes right up to 210⁰ and doesn't move. But watching the coolant sensor data, it shows the live temp and even though it was changing frequently, it stayed below the 210⁰ that the dash gauge was reading. Does anyone have a tip on how I can access the Trans temp other than through the DIC? Is there another Android app that might include that sensor data?

I was just the opposite of your scenario. On my 2016 w/20" rims, I had added the Rough Country spacers that gave me about a 2" level on front and matched the rear. I didn't need to change anything else out. I finally got around to changing out the tires last December and went with 275/60R20 Falken Wildpeaks. This size will give you 33". I have no rubbing at all. Then I finally picked up my 2021 Wildwood FSX Toyhauler in March. It's a 25' and even with correctly setup WDH, my sag in rear, although completely normal, put the rear too low and had my headlights pointed skyward at night. I then added the Airlift 5000 bags and air them up to just under 20lbs when towing. That seems to work just fine. When not towing, I run maybe 5-10psi and that keeps me level. So my point is a 2" spacer level should be all you need to run 33" tires.

Excellent info. Here is a site that explains what to do: https://learntorv.com/weigh-rv/

I like this idea so I want to try running my OBD2 Bluetooth scanner to see what is happening with my various temps. However, I also want to keep my Range AFM delete plugged in because I need to know the stats while running around with the Range plugged in. What are your thoughts about running an OBD2 splitter to accomplish this? I guess I could just try picking one up because they aren't very expensive but thought I would ask for opinions first.

I know on mine, I have the Range AFM disabler so it runs on all 8 all the time. I also have the "towing" package with the 3.42 rear and auto locking rear but I don't have the OEM brake controller. One thing I did notice (but may have just been my imagination or I just never paid attention) it did seem to take a longer before the water temp gauge went to the center 210⁰. It seems like it would warm up pretty quick in the past but seemed to stay just left of center a bit longer. It did finally end up on 210⁰ and stayed there. When I was towing my trailer through the grades in Arkansas and Missouri prior to the trans thermostat mod, both the water temp rose above the 210⁰ but not to the point of overheating and trans temp at times went to 220⁰ and had a hard time getting back down. On flat terrain, it would still rise especially when going through some of the smaller towns but stayed closed to 200⁰ +/-. I will be taking a camping trip next week and will finally get a chance to see how it does now.

Probably nothing. But I have OCD so little things like that tend to drive me nuts. But I found this thread on another forum that gives a decent explaination: https://www.eng-tips.com/viewthread.cfm?qid=56559

Ok, I will just pay attention to it for a little while. At least it stays below 190⁰.

So I don't actually drive a lot. Sometimes the truck gets parked for a week between trips. One thing I noticed after the mod while driving about 60 miles or so. Outside temps were around 95 and I got stuck in stop and go traffic on highway for maybe 20 miles or so. The temp on the trans went up to around 183 at highest. After traffic started moving, it finally started to drop but still stayed in the upper 160⁰- lower 170⁰ range. I did the reverse trip today. Outside temps were mid 70's. Traffic was pretty much wide open on highway. This time it still got to 173⁰ but this was cooler than last trip. I see guys reporting avg trans temps after mod of 130ish to 140ish. I'm confused why mine is running higher. It still hasn't hit 190 or higher like in the past though. The one thing that comes to mind is blocked air flow from the front causing the higher temps. I have on more than one trip ended up with a front end just plastered with bugs. This makes me think that the AC condenser and/or radiator fins may be a bit clogged. After getting to my destination, I did peek into the grille to check. I could see quite a few bugs up against the fins. I took my hose and put the nozzle on jet and tried to spray down as much as I could to try and break loose the debris. It does look better but I really can't tell if the fins are crudded up. What would be the best way to inspect and then clear out any crud from there? I know that usually it's best if you can blow or flush from behind but I really can't see any way of doing that. I'm guessing that maybe removing the grille might be a better way to get it cleaned but not really sure how to take the grill off easily. I guess I could do a search on YouTube. So does anyone have thoughts on this? Does the clogged fins sound like it may be the issue?

I did pill flip too and got caught in stop and go traffic for about 20 miles on highway in 95⁰ weather and I watched it rise. It ended up going to around 180⁰ but once traffic broke up, it went back down. I know before doing the thermostat hack, it would have been above 190⁰ and would have never dropped below that. So I guess it's a success. But I need to do some more testing in different conditions. Next week will be a big one as I will be towing my camper for first time after mod. Last time I saw temps sometimes reach almost 220⁰ but expect it won't get any where near there this time. I was going through some grades in northern Arkansas and S/E Missouri. This time will be more level heading to central Wisconsin.