Can we talk speedo calibration???

mikeyk101 · August 29, 2021

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.

bc-chris · August 29, 2021

i got the Hypertech 732501 Speedometer/Odometer Recalibration Programmer - yea... i know it's not the one you are asking about - but it worked great

before i bought it i contacted my dealership (via email) asking if it would void any warranties and they responded saying "no - it was fine to use". i made sure to hold onto that reply just in case

if you have warranty concerns i would recommend contacting your dealership and make sure you get a written reply

dieselfan1 · August 29, 2021

If your going to gamble on a rough country I think your wasting your money.

I was going to use the same one when I lifted my truck.

I never got it to work.

I went with a Superchips Flashpaq F5. Yes it leaves a footprint for the dealer to see.

It works as advertised.

Cost about $450 all said and done.

Speedo is dead nuts on. All shifts happen at a higher mph.

Idle raised up to around 675 rpm. I'm running the tow mode currently using 91-92 octane.

It definitely helps.

This setup with my exhaust probably adds maybe 20 -25 hp above 3000- 3500 rpm.

I run tow haul almost all the time too. I have to to get this big girl rolling since I'm still running the 3.42s.

I'm not ready to get into hp tuners yet but you never know.

Bash74 · August 30, 2021

I say anytime you go with bigger tires especially 35s or bigger you regear. Also just get a custom tune. Now I know you worry about the warranty but I have had warranty work done and never had a problem. The work I have had done had nothing to do with the tune or gears so it was still covered.

MikeBMW · August 30, 2021

5 hours ago, dieselfan1 said:

If your going to gamble on a rough country I think your wasting your money.

I was going to use the same one when I lifted my truck.

I never got it to work.

I went with a Superchips Flashpaq F5. Yes it leaves a footprint for the dealer to see.

It works as advertised.

Cost about $450 all said and done.

Speedo is dead nuts on. All shifts happen at a higher mph.

Idle raised up to around 675 rpm. I'm running the tow mode currently using 91-92 octane.

It definitely helps.

This setup with my exhaust probably adds maybe 20 -25 hp above 3000- 3500 rpm.

I run tow haul almost all the time too. I have to to get this big girl rolling since I'm still running the 3.42s.

I'm not ready to get into hp tuners yet but you never know.

Well, just ordered one.
Looking forward to getting the recalibation for tire size.
My $2500 Autel tablet doesn't have the ability, as far as I can tell.

mikeyk101 · August 30, 2021

1 hour ago, Bash74 said:

I say anytime you go with bigger tires especially 35s or bigger you regear. Also just get a custom tune. Now I know you worry about the warranty but I have had warranty work done and never had a problem. The work I have had done had nothing to do with the tune or gears so it was still covered.

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.

steelerdude15 · August 30, 2021

19 hours ago, mikeyk101 said:

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.

Yes, your local dealer will be able to do it, but only if you use factory sized wheels and tires. That is what my local dealer told me.

Edited August 30, 2021 by steelerdude15

lucas287 · August 31, 2021

@mikeyk101 I do all my own tuning via HP Tuners and have taken my truck in for two different powertrain warranty issues and they diagnosed/replicated the issue and fixed the problem with no questions asked. And one of those times I was too lazy to load the stock calibration back. This is ECM and TCM tuning, btw.

mikeyk101 · September 7, 2021

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???

Grumpy Bear · September 7, 2021

16 hours ago, mikeyk101 said:

How is the actual height of tires measured?

Put a paint dot on your tire and roll one revolution so that the dot leaves a mark on the pavement in two places. Measure the distance between the dots. Divide by Pi (3.14159). This is the rolling diameter.

MikeBMW · September 7, 2021

2 hours ago, Grumpy Bear said:

Put a paint dot on your tire and roll one revolution so that the dot leaves a mark on the pavement in two places. Measure the distance between the dots. Divide by Pi (3.14159). This is the rolling diameter.

Yup! With the FlashPaq, on my BFG 35s, I set it to 34.5 and achieved the proper MPH correction.
One has to do the actual measurement and not what's on the tire label.
PSI, truck weight and all that play into the factor of true diameter.
Pi times Diameter = Circumference, therefore, Circumference divided by Pi equals Diameter.

savagebob · September 8, 2021

Tires "grow" at higher speeds. That is the only explanation for greater inaccuracies at speed. More pressure will make them more stable.

We found that (on some higher power sports cars) lo profile tires would get more center tread wear with LOWER tire pressure at elevated highway speeds. That is the opposite of what is commonly agreed upon by the industry. Pumping them up to the 40s cured the center wear and stabilized the tire more.

mikeyk101 · September 8, 2021

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.

Edited September 8, 2021 by mikeyk101

Grumpy Bear · September 8, 2021

Or it could be that error is a percentage.

Look, if it's 1% off at 100 mph it has a 1 mph error. If it's 1% off at 10 mph it's 1/10 of a mph off.

Ergo the faster you go the greater the error in MPH but it is the same as a percentage of the speed.

It isn't tire growth.

:rolleyes:

Mawz · September 8, 2021

8 hours ago, Grumpy Bear said:

Or it could be that error is a percentage.

Look, if it's 1% off at 100 mph it has a 1 mph error. If it's 1% off at 10 mph it's 1/10 of a mph off.

Ergo the faster you go the greater the error in MPH but it is the same as a percentage of the speed.

It isn't tire growth.

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.