Full Skinny on Hypertech In-Line Speedomoter Calibrator

I have a question. I put in 33” tire size from the stock size and speedometer is not close enough so I am going to start playing with numbers but my question is do you have to get the ratio back to stock before changing it each time?

 

I recently purchased this and here is what I had to do to program it

my previous tire was a 265/70/16 firestone dest at2 camo with 681 rotations per mile



my new tire is cooper at3 xlt 285/75/16 with 637 rotations per mile via same size as Dick Cepek 32.56 in tire






681 / 637 = scaler of 1.069 difference


I was able to modify the size of the tires to get to either a 1.059 or 1.07 scaler





I went with the 1.07 scaler as its closer to 1.069

I imagine it will show me a slightly better MPG and Speedometer should be slightly faster.

Will be installing over the weekend so I will get back and update but does this logic of measuring rotations per mile make sense? I'm open to ideas and criticism if I should be doing it another way

TIA

 

Since this thread helped me make the decision to buy and install the Hypertech module into my 09 TRD (manual trans, if it matters) after gear and tire size changes, I figure it might be a good place to log an issue to troubleshoot.

I just completed the install of the Hypertech 730107 kit, went for a test drive and speedometer and odometer functions are not working now (they were directly before). All other aspects of the gauge cluster are functioning normally -- lights, tach, warning lights, etc.

Has anyone ever had this happen with this unit, and if so, what was the resolution?

~TLDR Details~
1. It's a 2009 Tacoma TRD with a manual transmission, 4.0L engine, 4x4
2. I completed the software setup before I installed the unit, including adjustment of the vehicle model and tire and gear ratio changes
3. No issues encountered during the programming step and installation -- went exactly as the instructions noted
4. Vehicle changes I'm calibrating for: Re-geared to 4.30 from 3.727 (3.73) at the diffs, and changed tire size from a 265/70R16 (30.6" for the specific tire) to a 265/75R16 (31.7" for the specific tire)
5. All other lights and functions are operational, including all other functions of the gauge cluster from lights to temperature, tach, etc.
6. On my ScanGaugeII, it is also notable that the MPG data stopped reading upon install of the module. Upon learning of the failure, I went through the software procedure again with the same result, hence this post...

 

Just to help other people finding this thread while installing and calibrating a Hypertech. I have a 2017 with 285/75/R16 and 4.88 gears... here's what I learned while calibrating for an accurate speedometer:
- Before programming and installing it, just go and drive a stretch of highway not using cruise control while using a GPS based speedometer to see what your correction factor needs to be.
- Speedometer speed divided by GPS speed equals your correction factor if trying to have speedo display actual speed. Most vehicle speedometers actually read slightly on the high side stock.
- When using Hypertech's tire size method, the correction factor was 1.073 which read ~4km/hr higher than I was going at highway speed.
- When I checked the box for regearing and put that in as well - speed was underestimated by ~30%. You DO NOT need to select regearing on a Tacoma.
- Instead of playing around with tire height or tire XXX/XX/RXX numbers, just check the box at the bottom to use correction factor directly.
- Pick a number close to your speed-based correction factor, then adjust higher or lower based on a high speed road test.
- At 1.050 correction factor, in the city 50km/hr matches on both. When on highway speedometer reads 111km/hr when going actual speed of 110km/hr.

Also - small variations in tire circumference even on seemingly identical tires, using different tire pressures, even tire wear over time, result in slightly different revolutions per mile which makes everyone's "perfect" correction factor slightly different. Hopefully the speed-based method will save people some frustration to get to the finish line faster.

 

Thank you, this methodology helped me get mine calibrated perfectly!