Speedometer calibration after regear

I'm sure this has been covered, but I'm using the search feature and I'm not landing the results I'm looking for.

I'm about to regear to Nitro 5.29s. How do I calibrate my speedometer?

Thanks in advance.


2019 Tacoma Off Road
285/75/17 Nitto Ridge Grapplers
OVTune 2.0

 

Don't know much about the what the setting does but I think vF Tuner does that? Someone else can chime in who has more experience. I know you can input your gear ratio and tire size.

 

Thant would be great if it does. I have the OVTune (before it was VFTune). After the regear; I'll update the tune to the appropriate 5.29.

 

Are you sure you can?

It would seem that if possible I could trick the tac to show less miles than what's real

 

Gears do not change your speedo, only tire size does. Ovtune/vfTune can not fix speedo error either.

You need one of the standalone modules mentioned earlier.

 

Right it would be, that why I questioned it

 

Interesting... I guess that makes sense though.
I think I read somewhere about the speedo being off after a regear and never thought twice about it

 

It's a common misconception, but speed is measured at the wheel using the abs sensors. The speedo correction modules also use a software backend that's generic across multiple makes and models that allows for gear based corrections, but it's an unused value for tacomas.

 

I assume you have an auto. Heard that the Hypertech/RC Calibrater's have an issue and aren't compatible with manuals.

 

Just got my own curiosity, what has changed between the current taco and a 2003 tundra I had gears swapped in? The gears made the speedometer read incorrect values (said I was going faster than I actually was).

Also, what is the point of changing gear size and tire size in vF Tuner if it doesn't change the speedometer values?

 

Older vehicles measured vehicle speed somewhere prior to the rear axle, normally at the transmission output (for 2wd's) or rear transfer case output (4wd's). This means the angular velocity needed to be corrected across the ring and pinion ratio in the axle to get the angular velocity of the wheel and then adjusted for the rolling radius of the wheel/tire. So just changing gears meant a need to correct the speedo.

Modern vehicles get vehicle speed by measuring angular velocity with wheel speed sensors. The gearing now has no effect as the speed is read directly at the wheel post all gearing. Just the rolling radius of the wheel/tire needs to be known in this type of system to get ground speed.

 

That is a fine answer indeed. Thanks for that clarification. Any chance you know the question I had regarding vF Tuner?

 

As far as I know vF doesn't do any speedo correction. I'd assume it just uses that info to adjust the engine map.

 

It isn't. The cluster (combination meter) receives a CAN message that indicates vehicle speed. I'll have to double check but 99% sure the skid control ecu puts this message on the bus.

 

@Boghog1

Ok so the meter gets both a CAN message and direct pulse line from the skid control ECU. I do not know how it uses this info. It then outputs both a direct pulse line and CAN message to other ECU's. So there's a lot of vehicle speed information flying around.

 

Probably right as it makes more sense that these speed calibration units still just work by modifying a traditional speed pulse signal.

 

I have a manual. Bought the RC calibrator when I went to 33s. No issues, works fine.

 

Regarding vfTuner, it's to adjust the shift tables for the new gears/tires.