Speedometer recalibration device

[ttrainxl]

Surely this has been thought of before, but could a device like a Guino or something be used to make your speedometer read properly with different tire sizes? The signal from the VSS is calculated for the stock tire size(right?), but could that signal be tapped into, put into a calculation for a different rolling diameter using a factor or multiplier, and have the Guino spit out a different number or signal to adjust the speedometer to the new tire size?

Reading the calibration instructions for the MPGuino, it seems this same thing could be done on the VSS to adjust the speedometer. It’s coding and factors or multipliers, yes?

Why isn’t this a more popular thing?

[Gasoline Fumes]

I assume it's possible. I even have an Arduino in my car already. If I knew how to write code, I would give it a try. My current tires are 8% too big.

[Piotrsko]

Most use an electronic sensor and no longer use a cable. There are provisions to easily change that pulse count using an obd style device to query the table or modify the factors with no coding involved.

[ttrainxl]

I want someone to make one of these devices where you can plug in your tire size and it calculates the difference, comes up with the correct factor, and either alters the VSS pulse or some other how causes the speedometer to read correctly.

[freebeard]

Tiny trianglar bits of tape manually stuck to the face of the speedo?

[Gasoline Fumes]

Originally Posted by ttrainxl

I want someone to make one of these devices where you can plug in your tire size and it calculates the difference, comes up with the correct factor, and either alters the VSS pulse or some other how causes the speedometer to read correctly.

The first part is easy!
https://tiresize.com/comparison/

[Piotrsko]

Divide by 3.59* then multiply by 5.87* is kinda hard to do in software without a math processor

* random numbers chosen for illustration

[ttrainxl]

Originally Posted by Gasoline Fumes

The first part is easy!
https://tiresize.com/comparison/

Yeah calculating tire size is easy. I can do that with a calculator. Making my speedometer read correctly is above my pay grade.

[Ecky]

There are dozens of off the shelf components you can use for this. Dakota Digital makes a few that are reasonably priced, and reliable, in exchange for how primitive they are to set up (switches, and some degree of trial and error). You can do this with an Arduino as well, and the code exists floating around the web. I may even have it in my vault. There is typically a small lag between input and output, as you need to buffer the input signal (do a rolling count over a period of time) before generating the output signal. You might find a more clever way to achieve this.

[ttrainxl]

What I’m saying is, I’m not tech savvy and know nothing about coding or what parts are what. I don’t even really know what an Arduino is. I am not the person to do this.