Speedo correction and tire size changes

[ajpturbo]

Just curious if there is a way to adjust the speedo if you make wheel and tire changes or in my case installed an STI gauge cluster? Normally changes can be made with tuning software as in my civic and mustang. I have my WRX tuned by opensource with romraider and I can't find and area that has revs per mile to compensate for larger or smaller tires.

It's not much but my STI cluster reads about 4mph high as verified by GPS and radar. I have OEM tires on my WRX, putting STI diameter tires may do the trick. But most new cars' clusters are electronic so changes are made with the flash.

Does the WRX have a speedo gear in the tranny?

[Sasquatch]

You might find this useful: Tire size calculator

[ajpturbo]

I know how to determine the size and diameter of tires and wheels. What I'm asking is if there is a way to adjust the speedo via tuning like older and newer cars do. It's fairly common.

[Donkey]

Not with Subaru's. The calibration is not in the ECU but the actual gauge cluster itself.

[ajpturbo]

So everyone that changes tire and wheel sizes just has to live with their speedos being off? Seems dumb.

[jgardiner]

Just like the old days when it was a gear in the transmission.

[DemonWRX]

There must be some way of correcting the calibration, and it should not take ripping the whole dash apart... though you may have to ask a dealer how it is done. Even with the old 'gear in tranny' setups there was a way (some you had to put an adapter inline, some you had to swap cables, but it could be done).

[Donkey]

There must be some way of correcting the calibration, and it should not take ripping the whole dash apart... though you may have to ask a dealer how it is done. Even with the old 'gear in tranny' setups there was a way (some you had to put an adapter inline, some you had to swap cables, but it could be done).

Sure. You guys go to Google and type in "speedometer calibration" then schedule an appointment with the closest shop. It's not impossible,it's just not happening through Opensource. The signal is split from the VSS signal between the ECU and the gauge cluster. You can probably change what the ECU perceives as the actual speed but not the speedometer.

[TreMoto]

Sure. You guys go to Google and type in "speedometer calibration" then schedule an appointment with the closest shop. It's not impossible,it's just not happening through Opensource. The signal is split from the VSS signal between the ECU and the gauge cluster. You can probably change what the ECU perceives as the actual speed but not the speedometer.

FROM Calibrating Speedometer WRX-->STI cluster - NASIOC

"I've done a couple cluster swaps (non Subaru related) that needed speedo calibration, and I've used this tool a lot:

HealTech Electronics Ltd. - Makers of the SpeedoHealer, GIpro, X-TRE, FI Tuner Pro, Brake Light Pro, MM5, OBD Tool

It's meant for bikes but it works great for cars too. This unit go inline with your speedometer signal wire and gives you the ability to change the output signal to the speedometer display. All you really do is bring a GPS and drive around, and then using the Speedohealer, adjust the signal till the speedometer matches the GPS speedometer display."

[Donkey]

I have used this: Universal Speedometer Signal Interface
But most speedo shops generally charged bewten $50-100 to recalibrate the factory system.

[MainFrame]

You can adjust the needle on the gauge itself, or change the size of the speedo gear in the transmission. For what it's worth, just about every car I know of reads about 4-6mph high.. although with the gearing, wheel, and tire changes to my car it actually reads low by 5-10mph depending on how fast you're going.