How do you calibrate the speedo?

[J.McDonald Knives]

I will need to calibrate my speedo for the new tires and was wondering how it is done.

[decke48]

a gps? seriously i think the only way to do it is if you find someone that can do open source to remap you speedometer defaults.

[Huffer]

You can't recalibrate without messing with the speedo sensor.

Get tires/wheels that are the same overall diameter as stock or else just remember what the % difference is.

[J.McDonald Knives]

the new percentage will be 5-6%. I know that truck tires are actually a bit bigger diameter than car tires so if i kept it as car tires it would be 5.3% over stock so I'm leaning more towards 5.5% for the BFGoodrich All Terrains.

[Grafton]

i was wondering about that too, my speedo is slow even with stock tires

[Kraziken]

There's a shop local to me that specializes in this type of service. I'm going there to get some work for another one of my cars. I can ask exactly what they are doing to correct the speedo.

[J.McDonald Knives]

There's a shop local to me that specializes in this type of service. I'm going there to get some work for another one of my cars. I can ask exactly what they are doing to correct the speedo.Thanks.

[decke48]

well with a cable speedo the only way to recalibrate is to change out the gear on the output shaft.

[J.McDonald Knives]

Can someone tell me if my speedo is cable or electronic? Made 10/96. BG 2.5 DOHC

[fastenova]

It's an electronic speed sensor. The only way to change it (as far as I know) is to either A) change the output-shaft driven gear in the transmission or B) put something to intercept and change the pulses coming from the speed sensor. I'm not sure how you'd do this, probably have to build a small device with a microprocessor that changes the pulse rate.

It's easiest to just get tires/wheels that are the correct dimensions.

[J.McDonald Knives]

I'll probably just have to calculate my actual speed with the new tires. I'm wondering how much it would cost to have it calibrated.

[Kraziken]

Just got off the phone with them.

So, the way they would fix the speedo for my vehicle (Chevy) is a hypertech program. Bascially they would be flashing the ECU. Cost is $350 because of the type needed for my vehicle they don't keep in stock.

So as a related question, I asked about the Subaru. Again it seems to be some sort of flash and he said it intercepts the signal from the transmission and changing the timing., most likely, at this point he said he wasn't exactly positive because he's never had a request to calibrate a Subaru. This shop has been around for 26 years.

He said most of the speed calibration they do are for trucks. My Subaru the speedo is just a hair off at 70mph, so I probably won't bother with it.