Speedometer vs VSS Pulses / Mile

[OptimizePrime]

My smooth brain has never heard of VSS Pulses / Mile until just recently. If you're familiar with it's purpose and calc, this won't be that interesting. If you have modified your wheel & tire size and / or changed the transmission final drive you're going to want to update this value in HPTuners so your speedometer reads correctly, RPD (if you have one) reads correctly, and what you're seeing in your logs is accurate.

In my case, I went from an F35 3.82 fd to an F23 4.17 fd along with some bougie wheels/tires and wondered why my speedometer wouldn't go past 20mph. This calculation is insanely easy.

Step 1 is to get your revs / mile. Head over to www.tiresize.com and type in your brand & size. In my case I was using 285/35/19 r888r's

Toyo Proxes R888R 285/35R19

tiresize.com

What you're looking for is the revs / mile figure. In my case it was 773

Step 2 is to take this number and multiply it by the number of teeth on your reluctor (speedometer ring on your diff). For F35's it's 85 and for F23's it's 29.

773 * 29 = 22,417 vss pulses / mile for F23
773 * 85 = 65,705 vss pulses / mile for F35

Insert this number into your vss pulses / mile input and write it to your vehicle. Your speedo is now accurate.

 

[Desert Sasqwatch]

That's for this information.

 

[Dsteinhorst]

Depending on ECU version, I think later ones have revs/mile. I believe my 09 N/A is that way.

 

[ctuinstra]

For reference, this is the '07 SS/SC.

 

[JohnK]

My smooth brain has never heard of VSS Pulses / Mile until just recently. If you're familiar with it's purpose and calc, this won't be that interesting. If you have modified your wheel & tire size and / or changed the transmission final drive you're going to want to update this value in HPTuners so your speedometer reads correctly, RPD (if you have one) reads correctly, and what you're seeing in your logs is accurate.

In my case, I went from an F35 3.82 fd to an F23 4.17 fd along with some bougie wheels/tires and wondered why my speedometer wouldn't go past 20mph. This calculation is insanely easy.

Step 1 is to get your revs / mile. Head over to www.tiresize.com and type in your brand & size. In my case I was using 285/35/19 r888r's

Toyo Proxes R888R 285/35R19

tiresize.com

What you're looking for is the revs / mile figure. In my case it was 773
View attachment 21438

Step 2 is to take this number and multiply it by the number of teeth on your reluctor (speedometer ring on your diff). For F35's it's 85 and for F23's it's 29.

773 * 29 = 22,417 vss pulses / mile for F23
773 * 85 = 65,705 vss pulses / mile for F35

Insert this number into your vss pulses / mile input and write it to your vehicle. Your speedo is now accurate.
View attachment 21439

Will this re-calibrate the odometer as well as the speedometer on an HHR SS ?

 

[OptimizePrime]

@JohnK Assuming it's just a few mph off because of wheels / tires etc and it's otherwise functional yes it should.

 

[JohnK]

@JohnK Assuming it's just a few mph off because of wheels / tires etc and it's otherwise functional yes it should.

Well, I did the F40 swap and had the speedometer recalibrated. When I noticed that the odometer still read the same as before the recalibration (1 mile recorded = 5 miles driven) I was told that the odometer requires a different calibration that the shop I was using couldn't do. Can you offer any help????

 

[Gtstorey]

Is the speedometer reading correctly now?

 

[OptimizePrime]

Well, I did the F40 swap and had the speedometer recalibrated. When I noticed that the odometer still read the same as before the recalibration (1 mile recorded = 5 miles driven) I was told that the odometer requires a different calibration that the shop I was using couldn't do. Can you offer any help????

As long as you input the correct ring gear teeth in your calculation to get the correct VSS pulses and your speed sensor works I would assume it'd work as it should. The shop just probably didn't have HPTuners or know it could do it etc.

 

[JohnK]

Is the speedometer reading correctly now?

Is the speedometer reading correctly now?

Within 1mph according to GPS.

 

[JohnK]

Thanks! I'll keep trying.

 

[Gtstorey]

I'm not sure what you could change that would be different for the odometer and speedometer. The total mileage is stored in the BCM, but I don't know which module calculates the distance. There maybe a logic test that doesn't like the data it's being fed, thinking it's to far out of what it expects. Maybe.

 

[JohnK]

I'm not sure what you could change that would be different for the odometer and speedometer. The total mileage is stored in the BCM, but I don't know which module calculates the distance. There maybe a logic test that doesn't like the data it's being fed, thinking it's to far out of what it expects. Maybe.

Maybe because it is a much lower ratio - there are 1/5 the gear teeth on the F40 as there were on the F35???? Agian, thanks for the help.

 

[Desert Sasqwatch]

Did you have the F40 transmission case drilled to have the F35 speed sensor installed. That's pretty much a requiem to get the signal corrected, then have the PCM tweaked for the F40 calibration. This information resides within the ZZP instructions from their F40 swap.

BTW, the PCM receives the speed data and communicates this to the BCM to tally up miles for the odometer.

 

[JohnK]

Did you have the F40 transmission case drilled to have the F35 speed sensor installed. That's pretty much a requiem to get the signal corrected, then have the PCM tweaked for the F40 calibration. This information resides within the ZZP instructions from their F40 swap.

BTW, the PCM receives the speed data and communicates this to the BCM to tally up miles for the odometer.

I didn't have the trans case drilled for the speed sensor - didn't know that was an option. The shop that did the swap used the ZZP conversion kit. There is a gear on the half shaft that the sensor reads (external of trans). I saw nothing in the literature that accompanied the kit about drilling the case. That sure sounds like it would have been a great fix. I'll talk to ZZP.
Again, THANKS to all for your help!!!!

 

[Desert Sasqwatch]

This is the F40 speed sensor:

This is the F35 speed sensor:

The F40 sensor is about 12mm diameter, the F35 is 14mm.

Believe the ZZP kit with the transmission has the case drilled for the F35 speed sensor.

 

[JohnK]

The ZZP kit comes with a Regal tranny. I have the Saab, so I didn't get a trans with the kit. If you can, the pic would be more helpful to me if it included more of the tranny so I could better see the sensor's location. I'm not sure if the sensor on my car is the F35 or F40. I think it is the F35 as I don't think the mechanic needed to purchase a new one, but not sure. Will check into that. Also, the sensor in the trans pic is not the same as the sensor pictured alone? Thanks!

 

[Desert Sasqwatch]

I have a Regal transmission, so photos of mine will probably not help. Sorry.