Does anyone know how to recalibrate the speedo for smaller tires?

[mudjeeper]

I recently switched my stock wheels off my truck to 454ss wheels with BF Goodrich tires, once I put the new ones on I noticed the speedo was saying i was going about 4 mph more than I was. Does anyone know how to fix this issue? Thanks

 

[1998_K1500_Sub]

Year / model? Because “it depends”.

 

[caminonut]

I recently switched my stock wheels off my truck to 454ss wheels with BF Goodrich tires, once I put the new ones on I noticed the speedo was saying i was going about 4 mph more than I was. Does anyone know how to fix this issue? Thanks

If you have a 88 to 91 and you’re comfortable at soldering, pick up a seven pin dip switch like these .
pop your cluster apart and remove the seven fuses in this picture.
Solder in the dip switch this will then be able to calibrate your speedometer with the tires that you have on your vehicle.

 

[Drunkcanuk]

Like @1998_K1500_Sub said, it depends on the year for sure.
On my 91 with a 4l60 there is a little gear in the tail shaft that can get switched out.
On other years there are DIP switches, others it's in the computer.

 

[PlayingWithTBI]

On my 91 with a 4l60 there is a little gear in the tail shaft that can get switched out.

Do you have a cable driven speedometer?

 

[RichLo]

Yes, it depends.

on a 88-94 dash and if your ok with 'good enough' you can physically pull the needle off and set the cruise control on a straight, flat, deserted road with GPS on your phone at a target speed (55, 60 or 65mph) and carefully push the needle back on pointing at that speed. It helps if you have a confident passenger to keep the truck steering straight while you do this.

 

[Drunkcanuk]

Do you have a cable driven speedometer?

I don't think it is a cable, but there was a wire I had to remove and reinstall for sure for the speedometer that was attached to the gear in the tail shaft.
I remember having to remove that gear over to my new transmission when I swapped it out. And I'm remember the directions from GM mentioned it was for the speedometer. Had a chart for different colors for different gear ratios and tire sizes to make sure the speedo was calibrated correctly.

 

[PlayingWithTBI]

I remember having to remove that gear over to my new transmission when I swapped it out. And I'm remember the directions from GM mentioned it was for the speedometer. Had a chart for different colors for different gear ratios and tire sizes to make sure the speedo was calibrated correctly.

Huh, FWIU all GMT400 trucks came with the VSS and a reluctor on the tail shaft giving you ~2,000 PPM (40/revolution), then you set your speedo with the jumpers on your VSSB (88-91) or DRAC (92-95). On my 88, with the EBL I wound up setting the VSS to 2417.11 (rounded off for Hexadecimal data tables) and my Dakota Digital based on mile markers to get it within 1 MPH using the radar speed traps around the neighborhood YMMV

 

[mudjeeper]

Year / model? Because “it depends”.

its a 96 sierra 1500

 

[mudjeeper]

Huh, FWIU all GMT400 trucks came with the VSS and a reluctor on the tail shaft giving you ~2,000 PPM (40/revolution), then you set your speedo with the jumpers on your VSSB (88-91) or DRAC (92-95). On my 88, with the EBL I wound up setting the VSS to 2417.11 (rounded off for Hexadecimal data tables) and my Dakota Digital based on mile markers to get it within 1 MPH using the radar speed traps around the neighborhood YMM

its a 96 sierra