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Discussion Starter · #1 ·
Hi there! I’ve been looking through the forums all day and haven’t found the answer I am looking for. I have a 1997 s10 4.3 v6 with 4x4. I’m trying to figure out how to fix my speedometer. I went from a 235/75r15 to a 235/50r18. How do I go about getting my speedo back to normal? I’ve heard about changing gears in the tail shaft and transfer case, as well as doing it electronically. My dash is all mechanical so I’m assuming I have to mess with the gears right? I also heard that these trucks didn’t come with a speedo gear, instead they have a speed sensor? Let me know what my options are! Thank you!
 

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Discussion Starter · #3 ·
It's electronic, as is your guages. Your speedo won't be far enough off to worry about, less than 5mph.
No it is something to worry about. It’s off by 5 mph when I’m going say 25 mph. But it thinks I’m going 95 when I’m actually going 80 so I hit my governor. (That is with my 205/60r15’s so I’ll be a little closer but it’s still going to be off) I’m also putting a lot more “miles” on my truck with 62,000 miles. Should probably be more like 60,000
 

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No one cares how many miles your 24 year old truck has on it, sorry. Tech2 is the best way to change the tire size in the computer.
 

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Discussion Starter · #5 ·
No it is something to worry about. It’s off by 5 mph when I’m going say 25 mph. But it thinks I’m going 95 when I’m actually going 80 so I hit my governor. (That is with my 205/60r15’s so I’ll be a little closer but it’s still going to be off) I’m also putting a lot more “miles” on my truck with 62,000 miles. Should probably be more like 60,000
No one cares how many miles your 24 year old truck has on it, sorry. Tech2 is the best way to change the tire size in the computer.
Just tryna keep them low 😂 I’ll look into it
 

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Tech 2 will only adjust to another stock tire configuration and in most cases you have to be on a paid link to GM. It's only $40 for 24 months to program one vehicle, but you'd need to be changing to an offered tire size and gearing for the drivetrain original to that model. You can't just go in and spec a tire size. I've tried. Unless someone knows a trick i don't.
ACDelco TDS
Not much other choices. HPT doesn't go back past 98.

Something else is wrong.
Your off +19%. The wrong direction.
Tire Size Calculator
When I plug your sizes into this calculator I get -5.5%
At 90 your speedo should be reading 85 with those 1.6" shorter tires.
Dakota digital makes a box for under $100 that you install into the speedo wiring and is infinitely adjustable.
Here's a screen shot:
348678


Did you also change the rear end? Swapping out a 4.10 rear from a 4 cylinder to a 3.42 from a 4.3 truck would put you about where you're at. Or maybe swapped computers? The instrument cluster gets it's speedo feed from the PCM after being processed from the raw feed of the VSS. Which is just a pulse count.
 

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Discussion Starter · #7 ·
Tech 2 will only adjust to another stock tire configuration and in most cases you have to be on a paid link to GM. It's only $40 for 24 months to program one vehicle, but you'd need to be changing to an offered tire size and gearing for the drivetrain original to that model. You can't just go in and spec a tire size. I've tried. Unless someone knows a trick i don't.
ACDelco TDS
Not much other choices. HPT doesn't go back past 98.

Something else is wrong.
Your off +19%. The wrong direction.
Tire Size Calculator
When I plug your sizes into this calculator I get -5.5%
At 90 your speedo should be reading 85 with those 1.6" shorter tires.
Dakota digital makes a box for under $100 that you install into the speedo wiring and is infinitely adjustable.
Here's a screen shot:
View attachment 348678

Did you also change the rear end? Swapping out a 4.10 rear from a 4 cylinder to a 3.42 from a 4.3 truck would put you about where you're at. Or maybe swapped computers? The instrument cluster gets it's speedo feed from the PCM after being processed from the raw feed of the VSS. Which is just a pulse count.
I mentioned going to my smaller tires which is where I get the 19%. The new ones I just picked up give it about the 5% so you are right. I guess I’ll just live with it because it isn’t off too much anymore. Just was wondering if there was an easier way like swapping the speedo gear in other transmissions
 

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Tech 2 will only adjust to another stock tire configuration and in most cases you have to be on a paid link to GM. It's only $40 for 24 months to program one vehicle, but you'd need to be changing to an offered tire size and gearing for the drivetrain original to that model. You can't just go in and spec a tire size. I've tried. Unless someone knows a trick i don't.
ACDelco TDS
Not much other choices. HPT doesn't go back past 98.
It doesn't cost anything to change tire size in the EBCM with the tech 2. It is a built in feature.
 

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I can't remember if the JET DST tuning can change tire size to other than a stock size or not. I haven't used mine in a long time.
 

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Don't know if a dealer would have the tools any longer to alter the tune in a 25 year old truck.
The Dakota Digital SGI-BT100 will work on any electronic speedo. @$95 probably less than most dealers would charge to hook up their gadgets. And most would charge you even if they couldn't do it.
 
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