Does anyone knows what it takes to calibrate the speedometer in my 98 Blazer?

 

I think that's new enough that you can just plug in a programmer, right?

You get some big tires, and now the speedo is off?

 

Right. I think that it's only off by 7mph slower than the actual speed

 

I need to get mine recalibrated as well. With the 33s, it's off by like 11 mph at 60.

 

I had my PCM flashed with my correct info (37" tires and 4.88 gears) and my speedometer is now within reason. Not perfect, but close enough.

I don't know if it's worth the cost to have it done just for that but I needed it done anyway, so why not correct the speedo in the process.

 

Tom, how far were you off, with that tire and gear combo?
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From the calculators online, if I regear to 4.30s, the speedo will be Almsot exactly back on, with my 33s. Unfortunately I can't find a set of 4.30 gears for the front, so I'll be going with 4.56s eventually. Looks like it'll put the speedo fairly close

 

To be honest, I never drove it before I got it flashed.

If you go with 4.56s, you have an excuse to upgrade to 35s in the future, right? ;-)

 

Don't know how long the front diff could hold up to 35s lol!

 

You just buy your own programmer or just take it to a place?

 

That's my understanding.