With the size of my tires my speedometer had obviously been thrown off, its around 5mph slower when under 40mph and about 10mph slower when over 40mph.

The question is, does the odemeter read off of my Blazers speedometer? If that's the case, then my truck could very well have 150K instead of the 100K it reads now - depending on how long these tires have been on the vehicle. This is something I couldn't find on any search and was wondering if anyone on here knew. If that IS the case, then I need to have my speedometer recalibrated ASAP! Because that's so NOT COOL if so....

Thanks to any answers, ahead of time! (as usual)

 

If the tire size is increased without recalibrating the speedometer/odometer in the PCM (for the newer trucks), then both the speedometer & odometer will read slow.

 

So thats a yes... I'm getting inaccurate readings! Swartlkk, what PCM tuner would you recommend (at the cheapest price possible) to re-calibrate?

 

If you can find a used hypertech, you can typically pick them up cheaper than a mail-order tune. The only hypertech model I see now is 32000 that is applicable to 1996-2007 GM vehicles. What you have to watch out for buying used hypertech tuners is that they are unlocked meaning that the tune was removed from the previous vehicle or the tuner will be locked out.

One other thing to note is that the hypertech tuner can only modify tire size up to 34" so you would have to play with the gear & tire size to get the same net affect. For example, if you have 3.73's with 35's, you may have to change the gear in the PCM to 4.10's and the tire size to 31.8"

You can check out the prices from PCMforLess.com, Wait4me.com, and BlackBearPerformance.com to see what they cost. You'll get more gains on the engine/transmission tune than a hand held programmer as an added bonus, but you won't be able to modify things if you change gears/tires without sending the PCM back in.

 

Gotcha.... don't think I'll ever go with different tires or gears so I may just sent it out for a tune. It'll be out of commission for a few days, but at least I know it'll be getting done correctly - the FIRST time!

 

I use my Tom Tom to verify my speedo and odo. satalites are much more accurate than my dash. Speedo's are only required to be 97% accurate by law.

 

if you send your pcm out to be tuned tell them what speed the speedo says and what the actual gps speed is. If you just tell them a tire size like i did theres a good chance it will still be off. Since your tires are not exactly 35in on the dot.

 

Well that's what i currently do. I use the "Ulysse Speedometer" on my android phone (ran by GPS) and its DEAD on. But I'd still love to get my stock speedo accurate, its EXACTLY as said before... 5mph slower when 40mph or less, but as i break 40 it jumps to a 10 MPH difference.

Thanks for that, ill definitely send that info ad well. I'm waiting to get EVERYTHING I want done to my truck (long list) and the very last thing will be a PCM tune, so its only done once!