Is your speedometer off?

For those that don't know, I have 36" tires. It drives me crazy having the speedo so far off. I knew how fast i was going due to a GPS. but figuring gas mileage is a pain & also how many actual miles I had on an oil change. Anyway I decided to fix it. If anyone is interested it will cost about $80 to have your speedo dead nuts on actual speed.

http://www.vehicross.info/gallery/data/500/IMG_1705.jpg
http://www.vehicross.info/gallery/data/500/IMG_1708.jpg
http://www.vehicross.info/gallery/data/500/IMG_1709.jpg
http://www.vehicross.info/gallery/da.../IMG_17101.jpg

If anyone else wants their speedo corrected to tire size let me know & I'll give you the contact info. ;)

That's great to know an option exists to match the speedo, I figured it wasn't available for Isuzu.

My speedo was 12% off for years and even though I got used to it, I always wanted it to match at highway speeds. Last year, I adjusted the speedo by adjusting the span manually on the gauge. I was able to adjust the speedo to be perfect at 65 MPH, but it would start deviating accuracy from that speed.

The speed accuracy looked similar to this:
75 MPH =77 MPH
65 MPH = 65 MPH
55 MPH = 56 MPH
45 MPH = 47 MPH
35 MPH = 38-39 MPH
0 MPH = 7 MPH

Before adjustment:
55 MPH = 61 MPH
65 MPH = 72 MPH
75 MPH = 83 MPH

Overall it was an improvement but there's still some error. Essentially, I just put most of the error at the low speeds.

Only problem with adjusting the speedo (either way), is that any tire size or gear change will throw the speedo off again... and some of us can't make up ours minds regarding tire/gear choices. :_brickwal

I would like the information. Thanks!

He built this box for my exact percentage it was off. So I'm sure you can get the correct gears to put in the box if you change tires again. He just had me go 40 on the gps & give him the indicated speed on the speedo, then the same at 50, & 60. Mine came out to a 1.25 increase. They offer other ratios that are more common for a little less money, but since mine wasn't a stocking item it cost a little more to build custom.
I'm very happy!!!:clap:

http://www.transmissioncenter.net/sp...n_______va.htm

about 1/4 of the way down the page it says GM/Dodge/Ford adapter.

the email contact for the guy that did it is. jim@700raptor.com

Quote:

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Originally Posted by ohiovx

It drives me crazy having the speedo so far off. ;)

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My speedometer does not have an off/on button

Quote:

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Originally Posted by circmand

My speedometer does not have an off/on button

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ROFL - yer killin me here son. Not quite the Mt Dew tru da nose moment ... but close.

My math tells me that I should be off by 6.4% (31.4" tires), but actual measurement, using my Iphone's GPS, shows that I am actually at 8%! I was suprized by such a descrepancy (probably due to using narrow stock wheels, for 285 wide tires). How did you come up with your correction factor? Did you compare it to a GPS?

36" tires "should" be off by 22%! That is a LOT!

I stated it above. What he wants you to do is use a GPS. When you are going 40mph on the GPS write down your indicated speed on your speedo. Then do the same at 50mph & also 60mph. Give him the #'s & he can let you know if it's a common ratio that he has in stock. Or if it isn't quite as common (like mine) he will build 1 for you. It's an easy fix for $80 or less. I'm really enjoying not thinking about how fast I'm actually going while driving now.:yesb:

I see they also have ratios that allow for conversion from MPH to KPH. This might be desirable to our friends up north.