Speedometer off 5 mph

That's correct.

I've never found my ScanGauge to be particularly useful on a regular basis (such as mounting it and looking at it while driving) because it doesn't provide a whole heck of a lot of information. My truck has a manual transmission so it doesn't show a trans temp reading as well.

 

I use mine for engine temperature. Saved me once already from overheating on the trail. Truck had hit 240 degrees and the stock gauge hadn't even hit the red yet. I was very thankful that day.

 

My Head Unit is iDataLink compliant so I'm running one of these. I love it. I can display a lot of different gauges (up to 5) tracking a variety of different things. However, since its reading off the OBD2, it displays unmodified MPH so I can't use it for that. My gauge cluster displays my true MPH.

I just don't like the idea of cutting/splicing stock wiring harnesses. The Hypertech is plug & play. I understand trying to save a few bucks but you may end up spending more fixing a mistake down the line.

-J

 

All that other stuff may be great, but I don't need all that stuff, I don't have a lap-top & wouldn't know how to use it if I did, & all I want is for my speedometer in my dash to be relatively corrected for my tire size. A 2.5" taller tire will, according to the tire size calculator, make your speedometer 5 mph. low at 65mph., When showing 65 mph. you'll be going 70 mph.

 

Yeah, you'd need a much longer USB cable to reach your desktop.
That, or keep pulling the dash apart.

-J

 

Wouldn't know what buttons to push on the desk-top either. Not as simple for some as it is others.

 

anybody know where a chart is to determine your tire height by the size? I am riding some LT275/65R20's
I don't even know what the stock tire size was on it

 

Look at your specific tire manufacturer website. Every tire is a little different.

 

On this site home page, click on tire size calculator. Like said there will be small differences from one tire to another, but probably as close as you can expect. looks like yours are 35.65" tall & 112" circumference.

 

True, but how much does that really matter?

 

If it's only 5 mph off how are they going to get blasted doing 20over?

 

When my trucks speedo says it's going 58 it's actually going 65 mph. 62 mph= 70 mph. Eventually I'll do something about it but it isn't high on the list.

 

So 20 mph was a stretch, but your speedometer to your actual speed will be nearly parallel to each other. So for example, if you're doing 10 mph actual, your speedo will display 9.5. As you increase speed say, to 75 mph actual, your speedo will be off by a much larger number. It shouldn't be a constant 'off by 5 mph through all speeds'. Easy way to check would be do drive 5 mph, does your speedo show you as going 0 mph? I'm sure there's a formula, I'll look it up in a bit. If your speedo is 'off by 5 mph through all speeds', it's more than likely something mechanical/electrical would be my guess.

-J

 

My speedometer seems to be exactly 5 mph off from speeds at 45 mph and higher. Pretty much exactly 5 mph. 50=55,60=65,70=75,etc. The way I know this is those construction radar signs. You know what ones right? Posted speed and the sign flashes"your speed"? Not very scientific, but I gotta believe they must be close.

 

Yeah, the math seems to be fairly close to what you stated.



I dont remember if you said exactly what your new tire size was, but the numbers dont lie.

-J

 

35x12.50x18

 

Yours.

-J

 

So, with larger tires, 35s (ok, ok 34.5s), my odometer is going to skewed low right?

I am not as concerned with the speedometer, as I am with the odometer driving all my self servicing (fluid changes, tire rotations, etc).

I'm curious how off it would be say for 5,000 miles.

 

Get a gps mph gauge and stick it on your dash.

Also the ratio can’t be too far off..I have 285/75/16 and just drove 15+ hours passing tons of sting operations..”80” the whole way people passing me constantly and I know I wasn’t going 85-90 mph.

 

I cant remember exactly, but I believe your odometer is pulled from your transmission rotations. The tech site was taken down so I cant confirm but there is a sensor or two on the transmission that tracks rotations/rpm(?) which ties into your gauge cluster via the computer. I ran a dash GPS for about 1500 miles when I first installed larger tires which had a built in trip meter. While my speedometer was wrong, after 1500 miles, my onboard odometer was only off by about 25 miles which I attest to the inaccuracies of the GPS.

-J