2nd Gen Non-Engine/Transmission smarty speedo setting

[DIESELWRKS]

I wont wear my tires out fast enough to have to factor that in adjusting my speedo. I know that what the manf. says the diameter is could be wrong. I know how to measure my diameter. my point is the smarty doesnt work and a dealership re-flash would be off as well. there are to many variables that every driver is going to have. I just have to keep trying different settings on the smarty to determine the closest at freeway speeds and settings for in town up to 45mph setting.

 

[AKaiser]

Best way to figure out the diameter of a tire is to measure its "rolling" diameter. Mark your tire on the closest point to the ground and that spot on the ground (so you have a line that runs through your tire and onto the ground). Drive in a straight line for 3 or 4 revoloutions. Stop when the mark on your tire is at the ground again. Measure the distance between your mark on the ground and the mark on your tire. Divide that by the rotations your tire took to get there. Then divide that answer by 3. 14 (pie).



So, for example: You made your marks, drove forward so the mark on your tire made 4 revoloutions, and measured 412 and 1/4" (412. 25) between the marks. The math should look like this: 412. 25 Divided by 4 = 103. 0625 divided by 3. 14 (pie) = 32. 82245222929936305. Your tire is 32. 82245222929936305 inches tall.



The more revouloutions you use the less error you will have. This is how I have always set the pinion factor (tire size and/or gear ratio settings) with the DRBIII, and it has worked perfect. It also factors in tire pressures or tire squat.

Kevin

That's how we did it on farm tractors before they came out with radar. BTW, it's Pi, not pie. Just remember Pi R Squared, but Pies are Round.

 

[KAlder]

If you want the dealership to set it, it is set by revoloutions per mile. You should figure out with the rolling diameter, because most techs will use the dimensions on the tire (which is not accurate). If you figure out the revs per mile and tell them to set it to that it should be pretty accurate.

 

[Bob4x4]

I wont wear my tires out fast enough to have to factor that in adjusting my speedo. I know that what the manf. says the diameter is could be wrong. I know how to measure my diameter. my point is the smarty doesnt work and a dealership re-flash would be off as well. there are to many variables that every driver is going to have. I just have to keep trying different settings on the smarty to determine the closest at freeway speeds and settings for in town up to 45mph setting.

If you were to check your speedo with a gps,stock tires,you would find it is not accurate either. The police cars come with CERTIFIED speedos to overcome this. To get the highest accuracy where it counts most,freeway speeds in my opinion. Calibrate it at 60 mph,It will still be close at 80 and at 40.



Bob

 

[RJWEST]

The speedo is not that accurate, the error is in the indicator head...



You can get the Odometer dead on and still have speedo error,

depends on how good the MPH indicator is, Smarty can only calibrate

1 parameter , Miles traveled, or mph ( possibly both if you are lucky to have an ODOmeter and MPH ind that agree )



I set my Smarty by tweaking the diameter to match GPS speed,

Than verify with Mile markers on Interstate ( at least 50 miles and several

tests ) GPS speed within 1/2 MPH of indicated... .