Tire size speed corection

ByReaL · Post by **ByReaL** » Thu Apr 19, 2007 5:30 am

the ecu gives the speed considering that you have the standard tire size on the car, if the tire size was changed this will not be so acurate,

this enhacement is for adding an option to insert old (standard) tire size and the new tire size and the software apply a corection to the speed acording to this values.

in my opinion this enhancement is a verry low priority, but is good to be added if you remain without ideas about what to add new to the software

Matt · Post by **Matt** » Thu Apr 19, 2007 11:39 am

I've added it to the list but dont even know how to caclulate this .. any ideas how the adjustment factor would be calcualted?

cheezmonta · Post by **cheezmonta** » Thu Apr 19, 2007 2:51 pm

Only way to make it work would be to go measure the tire diameter and do the math against the cars gear ratios and rpm. You could then input the percentage of correction needed and let the ECU do the rest.

ByReaL · Post by **ByReaL** » Thu Apr 19, 2007 5:23 pm

or maybe there is a "K" constant for this that can be altered

seams prety logical that the speed is the info from the sensor x something, if that something can be changed then the problem is solved, if you know the ram address for the speed, maybe you can look in the disasambled code and see if any math is done to the info comeing from sensor before it is writed at that address.

Matt · Post by **Matt** » Thu Apr 19, 2007 5:56 pm

I know NissanDataScan takes in tyre sizes for its 0-100kmh measurements to account for differences so it is possible, i just dont know the calcs

With NIStune.... we read in the raw sensor data and then perform processing to it (recalculation)

For speed input, pulses from the speedo unit are converted into a number by the A/D converter which the ECU uses. This as a real life figure is x2 for R31 and most others by NIStune for display

We can adjust that xK by a decimal number of some sort but it would be a fairly small number