speedometer

[itsmejimr]

recently changed out the stock 16" rims with custom rim in a 17" and a little lower profile tire. To be more precise- oem tires and rims  PP225/760/r16 to a 225/55/17. Had a copy of a tire chart comparison,that shows approx. difference in the actual highway speed change in MPH it could make. It listed it at about 3 to 5%. Have a real time radar detector with real time speed through a GPS. Problem is my speedometer, compared to the GPS is as much as 20 to 25 mph slow at 60-65 on the highway. The speedometer needle doesen't even move off 0 till 15 mph according to the gps. I have unhooked the negative Battery in order for the speed sensor to try and make the necessary changes to the ecu but this did nothing. I have now replaced the speed sensor and still no  changes to speedometer needle speed and actual gps speed. I can,'t believe I could be the only owner of a Lexus or any other automobile who has experienced this problem.  This situation all has taken place since the tire/rim swap. Speedometer always worked properly before, but now?????

 

 

Anyone withcomments, questions or possible solutions, please comment, thanks.

[ColinBarber]

Do you still have the old rims to put back on to test? As you say the difference in size shouldn't make that much of a difference and could just be coincidence and the speedo is starting to play up.

[itsmejimr]

2 hours ago, ColinBarber said:

Do you still have the old rims to put back on to test? As you say the difference in size shouldn't make that much of a difference and could just be coincidence and the speedo is starting to play up.

Thanks for the reply, and no, left the old rims and tires. Had a chart with the comparisons and, yes, figured they wouldn't have made such a drastic change but it is tghere. Can leave a stop ligh and the speedo doesn't even move till at least 15 mph, reading my gps. speed.. All started after the tire/rim change. Thought the driveshaft, fly wheel and rear end rotation, after the disconnect of the Battery and then letting the "wave length being read by the speed sensor would pass all the new info to the ecu  and letting the computer make all the new adjustments, never believed it wouldn't catch up. Even the newly installed sensor didn't change a thing. Coincidence??? Not a big believer. There are no changes in transmission shifting, stalling or anything else associated with a bad sensor. Thanks again but maybe another member has a different idea.  If I didn't have that real time gps built in, probably would no longer have a driver's license.LOL