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Archive for March 9th, 2006
Switching to Tires with Lower Speed Rating
Posted by Tim on March 9, 2006
I have a 2005 Toyota Avalon with 215/55R17 93V tires. Is there any reason that I can’t replace them with T rated tires with the same load rating? I know what the speed ratings mean and I do not ever drive over 75, sometimes 80 but very seldom. T rated tires are a lot smoother tire over bumps.
If the car came from the manufacturer with V rated tires, you should replace them with V rated tires for your safety and the safety of anyone that may drive your car in the future.
EFFECTS OF LOWER TIRE SIZE AND ODOMETER READING/ENGINE RPM
Posted by Tim on March 9, 2006
I recently changed from a 245/50ZR16 with a 25.7″ diameter tire to a 245/50WR16 with a 25.6″ diameter. I noticed that after this change, the odometer was reading about 1/20th of a mile short of an actual mile when comparing to the mile markers, but oddly enough the engine RPM’s are higher. When I had the 25.7″ tall tires, the engine rpm’s at 80 were 2,000 rpms. Now with the 25.6″ tall tires, 2,000 rpms registers at 73 mph. It seems to me here that with a shorter tire height, the rpms should be higher, but it should register more than a mile for every mile on the odometer. Any thoughts? Could one tenth of an inch in wheel height make that much difference in speedometer reading and engine RPM?
For any vehicle, it stands to reason that smaller diameter tires will result in higher engine RPM's at the same speed. It also seems to me that the odometer should read just as you report, less distance traveled for the smaller diameter tire. The odometer reading is based on counting tire revolutions. It is calibrated to determine distance based on the number of revolutions the tires turns. The tire with the smaller diameter has not traveled as far at the same number of revolutions as the larger diameter tire.