incorrect reading?
For example I was driving the speed limit(65mph) and I got pulled over for doing 76mph. Please explain why the aspect ratio would do this
-Thank you
2006-10-06 16:36:28 · 6 answers · asked by Anonymous in Cars & Transportation ➔ Other - Cars & Transportation
Because the speedometer measures your speed by counting rotations and is programmed to display your speed by calculating a certain number (call it X) times the number of rotations. When you increase the diameter of the tire, it takes longer to complete one full rotation than it did previously, therefor throwing off the result. To adjust, you have to change your X (sometimes by reprogramming the ECU, sometimes by changing a plastic gear in the transmission to one with less teeth, etc.)
2006-10-06 16:42:24 · answer #1 · answered by Lloyd 5 · 2⤊ 0⤋
The difference is the distance around the outside edge of the tire.
It takes a fifteen inch tire loger to spin around than it does a thirteen inch tire. This changes the ratio of the transmission speedometer gear to the tire. This gives you the eroneous speed reading at the speedometer head.
2006-10-06 23:43:27 · answer #2 · answered by It All Matters.~☺♥ 6 · 0⤊ 0⤋
You must have REALLY increased the diameter of your tires to change your speed 11 mph. Of course, one advantage of that is that you may just get better gas mileage, unless you are overloading the engine. It will have to work harder to turn those larger tires.
I onced put smaller tires on a Datsun pickup and when I was running 60, the speedometer said I was doing around 70. It also lowered my gas mileage because of the excessive RPMs. Pops
2006-10-06 23:58:55 · answer #3 · answered by Pops 6 · 0⤊ 0⤋
Your brand new car speedometer is set to the factory diameter of your standard wheel. When you change the diameter of your tires then you are in affect "fooling" your speedometer because its still set to the diameter of your old factory wheels.
This means that your speed will not be accurate. And if your tires are bigger then what they were your speedometer will show you going slower then your actual speed. If you get smaller tires then it will show you going faster.
2006-10-06 23:43:10 · answer #4 · answered by gillamacs 3 · 0⤊ 0⤋
Changing tire size is similar to changing gear ratios. At 3000RPM, an engine with the transmission in fourth gear will propel a small tire slower than it will a larger tire.
http://science.howstuffworks.com/gear.htm
2006-10-06 23:41:07 · answer #5 · answered by Frankie P 4 · 0⤊ 0⤋
Simply put, the taller tire has a greater circumference, more tread, more distance per rotation of the wheel
2006-10-06 23:45:59 · answer #6 · answered by Carpe Diem 2 · 0⤊ 0⤋