tqlla3k

iTrader: (1)

To those who have had their cars on a rolling emmissions machine, does your speedometer move, while you are getting emmisions done?

I am trying to figure out if the Speed is calcualated off the Drive wheels or the front wheels.

ISZach

Yes it moves because the wheels are spinning.

tqlla3k

iTrader: (1)

So the speed is determined by the transmission and not sensors in the wheel. I want to get larger profile tires for the front of my IS350 currently 225/40/18, and people on the 350 forums have been telling me the speedo would be off.

my rears would remain the same at 255/40/18

rominl

iTrader: (4)

doesn't matter. my gs400 has overspec tires, and i pass smog twice already no problem

Ramon

I believe the speed sensors are on the tires. They have been on every other car i've looked at anyway. Assuming the IS is no different then changing the overall diamater of the wheels will throw off your speedo a tad.

MichealIS3

If it's on the 350 you should be okie. Because it's RWD, the speed will base on the rear wheel any way. Changing the front tire won't affect the speedo as long as you keep the rear close to stock diametter.

tim817

I called my dealership and asked them about how's the speed is calculated before I put new tire and wheels on. They told me the IS350 use rear wheels because they're rear wheel drive.
If you want to double check to make sure, jack your car up on the rear , get into your car , engage Drive then give it a liltle gas. If the speedo needle moves the your car is using the rear wheel to calculate the speed.

TimboIS

Most modern cars get the speed from a sensor in the transmission.

tqlla3k

iTrader: (1)

In another thread, didnt you say

Why have you changed your point of view? I was certain that the Speed is calculated by the tranny, but wanted to make sure. Before I change my front tires