RTdawgs

The following was noted while driving home from the SE4RJ at Tellico last weekend:

Vehicle 1: Mine, 2000 4R, 285s, 4.10s
Vehicle 2: Paul's (Bratik), 2000 4R, 285s, 4.88s

Our spedometers were reading different miles per hours while traveling at the same speeds. this is expected.

Our RPMs were also different (as expected).

Our odometers read the exact same numbers. We filled up at the same gas station in Murphy, NC and after making a stop in Alpharetta, GA, both of our trip meters read the same mileage!

So...whos got an idea? most people have been using a corrected mileage for calculating miles per gallon and other mileage realted calculations, but maybe the odometer is not effected by tire size.

i am going to compare to my GPS tomorrow.

Darren

Interesting find there, detective. Hmm.

How far off were the speedometers at higher speeds?

bamachem

Either he paid for 4.88's and got 4.10's, or the odometer sensor is somewhere on the rear axle after the differential... You both have the same tire size, hence both of you would read the same INACCURATE mileage. That's the only way I can think that you would end up with the same uncorrected mileage. What about the RPM's? Did you compare them at the same speed?

RTdawgs

so we both have the same innacurate mileage?

hmm...im testing with the GPS today.

Robinhood150

Any update?

BruceTS

On my 99' the odometer sensor isn't on the transmission or T-case, but somehow built-in to another system, probably the ABS. I haven't been able to narrow it down, since none of the wiring diagrams that I've looked at show this specifically, only the sensor attached to the t-case. The reason I'm guessing ABS is the non-ABS rigs I've seen have the T-case sensor.

What I have noticed is the mileage reading only changed with different size tires, but the gear changes didn't affect it at all. Example with my 265/75-16 BFG AT's and 4.88 gearing, using GPS, my Speedometer was off by 1 mph @ 65mph, but with my 315/75-16 MTR's it shows 60mph with an actual of 65mph. When I did my gear change my odometer reading didn't change, only RPM's....

bamachem

That makes sense... The abs uses a sensor to determine the speed of the wheel as it's turning. Toyota probally built the ODO into the ABS system in order to prevent people from disconnecting the speedo cable to keep the miles off the ODO. I wonder if you pulled the ABS fuses/relays if the ODO would also quit. It's a quick check if you want to find out.

Also, no matter what the case may be, with 285's, the ODO is still off by a percentage compared to the stock tire size (3.5% with 265/75's in my case), so correcting the mileage to determine fuel economy is the correct way to calculate it.

jx94148

This is very interesting. Do some more testing and post up to confirm what's going on here.

User 051420

That is indeed very weird. I also have 285's now and I REALLY want my speedo/odo corrected. According to some online calculator, my speedo reads 4mph slower than I'm actually going (265/70's vs. 285/75).