I once plugged in my car analyzer and the speed it reported was about 3-5 mph lower than indicated on the speedometer. So for some reason there is a discrepancy between the speed sensor and the speedometer (which is just an electronic meter after all).

 

My speedo is always off 2-3 mph when compared w/my Garmin GPS. Not so bad when passing radar traps.
I have stock tires and rims.

 

Hey, at 140 mph, I'm not worried about 2 or 3 mph!

Now, if I can only find a tall enough cliff with a big, soft pillow at the bottom...

 

I have compared my GPS to the speedo many times and find it to be about 3 mph off. I have stock wheels. I am really dissapointed with the factory cruise control. It is slow to activate and slow to respond. Going up a up a hill the Xb will lose 6 mph before the cruise kicks in. Can this be adjusted?

 

Ok lets say the speedo is 2-3 miles difference.Reading 70 but going 68 with stock size tires.What size would you need to compensate for this.Would you need taller or shorter tires????

 

You'd need taller tires.

Think about it...how could you go faster with the tires revolving at the same rate? You'd have to increase the tire diameter, so that each time the tire goes around, the car has traveled farther and (if tire RPM - which is essentially what the speedometer measures - has remained the same,) faster.

 

Also, you need to remember that it is a gradual increase. You aren't going to drive 10MPH and have the speedo read 15 MPH. It may only be .5 MPH off at that speed, but at 85-90 MPh, it may be off 5 MPH. I have slightly taller tires, so it reads lower than what my Garmin GPS reads.

 

A larger tire would correct this. You would be traveling faster with the same revoloutions.
It depends on where the speedometer pickup is It might not change at all..

 

Where could the speedometer pickup be placed where the speed wouldn't change regardless of tire size?

 

 

I used to ride street bikes and I owned quite a few.My Honda 929 had an electonic pic up for the speedo on the trans.My ZRX 1200 picked it up from a cable on the front tire.When I would change sprockets on my honda I needed a calibrator to correct it.On the ZRX it didnt matter cause it was off the front tire.

Iam going to check my speedo on the box with my gps and maybe try a little taller tire to see if this will correct any difference in MPH.

 

Do you have any details on how that worked? Did it read from the hub, or did it actually have something like a roller pressing against the tire tread? A roller would give an accurate odometer reading across all tire diameters, if it worked consistently.

 

It read from the hub.It had a gear in the hub and a cable running up to the speedo.

I also checked my speedo in my xB yesturday with my Garmin GPS and it read at 70mph indicated the GPS read 68.It seemed to be 2MPH off from about 40 on up.Under 40 it was really close.Iam sure the faster you go the more error there would be.

 

It's probably intentional. I know of some cars that alter the speed displayed vs the actual speed intentionally, while still using the actual speed for the odometer, mpg, and avg speed displays in the trip computer. It's funny cause you can have your cruise control set on one speed, then reset your avg speed calculator and it shows a different speed.

 

^^^Well, my ODO was off 50 some miles per tank according to my GPS

 

I wonder if year makes a difference here as well. I have a 2006 xB and I checked my odometer with the mile markers on the highway. When I traveled 6 miles on the highway my odometer read 5.8 miles traveled. So based on this I would say that if I traveled 60 miles on the highway my odometer would read 58 miles. Does that mean when my speedo says 58 mph I am really going 60 mph? This seems to contradict what other people are saying about their speedo being 'fast'...

 

Speedometer was fast on every car I've ever owned by 2-3 MPH. I just assumed car makers did it on purpose to cut down on speed and speeding tickets.
My xB odometer may be slow. I drove from mile marker 77 to mile marker 176 and my odometer only adcvanced 95 miles. I assumed the mile markers on I-95 were off but after reading the posts maybe the xB is off. But why would the odometer be slow when the speedometer is fast? Aren't they calibrated together?

 

I could be wrong, but I got the info from Tomas (on this site) and he seems to know his Scions.

 

I just pass by a speed trap a few times to check....worx perfectly...HAHA..

 

lol.

I have also been reading it was slow but my odometer is definatly not slow. Is their a way for the speedo to be off and not the odometer? If not maybe they changed the calibration on the 2006. I will also through this out there but this is a brand new car, maybe after 20,000 miles of tire ware mine will be slow too.