Since everybody says the speedometer is off by a little bit from the factory, would that affect the times that is posted for 0-60 times by a VERY slight bit?

I'm assuming they plug some computer into the car to get this data, but...wouldn't it still be getting the same signal that the Speedo uses?

 

0-60's are usually checked via a stand alone computer and/or radar.

If the speed is off I don't think it's by much.
I pass a radar speed thingy near a school zone and whatever my speedo reads is what the school zone radar thingy reads.
So it can't be off by much.

 

When I got lighter wheels my speedo says i'm going faster than I am by about 1 or 2 MPH.

 

it'd also affect the 'real' mileage reading on the car.

fwiw, according to my GPS, the speedo reads 1mph fast at 75mph

 

Did you change the overall size?

I know that smaller wheel/tires can give errors and larger wheel/tires can do that as well.

I believe smaller will make the speedometer read faster and larger wheels will make it read slower.

 

the speedo is fast by about 3% to 3.5% on stock tires.

many believe that this is done on purpose to run out the warranty faster. i personally wouldn't put it past them.

 

^I could believe it I suppsoe...mine is about 1mph faster than radar

 

That depends on how the odo is calculated. I would hope that since there are such strict legal ramifications about the odo reading that there would be something that says the odo reading cannot be calculated from the speedo, but the number of shaft or wheel hub revolutions.

Has anyone's speedo ever broken? If so, did it have an effect on the odo?

 

I know I went by a radar station thing and it read 52 while I was going 57. So it's off a small bit, I just found it kinda weird.

 

Speedometer itself may be broken, but the mechanism to measure might still work..

But yeah, I'd imagine there be some industrywide standard to measure for the odometer..

 

Speedometers are not accurate in any vehicle, its just the nature of the beast. Since 1997 the law in the US is no more than 5% inaccuracy stock from the showroom. Tire wear and changing to different over all tire sizes will have an effect on speedo readings that is not covered by the law- so no recourse against the manufacturer.

 

Fail.

 

It'd be nice to explain why =p

However, I did go and google things up, and basically the odometer would read off the gears themselves, not the wheels. Just because your speedometer is off doesn't mean the odometer readings will be inaccurate.

 

yeah alot of cars(not sure about ours) have the speedo gear right before the tailshaft in the trans....

 

Win.

 

The speedometer on the family's van (2003 Dodge Grand Caravan) has broken twice since we got it in 2002. To my knowledge, this has not affected the odometer readings. But then again, I'm not 100% sure whether or not the speedometer was truly broken, or if it was just the mechanism that moves the needle that was broken since we brought it into the dealership to get it repaired.

 

Fail. Again. Keep trying.

 

Mine is about 3% off. Going by those residential radar signs, my speedo is faster by about 1MPH at 30MPH.

 

I'm not following.

 

The radar signs can be off also from weather, and moving them. They have to calibrate them either every 3 or 6 months I believe, and to know if they are, there is a sticker on them that has the last date it was done.

 

Good info.
I forgot about the calibration and I did not know about the weather part.

 

My own little test goes as follows:

3M has posted limit of 30mph on their campus. They have the radar guns and the signage posted all over the place (IF I speed on their campus, my wife gets a fine deducted from her paycheck). I set my cruise to 30mph. Their speed gun displays accurately, 30mph. I've done this several times from 29-36mph, all accurate.


One of the streets I take home is posted as 40mph. The cops in Leander monitor this stretch of road very frequently. EVERYDAY, I see somebody pulled over for speeding...mostly early in the morning when it's still dark and you can't see them.. (but my trusty ol Escort lets me know they are there!). I set my cruise from anywhere from 39mph to 46mph along this stretch. It reads accurately. I dare not go any faster for fear of getting busted. So, my little, unscientific test shows our speedos to be accurate. Stock gears, stock wheels.
why some are off..unless you've change your wheels or gears..

 

Every car is off somewhat, tyre size/inflation and wear affects the readings, as does tyre slip, so they're normally set to overread slightly so that you can't be accidentally speeding even in the worst circumstances.

 

There's a difference between the vehicle speed sensor and the wheel speed sensors. I'm assuming the RX8 uses the same setup as most cars I've had...

Wheel speed sensors are used for ABS and traction control and measure each wheel's rotational speed. The vehicle speed sensor on the output shaft of the transmission generates electrical pulses that are read by the microcomputer in the instrument cluster. The pulses are used by the odometer to calculate distance travelled and the speedometer to determine velocity. Wheels speed sensors are not used by the speedometer or the odometer.

If you change either the differential gearing or the overall diameter of the wheels, you will introduce EQUAL error into both the odometer and speedometer readings.

There is no way for the car to "self-calibrate" the speedometer. Going back to the original post, it's one of the reasons why using the speedometer to measure 0-60 is ridiculous. The magazines use an expensive and sophisticated version of the G-tech to do their measurements, which contains multi-axis accelerometers to accurately read acceleration and derive quarter mile, skidpad and braking performance numbers.

Ok. Tell me where I'm wrong.

 

It couldn't have hurt to provided this answer beforehand =p

But I understand your post. Thanks for the info.