Hot answers tagged

22

There are pros and cons of each, remember you can easily spin or lock up the rear wheel, and in fact the rear wheel may be far less often at the correct speed. So the decision on this stems from physical connectivity it's much easier to connect from the front wheel to the odometer which is on the handlebars than to route from the rear wheel, up under the ...


12

You can calculate the size of the effect from simple geometry. Tire wear reduces the diameter of the tire, which reduces the circumference of the tire. New passenger car tires typically come with 10/32" to 11/32" of tread depth (source). Tires are considered fully worn-out when only 2/32" of tread remains. So the tire has lost 8/32"--9/32" on the radius, or ...


12

The front wheel is used in most cases with mechanical speedometers (though there are exceptions) because it's just easier (and probably cheaper) to couple the front wheel to the mechanism. Additionally, a mechanical speedometer uses a cable. The longer it is, the less reliable and accurate it becomes, thus the speedometer takes the speed from the nearest ...


11

Its not a rule of thumb that the Speedometer is connected to the front wheel. There are many Suzukies and hondas in my country that have the speedometer connected to the rear wheel. As Rory stated, the only reason I guess is due to the convenience factor since the front wheel is closer to the cockpit.


10

At risk of sounding facetious, yes it is normal. It's due to gravity. The steeper the slope the greater the acceleration. Exceptions include: some off road vehicles which use intelligent engine braking for downhill, but even they will only cope up to a certain slope angle, loss of grip.


9

The only thing your car can sense is the number of turns of some part of the drive train. In the old days it was a gear right off the transmission, and today it's an electronic sensor in the transmission or somewhere in the drive train near the wheels. It's going to be a sensor that can determine how quickly the wheels are rotating. The way to calculate ...


8

The speedo will be a standard linear voltmeter. Vehicle speed sensors are usually attached to either the gearbox output or the differential and produce a pulsed output at a frequency proportional to the vehicle speed. On a 'normal' speedo, the ECU will read the pulses from the speed sensor and produce a linear voltage proportional to the vehicle speed to ...


7

It could be the gear ratios in your car. Vehicles that are geared lower will hold their speed going down hills using the concepts of engine braking, while vehicles geared really high will be more likely to gain speed as a result of little to no engine braking. The other cause could be your idle setting. If your car is set to idle really high, it's going ...


7

That's the check engine light, or CEL - if it lights up, you have a problem with the engine and should stop and investigate it. If it's blinking, count the number of flashes, as this will indicate a particular error code which can help you to determine what is wrong.


6

All of my competition cars have had speedos, some of which didn't work at all. I have never once been in a race and had time to take my eyes off what was happening around me to look at the dials. This is why competition cars tend to equip their dashboards with bright lights which come on when attention is required. The times a speedo is useful is during ...


5

Manufacturers deliberately calibrate their speedos incorrectly. They make sure the speedo always reads higher than the actual road speed, and there is a very good legal reason for this. Speedometers must never read lower than the actual speed (European law (ECE-R39) says speedometers cannot show speeds less than the actual speed. Other countries have ...


5

Most speedos in the dash for modern electronic based cars, have a sensor in the output shaft of the transmission. It is a simple reluctor wheel and Hall effect sensor, or a gear driven motor which can then produce a signal for the PCM to interpret. Cars can also use the same method off of the anti-lock wheel sensor to get a "speed" indication. The more ticks ...


5

Generally a 30 zone implies you are in town, where you are subject to children, pets, footballs, stopping traffic etc. Cruise control is for long distances at a constant speed where you are not subject to rapidly changing risks - not for stop-go situations. In town you should be concentrating on what is going on and adjusting your speed constantly based on ...


5

I would bet the electronic speed sensor in the transmission is malfunctioning. It should look something like this: It suggests it is located at the top of the transmission, so should be fairly easy to get to. One plug, one bolt.


5

There are four possible culprits: The vehicle speed sensor which plugs into the back of the differential The wiring from the speed sensor to the back of the instrument panel The printed circuit board on the back of the instrument cluster The speedometer itself As always with electrical problems, test the simplest/cheapest component first. In this case, ...


4

Depending on the age of your Jeep the recalibration involves either swapping speedo drive gears in the tranny or reprograming the computer. The reasons for having this done are that modern vehicles use many data points for different systems and they all interconnect at some point. ABS, transmission shiftpoints,traction control, cruise control are all looking ...


4

The speed is very simply calculated from number of rotations of the axle multiplied by the circumference of the tyre. All that onboard computer then does is then divide by time to get average speed.


4

There are two basic approaches, you can tap a speed sensor directly before it reaches the computer, or use OBD II signals (generated by the computer). Sensors usually generate a voltage, so you have to find the wire you are interested in and then install an analog-to-digital converter. This then has to either go directly to a COM port (if your computer has ...


4

UK type approval states that a speedometer may read with upto a 10% error provided that the speed shown is either true or over. A speedometer may not under read when a car is new. Most manufacturers therefore calibrate their speedos for a slight overread. You must also remember that the difference between tyres with new tread and those worn to the UK ...


3

There are many variations, and no consistent method across manufacturers. That said, your theory is not correct - you are more likely to get the legal highway speed somewhere near the top because that is an area where the eye can easily see variation. Even within manufacturers there seems to be a lack of consistency. Where they use the same clocks across ...


3

If the vehicle has a speedometer cable it may be frayed causing the fluctuating of the needle. It's also possible that the speedometer needs to be rebuilt.


3

The older mechanical speedometers were cable driven. The cable is more like a very tight coil spring with a small square driver crimped on each end. One end was driven by the transmission the other end drove the speedo head. The speedometer was calibrated to the vehicles tire size and final gear ratio by installing specific speedometer drive gears in the ...


3

Back probed the VSS and the input signal at the instrument cluster. Yellow = Pin 17 (signal) at the instrument cluster Green = Pin 3 (signal) at the VSS Red = Pin 2 (ground) at the VSS That obviously doesn't look right. Pin 2 (red trace) isn't grounded. Looking at the sensor diagram it should be a 12v square wave. So where's the ground? Visual ...


2

Some of them have a GPS reciever, accelerometers and a phone in them, and regularly upload data back to the insurance companies - some of the ones that have been featured on the TV in the UK come with online accounts so you can log in and see the performance data. I've never quite worked out how they are supposed to cope with multiple drivers in the same ...


2

Your behaviour could affect her premium then - these black boxes typically track speed, style of driving, how harsh you are on acceleration and braking, the times of day you drive etc. They collect this data all the time - some insurers collect data from them regularly, others only in the event of an accident - either way, if you do not stick to the driving ...


2

Yes. That is a significant difference so your speedo will be out by a lot. In some regions it is required by law to have an accurate speedo!


2

Size: YES. Wear: Yes... but it's negligible. If the bigger the tire the slower the speed on the speedometer. The easy fix is to just use a GPS in addition to the speedometer. Since you are monkeying with ratios the speedometer will be off by some percentage. So the faster you go the more the meter is off. I put a smaller wheel on my motorcycle. Now the ...


2

Considering that all cars after 96 I believe have OBD installed, it is possible to make a device that records your every move (I am actually making one as we speak). ODB may do this already (the car needs this info for other tasks). However, this is not necessarily court approved and depending on the offense and the level of court it may not be admissible.


2

Having owned a 97 Taurus which is a Sables cousin a common problem is the vehicle speed sensor. If the sensor completely fails it is easy to diagnose. Mine slowly failed over a two week period during which time it would shift into nuetral, have eratic speedometer readings,and would shift up or down at odd times or work perfectly fine. The coolant resevoirs ...


2

I assume you're using a factory speedometer. If so, are your wheels factory size? Wheels being the wrong size is a sure-fire way to throw off your speedometer.



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