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10

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 ...


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.


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 ...


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

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, ...


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

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.


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 ...


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.


2

This very much depends on the incline. If it is a slight incline, I would expect that the vehicle would still accelerate, but probably not if you are going fast (Over 30 mph, say). If it's more than a 5 degree incline, then you could probably go highway speeds without touching the gas. If you find yourself riding the break, as has been suggested, try ...


2

The 92's are known for their speedometer failures. I bought a replacement speedometer from www.techbargains.com. Kinda. It's made by Garmin, and when I put it on the dashboard it tells me how fast I'm going. And where I'm at, and what direction I'm going, as well as my elevation from sea level. AND I can enter an address and it tells me how to get there. ...


1

Zaid has covered the mechanism of the gearlever and its switch and relay. The speedo is made up of a driving wheel on the transmission output, which is an interferance fit, which can go bad, and not do any driving of the speedo transducer. The speedo driving wheel drives the transducer, which gives out a sequence of pulses to the ECU to give a 'speedo ...


1

Is the speedometer reading low? Do people regularly ride your bumper and honk at you? If so, then the speedometer needle shaft could be rusty or sticking. If the car actually doesn't move until the tach hits 2K, then I'd suspect your torque converter (or clutch, if it's a manual, but you'd probably notice that slipping at other speeds too).


1

If the alternator bench tests okay, but doesn't work on the car, suspect the small wire connected to the alternator. This wire should be getting 12 volts when the car is switched on. It gets its power from the ignition switch through the battery light in the dash. Does the battery light come on when you turn the ignition on with the engine off? If that bulb ...



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