Why Does A Speedometer Lock After An Impact? (Solved)

When it comes to safety, the speedometer should be the one instrument you should be regularly checking when you are driving because you have to make sure that you are driving at safe speeds.

However, one of the things you may have noticed in relation to older cars is that their speedometers tend to lock up and freeze during impact.

So, why does a speedometer lack after an impact?

Older mechanical speedometers lock after impact because they lose power on impact and would freeze on the speed of the car during the impact so that the authorities could see the speed of the vehicle during the accident. However, this isn’t the case for newer digital speedometers because the speed is stored in the ECU.

Car crash driver speedometer lock

Speedometers are neat safety devices that allow you to keep yourself safe by driving at safe speeds.

However, even if you end up in an unfortunate collision, the speedometer is still there to make sure that there is proof that you were driving within manageable speeds as the speedometer ends up locking.

So, in a sense, a locked speedometer after impact serves as evidence of whether or not you were driving within the speed limit.

Do speedometers stop when you crash?

One of the most obvious roles that the speedometer of your car has is to keep track of your speed.

Of course, there is a good reason why you need to keep track of how fast your car is going as this allows you to make sure that you are driving at safe speeds.

When it comes to driving, safety should always be first because you need to make sure that you and those around you are kept safe from reckless driving or accidents.

You already know, accidents can easily happen on the road especially when it comes to those who are driving recklessly on roads that have speed limits.

So, in that case, your speedometer should be able to help you keep your car within the proper speed limit especially when the safety of everyone around you is involved.

That said, when you do end up figuring yourself into an accident while you are driving regardless of whether or not you are driving within the speed limit, you might be wondering whether or not your speedometer will still reflect the same speed your car was at the moment of impact.

After all, this can be the proof that you need to show when you want to keep yourself free of any liabilities.

So, do speedometers stop when you crash?

In the case of older mechanical speedometers, yes, they do stop or lock up whenever you found yourself in the middle of a crash.

At the moment of impact, the speedometer should freeze at the speed your car was at, and this is due in large part to how the speedometer loses power due to the crash.

This has also been quite useful for the authorities as they will be able to check the speed of the car during the moment of impact.

So, if you are talking about two or more vehicles that are unfortunately part of the accident, the authorities could easily look at the speeds of the cars without having to check whether or not there were cameras that caught how fast the cars were going.

And by simply looking at the frozen speedometer, they could ascertain which cars were not driving within the safe speeds.

As such, the fact that a speedometer freezes at the moment of impact is a way for authorities to ascertain who is liable for a crash.

It is also a way for you to rid yourself of any liability in case you know for certain that you were driving safely when you found yourself in the collision.

This is how important the speedometer is not only while you are driving but also at the moment of an unfortunate road accident.

However, this shouldn’t be something that works with newer speedometers that run on electric or digital mechanisms.

That’s because newer speedometers rely on the engine control unit or ECU to keep the records of all of the instruments of the car. The ECU, in this case, is considered the black box of the car.

So, in electronic or digital speedometers, the speedometers don’t tend to freeze at the moment of impact as they may end up going back to zero.

But the authorities can always check the speed of the vehicle at the moment of impact by looking at the records in the ECU, which stores the car’s speed.

As such, the speedometer still serves its role as a way of providing evidence in case you want to prove that you were driving safely.

What would cause a speedometer to stick?

When a speedometer locks or freezes, the usual reason why this happens is due to the fact that the speedometer loses power.

Most speedometers immediately lose power at the moment of impact so that the car would be able to keep a record of how fast the car was going when the crash happened.

So, the reason why this happens is due to how the speedometer is designed to lose power similar to how an electrical issue with the car can force all of your instruments to lose power as well.

As such, it is not only a collision that can cause a speedometer to get stuck or freeze because a sudden loss of power or electrical issues in your car can also cause this.

Is the speedometer easy to get damaged?

If you are talking about older speedometers that relied on gears and wires, you could say that the speedometer can easily get damaged even with the slightest impact.

That’s because the impact could cause a lasting effect that could damage the moving gears and parts in these speedometers.

That’s why, when a speedometer locks up during impact, it is also most likely damaged.

Meanwhile, this shouldn’t be the case for the newer speedometers that make use of electricity or digital technology.

That’s because newer cars all rely on the ECU or the car’s black box for all of the data on the vehicle’s dashboard.

In that case, because the car no longer uses simple mechanisms instruments, newer speedometers are more likely to be more durable than their older mechanical counterparts.

Then again, most cars that are kept safe and are regularly maintained have speedometers and other instruments that don’t end up getting damaged throughout the vehicle’s entire lifetime.

So, as long as the vehicle doesn’t find itself in an accident regardless of whether or not the crash is minor or major, the speedometer should last for a very long time and will not easily get damaged.


Collisionscience.co.uk: Speedometer Examination

Transport Research Board: Post-Collision Speedometer Readings And Vehicle Impact Speeds

Quora: Speedometer Lock