Why Do BMW Speedometers Read High?

BMW purposefully sets their speedometers to indicate HIGH by several to more miles per hour than the actual speed, as you are surely aware. The mistake or overestimation of speed varies, and the faster you are moving, the more “optimistically” it reads.


In my experience, the speedometer tends to read around 3 mph higher than the actual speed at interstate speeds. With BMW, this has long been the situation. That’s how my old 1997 E36 was. Some folks will claim that their Mercedes, Toyota, Nissan, or whatever reads the correct speed, even if other brands may be more accurate. I’ll say this: BMW deliberately configured the speedometer to read high; it’s not that they can’t build cars with accurate speedometers. The rationale is sometimes cited in part due to European legislation stating that a car’s speedometer should never display a reading lower than the real speed. However, just use a GPS to calibrate your vehicle and make the necessary adjustments.

Why do odometers on cars read high?

We occasionally get inquiries from AA Members wondering why the speedometer on their car shows a higher speed than their GPS or digital speed meters on the side of the road. Does this imply that it is flawed or untrustworthy?

First and foremost, the majority of speedometers in cars are made to overstate the rate of travel. Modern autos are obligated by international law to overestimate their actual speed. A European standard that states that speedometers cannot show readings that are either less than the vehicle’s actual speed or higher than the vehicle’s actual speed by more than 10% + 4 km/h is the one that applies to many vehicles sold in New Zealand.

What does this mean in terms of actual driving? Another way to look at it is to say that the speedometer must have a reading of no less than 90 km/h and no more than 103 km/h at a true speed of 90 km/h.

This eliminates any defense you offer a police officer who pulls you over, such as, “My speedo said I was under.” In all likelihood, your speedometer would have shown that you were moving much faster than the officer’s reported 105 km/h.

To help combat the increased volume of traffic and reduce the danger of accidents, a speed tolerance of 4 km/h is normally implemented on New Zealand roads over the Christmas/New Year season. You hear from some people who react badly to tolerance more and more often that accidents are not caused by speed but rather by the drivers themselves.

The tolerance does not increase or decrease the speed limit. The only difference is that you’re more likely to be stopped if you choose to go above the limit, thus penalties will only be more severe for those who choose to ignore it in the first place. The 4 km/h limit provides a modest buffer for speed creep, downhill travel, or the use of alternative wheel and tyre combinations, all of which may, in certain cases, have a negligible impact on the odometer reading but are the owner’s obligation to maintain. The speedometer reading can also be influenced by tire pressure; under-inflated tires might cause the speedometer to overestimate actual speed.

While you could believe another vehicle is moving slower than the posted speed limit, that may not actually be the case due to the standards for car manufacturers, the impact of wheels, tyres, or tyre pressure, as well as other factors.

34 of the 379 fatalities on our roads in 2018 occurred in December. We all have a responsibility to drive safely this summer. However, the quicker you’re going, the less time you have to react to risks and avoid risky circumstances. Of course, driver mistake and bad vehicle handling contribute to the road toll. There are even more reasons to obey your speedometer now that tourism is rising and bringing more drivers to our roads who are unfamiliar with them.

Are speedometers high-reading?

Finally, as the rubber on your tires deteriorates over time, the circumference steadily shrinks. Worn tires alone can reduce the accuracy of your speedometer by more than a percent. Most speedometers are made to read slightly higher than actual speed in order to counteract all of this and assist you avoid receiving a speeding citation.

Can you calibrate a BMW speedometer?

Instead of the speedo registering 2-4 miles higher than my actual speed, I installed non-run flats and sport wheels on my Z4 that were larger than the OEM wheels and tires. This solved the problem.

The end result is an 80 mph speedometer difference of 1 mph. Very near to me. Many E90 users believe that it is impossible to accomplish since they need to flash the KOMBI module to the most recent version in order to have more than two settings for the parameters stated above. Some people tried to add their own values, however KOMBI doesn’t appreciate custom numbers and gives a BC error.

BMW Speedos: How reliable are they?

Additionally, GM’s domestic goods are the most accurate by manufacturer, and BMW’s are by far the least accurate. Another pattern: While 90 vehicles displayed speeds greater than 71 mph, only 13 of our 200 test speedometers indicated speeds below genuine 70 mph, and only three of those were below 69 mph.

Why does my speedometer show a higher speed than I am traveling?

Tire rotations are used to calculate a speedometer’s reading, although other factors including tire size, pressure, and changing road conditions can also affect it. Because of this, automakers build speedometers with a slightly inflated reading to account for these effects and prevent you from inadvertently exceeding the posted limit.

How far do speedometers read over?

Measures of speed and the law Never let the speedometer display less than the actual speed or more than 110% of the actual speed plus 6.25 mph. Your speedometer can lawfully read up to 50.25 mph, but never less than 40 mph, if your actual speed is that amount.

Why does my speedometer show an incorrect speed?

Speedometers may display the incorrect speed. The age of the vehicle is a significant influence, as older cars with many miles and wear on them frequently have speedometers that are not as accurate as they formerly were. The load on the vehicle, tire temperature and pressure, and tire wear are further considerations.

Do auto speedometers reflect actual speed?

With a few minor modifications, UK legislation is based on the EU norm. A speedometer must never display more than 110% of the actual speed + 6.25mph, nor can it ever display less than the actual speed.

In this case, your speedometer could lawfully read up to 50.25 mph but never less than 40 mph if your actual speed is 40 mph. Or, to put it another way, if your speedometer reads 50 mph, you won’t be going any faster than that, however it’s possible you could be going only 40 mph.

Car makers typically purposefully calibrate their speedometers to read “high” by a set amount to ensure that they are in compliance with the law and that they are never showing less than genuine speed under any foreseeable conditions. Your satnav doesn’t need to include any fudge factors because it is not the official tool for measuring a car’s speed.

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Why can BMWs only travel at 155 mph?

The Gentlemen’s understanding They agreed to restrict the majority of their standard edition vehicles to a top speed of just 155 mph. Each brand voluntarily entered into this agreement to assist not only the environmental conditions but also road safety.

Does the speedometer display the top speed?

  • Even though the automobiles aren’t built to run that fast, the majority of speedometers top out at 140 or 160 mph.
  • The method helps automakers meet their need to mass-produce common gauges for various vehicles.
  • Additionally, it offers psychological advantages to drivers who might like to view themselves as novice racecar drivers.
  • The drawback is that some people might speed dangerously because they feel overpowered in their vehicles.

The majority of us do not own a Bugatti Chiron, a supercar with a top speed of about 300 mph. There’s a good chance that the minivan or car in your driveway can only actually reach 140 or 160 mph.

However, even if you floor your family roadster, you probably won’t go much faster than 100 mph, leaving a large portion of empty space on your speedometer at the 120, 140, and (if your car talks seriously fast) 160 mph marks.

This is illogical from a design standpoint: why bother creating a gauge that misrepresents the car’s actual capabilities? It turns out that the solution is a little more intricate.

Are speedometers completely reliable?

The accuracy requirements for speedometers are also outlined by UK speedometer rules, which are based on a European Union standard.

According to the law, speedometers cannot ever understate a vehicle’s speed while also never exceeding 110% of the real speed + 6.25 mph.

Therefore, if you’re traveling at 40 mph, your speedometer may display up to 50.25 mph, but it will never show a speed below 40 mph. Car manufacturers adjust their speedometers to slightly overreport their vehicles’ speeds in order to comply with the law.

Does calibrating speedometers need to be done?

To ensure that the torque produced by the magnetic field appropriately represents the speed of the car, all speedometers must be calibrated. This calibration must take into account a number of variables, including the final drive ratio in the differential, the diameter of the tires, and the gear ratios in the drive cable. All of these elements have an impact on the car’s overall speed. Consider the size of the tire. A complete turn of an axle causes the tire it is attached to to complete a full rotation. However, a wheel with a smaller diameter will move slower than a tire with a bigger diameter. This is so because a tire’s circumference is equal to the distance it travels in a single revolution. Therefore, a tire with a 20-inch diameter will turn around every 62.8 inches. A tire having a diameter of 30 inches will travel over 94.2 inches greater distance.

The manufacturer performs calibration to account for these variations and sets the speedometer gear to match the ring and pinion ratio and tire size that are installed at the factory. If a car owner makes modifications that cause his or her vehicle to deviate from factory specs, he or she might need to recalibrate the speedometer (see the sidebar below). A speedometer can be readjusted by adjusting the permanent magnet, the hairspring, or both. The magnetic field’s strength is typically the most easily modifiable factor. A strong electromagnet is needed for this, and it can be used to change the speedometer’s permanent magnet’s strength until the needle lines up with the input from the revolving drive cable.

A speedometer can never be completely accurate. In reality, the majority of manufacturers design their speedometers to fall within a relatively small tolerance band, not more than 1% to 5% too slow or too fast. If an automobile is kept in factory-spec condition, the speedometer should continue to read speeds in this range. However, a car’s speedometer could need to be recalibrated if it is upgraded.

One of the most frequent actions taken by automobile owners that can alter the accuracy of the speedometer is changing the tire size. Larger tires can cover more land in a single full revolution, which explains why. A good example is provided below.

The factory-installed tires on your car have a diameter of 21.8 inches. This indicates that each tire has a 68.5-inch circumference. Let’s imagine you wish to install new tires with a diameter of 24.6 inches to replace the factory tires. With a circumference of 77.3 inches, each brand-new tire moves nearly 10 inches farther with each full rotation. Your speedometer will now show a speed that is almost 13% too slow, which has a significant impact. Your car will actually be moving at 67.7 miles per hour when the speedometer indicates 60 miles per hour!