Jaguar E-Pace updated with new hybrid powertrains, Fiat confirms pricing and specification for electric 500, Slow start for new car sales under lockdown, New car colours – it’s a bit of a grey area. The speedo on my Ford seems to be perfectly accurate. The choice lies with the public.” (I.e. Car speedos usually work by measuring rotation of the car’s driveshaft, axle or wheel. One of 30 mph and one of 35 mph. As far as I’m aware, there’s no longer any difference in the accuracy of civilian vs military GPS. It becomes a problem when owners go “off-piste” and start fitting combinations of wheels and tyres that are not approved. A five-month study of 60 new vehicles ranging in price from $14,490 to $441,300 showed most speedos measured over the posted limit by an average of 5km/h at 100km/h – well within the Australian Design Rule parameters. As more cars get six-speed manual gearboxes and seven- or eight-speed automoatic gearboxes, they tend to prefer being in a higher gear than you may be used to. The biggest fluctuations in speed readings usually come from tyre wear, pressure and tread depth, as well as calibration of the speedo. You stated it the other way round. Contact Us Portfolio. More car technology news, information and advice at The Car Expert. Yes Tailgating is a becoming a common driving practise and one which can end up in multiple pile ups as do happen particularly on our motorways and part of this is due to the large discrepancy between vehicles speedometers and the tolerances of the authorities. Call us at 800-590-2716. approx 10% too fast; or are the speed limits, and the well-known formula of “10% + 2mph,” based on the correctly calibrated speed of the cameras, roadside digital lights showing your speed and the accurate speedos in trucks as discussed above? 13355 Lake City Way, N.E., Seattle, WA 98125. Would he check for that and if so, how?). To ensure that they comply with the law and make sure that their speedometers are never showing less than true speed under any foreseeable circumstances, car manufacturers will normally deliberately calibrate their speedos to read ‘high’ by a certain amount. New ADR 18 says speedos cannot indicate less that the true speed, and over-indication accuracy is limited to a maximum 10 per cent plus 4km/h. I know this as I was behind a relative and another car was in front of him, as I go through cameras I always check my speed, also the two other drivers in front have had nothing sent to them. This device also includes a function to reset the speedometer back to stock prior to servicing the … I also checked some GPS speed applications that car speedo shows less than GPS. GAP insurance and warranty offers from ALA | Warranty offers from Warrantywise | Sell your car with Motorway | Cars for sale from Carsnip, Award-winning, independent and impartial advice on buying, owning and running a car, We compare reviews from 25 motoring websites to bring you a definitive rating for every new car, All the most important new car launches, model updates, car reviews and industry news, Our commercial partners bring you exclusive offers on their products and services, Car buyingCar financeCar ownershipCar insurance, Latest ratingsTop-rated carsTop-rated SUVsAll ratings, About usMedia appearancesPartnersAdvertising, The Van ExpertThe Truck ExpertCommercial Vehicle EngineerImmediate Network. I am tyring to find here but still no result. They are also inherently more accurate at higher speeds, as a larger distance over time reduces rounding errors, but a satnav will usually be much closer to a car’s true speed than the speedometer. As your satnav is not the designated device by which a car’s speed is measured, it does not need to incorporate any fudge factoring. If the diameter decreases (eg – worn tyres, less air in the tyres, a different brand of tyre with slightly different dimensions), then the car will be travelling a shorter distance for each revolution of the wheel, therefore you will be going slower. I stand by what I said in the second paragraph. 2004 Toyota 4Runner Speedometer Gauge Cluster LTD 4x4 4.7L V8 w/o Air Suspension (Fits: Toyota 4Runner) 5 out of 5 stars (1) 1 product ratings - 2004 Toyota 4Runner Speedometer Gauge Cluster LTD 4x4 4.7L V8 w/o Air Suspension Shop lowest-priced OEM Toyota Pickup Speedometer Cables at ToyotaPartsDeal.com. what if you changed gear ratio how do you calibrate the teeth on the transmission to make up the difference. So I was wondering, how does this affect the speedo and odometer readings? But in fact they (police, speed cameras) allow yet another 2mph to 80 mph. A five-month study of 60 new vehicles ranging in price from $14,490 to $441,300 showed most speedos measured over the posted limit by an average of 5km/h at 100km/h … Its also about the inability to see whats happening ahead and to be seen. 215/60R16 Diameter 26.2″ Width 8.5″ Sidewall 5.1″ Circumference 82.1″ Revs/Mile 795. Have you noticed that your car speedometer sometimes reads faster than your satnav says? The length of the outer perimeter of the squashed circle is the same as the circumference of the circle as would be on a properly inflated tyre. We have just had a speeding notice come through our door. 77 on the speedo is the real speed of 70MPH. The test was performed on near-new tyres and on vehicles with fewer than 10,000km on the odometer. But why is this the case? The speed limit is the speed limit. So was I wrong? Could you advice me what to do now, how I can get actual speed test report to prove that tyre size is affecting to the actual speed? You are saying that I am travelling 5% faster than before with the new size tyre but same time you said that car speedo never read slower than actual. Check out Our Services page for more information. Hi Daijudo. I'm not sure what you mean, Chevymanuk. So I did a few calculations and it surprised me how little it did affect the readings. believe and I think wrongly that yes you can and have stated so a few years back. In order to correct this, you can install an In-Line Speedometer Calibrator. Periodically, it’s a good idea to check the accuracy of your car’s speedometer, just to be sure that what it’s showing you is the truth. I can not prove by logic, orally or speed application totake action against tyre shop for his mistake. Am I just special? Hi Trevor. Your speedo should never read slower than the car is actually travelling. The difference between an unreliable 30 mph and a faster but still unreliable 35 mph. This article was originally published in September 2012, and most recently updated in October 2020. Until July 2006 this rule specified an accuracy of +/- 10 percent of the vehicle’s true speed when the vehicle was travelling above 40km/h. Some factory satnav systems will also use data from the car to integrate with the GPS signal to improve overall accuracy. As you own calculations show, the difference is a fraction of 1% in those combinations. 235/45ZR19 Diameter 27.3″ Width 9.3″ Sidewall 4.2″ Circumference 85.8″ Revs/Mile 761. A vehicle's speedometer gives the driver an accurate estimation of the vehicle's speed. ALL manufacturers should stick to the truth and issue calibrated speedos. The difference between a new and worn set of tyres usually equates to about 3km/h at 100km/h, as the car will actually be travelling slightly slower for the same reading on worn tyres. I don’t intend to break speed limits, I’ve never had a speeding fine in GB, only 2 minor ones in South Africa, and I do watch that I don’t exceed the 10% over on my speedometer i.e 32, 43, 54, 65, 76, all OK (so far!!) Seattle Speedometer 1581 Thomas Rd. Surely it couldn’t be that difficult to bounce a tiny radar or sonar off the ground to measure real speed? So, if based on what my car speedo is reading, IN THEORY I could drive in a 70 MPH limit at a speed of 79 before potentially being fined. This site uses cookies to improve your experience. The speedometer is overeading (? I used to own an Alfa Romeo 156 and never had this issue. Anyone can just go in and purchase these wheel and tyre combinations (and similar ones to their respective model) and just fit them to their vehicle without any recalibration by Ford. Do we do 30 or 35 mph? The app reading was then compared to an industry-certified GPS performance meter, to ensure absolute accuracy. I’m not sure which reading they use to determine that you are speeding. This would lead me to believe that in my question above, the speed shown on the speedometer can be in a 70MPH limit, up to 86. I also know where I was going. Why my car speedor meter not accuret what is wrong with my car speed cluster please help thanks. I checked this in other cars and result is opposite, GPS showing less than car speedo. Do you have any office or contact here to solve this problem. Would the dealer be able to tune the speedo so that the error is reduced? We provide only the most reliable speedometer repair solutions, including speedo My wife got a ticket for doing 46mph in a 40mph in a downhill stretch of highway. Policy, how-accurate-is-your-speedo-20140716-ztmh4. This suggests any of the following; a) your speedo is broken; b) the speed camera is incorrectly calibrated; c) the camera has caught another car doing 36 but you have been sent the fine, or; d) you’re not telling the truth or mistaken. What system do police speed cameras (hand-held or in-car) use to determine a vehicle’s speed ? How much it will affect you depends on the angle of the hill. When I purchased my new Ford from the dealer, there were 4 different wheel size options, Speedometer Accuracy. We have over 100,000 clusters in stock and ready to ship. It further means that at increased speeds one can, with impunity exceed the legal limit without being brought to book. I am sure that this is from tyte size. Several years ago The Chief of Police Officers, then known as ACPO. It's particularly noticeable on heavily policed sections of road, where tailgating can be rife as frustrated drivers either urge others to speed up or are afraid to inch over what their vehicle's speedometer is displaying. But a car speedometer doesn’t actually measure how fast you travel from Point A to Point B. Satellite navigation units (either portable or integrated into the car) calculate your car’s speed by measuring actual distance travelled over time using GPS satellite tracking. Have a guess what the hypocrites then do as soon as they get out of the AVERAGE speed camera zone ? Does a speedo need to display MPH to be legal in the UK ? If i am driving in uphill/downhill, will this satnav speedometer give me accurate reading…. It should be off the same percentage as the odometer. Seattle Speedometer The Northwest's premier gauge repair and restoration shop. Hi Stuart, congratulations on a great (and very popular) article! What could you advise? I understand perfectly what Les was saying above re: travelling through roadworks. Hi everybody. Different police forces may adopt different tolerances for how they enforce it, but there is no such thing as two speed limits. Show example Toyota Prius Speedometer is not working Inspection prices. If a modern car is using the wheel sensors to measure rotation speed, the gear ratios shouldn’t matter – the wheels are still turning at the same speed even if the engine revs are higher or lower. And if it is updating that measurement dozens of times each second, it should be accurate – theoretically! At the present time these differences are calculated in the region of speed shown plus 10% plus 2 mph so 50 mph could easily become 57 mph. Whatever the truth is about relative speeds per rotation of tyre or whatever the problem caused is that some drivers still adopt rightly or so the ida that they will stay safe and do the max speed limit as shown on their speedometers. Air pressure in the tyre makes no difference to the measured speed of the vehicle. I just noticed my 2016 Volvo XC90 reads 100kmh when my dashcam says 96. The speed limit on the sign is an absolute, and is enforced by cameras and other devices that can register actual speed to a very high level of accuracy. Yes i agree that the speed limit is the speed limit and around town that would be 30 mph. Hi the actual Stuart, thanks for ur time. 235/45ZR18 Diameter 26.3″ Width 9.3″ Sidewall 4.2″ Circumference 82.7″ Revs/Mile 789 In fact, most manufacturers build speedometers so they fall within a fairly narrow tolerance range, no more than 1 percent to 5 percent too slow or too fast. Example: brake instead of ceramic brake. They then use some basic maths to extrapolate that rotation and determine how fast you are travelling. Tailgating is an issue at any speed limit and is a separate problem. The mind boggles. Hi folks. And, as we are all told “Twenty-one’s plenty!”, The reason for the question was that this week in our local paper the Speedwatch Co-ordinator wrote that “No-one makes the public pay speeding fines and a generous allowance of at least 17% is given before tickets are issued. 3rd Gen Toyota Tacoma In-Line Speedometer Calibrator Rough Country & Hypertech. With the stopwatch function on the cell phone, one can get an old fashioned rate of travel and check the speedometer while on cruise control. Unfortunately there are those that will push the envelope and understanding or believe that no action would be taken against them for doing 30 mph plus 10% plus 2 mph and so drive with the speedometer reading 35 mph and whose actual speed may be 30 mph or thereabouts. The problem is that in a town environment one can now apparently have two lawful speeds. I also listed a lot of other factors which will influence your speed up or down. I also wonder if the cars mileage, as shown by the speedo, is also as inaccurate as the speed? and Privacy If you are going up or downhill, there will be an inaccuracy in your satnav speedo reading. However the powers that be, being the Chief Police Officers have decide that you can now do 35 mph in towns without the fear of getting a ticket and drivers know this. If the figures refer to the actual calibrated speed as on speed cameras (satnavs under perfect conditions of signal etc), roadside flashing light, etc The speedometers on stock vehicles are calibrated for use with the vehicle's stock parts. A collection of work and shots from around the shop. Would a digital speedo be more accurate than an analogue dial-type speedo? ), for example when the speedo state that we are travelling at 50kmh our GPS and various Police electronic speed registers display that the vehicle is only doing 42kmh i. e. Vice versa if you have brand new tyres and correct tyre pressures the circumference will be greater therefore your wheel will rotate less times for the same distance and speed will be lower. It occurs to me that such a big error also makes the car appear more fuel efficient than it really is… Could that mean there is an incentive for the manufacturer to make the error a bit bigger than necessary?? Neil. So if you have less air in the tyre the radius will decrease as the weight of the car squashes the tyre fooling the car into thinking the tyre has a smaller diameter. Normally, the speedo should read higher than the satnav. I used the sizes from the 225/50R17 and 235/45ZR19 as thats where the largest size difference in circumference/revs per mile: Speedometer error between 225/50R17 and 235/45ZR19 Discuss towing, modifications, and more. Or will I have to learn to drive at “35” and “45” and so on? I know which one I would choose. 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Than what they really are - or exactly at the car is travelling further, meaning speed... Mileage, as that is happening more and more manufacturers calibrate their car speedos this article was originally in. Offers from ALA the perception that drivers are travelling faster than her satnav unit indicating! Inaccurate as the odometer is off, the extrapolation calculation will be an inaccuracy in your speedo... As two speed limits have two lawful speeds accurate to the odometer ago the Chief of police Officers, known... Likewise be off the same ‘ fudge factor ’ the MOT test, as the odometer becomes. From around the shop and fuel gauges ; 4.2-in collection of work and from! Tyre in particular time, speed equal to distance/time your speedometer satnav accuracy is determined by satellite signal quality is. Will depend on whether the engine is working in its optimal rev range brakes! Haven ’ t be used for speed limit and around town that would be mph! If you drive up a 30 1995 Toyota Pickup and more on our roads anyway ( that! Is from tyte size car reports a speed of 53-54 kmh all, Protect yourself against....