Speedometer shows 2 MPH faster than actual speed. Share this conversation. Ask Your Own Chevy Question. Joined Dec 1, 2018 Messages 22 Reaction score 9. What this means: For a vehicle travelling at a true speed of 100km/h, the speedo must read between 100km/h and 114km/h. Thanks for any help. A higher value alerts the driver about the speed and prevents him or her from speeding. Chevy Mechanic: GM Tech (Cam), Chevy Technician replied 11 years ago. Up-sizing, or installing a taller tire, will lead to a speedometer reading that is slower than your actual speed. … A speedometer will read a speed slower than the vehicle’s actual speed when you replace your standard tires with larger ones. If it has, say 22 teeth now, you'd need 22 x .15 = 3.3 more teeth on the gear, so you'd get a 25 tooth gear. A new rear axle speed sensor did not fix. This is because a taller tire will have a larger overall circumference, which will cause it to travel more distance per revolution than the original equipment tire. I've noted that my speedometer is reading 3-4 mph faster than my indicated speed on my GPS. A speedometer will read the same speed as it is with the original tyres. GM Tech (Cam), Chevy Technician. As soon as I made it through that, a state trooper in a car blasted me with radar from behind. 15 inch rims. If it's at 60 mph, then that's about 9/60= .15 so it's 15% off. But it is essential to know that using bigger tires would alter your speedometer calibration, and you may need to recalibrate it to get an accurate reading of your vehicle’s speed. Speedometer reading upwards of 20 mph faster than I'm going. My speedo is 2mph under what police radar setups show. What would cause this to happen? 131 months. Monday 23rd January 2012. Anyone else noted this descrepancy? It'll gradually read from 8mph faster than actual speed, and as you increase speed it'll read almost to 20mph faster than actual speed… Speedometer Reading Faster Than Actual Speed, by a LOT. Now count the teeth on the plastic gear on the transmission end on the speedometer cable, is should have something like 18 teeth. Should I go to a 19 tooth or 17 tooth gear to adjust the reading? Sometimes, the speedometer on my '73 Chevy will read faster than I'm traveling. After I passed the officer, I sped up to 75 mph and was immediately hit by a laser trap just down the road from the radar. You need to slow it down, so you need more teeth on the driven gear. Before you ask why, ask if, or something. The speedometer read 5-15mph than my actual speed, running stock sized wherls. My GPS tells me my speed, and I think it's very accurate. Therefore your actual speed is higher than your speedometer reads. It only happens above 45mph, and there's a strange whirring noise coming from the gauge itself. I don't know quite how far off it is, but I'm estimating that when it says I'm doing 90mph, I'm really going maybe 70-75mph. I picked up a radar signal on I-91 in VT and slowed to 70 mph. If the speedometer reading is lower than the actual speed, the speedometer is slow. Because speed is defined as the distance covered per unit of time, your actual speed will be greater than the speedo reading. Speedometer reading faster than I'm going. This assumes no other changes such as tire or wheel size, engine changes or transmission changes. That means I'm running about 4900 RPMs (give or take some) at an actual 65 mph. It doesn't happen every time I go over 45mph, but when it does, it bounces all the way up to 90 - 100mph when I'm only doing about 60 - 65mph or so. Someone once told me one tooth adjustment will deliver about a 5 mph correction. You may recalibrate a speedometer in a few simple steps. Page 2 of 2 < Prev 1 2. radioprius1 Climate Conspirisist. By Kolton285 So, I recently started driving my dad's old 98 Chevy Silverado Z71, and I've noticed the speedometer is reading upwards of 20 mph faster than I'm actually going. Yellotsacul Member. My speedometer shows 65 mph at 4500 rpms, but according to my GPS my speedometer is off and it will show an indicated speed of about 71 mph at an actual GPS speed of 65 mph. Thus, with each revolution you are traveling further than before. Dec 10, 2019 #3 Your speedometer reads slower than actual because the … I have a 2007 F250. 10 MPH too fast at what speed? That means that a displayed 15mpg is actually 15*1.12= 16.8mpg actual . I swapped the rear axle in my '93 RMW due to a bad pinion bearing. On other cars I've driven, the GPS has either been dead-on, or … speedometer is reading faster than vehicle is actualing going and causing the fuel shutoff to take effect at 100 mph when I am only going 45 - 50 mph. It is fairly easy to see how your speedometer compares with your actual driving speed. Tyre pressure can also have an effect on speedometer reading; under-inflated tyres can result in the speedometer over-estimating the true speed. I have all stock sprockets. Actual MPH = 60 / minutes x number of miles traveled. A new instrument cluster did not fix. For this reason, you often find a specific colored speedometer gear for different tire sizes and rear differential ratios. If the speedometer reading is higher than the actual speed, the speedometer is fast. Answered in 5 minutes by: 12/18/2008. If it is the speed sensor on the trans, what happens if it is removed, will the oil come pouring out? Reactions: wangstarr03. The speedo on my '98 K2500 reads very high, about 23-25% higher than actual. Show Less . My 2003 Cadillac CTS 3.2 V-6 Speedometer is reading approximately 25 MPH over the actual speed. Doing the calculations using the above equation: My 996 over reads by 5mph at … The speedometer in my 1965 mustang indicates 10 -15 mph faster than I am actually going. Ever since the swap was done, my speedometer is way off. Compensating for the new tires, which are only .2" smaller in diameter (.63" difference circumference) the speed difference should be only .6 … I've done some searching and haven't been able to come up with the fix for my particular problem. Not all speedometers read 2 mph faster than the car is travelling. 45 indicated is actually about 36, 85 indicated is actually about 69. I have a cable driven non-adjustable speedometer connected to a TH-350 trans and my speedometer is always 7mph faster than actual speed. 3 Answers. Is the speedometer shot or is it just the cable that needs changing? Odometer accuracy is no longer defined. Reading numerous websites, the gps speed is supposed to be accurate. For instance, if it's 10 MPH off at 100 MPH, it's 10% off - and that will make it read 66 MPH when you're actually traveling 60 MPH. When you go to bigger tires the circumference of the tires is larger, meaning the distance around the tire is longer. After multiple parts, I finally fixed the problem. Back to the basics, if your speedometer is indicating too slow for a given roadspeed then you have to turn it faster. For safety reasons, manufacturers calibrate speedometers to read higher than the actual speed of the vehicle. Discussion. We're not just talking like a couple or five mph. This is because of the inner workings of the speedometer calibration. LordHaveMurci. _____ A useful speedometer calibration certificate will show a speedometer reading that is slower than the actual tested speed. Also you read higher speed if your tires is smaller than stock tires. This type of implementation provides car makers with some flexibility to change calibration by changing the size of the gear that mounts on the transmission. This calculator is designed to determine the difference between the indicated speedometer speed and the actual speed after a change of gear ratio on the ring gear and pinion. Enter the ratio of the original ring gear and pinion (changed from) and the new ring gear and pinion (changed to). Bigger tires=bigger around=faster actual speed than your speedometer In my case, the truck is going 12% further and faster than it realizes. Joined Nov 1, 2009 Location Alabama TDI 2006 VW Jetta TDI Package 2 Nov 19, 2009 #1 Hello everyone. Changing the stock parts, including the vehicle's tires, can throw off the speedometer calibration; larger tires cause the speedometer to read a speed slower than the vehicle's actual speed while smaller tires cause the speedometer to read a speed faster than the vehicle's actual speed. The speedometer is original but at some time or other the c4 transmission has been changed out. I recall reading an article on C&D, the test result of speedometer accuracy shows all cars read faster than their actual speed with Bimmer being the extreme, read almost 10% faster. Show More. Reply Prev 1. of 3. If they make one. speedometer reading faster than actual speed I have this problem with my 85' 190E where the speedometer is reading at least 10 mph faster than what I'm actually doing. 3 Next Reply Author. 8 to 10 mph at what speed? The car rides fine, with minimal change in handling, but I noticed my speedometer reads 3 mph higher than actual speed as compared to the speed indicated on my portable gps. otherwise you get to find a drive gear (on the output shaft) with fewer teeth. One way to check speedometer accuracy requires an empty, flat highway with mile markers and a speed … Joined: Aug 13, 2009 1,355 154 0 Location: Iceland Vehicle: 2010 Prius Model: II. Does anybody else know if there is any relationship with this problem and my faulty cruise control. Your speedometer is reading how many revolutions your tires are making not how fast they are spinning. Mine measures 4 mph faster than I am going and I certainly was glad it did Friday night. Or get an adapter box made. Speedo reading vs actual speed. That means less teeth, not more. In this particular case, let’s say that your speedometer was reading 55 mph. However, there is a limit as to how high or low a speedometer is allowed to read. 10,542 posts. #21 radioprius1, Oct 1, 2009. Category: Chevy. The faster the tail shaft spins the higher the reading on the dashboard. The speedometer driven gear will make the speedometer read incorrectly by a percentage - not a specific miles per hour. The speedo must not indicate a speed less than the vehicle’s true speed or a speed greater than the vehicle’s true speed by an amount more than 10 percent plus 4 km/h. Take the ratio of indicated speed vs actual speed, ie 55 indicated / 60 actual = 0.916, or about 8% low. I always keep my GPS on because I travel a lot. 1965 mustang speedometer indicates too fast. Since they can never be exact, Speedometer systems are designed to err on the side of higher speed readings than actual. Thread starter Gray06TDI; Start date Nov 19, 2009; Gray06TDI Member. If the speedo isn't tracking accurately, especially reading faster and putting miles on the odometer faster, this will make my warranty expire faster. Discussion in 'Gen 3 Prius Technical Discussion' started by windmilljumper, Sep 29, 2009. I presently have an 18 tooth gear in the trans. All vehicles come with speedometers that read a faster speed than actual. If the speedometer shows a speed higher than the tested speed, then the certificate is actually harmful to a speeding case, since the driver had reason to believe the vehicle was traveling faster than the actual speed. … Or low a speedometer is slow calibration certificate will show a speedometer will read faster than I running. My speed, and there 's a strange whirring noise coming from the gauge.. The tire is longer with speedometers that read a faster speed than actual speed 's very accurate Dec 1 2018. I go to a bad pinion bearing true speed of 100km/h, the truck is going 12 % and. 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