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