Meeky Moose Posted August 16, 2011 Share Posted August 16, 2011 ok, so my 91' legacy just turned 100k today when it had the stock 185/70/14 tires on it the speedo was about 4mph faster than i was going according to my gps on a flat straight road.. when i put the 205/55/16's on it it was dead on with my gps.. now its got 205/50/16's on it and the speedo is back to 4mph faster than i am actually going.. it makes no sense to me, but is there a way to change the speedo gear to correct it? i know theres a difference in tire size so that would make the speedo change, but why would it be off with the stock tires on it? i know on jeeps the gear is super easy to change, just never looked at changing on it a scooby.. and my 93' impreza came with 13" tires stock... lol it goes against common knowledge.. i'll have to take a pic of the vin tag to prove it.. Quote Link to comment Share on other sites More sharing options...
curtisbad Posted August 16, 2011 Share Posted August 16, 2011 the difference with the different tire sizes makes sense conidering the 205/50/16's are basically the same diameter as the 185/70/14's. as far as your speedometer not matching your gps , are you sure the speedo is to blame and not the gps? i'm no gps expert never having had one , but is it possible that it could be out of calibration or something? i don't know. i've also never adjusted a speedometer on a subaru. i know mine is about 5 mph off. i've just learned to deal with it. if i want to go 55 mph i just go 50 on my speedometer. i guess that's the redneck mechanic in me. curtis Quote Link to comment Share on other sites More sharing options...
Meeky Moose Posted August 16, 2011 Author Share Posted August 16, 2011 the difference with the different tire sizes makes sense conidering the 205/50/16's are basically the same diameter as the 185/70/14's. as far as your speedometer not matching your gps , are you sure the speedo is to blame and not the gps? i'm no gps expert never having had one , but is it possible that it could be out of calibration or something? i don't know. i've also never adjusted a speedometer on a subaru. i know mine is about 5 mph off. i've just learned to deal with it. if i want to go 55 mph i just go 50 on my speedometer. i guess that's the redneck mechanic in me. curtis mines just the opposite, if i wanna run 75 down the freeway i have to run 80 on my speedo Quote Link to comment Share on other sites More sharing options...
Fairtax4me Posted August 16, 2011 Share Posted August 16, 2011 GPS measures speed based on change in position relative to the satellite the unit is tracking from. So the only reason it would be wrong is if there is some sort of obstruction between the unit and the satellite (trees, building, tunnel, etc). My sedans speedometer reads 3 mph high. Quote Link to comment Share on other sites More sharing options...
johnceggleston Posted August 16, 2011 Share Posted August 16, 2011 your sppedo being off could ba as simple as some one put the needle on wrong. that is the only way i know to adjust one. it is a pain because you have to do it while driving the car. as far as the tire size changing it. a different size tire will change your speedo reading, but it should change it a percentage, like 2.8% for 185/70/14 to 205/55/16. this means your speedo will be changed about 1mph at 35, but 2 mph at 70. the tire sizes you are dealing with will not change your speed 4 mph. have your speedo calibrated, if it is an auto trans put the fwd fuse in under the hood unless it is a 4 wheel dynomometer. 5 speed trans MUST be done on a 4 wheel dyno. Quote Link to comment Share on other sites More sharing options...
Meeky Moose Posted August 16, 2011 Author Share Posted August 16, 2011 ohh thats the other thing i forgot to mention was, its 4mph off at 30mph and at 100mph.. doesn't matter its always 4mph off.. Quote Link to comment Share on other sites More sharing options...
Rooster2 Posted August 16, 2011 Share Posted August 16, 2011 I have owned a number of cars that the spedo is off by as much as 5 mph. It is not uncommon. Cars are just made this way. It is better to just live with it. There is no ez way to fix this. Your GPS is prolly giving you a very correct mph reading. Quote Link to comment Share on other sites More sharing options...
Chip Posted August 16, 2011 Share Posted August 16, 2011 The most accurate way of checking your speedo is to use the mile markers on the side of the highway,(Interstate). They're usually in 10ths of a mile with the actual miles indicated every mile. Set your odometer at 0 at one of the mile markers and drive 10 miles. As you drive past the mile marker 10 miles later, take note of your odometer. Seeing as the odometer and speedo run off the same gear or sensor, you'll be able to calculate exactly by what % you're off. Quote Link to comment Share on other sites More sharing options...
johnceggleston Posted August 16, 2011 Share Posted August 16, 2011 (edited) since the speedo is off 4 mph at every speed, the needle is off. you can fix it but it is a pain. you have to remove the instrument cluster and then re-install it with out the clear plastic cover. gently grab the needle at the splindle and pull it off. be careful, they break very easily. now using your GPS, drive 60 mph. while driving 60 mph re-install the needle point to 60 mph. test drive to be sure. and then go home and put it all back together like it should be. (for safety sake it is probably a good idea to have some one else drive the car while you re-install the needle. ) i tried to re-set the needle with the speedo out of the car, no good. it moves as soon as the car powers up. i tried to re-set the speedo with the car on and the speedo in place, no good. it was impossible to get it to point to zero. you have to be driving a constant speed and then set the needle to that speed. and you have to do it without breaking the needle. or buy a replacement cluster. it may be more accurate. re-setting the odo is easy. Edited August 16, 2011 by johnceggleston Quote Link to comment Share on other sites More sharing options...
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