Speedometer inaccurate above 45 MPH...
08-06-2010, 10:47 PM
#1
Speedometer inaccurate above 45 MPH...
Alright everyone.
I just picked up a 96 Maxima. According to my GPS, the car's speedometer is off by about 7 MPH too high when traveling above 45MPH. For example, if I were to set the cruise at 70 MPH, my GPS says I'm traveling at about about 77-78 MPH.
Well, I figured the GPS speed indicator may be a bit inaccurate
. Well, this was not the case, as I tried the GPS in my 2001 Maxima and got accurate speed comparisons throughout the entire speedometer. Also, when driving the 96 and following my 2001 Maxima with it's cruise set at about 70 mph, the 96 would read about 77-78 mph.
Strange.
Well, it gets even crazier. Anything below 45MPH, the GPS is dead-on accurate with the speedometer of the 96. When the cruise is set at 45MPH or less on the 96, it stays with my 2001 Maxima set at the same speed. As soon as I creep up past 45 MPH, the speedometer starts to read higher than my actual traveling speed as indicated my my GPS.
I'm stumped as I have never heard of the speedometer being inaccurate above a certain point. I've only heard of issues with the speedometer being inaccurate throughout the entire speedometer range.
Any suggestions? Faulty speedometer?
I just picked up a 96 Maxima. According to my GPS, the car's speedometer is off by about 7 MPH too high when traveling above 45MPH. For example, if I were to set the cruise at 70 MPH, my GPS says I'm traveling at about about 77-78 MPH.
Well, I figured the GPS speed indicator may be a bit inaccurate
. Well, this was not the case, as I tried the GPS in my 2001 Maxima and got accurate speed comparisons throughout the entire speedometer. Also, when driving the 96 and following my 2001 Maxima with it's cruise set at about 70 mph, the 96 would read about 77-78 mph.Strange.
Well, it gets even crazier. Anything below 45MPH, the GPS is dead-on accurate with the speedometer of the 96. When the cruise is set at 45MPH or less on the 96, it stays with my 2001 Maxima set at the same speed. As soon as I creep up past 45 MPH, the speedometer starts to read higher than my actual traveling speed as indicated my my GPS.
I'm stumped as I have never heard of the speedometer being inaccurate above a certain point. I've only heard of issues with the speedometer being inaccurate throughout the entire speedometer range.
Any suggestions? Faulty speedometer?
Last edited by tcaughey; 08-06-2010 at 10:51 PM.
08-06-2010, 10:56 PM
#3
I'll actually check this out tomorrow. Everything is stock. Stock honeycomb rims/suspension/etc.
I guess I assumed the tires were the correct size, haha. I always overlook the simple things. There is the possibility that the tires may be a bit too big even though they look "stock" size.
But even if they were a bit too big, would they only affect the speedometer readings about a certain point like that? Seems a bit odd, but anythings possible. I'd think that taller tires would throw the speedometer off at all speeds.
I guess I assumed the tires were the correct size, haha. I always overlook the simple things. There is the possibility that the tires may be a bit too big even though they look "stock" size.
But even if they were a bit too big, would they only affect the speedometer readings about a certain point like that? Seems a bit odd, but anythings possible. I'd think that taller tires would throw the speedometer off at all speeds.
Last edited by tcaughey; 08-06-2010 at 10:59 PM.
08-06-2010, 11:27 PM
#4
My car has 225/55/16's instead of the stock 215's thanks to the previous owner. (and one new Arizonan brand discount tire special on the back...who buys just one new tire?)
According to the miata.net tire calculator this is only 1.7% difference in speedometer readout. So if I'm going an indicated 80 mph I'm really traveling 81.36 mph. So, if you're dead on accurate at 45 and 7-8 mph low at 70 then something isn't right. The 7-8 mph difference calculates to around 10% error. If you have stock wheels then you'd have monster truck tires to get that amount of error...plus it would be noticeable at 45 too.
So, two scenarios are possible. One, your speedometer is broken/faulty. Or two, your gps and other car's speedometer aren't that accurate. (which is less likely since they confirm each other and your error at the same speed.)
Do our cars have cable/gear driven or electric speedometers?
According to the miata.net tire calculator this is only 1.7% difference in speedometer readout. So if I'm going an indicated 80 mph I'm really traveling 81.36 mph. So, if you're dead on accurate at 45 and 7-8 mph low at 70 then something isn't right. The 7-8 mph difference calculates to around 10% error. If you have stock wheels then you'd have monster truck tires to get that amount of error...plus it would be noticeable at 45 too.
So, two scenarios are possible. One, your speedometer is broken/faulty. Or two, your gps and other car's speedometer aren't that accurate. (which is less likely since they confirm each other and your error at the same speed.)
Do our cars have cable/gear driven or electric speedometers?
08-07-2010, 09:11 AM
#6
^^^ That's exactly what I was thinking. Of course, we all hate replacing parts that we are unsure of. It's a waste of money most of the time, but I think this is the first thing I'll try.
08-07-2010, 11:14 AM
#8
yeah that would be my first guess... i wouldnt just go throwing parts at it though. im sure someone has had a similar situation out there.
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