Speedo off by 3mph, OEM 15/16

[BTL3.0]

need some help from the experts..i apologize if this is in the wrong Forum..please Move if need be.

i like to use GPS when going out of town so i don't get lost. Glad i did because from 60mph + my speedo is 3mph off..meaning the cluster needle is on 60 but my GPS is telling me 57mph...

oem 15/16..
205/50-15
225/50-16

i've even tried a different GPS and still samething..so my cluster is showing i'm going FASTER by 3mph then what the car is actually traveling by.

i don't think this is normal..put on Cruise Control for 60mph on the cluster..Gps said 57mph..cruise control left on for 10mins on the interstate.

only happen 60mph+ ..everything below that matches up with GPS reading..40 cluster = 40 gps...50 cluster = 50 gps.. 60 cluster = 57 gps.

anything i can do??

thanks

 

[ktbaia]

You can adjust the speedo. There are posts on here how to do it (I did mine, which was off by 3mph @ 70 mph). However, I would guess the adjustment in linear across the speed range, so it may make your speedo off at the lower speeds where it is correct now.

Nothing ventured, nothing gained. It's worth a try anyways.

 

[nsxtasy]

It's not uncommon for speedometers to be off by a few mph, and it's perfectly normal. There are many, many sources of variation from actual. Just to name a couple of them... The difference in tire diameter between a brand new tire and one that is worn and ready for replacement is about 2 percent. And tires labeled as the same size (such as 205/50-15 and 225/50-16) can vary significantly in actual size.

 

[Briank]

On most all cars the speedo will indicate a higher speed then actual. They are designed that way and the standard is more like 5 mph high.

 

[BTL3.0]

wow, i really did not know all that..the reason i ask for help is because my last car, i can recalibrate the needle to read exactly as the GPS and match up with local speed monitor the city post up..like around construction zone...so i guess i should be worry too much then huh?

thanks for the input everyone..now on to the next problem..oem radio with very little volume..**sigh**

 

[Briank]

thanks for the input everyone..now on to the next problem..oem radio with very little volume..**sigh**

I can fix that, email me. :smile:

 

[A.S. Motorsport]

That's very common.
Although like said you can recalibrate it.

 

[BTL3.0]

if you guys are referring to the needle calibration in WiKi, i don't think i would feel comfortable doing it..it said u need to arrange for a dyno and what not..
like ktbaia said, it probably screw up the correct reading down on low speed, but higher would be corrected..

 

[A.S. Motorsport]

if you guys are referring to the needle calibration in WiKi, i don't think i would feel comfortable doing it..it said u need to arrange for a dyno and what not..
like ktbaia said, it probably screw up the correct reading down on low speed, but higher would be corrected..

Very likely although there are specialist companies any way 95% of cars don't have accurate speed readings.

In europe there even is a 5% margin on speeding tickets because of this.
So at if your speeding over here at 100 miles police must subtract 5 miles due to this.

 

[oscar_driver]

Agree with ALL ABOVE, manufacturers are a bit optimistic but that is STANDARD, they do that on purpose, so, if you are doing 160 on your nsx, means you are around 150-155

 

[stevenlee]

IWantNSX, Don't be intimidated by the thought of having to get on a dyno to calibrate your speedo. It isn't necessary. I used 2 different GPS systems in my car and found that they were reading the same speed, so I used them as the control. I then adjusted the speedo "pot" and took a test drive to compare my speedo with the GPS speeds. I pulled over and parked 2 or 3 times and made minor adjustments until my speedo matched the GPS. It was free and easy and only took a few minutes to adjust.

The confidence of knowing your correct speed is worth the small effort to calibrate your speedometer. Mine was reading a few miles slower because of larger tires.

P.S. The article you referred to says to use a "non-metallic" screwdriver to adjust the "pot". I used a metallic screwdriver and it worked fine.

 

[ktbaia]

I agree with the above. I adjusted mine because it was reading fast, and I figured it was artificially putting miles on the odometer as well (well, maybe not). I didn't use a dyno, just a GPS and it worked fine. As far as it being linear across the speed range - it probably doesn't matter. If you are off by 2 mph at 60 mph, you are only off by 1 mph at 30 mph. You probably really can't read the speedo in a moving car that accurately. I would suspect that if you are really off mark at high speed, you are also off, proportionally at lower speeds - its just hard too read the discrepancy because it is so small.

 

[BTL3.0]

understood..
i will give it a try when it starts to get warm up..i have a GPS, so that helps..