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Dash Speedo / HUD accuracy

jprixgt

jprixgt

New member
So, I was on the highway the other day and set the cruise control to 75 according to the heads up display. The needle on the dash speedo was pointing in between 75 and 80. Which one is more accurate? Wondering primarily out of curiosity.
 


HUD. The needle is driven by a motor that receives the same digital value as the HUD. If it's not showing to the right spot it might need to be adjusted.
 
Thanks....primarily just curious, but nice to know which to pay attention to when trying not to get a speeding ticket.
 
The HUD is just as accurate as a GPS. Which IS 100% accurate.
 
at the dealership they will tell you if they are between 5mph of each other, its in spec, i dont agree, go by the hud though as everyone else said, the motor could vary in the IC.
 


I think the main reason is because of the actual gauge spedo layout.
 
The HUD and the gauge needle receive info from the PCM which is measuring pulses from the VSS. The discrepancy comes from the needle being off cal or the gauge markings not being perfectly accurate. The HUD will always be right since it displays it digitally.

Now, if you don't make adjustments, using a different rolling diameter tire will throw it off since it doesn't know that you changed anything.
 
Sabrewings said:
The HUD and the gauge needle receive info from the PCM which is measuring pulses from the VSS. The discrepancy comes from the needle being off cal or the gauge markings not being perfectly accurate. The HUD will always be right since it displays it digitally.

Now, if you don't make adjustments, using a different rolling diameter tire will throw it off since it doesn't know that you changed anything.
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how much would you say an inch throws it off? basically a 1/2 inch all the way around? how do you calibrate you speedo?
 
gotboost3 said:
how much would you say an inch throws it off? basically a 1/2 inch all the way around? how do you calibrate you speedo?
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Go here and put in the original stock tire size and your new tire size. It tells you all the differences:

Tire size calculator

For calibrating the speedo, you just take info from that page and someone with a tuner adjusts the "pulses per mile" value in your PCM.
 


Yep your's would be off if the height of the tire / rim combo changed.
 
TDCRacing said:
The HUD is just as accurate as a GPS. Which IS 100% accurate.
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Oh come on, do you really want to make that statement? The HUD is still controlled by the VSS, so everything will play a part, down to tire wear and inflation, let alone that different tires of the same size will be slightly different. If the owner changed to a different tire size, it won't even be close.

GPS isn't 100% accurate, either. The receiver I use is speced to be accurate to .1 knots at a constant speed, it'll be further off while changing speed, and this isn't the standard receiver in a consumer tom-tom or anything.
 
Scimmia said:
Oh come on, do you really want to make that statement?
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Sure do. Do you really want me to take a video to prove it to you?



GPS isn't 100% accurate, either. The receiver I use is speced to be accurate to .1 knots at a constant speed, it'll be further off while changing speed, and this isn't the standard receiver in a consumer tom-tom or anything
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Constant speed is what i'm talking about here. We are not talking about if the user changed their tire size. Did you not see where I already posted up that that WILL throw everything off? I think everyone knows that that has half a brain anyway.


I'm sorry that .1 knots is not accurate enough for you but I think it will suffice for most users.
 
As I said, ANYTHING will throw it off, down to tire wear and inflation, plus the factory calibration isn't generally the greatest, either. Saying that HUD is 100% accurate is very bad info, there's a reason cops have to have their speedometer calibrated regularly if they want to be able to pace someone.

Saying it's as accurate as GPS just shows a lack of understanding of GPS technology.
 
Scimmia said:
As I said, ANYTHING will throw it off, down to tire wear and inflation, plus the factory calibration isn't generally the greatest, either. Saying that HUD is 100% accurate is very bad info, there's a reason cops have to have their speedometer calibrated regularly if they want to be able to pace someone.

Saying it's as accurate as GPS just shows a lack of understanding of GPS technology.
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I think you have taken this thread yet again to an undesirable techinical level.

Cop's don't pace anyone anymore to catch them speeding.And they also don't get there spedometers recalibrated on their vehicles. And did you know that law enforcement,emergency vehiclesand the military use GPS's to monitor their speed. And when they reach a certain speed an email is sent to their supervisors to let them know they have reached that maximum programmed speed. And all with GPS's

But they are not accurate right?

Let me ask you this. What IS more accurate than a GPS???? :th_scratchhead:

The OP was simply asking what was more accurate. Speedo or HUD. And through my several tests the HUD has proven to be more accurate.

And that IS all he wanted to know. Not how accurate a GPS actually is.

I don't think I EVER said that a GPS is 100% accurate now have I? And i'm not even sure that if you had an 1/8 of tread ware that the VSS would even be able to register that small of a change.
 


And once again, you've completely dodged my point. Yes, the HUD is more accurate than the speedo. My point is simply that the HUD is NOWHERE NEAR 100% accurate as you stated. I brought up the specs of GPS to show that even GPS isn't 100% accurate, and it doesn't have all of the variables affecting it that a ground speed sensor does.

Once again, THE HUD IS NOT 100% ACCURATE.
 
Scimmia said:
Once again, THE HUD IS NOT 100% ACCURATE.
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Yeah.... Well no one said that it was or asked if it was, So i'm not sure where your going with this.

Just don't act like im an idiot (that's how what you said came across to me.) and next time and we won't have these problems. ;)
 
what if everyone else is off and all this time 1mph was really .99 mph? lol see my point, who gives a damn as long as your 1-2mph accuracy range.
 
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