Dash speedometer vs. HUD speed
Thread Starter
Le Mans Master
Joined: Sep 2008
Posts: 7,163
Likes: 1
From: central OH
Dash speedometer vs. HUD speed
Just curious if any of you have noticed this or if this is only my car, but the speed shown in the HUD differs by about 1-2 mph than what shows on the dash speedometer (dash shows faster). Does anyone know which is more accurate? Or why they show different in the first place? Thanks for any help.
Instructor
Joined: Jan 2007
Posts: 139
Likes: 0
From: Scottsdale AZ
Race Director
Joined: Apr 2008
Posts: 17,373
Likes: 6
From: Chatsworth California
Yes, my Grand Prix GTP does the same thing. I was told it is normal. They said it takes a second longer for the signal to reach the HUD. That is why it is delayed a bit. They both are suppose to be calibrated together.
Burning Brakes
Joined: Dec 2004
Posts: 793
Likes: 0
From: Wheaton Illinois
I noticed the same. However, we have a lot of those radar setups on the roads, the ones saying "Your Speed", and when I go by, I have checked the radar speed with both the HUD and the Speedo. I find at speeds under 45, both are dead accurate on. As I hit higher speeds there is a one to two mile an hour difference.
Drifting
Joined: Jan 2007
Posts: 1,884
Likes: 174
From: Melbourne FL
St. Jude Donor '09 & '11
I've seen a reply on this before some months ago. Seems like the digital HUD rounds up the analog indication on the speedo. My HUD has always been 1 mph higher than the speedo since new.
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Burning Brakes
Joined: Nov 2006
Posts: 924
Likes: 7
From: Smith River CA
The difference is caused by two factors which are additive. The first factor is that the analog gauge has some error and the second factor is the digital gauge has roundoff error. Add these two errors together and you can have 1 to 2 mph difference in the readings. Not to worry, it's perfectly normal.
Advanced
Joined: Sep 2004
Posts: 69
Likes: 0
From: Erial NJ
I see something similar, but it's when I compare the cruise speed setting to the HUD. I'll see the DIC say it's setting the cruise to a speed that's a couple of MPH off from my current speed per the HUD, and it maintains my current speed.
Haven't tried it at low speed, as I usually don't bother with cruise when I'm driving slowly, as it usually doesn't last that long.
Haven't tried it at low speed, as I usually don't bother with cruise when I'm driving slowly, as it usually doesn't last that long.
Le Mans Master
Joined: Jun 2007
Posts: 7,610
Likes: 12
My dash is 1 to 2 mph less than the HUD, but I think I got it figured out. When I take my eyes off the road to look down trying to focus on that analog speedometer, my foot automatically comes off the gas pedal a bit 
Safety Car
Joined: May 2006
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From: Providence Forge, VA
St. Jude Donor '08-'09-'10-'11-'12