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Discussion Starter · #1 ·
I realize the built-in speedometer error (reads fast by 3-4mph) has been discussed ad-nauseum, but I've been unable to find any posts describing if this can be eliminated somehow by an electronic recalibration process using a VAG tool or similar? I'm sick of being passed by everyone when I'm going "75" and psychologically I just have a real aversion to travelling constantly at 80 or faster, even though I know its not really "80".

I just want to know how fast I'm actually going, is that too much to ask!? :banghead:
 

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I realize the built-in speedometer error (reads fast by 3-4mph) has been discussed ad-nauseum, but I've been unable to find any posts describing if this can be eliminated somehow by an electronic recalibration process using a VAG tool or similar? I'm sick of being passed by everyone when I'm going "75" and psychologically I just have a real aversion to travelling constantly at 80 or faster, even though I know its not really "80".

I just want to know how fast I'm actually going, is that too much to ask!? :banghead:
Not every speedometer is the same. I think it error may be different depending on tire pressure tread wear, etc. For instance, Firestarters speedo was only 4-5 MPH off even at top speed, but another guy who had the same car, his speedo was 10mph off at a slightly slower speed.
My speed seems to be off by about 5 MPH since when they have the radars saying "your speed is" it always shows about 5 MPH slower than my speedo.
 

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I put a little bit larger diameter tires on and this has reduced the speedometer error some. However, I find the speedometer error to be a good "feature" because it helps me avoid tickets and makes me feel like I am breaking the law.:thumbup:
 

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Hah, I was thinkin of going to 17's on my car mostly to see if it would bring my speedometer closer to actual speed. Mine's about 4 MPH fast on the highway
 

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Discussion Starter · #5 ·
Yeah, I put 17s on earlier this year, no change. But that makes sense since the diameter didn't change (225/45R17) over the stock 15s.

Whenever I pass one of those speed checkpoints I usually show ~4mph fast - speedo says 37-38mph and "your speed" shows as 33-34mph.

I'm really hoping there's an electronic tweak that can be done here to fix this annoyance.
 

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Mine consistantly reads 3 mph slower on both GPS and the radar signs that you see. I'd really like for it to be just "right." I'm hoping that the solution for this isn't hard. It used to be between 1 and 2 mph, but then I got my dash cluster replaced under warranty (fading display) and now it's off by more. Just enough to bother me. I'll search a bit and see what I can find.
 

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Yeah, that's what i use for reference, the climatronic, kind of hard looking down at that around town though, then you have to turn it off to adjust the fan or temperature also
 

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Use the digital speedo on the climatronic.
Yup.
I believe the articles been posted, but german car comapnies are required to never have thier speedos go over in a huge variety of situations, so they increase the speed shown. However, they don't read the wrong speed :)
 

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I put a little bit larger diameter tires on and this has reduced the speedometer error some. However, I find the speedometer error to be a good "feature" because it helps me avoid tickets and makes me feel like I am breaking the law.:thumbup:
Agree re: tickets. I set my cruise alot even at relatively low speeds to avoid combination of heavy foot and daydreaming. Set at speed limit + 10mph and I figure I'll be safe, except for school zones. Very easy for me to see 40 and know it's 38, 60 is 57, 80 is 76, etc.
 

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Discussion Starter · #13 ·
Yeah, I have seen the articles about why they do it and how to get the real speed from the climatronic unit.

Alas I don't have a climatronic.....2003 GLS. DOH!

I saw someone indicate they pulled the needle off to replace their gauge faces. I'm not necessarily inclined to do that just to fix 3-4mph of error but has anyone tried that?
 

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i never checked how off my speedometer is :/ i should probably do this..hell i could be going alot faster than i think i am..or even worse SLOWER!
 

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Discussion Starter · #16 ·
So the local fuzz placed one of their portable "Your speed"{ing} units on a side street on my daily morning route the other day, so I decided to conduct a little non-scientific experiment. Mainly I was curious about two things,

1) Is the error on the speedometer linear, and
2) the actual error at 80mph indicated

I currently have my non-winter P225/45R17 rubber mounted on my '03 B5.5. I haven't seen any notable differences in radar indicated speed between these and the stock 195/65R15 when they were mounted. This is expected as the O.D. is almost identical for these two sizes.

It was a 30mph zone so I was a bit restricted, but I was able to get indicated (speedo) vs. actual (radar) readings at 3 indicated speeds by carefully setting my cruise control - 20, 30, and 40mph. The radar actual values for these points were 18, 27.5, and 37mph respectively. (I say 27.5 since the display was continuously flipping back and forth between 27 and 28.) Then I plugged the values into excel and line graphed both the reference and actual points and looked at the results.



Inspecting the results for the three actual data points (18, 27.5, 37mps) shows that it DOES appear the system is linear, with a fixed percentage error built-in. Given the margin of error in the data it makes it impractical to formulate an accurate equation. So I estimated the "expected" values based on the data trend (~3mph of error at 40mph equates to ~6mph of error at 80mph indicated) and manually extrapolated the remaining data points to create a straight line chart which was consistent with the actual data points.

This analysis, as rudimentary as it is, confirms what my "speed awareness" sense has been telling me all along. When I'm doing "75" on the highway, its really more like 69-70mph, and certainly explains why I'm being passed by pretty much everyone. But at the same time, I just have this psychological issue with driving around at and indicated 80-85mph (really 74-79) which is what the traffic mainly seems to flow at these days.

I understand why positive error is included, but I think ~8% at 80mph is a bit excessive.
 
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