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Discussion summary
YOUR RESEARCHActual vs Displayed Speed
Leading reported evidence
Run stock 225/295 tyres too
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Leading evidence: 'Run stock 225/295 tyres too' (no explicit attributable resolution; this is a reported action or suggestion). Across 1 matching discussions, The most frequently discussed action is 'Run stock 225/295 tyres too' (1 discussions). For that action, 0 discussions report a resolution and 0 report an unsuccessful attempt. No action has an explicit, attributable resolution report under the current rules. These are forum reports and suggestions, not a confirmed diagnosis.
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Suggestion
All I know is that mine is within 1-2 mph both on my iPhone GPS when testing on the Waze app, and same on the speed signs in our city that tell you if you are going too fast.
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Suggestion
You can also also use a GPS app on your phone to validate your own readings.
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Suggestion
All I know is that mine is within 1-2 mph both on my iPhone GPS when testing on the Waze app, and same on the speed signs in our city that tell you if you are going too fast.
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Lots of major road construction near me, hence lots of K band roadside speed signs warning drivers of posted vs their actual speed. Every time i drive my 03 4s past anyone of them it consistently indicates that my car�s speedometer reads 3 mph faster then radar says. Since I'm basing this on at least 5 different radar signs i trust that the signs are accurate and my speedometer isn�t.
Does Porsche do this on purpose?
PS....i guess my top speed is now only 139, not 142....
It's my understanding the Porsche, and other European manufacturers do this intensionally. I've been told a few versions of why, but the one that seems to make sense is the one that refers to a European law that penalizes manufacturers if their speedos display low (slower than actual). As the story goes, this is why they set them to read high, to compensate for some variance in tire and wheel sizes an owner may instal.
Years who road and track had a big article about this, and yes, they get penalized if the Speedo tells you slower than reality so they intentionally make it read faster than reality to avoid risk.
Mine reads very accurately/consistently 3mph over actual speed. You can verify via GPS...(you don�t have to wait til you pass one of those speed display signs 😉
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Mine is consistently 3 mph over as well, as compared with the display on Waze or the DashCommand app. My Volkswagen does the same thing, MK-I cars can display the actual KPH in the climate control unit. I forget how but I've done it.
I've read the same thing about European Union regulations,
Mine 99 is also +3 (higher indicated than actual).
You can also also use a GPS app on your phone to validate your own readings.
My wife�s Audi Q5 is +0 (dead on), and coming from her BMW X3, which was +6, we really have to watch our speed. Don�t want to get caught doing 25 over when we are aiming for 19 over, as there�s a big difference in penalty between the two.
Normal condition for almost ALL vehicles. Just had a customer at the shop with a for d explorer complaining that her speedometer was way off. what is found (which is typical) was at any speed lower than about 45mph the speedo was dead on. then from about 55+ they are consistently off by 2 - 3 mph with the dash reading higher than actual speed.
My ‘99 is high by 3 mph from 30 to about 50, then is off by 4 mph. This is the farthest off of any car that I have every owned. I get the reasons, but Porsche kind of took it to extremes. Based on GPS, our VW GTI and BMW 335i are both about 1 mph to 2 mph high, which is what is my experience with most other cars that I have owned.
Not a big deal, I just have to remember when I drive the BMW to not drive an indicated 53 in a 45 like I do in the 911.
Daryll
Mine for whatever reason is closer to 4-5MPH higher than radar. C4S running stock 225/295 tyres too. My 2011 A4 is only about 1MPH off, Lexus RX350 is about 2 off.
No idea, and on the Bimmerfest forum they have the same issue we are talking about here. All I know is that mine is within 1-2 mph both on my iPhone GPS when testing on the Waze app, and same on the speed signs in our city that tell you if you are going too fast. Maybe they made a mistake on mine, who knows?
I will say my 911 is the farthest off of any car that I have had since I have owned a GPS or now iPhone.
Daryll
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