Speedometer calibration ?

I would guess her annoyance was caused by the fact you made her to drop the phone and mess up the text to which she was replying!

 

Sudden lane-changing is far more dangerous than driving fast (there are stats which show this!) The are videos and analyses of exactly why this is so, and I think that speed-limits should be abolished! Provided that drivers learn lane-discipline (and the rules are enforced!)

 

It is NOT a fact. You need to get your ego in check.

 

OK then, provide your proof.

 

Doesn't speeding cause sudden lane changing at extra high, extra dangerous speeds?

 

Considering that some fraction of commercial tractors have speed limiters set to about 65 mph, then any such place must;
(1) have a posted speed limit of 45 mph or lower, or
(2) not allow those commercial trucks to use such roads.

 

Not if lane discipline is maintained. Not like here in the NE USA, when I moved here in 1983 (from UK) the first time I drove on the highways, I was frightened to death by the total lack of lane-discipline! Being passed on either side! Totally unheard of where I learned to drive (UK)... ...and it has become worse than ever!!

From the inside: slow lane, medium lane, fast lane - keep to your lane and keep up with the traffic!

 

there seems to be 2 basic kinds of idiots on the roads around here - not including morons that drive with their phone in their hand - the jerks that have to go way too fast are the most dangerous, but then there's the twits that want to go exactly 55 in the passing lane, like its their sworn duty to slow all the rest of us down. both of these kinds of idiots cause dangerous swerving and weaving. hint: if you're being passed on the right side by multiple cars, you need to use common sense and move to the right as soon as its safe. if you think you're doing a public service by impeding all the faster traffic, you're not. you're just being a stupid dick and increasing the chance of a bad wreck. move over and let the speed demons go. sometimes you get to point and laugh when you see them pulled over a few miles later.

on topic, 205/60R15 tires will get your speedo closer to the actual speed. I don't know what size works best if you're lucky enough to have touring wheels. I have 215/55R16, and my speedo seems to be right on the button, but they might be a little wide for the touring wheels.

 

Speedometer Calibration

 

I suspect they give it a good try in places. 20 kmh over seems like the norm some places around here. Be that as it may: it's not a democracy. The argument that everyone else is doing is self-fulfilling, but that doesn't validate it. All it takes is a few drivers with a concience, and maybe the upward trend can be reversed, I do not know.

 

I suspect the upward trend will be reversed rather quickly once self driving cars are rolled out to the general public and start reaching critical mass. Many will be programmed to obey the speed limit. And as a test demonstrated last year, such a car can be driven from coast-to-coast without being a traffic hazard.

Plus, for research and quality control and liability reasons, these cars will likely have very good video and radar / lidar documentation of what was happening all around them when crashes and other incidents inevitably do occur. I am suspecting that these recordings will reveal a considerable amount of human error and misconduct, and eventually start putting pressure on the remaining human drivers to improve their behavior.

 

I also changed tire size as recommended here on priuschat and have matching speeds on my GPSs and speedometer. As the tires wear down, it will change 1mpg (and is a early indicator of needing new tires!).

Off topic: My next door neighbor is one of those gas hogging, SUV driving "twits that want to go exactly the speed limit in the passing lane." It is a very scary experience getting on the highway with her. And that is against the law, too. But she is one in a thousand compared the number of speeders. And then there is the new trend of ultra-speeders who are using the right-hand lane for hyperspeed lane changes. Now that is really insane. Note: it is perfectly alright to pass at 55mph(or slower) in the passing lane. You just need to be PASSING another vehicle (such as a truck on a steep incline). Speeders don't seem to understand this very important fact.

 

I presume you meant 1 mph, not mpg?

And how are you figuring that? If it is from just the reduced tread thickness applied to the simple circle equations, then I believe you won't find the change to be anywhere near that much.

This would be a great time to record experimental data, which I have so far failed to do. With a tread depth gauge, record current tread thickness and speedometer calibration factor. Then every time the tread thins another 1 or 2/32nds, re-calibrate and record. Then show us a plot of the results when the tires reach end of life.

Based on past discussion about tire RPM (revolutions per mile), I'm expecting little change, certainly much less than proportional to reduced tire diameter. RPM is supposed to be much more closely tied to the length of the steel belts beneath the tread, than to the tread thickness & overall tire diameter.

 

Dream on!

 

I don't much understand the concerns, with a speedometer that reads 1~2 mph faster than accurate. And even less understanding, for the need for mechanical intervention, say alternate tire sizes, to "correct" it.

My take, the simplest thing to do: nothing. Take the speedometer at face value.

 

yeah but bigger, wider tires look better too.

when i was a young man, i used to bury the speedo on my chevelle regularly, through traffic, one lane roads, wherever. I'm not quite sure why i didn't die, or even wreck the car (i still have it). now that I'm an old fart, i realize what a jerk i was back then. but it was fun...

 

LOL! Ya, mph, not mpg!
Here's some real data: my speedo was about 2mph off with the original (and awful Goodyear) worn tires. When I put the new, larger size tires on, the speedo suddenly matched the GPSs. But that's a relatively big jump in circumference. After about half the tread life on the new tires, I've noticed a 1mph difference. And this is the second set of tires I've noticed this change. My guess is that the tires don't quite perfectly match the GPSs, so a small change in circumference is just enough to make the speedo read one mph off. In any case, I am happy with the results of the tire change(s).

 

Actually, modern GPS units under most conditions without signal blockage by trees, etc. are VERY accurate, and much more accurate than most automobile speedometers. If you search for GPS speed accuracy on the web, you will find clear documentation of this. I am not allowed to post a link here.

 

Just one more example of the adage "Lawyers and insurance men are ruining everything."

In the FWIW department, I suspect most of you will find your speedo is actually off by a percentage rather than a specific mph. Through LOTS of testing I've determined my '06 is off APPROXIMATELY 3%. What that means is, at an indicated 26 mph I'm actually doing 25, at an indicated 47 mph I'm actually doing about 45. The reason it's a little askew is due to the digital speed reading. Since it can't show fractions of a mph it defaults in one direction, higher or lower. I have verified this all the way up to an indicated 85 mph at which point I'm actually doing 82.45.