Regarding the rather laggy speedometer (from the best motoring video),

Where might this lagginess come from? I'm not sure how speedometers generally work, but if theyre a straight copy of what the engine CPU sees, and if engine cpus see millions of data points per second, isn't that a bit worrisome?

If it is an artifact simply of the speedometer display, would that be easily fixed?

Essentially, how would you (anyone) recommend a way to have an ultraquick speedometer?




hmmmm, now that i think about it, maybe there is a reason the speedometer update is so slow... i mean it can't be faster than it takes for a person to read it, correct? Is this the case here?

 

regardless, it doesn't' matter: it'll show your speed accurately when you're cruising which is when it's important... why do you need millisecond accurate velocity updates when you're accelerating?? it doesn't matter 'cause no one plants thier foot and just watches the numbers go up, they look ahead... at least i hope they do...

because i don't know how the speedometer works, i can't guess at why it's slow to update, other than the computer takes a few measurements, and then averages them over that "lag" time?

 

I imagine that Mazda designed it that way intentionally. We do the same thing with some of our electronic gauges to stabilize the readings. Just think about this for a second. Would you prefer to look at a speedometer that refreshes once per second (ex. looks a little sluggish when accelerating) or would you prefer a display that refreshes 15 times per second (ex. updates quick enough to show acceleration but bounces frantically between numbers when you are maintaining a constant speed)? This is just my opinion but i think Mazda made the right choice by selecting a refresh rate that would make the speedo easier to read while you are cruising.

 

yup.

 

The next time you are in a late model car, check to see how quickly the analog speedo responds. 99.9% of them are actually just as "sluggish" as a digital speedo. Do this test, brake hard (no need to use the ABS, just hard) from 45 mph or such to a complete stop, and see how long it takes for the speedo to get to zero.

---jps

 

The speedo's get they're feed from a magnetically induced pulse on the drive shaft. It takes quite a few passes of the magnet by the coil to create enough pulses for the computer to generate a speed based on the time between pulses. So that adds a big part of the lag, then you add in the filtration of the signal by averaging the last X samples over time, that was mentioned above, and you see a lot of lag. And like said before, it is good engineering practice to filter datapoints to improve readability. All of our meters at work (work on a nuclear reactor) have this filtering, plus they are designed to work within the tolerances of the SECOND finest digit, so that the oscillation between the finest digits are not needed except for measuring trends.

 

I actually know the reason behind why the speedometer seems a bit "Sluggish." Back in the Early 80's, GM started pumping out these Digital Speedo's on their more luxury cars and at that time. It was a bit of big deal, they market these DigiSpeedos as "new technology that allows accurate reading on the car's speed down to the 1MPH (or 1KM/H in Canada )".

What ended up happening was that drivers were so annoyed by it because of two things :

1) the Speedo Digits keep kept go up at down because the speed of car is always changing slightly and it was definitely somewhat of a distraction for most of the drivers.

2) When cruising, most Drivers had a tendency to try to maintain a some what "constant" speed and because of these little Speedo
's kept going +2MPH -3 MPHS around their desirable cruising speed, GM got complains from "My Car can't seems to maintain at a constant speed" to "I got so concentrate at trying to maintain a constant speed, I almost ran into the guy in front of me." ( you, know what kind of people I'm talk about here.)

Anyhow, ever since that time, manfacturer learned their lessons, and start making Speedo's which are "less accurate" and more importantly "Updates less often" that way, the driver would psycologically feels more in control of the car.

Therefore, before you start complain about why the RX-8's speedo's doesn't seems to updates often enough and go up and down like that digital speedometer in those car racing arcade games, think about how annoying that little thing would be when you are cruising down the high way, looking straight up and this little light in the lower part of your vision keep "flashing" every 1 second during the whole trip.

Hope this helps you better appreciate your new RX-8

 

Point well made.

 

Thanks!

Yeah, sure it all makes sense now ... but I'm still worried that I might miss an anolog version too...



Only time and a few test drives will tell.

:D

 

You hit the nail right on the head Speed!.......

It worked the same way on my 93' Nissan 240SX coupe with heads-up display.

 

Maybe the gauges will have a test mode. For example, on my girlfriends tribute ("Also did it on my moms Focus") you hold the Trip down while you start the car until the digital odometer reads "TEST". When it goes into this mode, you can cycle thru the menu's by pressing the trip button. Eventually you'll see a digital speedometer and tachometer. The spedo is accurate to a 1/10mph and is works in a realtime mode. It's cool if you have a friend with you and a stop watch :D

 

I dunno about you, but should I find myself in the cockpit of an rx8 I'll be staring at the road and or the monster tach over the speedometer

I personally don't like digital readouts becuase they are distracting. But as long as they found a way to make it disapear into the background, I'm cool with that.

 

personally, i think the digital readout is a mistake to some degree. I find it much, much more pleasing to the eye to gauge the movement of the speedo needle. Watching a digital display change, whether quickly or not, seems alien to me. Honestly, it is prolly just b/c i have never had to deal w/ a digi speedo before and that once i get used to the car, its acceleration and braking then i can predict the speed changes based on my accurate ***-dyno.

That being said, i think the digi should update at least twice a second, however, the accuracy of the current speed can be sacrificed alittle during accelerating/braking. Think about that, do you really ever know haw fast your analog speedo is going to the accuracy of < 1 mph??? No chance. The engineers could easily build in low level intelligence that would diplay increments of 1mph that would not suffer the franetic problems of 80's digi displays. That being said, since all the gauges in the dash are electrical anyway, there's a good chance that an aftermarket supplier could design a new pod with an analog speedo in it! Somethin to think about.

 

Sad as it may sound I quite like the idea of the digital speedometer because I spend a fair amount of time flying simulated jets and of course the heads-up displays feature digital speed gauges. I'll bet you get used to it and eventually love it.

 

What is the speedo for???

The only time I look at it is when I see a cop ahead or behind, or when I am setting up my cruise control. The rest of the time I look at the car ahead to make sure I am not on his bumper. OK I do look at the speedo when the guy ahead of me is in the fast lane and going slower then I am and I want to know if I should slow down or flash them.

To shift I listen to the sound of the engine.

If you are watching the speedo you are not watching the road.

 

Midnight, perfectly stated (hey another ottawa member! Did you order yet?).

I rarely look at the speedo, you should be able to "feel" your speed, I usually look to see and I'm usually right at the posted limit.

P.S. I'm hoping an Ottawa member, Mac or Midnight (hint hint) will bring their 8 over so I can take a looksee before I order next year!

 

You can't shift by listening to the engine in a rotary

You'll never realize what RPM you are!

 

How about this: In this computer age it should not be so hard to make the speedo update quicker under certain conditions, for example throttle application % . So when the car is accelerating the speedo updates quicker, when the car is maintaining speed, speedo updates slower.

 

Hehe ..even though I never drove a rotary powered car, I suspect it will take some time to get used to this, for us piston engine people..

 

When your accelerating, the pitch of the engine changes, as well as the volume, it is just as easy to shift by feel, and sound in a rotary as it is in a piston. when maintaining a constant speed such as on the highway however, I have many times looked down at the tach only to be suprised i was cruising about 80 mph in third gear (very responsive, but gas milage sucked). Of course i never paid much attention to any of that, and just shifted when the redline buzzer came on most of the time.

 

Sh'yeah, right.

It's not an electric engine, you can shift by ear just as easily as any other engine.

---jps