Speedometer inaccuracy (Long trip verification)
 

I just got back off my 6500 mile trip in my RX-8. I had lots of time to evaluate this and that.

Here are my concerns and complaints:

Heating of the feet is not comfortable. Too much air is put to the back seats. There should be an option to close a damper for the back vents.

Cycling of A/C when hot outside (Going to address with dealer)

MPG is low. The best I came up with was 23.1 mpg at 60-65 mph.

Intermittent oil light at 80-82 mph. (Going to address with dealer)

Speedo out of calibration This is my biggest complaint of all. I calculated numerous times while on my trip to verify the accuracy. The speedometer is not accurate (verified by about two mph via those construction area radar guns that tell you how fast you are going) and have calculated the odometer error based upon mile markers (performed 8 times in different parts of my trip). The odometer is off 1/10 of a mile for every 6 miles driven. With this information, you can calculate the following:
6 miles = 1/10 mile error
60 miles = 1 mile error
600 miles = 10 mile error
6000 miles = 100 mile error
60000 miles = 1000 mile error

With this information, it appears that for every 60.02 cars that Mazda sells, they are able to negate one car with warranty at the end of 50000 miles. To me, this is a problem that needs to be addressed and fixed. In reality, I am only getting 49167 miles of an actual warranty.

Don't get me wrong, I love this car. There are alot more things that I like than dislike. But I feel that the odometer/MPH issue should be resolved. I will keep you guys posted as to my progress.

I can understand most of your complaints (I need a new oil pan as well), but the mpg you got was great. I've gotten at most 25.5, and that was ONCE. Most of my highway average around 22-23. I think you need to drop that off your list of concerns :).

"Heating of the feet is not comfortable. Too much air is put to the back seats. There should be an option to close a damper for the back vents."

I put duct tape over the back seat outlets, which are under the seats. The airflow to the front footwells increased significantly.

how much is the speedo off by?


EDIT:
oops, never mind
________
Medical cannabis seeds

Re: Speedometer inaccuracy (Long trip verification)
 

:confused: First, speedometer - it's against federal law for a vehicle to indicate slower than it's actually going - so EVERY manufacturer that sells in the US calibrates their speedometers to indicate very slightly faster. 2 mph at highway speeds (as many of us have already found and posted) is more accurate than many vehicles on the road, and certainly within allowable tolerances. Nothing will be done (nor should be done) about this.

Second, odometer - just what sort of accuracy do you expect? It's within 1.7%!!! Again, well within required limits! Don't bother, there is nothing that can, will, nor should be done about this.

Regards,
Gordon

I wasn't aware of the laws.... I will enquire when I take it in for scheduled maintenance and see what they say.

Sounds like what I have been saying for a while, that the speedo and/or odo are wrong.

PS, did you also notice that the trip ODO is off from the main ODO? It's about 1 mile off for every 2000 miles driven...

These concerns are very interesting and informative, but in my opinion, extreme nit-picks.

"First, speedometer - it's against federal law for a vehicle to indicate slower than it's actually going - so EVERY manufacturer that sells in the US calibrates their speedometers to indicate very slightly faster. 2 mph at highway speeds (as many of us have already found and posted) is more accurate than many vehicles on the road, and certainly within allowable tolerances."

Funny. I have a Benz that has both analog and digital and the digital is 2 mph faster than the analog. Benz tells me the digital is more accurate since it's entirely electrical versus the analog which is electro-mechanical. That said, I don't think the highway radar signs are necessarily all that accurate. If they were, cops would be using them to write tickets and I never heard of that being done. So, on another note, if anyone thinks the 8's speedo is off, check out someone who owns a BMW 3 Series. Even the M3 is notorious for its highly optimistic speedo. I've read that it's as much as 10 mph faster at 80 mph than it is really going! And the ODO is always going to vary a little depending on tire inflation, wear, etc. (as will the speedo). Oh, and if the oil light comes on, even intermittently, you're maybe 1 qt. low...that's halfway between the marks on the dipstick. Add oil. I've used about 2 qts. in 2700 miles. Rotary engine use oil to operate properly.

Please don't drop the mileage complaint when talking to Mazda. You reported a best of 23.1 at 60-65, presumably out of many road tankfuls on a 6,500 mile trip. That is a very modest pace, at which you should get better than the EPA 24. My average of three tanks on a 750 mile road trip was 22.5, vs. the 25 EPA for my AT. City mileage is also 2/3 mph under the EPA number. That shortfall add$ up.

Between the construction area radar gun, the highway mile markers, and the RX-8's speedometer/odometer, I'm not sure you could really say which one is more accurate than the others. I think you have just as much basis (i.e., not much) for claiming that the highway mile markers are not spaced correctly! Maybe this is a government public works problem!

Yes, all speedometers read a touch low, they aren't allowed to read high, so the automakers do a bit of known "error"... IIRC european cars are especially bad at this...

Wasn't there a thread where someone checked the speedometer w/ GPS, and found that it was actually pretty close?

Yep, I found that mine was within 2% all the way to triple digits, when compared to my GPS.

All this sounds very scientific but....

1. Those construction sight radar guns are notoriously inaccurate. They are there simply to remind people to think about how fast they are going compared to what the speed limit (much like the effect that video cameras and tv's showing you walk into a grocery store have in keeping people from shoplifting).

2. Have you ever thought of who placed those milemarkers? Do you think they were terribly concerned with the fact that people will be performing scientific studies with them? I can't see them out with a ruler making sure they they were all placed in the perfect spot.

I'm not saying that there isn't a possibility that our spedo's and odometers are inacurate but that you have to use better methods of proving it.

Also, if this is the biggest thing you are upset about....WHAT A GREAT CAR! :D

You kidding? How did you get 25? My car, and with many people's around here, the poor things only get below 20mpg.

I have Blue RX8 (not that the color matters), GT package with Nav system. I have light loads with a package, cleaning stuff/extra oil quart, and myself in the car for most part. Once a while a tag-along passenger. I live and drive in sunshine California with a bit of hills (No, not SF kind of radical hills). I am babying the car big time, keeping rpm around 3000, barely touch 5000 if I do acelerate, avoid next door commuting as much as possible (commuting .05 miles away). And local only, I get 15.5mpg on average. And when I do freeway cruising (driving from LA to SF), I get 18.7mpg.

Typically, my best mpg (highway only) is from full to E, I could crank in around 260 miles within that 13.9 gals. I have done it 3 times, with my total mileage up to 7200 miles driven so far.

Can you post more info regarding your finding later on? I will monitor this with my GPS too. But where I live I have some hills so it won't be too accurate whereas the altitude will make the distance longer than it shows on GPS (which presumes all land is flat). The GPS is still using 2D system.

Tested against my Magellan Map330 handheld GPS mounted in a dashboard cradle. At 70mph indicated, the GPS speed was 68.9mph; at 100mph on the clock, the GPS said 98.7.

That is prety much my discovery using a hand held GPS. I consistantly read 2-3 mph slower on the gps than the speedo. So 70 on the spedo is a gps 67 or 68. 80 is 78ish. I sort of think of it as cheap insurance. I think I'm doing 85 (speed limit 75) and I am only really going 82. Cheap thrills I know, but maybe the cops will be less likely to nail me for doing 7 over the speed limit versus 10.

I thought it was just my car but as I see many of the 8 are having the speedo problem. I knotice it with in a month. Wend the miles register was almost 1k in one month and all I was driving was to work and back. (55-60 miles) with just one trip of about 60-80 miles in the same state Fl. I told my service rep and spoke to the General manager. They did not take my word for it. Im going to let them know my new findings.:confused:

I don't know what problem you're having, but what we're all saying here is that a slight variation from actual is normal - the numbers being talked about in this thread are normal and reasonable, NOT a problem!

Regards,
Gordon

I agree.
The numbers that you guys are posting are 2% or less. This is pretty typical of vehicles.

BTW, mxmedina.
At a 2% variation, that is only 20 miles over 1K. Can you honestly say that you didn't drive the additional 20 miles over a month? Your guestimate of your typical comute varies by 10% (you said 55-60 miles).

I know I am putting way more miles on my car than on previous cars. But that is because I..
1) Take all the twisty back roads.
2) Look for every excuse possible to drive.

I'm sorry, but I have a problem with this in principle. Mainly because the advantage is all Mazda's, the disadvantage all mine.

1) The warranty is for fewer real driving miles than they claim. That means that Mazda has to support the car for a shorter period of time, and I am responsible for the car's problems sooner.

2) The cars' average miles before breakdown will be larger than in truth, giving a falsely inflated public impression of the vehicle and company.

3) When I go to sell the car, there is a slightly lower resale value due to inaccurately added mileage.

4) I spend more $$ on oil changes and maintenance, or spend the money closer together.

Your warranty is for odometer miles, not actual miles (however they might differ). There is no other way to measure, is there? Even a GPS doesn't properly record distances when significant elevation changes are involved. Would you seriously suggest that people who regularly do burnouts or spin the tires on snow/ice should have a warranty adjustment to compensate for the odometer increase in mileage when the vehicle didn't actually travel those miles? How do you suggest Mazda should be compensating for tire wear, since of course as your tread wears, the tire becomes shorter in diameter, introducing more discrepancy between actual and indicated mileage?

This isn't a Mazda problem, it's common to EVERY VEHICLE ON THE ROAD. Odometers have legal precision requirements, and that's all - they are not required nor expected to be exact, just within a certain percentage.

If you really feel that your car is going to fall apart in the final 800 miles before warranty expiry and you might just miss out on warranty coverage (dang it, where is that rolleyes smiley when you really need it?), consider that most manufacturers will provide warranty coverage of a failure if it occurs just outside the warranty period (ie within 1000 miles or 1 week of warranty expiry).

Regards,
Gordon

Have you ever done this test before, or are you just this obsessed w/ your new car ;)?

Every car on the road has these issues...
Heck, if you're that concerned about it, switch to a higher-radius tire, you can cheat mazda! :eek:

I have an easy solution for you...
Go look up different profiles of tires (the online places list all the info as far as tread width, tire diameter etc).
Find a tire that is slightly larger in outer diameter, probably will be slightly wider anyway. A slightly larger diameter tire will travel further per revolution. Try to find something about 2 or 3% larger in diameter if you want to be close, or go larger if you want milage to underreport slightly.