My testing has resulted in readings very close to EENY. Although having a speedo that is inaccurate is very annoying, I'm more concerned that I will be out of warranty before I have actually attained to true miles the Mini is covered. In addition, the MPG readings will be higher then actual since the number of miles traveled will show higher on the odometer then the car has actually traveled.

One interesting thought I had regarding the odometer: When you go to sell your mini, if required by your state, would you be breaking the law if you certify the odometer reading even when you know it has not provided accurate information?

Our mini will be going in for service soon and we will see what they have to say on this issue. I had a previous vehicle that had the same problem and the dealer was able correct it.

 

The amount of misinformation in this thread is astounding.

1. GPS steady-state speeds are extremely accurate and are probably the easiest and more accurate way to calibrate any vehicles speedometer. Mile markers and stopwatches are Okay too if you're careful in measurement.

2. By law, speedometers have an accurancy tolerances but it is NOT +/- "X" where X is a single number. In fact, in most countries, it is +10%/-0%. Basically the law says that the speedometer may read significantly high, but can never read low. This is done for safety reasons - a speedometer that reads too high is not a safety concern but one that reads too low is.

3. Most car mfgs delierately design their speedos to read about 5-8% high. This provides for variances in stock tire diameter, sample-to-sample speedometer variance, etc. The Mini's inaccurate speedometer is not a Mini thing - all cars tend to have optimstic speedometers. If it's over 10%, you may have one that is out of normal bounds.

4. Odometers have a different accurancy standard than speedos and it is typically +/- 3% or thereabouts. The reason that this is a "centered" standard is because there is no safety issue associated with the odometer reading too low.

5. Because of the different tolerances applied to speedos and odos, it is common for there to be a built in bias to have the speedo read high, but the odo read more or less accurately. This seems counter-intuitive since both use the same data, but that's the way it has ended up as being more economical for the mfgs to mass-produce vehicles that meet standards.

6. Honda did settle a class-action lawsuit for deliberately designing odometers that were biased towards showing more miles than actually transpired - if a mfg does this, then they spend less on warranty repairs and leases expire prematurely. The data indicated that Hondas still met the industry standard for acccuracy, but the plantiffs were able to show that Honda consistently biased their design to their advantage and they found a sympathetic audience. Other mfgs may face similar suits, but before you start thinking this is a good thing, consider that the the lawyers who broght the suit are are claiming $9.8M in fees with at best a few milllion going to actual car owners for excess lease payments or denied warranty claims. This cost, of course, will be paid by every person who buys a Honda in the future. The lawyers are licking their chops to go after other mfgs now.

- Mark

 

While we're clearing up misinformation, can you please provide some sources for your information Mark? I'm not discounting it, "from what I've heard" I agree with everything you've said...except that it seems that in general, domestic brands have a more accurate speedometer than german brands.

 

I have checked the several cars I've owned over the past 15 years or so--since getting a GPS. The have included a '93 Ford Explorer (ghastly car), '03 Honda Element, '00 Honda Civic, '87 BMW 325iS, '07 MCS, and a couple of others. They were surprisingly consistent from brand to brand and year to year. In the 30-70 MPH range my cars have been about 2-3 MPH slower than the indicated speed as given by the speedo. I'm surprised at the 10 percent differences that some people are finding.

And Mark, whatever your source, I think it is accurate. I would make one note: safety is not only related to overstating speed. It is related to avoiding any large inaccuracy that leads to large variations in speed of the vehicles traveling in the existing traffic flow, higher or lower.

How nice it would be if carmakers and lawmakers could agree on laws and policies that give car owners accurate data about all aspects of their cars' operation. This relates to all areas. Fuel gages, ODO's, etc., are all "adjusted" based on the assumption that the majority of drivers are somewhat moronic and need to be protected from themselves.

End of rant.

cheers,

Joe

 

I recall a friend in high school who had a Plymouth Valiant. He complained about its optimistic speedometer. This would have been around 1965 or so. This issue has a long history.

It probably wont be long before technology allows speedometers to be extremely accurate without great expense. I wonder what car makers will do then?

 

I've never been able to scare up a hard speedo accuracy specification at the DOT web site, so it's probably buried in some kind of 3,000,000 page safety specification. There are references on the web to European standards that confirm the -0%/+10% standard but it varies from country to country. The mfgs don't want to screw around with having different parts and calibrations for different markets, so they surely try and find a fudge factor that works for all markets, and currently that fudge factor appears to be around 5-7% high.

One example:

http://www.theyworkforyou.com/wrans/...01-03-12a.59.3

The following is from a VW technical bulletin:

TT-06-19

"2005-2006 A5 Jetta and A5 GTI, Speedometer Display
If you receive a customer complaint that the speedometer displays a vehicle speed that is slightly faster than the actual speed, this is normal. The speedometer is operating per manufacturing specifications. Volkswagen does not manufacture vehicles where speedometers read slower than actual speed. To allow for possible differences in overall tire diameter with different tire manufacturers and wheel sizes, a factor is designed into the speedometer function that increases the displayed speed. This factor does not affect odometer readings, which show actual distance traveled. Do NOT replace ANY parts for this condition."

So no, I can't provide a hard reference for what I'm saying, but I'm an extremely trustworthy guy. ;-) And in any event, it jives with common sense, how consumer devices are mfg'd, and how the bureaucrats/safetycrats like to work.

Certainly, if anyone truly is approaching a 10% speedo error, I'd take it up with the dealer. But the typical 5-7% error is just the way it is.

Keep in mind that there are other factors at work here to cause mfgs to build optimstic speedos. For example, consider the issue of lawsuits. Imagine this exchange: "So, Mr. Car Builder, you're telling the jury that you knew you were shipping a high percentage of your cars in which the speedometer was going to tell the driver that they were driviing SLOWER than they really are?" Oh, the horror. And then there are simply the bragging rights - everyone likes to think their car is insanely fast, so why not fudge the number to make them feel their car is faster? And anything the mfgs can do to slow down their drivers pays dividends in reducing accidents, tickets, and other bad things that do nothing to endear a car to it's owner.

Speedo error for a variety of reasons is just there. Best just to find out what it is and compensate. And realize that odometer error is an independent issue.

- Mark

 

Thanks Mark. I agree with all your points. Thanks for posting your info!

 

Nice write up Mark! Appreciate the post.

 

Okay, I said earlier that I would check my speedometer against my gps. Here are the results:

. 15.0 mph displayed = 14.0 mph on my gps

. 40.0 mph displayed = 37.5 mph on my gps

. 70.0 mph displayed = 66.0 mph on my gps

The speedometer averages ~6% lower than the gps readings.

I was surprised the other day by the fact that I was being passed rather frequently while driving I-25 from Santa Fe to Albuquerque. That's not the norm for me. Now I realize that with my display at 79 mph I was actually doing around 75 (it's a 75 mph zone). Now I don't trust the speedometer so much. From now on when taking long highway trips I think I'll just leave my gps plugged in and set my cruise control based on its displayed speed (then add 4 mph as is my custom).

Late entry: I had expected the gap to widen as I increased speed but at 80 mph there was only a 3 mph error (to hold 79 I set the display at 82).

 

Thanks for sharing your GPS comparison Ken! It sounds like the MINI's are pretty consistent in their displayed speedo so far.

 

I know a state trouper, and they have "corrected" speedos in their cars... he followed me on a stretch of I-75 and at an indicated 70mph in his cruser, my '06 MCS was reading 74mph....

Easiest fix IMO is going to 215 x 17 tires when these run flats wear out.

 

I just got home from having new tires mounted on my wife's '07 MCS. With GPS (Garmin Stree Pilot 2720) here are my results:
65 indicated = 62 gps
60 indicated = 57 gps

I'll post up more data as it becomes available. This is with a brand new set of 205/45-17's.

 

Let me show how temperature/tire pressure can affect the reading. not a MC though, it's a malibu.

In the winter i have tires inflated to 32psig, i got exactly 99 miles on reading while actual miles is 100.

last weekend the tire pressure was around 35 psig, i got 98.1 miles on reading with actual mileage 100.

I'm driving regularly each weekend on a 2*240 miles stretch. I take it that the mpg is done by relating wheel rorations against time. Both are reading against the milestones on the highway. One stop at rest area which is between the lanes won't cause >0.1 miles of error.

Both are just one data point which isn't quite up to my standard. I can take more readings later.

 

Great info Mark. I had my mini to the deale today and they indicated the speedo reading were where they would expect them to be. I did some testing on the odometer side on the way home from the dealer using a 50 mile stretch of highway. My mini is only a little of 2 weeks old with 1000 miles on it and the tires inflated to the recommended setting. Based on the 50 mile segment, the odometer read 50.8 miles vs 50 actual. This would put the error at 1.6% which fits within the range you gave.

 

Thanks for the other GPS postings - agree, they're about exactly in agreement. Magic number seems to be 6% off.

Rule of thumb: Whatever speed is displayed, take 5% off to estimate actual.

Easy examples:

If 60 mph shown, take 1/2 of 6 = 3 mph off, for 57 mph actual.

If 40 mph shown, take 1/2 of 4 = 2 mph off, for 38 mph actual.

etc.

 

Our speedometer also reads high. Approximately 5% high (60 = 63). According to my dealer, this is by design and all BMWs have this design. I then questioned the accuracy of the odometer and their reply was that the odometer reading was done differently and was accurate. I am interested in your test. I will also do one of my own.
'07 MCS Astro Black

 

Since purchasing my 2008, I have felt that the speedometer was not correct, aproximately 5 mph slower than posted speed. Having recently purchased a GPS for another vehicle, I checked its speed indicator with my speedometer and found my speedometer to be aprox. 5 mph slower than the GPS speed at 55mph.

I called a Mini dealer and they said Mini's are similar to BMW's. Their speedometer are set for an aproximate 10% difference. This just does not seem to make sense. Why would an auto manufacture calibrate their speedometers to read a non-true speed. I have a hard time beleiving that the federal government would permit this

Can anyone explain this to me. Maybe my thinking needs to be recalibrated.
Wisconsin Johnson

 

If you had done a search before posting you would have found this long thread:
https://www.northamericanmotoring.co...eter+accurancy

 

Robin

Thanks for the redirect. I am new to using this forum and must not have used the correct "word" when I tried to search. Seems my new discovery has been around. Have a good day!

W J

 

So I also tested out my speedometer and found it to be about 10% off. So I want to keep the resale value of my car as high as possible so I was thinking of switching to a larger tire to make up the difference. If stock is r17 205/45 and I went with either a r18 215/50 or a r19 215/45 that would get me about 10% more travel at the same rpm. I never plan on lowering my car at all, would either of those fit or would both rub?

 

On my 2009 JCW with Dunlop all season tires my Garmin GPS says I'm doing 68mph when my speedometer reads 70mph. The Odometer is right on at any speed. I checked it against the mile markers on I-95 as well as I-75 many times. Any speed below 50mph the speedometer is only off by 1mph. I don't think this is really to far off. At least it is off the good way. It may save me from getting a ticket someday.
Ronnie948

 

All that is going to do is to make the Odometer read incorrectly.

This also WILL NOT affect your resale value. the new purchaser will not know the difference.

Also of note for you it that the accuracy will change by more than 1.4% during the life of the tires anyway.

Also of note is that all European cars are this way due to the laws in Europe on speedometer accuracy.

Search here and you will find a bunch of threads on this subject and many of them explain all that goes on behind the scenes with this even a full break down of the math behind the 1.4% change as the tires wear.

 

If anything it will make the odometer read correctly. If my car is saying I'm going 10% faster than I really am, then when my odometer reads 50,000 miles the car has really only seen 45,000. So less miles on the car, equals higher resale value. I have brand new tires on it right now so it's only going to get worse.