speedo accuracy on your R-1150-RT

[r11rs94]

I just receintly installed a ZUMO on my RT. Noticed the speedo approx 4MPH higher than the GPS unit reads. From what I've read on past threads< I was expecting much worse. What say you other RT riders with GPS.

[tkbaker4]

About the same on my RS.

[DrPaul]

4 mph is exactly the gradient between my R1150RT speedo and my Zumo 550 with the speedo reading higher. BMW gets an "A" for precision and a "C" for accuracy. That's probably saved me a few speeding tickets!

DrPaul

[kgadley01]

my 99 RT reads 4 mph fast. I don't have one of those zomo things. I still trust a good old American roadmap. now this is for everyone else that doesn't have one of those zomo things. to check your speed, time yourself between mile markers on the super slab. divide the seconds INTO 3600, this will give you your true speed.:thumb

[awagnon]

Mine is about 5% off of whatever speed I'm going. If I'm going 50 mph, it's about 2.5 mph off. About 4 mph off at 70 mph. etc. It's the law that they read high and never low.

My son-in-law had a speedometer on his V-Strom that read about 6-7 mph high. He found someone who made perfectly matching dial faces to replace the original that corrected the error. After he replaced the face, it was exactly on the money.

I used the speedo on the GPS most of the time anyway.

[Andy VH]

I think that ANY cable driven speedometer on ANY brand motorcycle is going to read something like 5% to 10% off the actual cycke speed. Its just the nature of a cable driven speedo. Electronic speedometers reading from a magnet sensor on the front wheel would be much more accurate. But the manufacturers, Japan, US (Harley) or German have gotten by cheap for decades using cable driven speedos.

Just the nature of the beast and what the market will put up with.

The speedometer on my R1100RS has always read about 5mph higher than my actual speed and it really doesn't bother me one bit.

[Greenwald]

Not to buck the trend, but mine actually reads 3.1% in the other direction.

When the speedometer indicates 70 MPH, I'm actually traveling about 72 MPH. Also means I have more miles on my bike than the odometer indicates (a 'Plus' for purposes of my 3 - Yr. Warranty!).

As for ..."it's the law that they read high and never low."

That's a new one to me. Does this happen to be a Federal Statute that I am unaware of, and could the author of that post quote me the federal number (for research purposes only - not kicking sand in anyone's face).

No such law here in WI. Never was brought up in court by even the smartest lawyers (oxymoron alert here!) for what few individuals, of the hundreds of speeding citations I issued over my career, contested any ticket. Never lost.

And by the way, as for those hundreds of citations, they were never BMW riders, MOA members and they were all bad people.

[Andy VH]

For those who must have a an accurate speedometer, inexpensively, get a quality bicycle speedometer/computer and install it on your motorcycle. Brands like Cateye or Sigma offer many features, some are even wireless, and once the comupter is calibrated to the tire size they are very accurate.

Since my speedometer reads about 5mph high, it automatically keeps my actual speed in ranges that don't even interest the officers. My speedo says 75 when I actually am doing about 71, good for a 65 mph speed limit.

Surprisingly, my odometer is much more accurate.

[BeemerMike]

Mine is about 5% off of whatever speed I'm going. If I'm going 50 mph, it's about 2.5 mph off. About 4 mph off at 70 mph. etc. It's the law that they read high and never low.

:scratch "The law"? I think it may be "BMW's Law", i.e., it is something that BMW does to all of its vehicles. According to my Garmin 276C Plus, my Z3 reads about 4% high, but my Jeep Liberty reads dead on (less than 1 mph difference at all speeds).

[rmarkr]

Both my BMW's read 5mph high throughout the range. The mileometers are almost dead on. (vs the Zumo). Fitting a non-stock rear tire will obviously alter things.
I suspect the error is designed in for legal protection.
:blah

[Fritzc]

According to my Garmin Street Pilot, My speedometer (R1100RT-Police Bike) is dead on accurate at any speed. :thumb Is there a margin of error for GPS?:scratch

[Greenwald]

According to my Garmin Street Pilot, My speedometer (R1100RT-Police Bike) is dead on accurate at any speed. :thumb Is there a margin of error for GPS?:scratch

Unlikely. Garmin makes a quality product.

Their units routinely 'capture' 8 - 12 of the geosynchronous satellite signals, providing such precise triagulation, that I would believe what your GPS is telling you, and rejoice that you own one of the rare BMW's with a perfectly accurate speedometer!

[OfficerImpersonator]

Mine is dead-on - and verified by my GPS.

But then, my speedo is certified :ear

[kgadley01]

if you own any police model your speedo should be accurate. a friend of mine has some aftermarket gadget on his goldwing that makes his speedo dead on. I don't know if they make them for BMWs or not.:dunno

[Mr. Frank]

I'm about 5% high. Interestingly, the error is less when it is cold out.

[OfficerImpersonator]

I'm about 5% high. Interestingly, the error is less when it is cold out.

That makes perfect sense. A cold tire has a smaller circumference than a warm tire, so a cold tire takes more revolutions per mile than a warm tire, so it will appear that you are going faster than you really are.

What does surprise me is that the difference is noticeable.

[Mr. Frank]

I'm basing my observations on GPS and a Sigma bicycle speedo. I don't think it is the tire's circumference because I check air pressure regularly. I always assumed it was some kind of drag in the speedo and/or some electrical effect. By cold I'm thinking 30's and 40's as compared to 70s and 80's.

[nortonrt]

My '03 R1150RT meters about 4 mph low vs. GPS at just about all speeds.

[FatBaxter]

I was told years ago that BMW intentionally designs their speedos to read higher than what you're actually doing. It's their idea of keeping you somewhat safe from yourself, in that you're not really moving as fast at the speedo says. Fine German social engineering.

"Dat iz der vay ve buildt it, und you VILL like it like dat!"

One of the previous commenters noted the speedo on his police bike was dead on. Well, it's a police bike -- of course those models are accurate.

At any speed above 50, I subtract 5 MPH from what my speedo reads to guesstimate my true speed. It worked for my '82, and now for my '99.

[Mr. Frank]

I've also heard it is to cover the situation wherein a person puts on an oversize tire, although that would seem to apply to rear wheel speedo drives only.