Speedos Off

[Taylor 1983]

Anyone else experiencing their speedo off by 2 MPH? This is my second bike since 2009 that the speedo is off by 2MPH? My dealer tells me that Berlin knows this and it's based on BMW's desire to help riders not collect tickets. This also means riders complete warranty sooner with a little help from BMW. Has anyone else experienced this? My measurement is based on GPS reading.

[mountainmann]

It is common for nearly all manufacturers to have the speedometer overstate speed by 3-4%. Many forum threads on this subject. The speedometer and the odometer are not mathematically connected on BMWs and probably most other vehicles. The odometers tend to be accurate, and if you have a GPS connected to the bike's computer, the odometer may even be dead on accurate based on true GPS speed.

[Taylor 1983]

This is the first I heard odometer isn't linked?

[mountainmann]

Actually, in the absence of a GPS, the speedometer and the odometer may be linked, with the odometer reflecting exactly one mile traveled when the speedometer is registering say 62.5 mph. Since BMW designs the intended error into the speedometer reading, they would then know how much to adjust the odometer to get a correct distance travelled.

[WBinDE]

2% is pretty close, that's all BMW will guarantee for police bikes. They also say the difference between a new tire and a worn one is 0.5%.

 

My RTW indicates about 2% fast, I'm OK with that, my K16 was 4% fast.

[mneblett]

BMW speedos used to be off by a lot more than 2 mph!

 

Manufacturers try to avoid the speedos *ever* reporting lower than actual speed, and have to take into account things tire diameter variation.

 

And as a separate matter, IIRC BMW was once sued by a guy that claimed that his horrible accident was caused by his speedo reading lower than his actual speed (i.e., that he wouldn't have driven so fast if he knew the actual speed (riiiight ..) ).

[bdfbeemer]

Mine is off much more than that. The faster I go the greater the error. I use the gps for my speedo.

[Dave Stephens]

So is it safe to assume that the GPS reading is more accurate than the bike's speedo?

[mneblett]

Yes, *IF* you are riding in a straight line at constant speed.

 

But ...

 

The GPS updates about once per second. Speed is determined by dividing the distance traveled since the last update by the time between updates -- an approach that assumes constant speed between update points.

 

If you are accelerating or decelerating, the reported GPS speed will be inaccurate. If you are in a tight curve, the GPS does not use the distance travelled around the curve, it uses the distance between the update points (the shorter direct line), again resulting in inaccurate reported speed.

 

The bike's speedo reports the instantaneous wheel speed, so it is always "the same" (even if the needle is not pointing to absolute truth).

 

I know my speedo is off 1 mph at 30 mph, and 2 mph at 70 mph -- that is enough for me to know how to read the bike speedo when I'm not traveling in a straight line at constant speed. Otherwise, I use the GPS speed.

[bdfbeemer]

This morning the bike speedo said 100 the gps 94.

[mneblett]

This morning the bike speedo said 100 the gps 94.

Hypothetically, of course.

[mountainmann]

Here's some more techno babble.

 

The speedometer will increase the amount it overstates the speed as:

 

- The tires wear down

- The weight on the bike increases

- The tire pressure is lowered

 

[Selden]

This isn't a BMW thing. As far as I am aware, NHTSA has a compliance formula, and can fine manufacturers for excessive speedometer error, with a very low tolerance on under reporting speed, with a much larger tolerance for over-reporting speed/mileage because of its impact on mileage-based warranty. With those constraints, everybody aims to report a higher than actual speed. I can't ever remember owning a vehicle that under reported. I have a 2009 Honda Fit, which was ~3-4% optimistic with the OEM tires; I went one size larger, and the speedometer/odometer is now 99.99% accurate, compared with readings from a GPS. When the tires were new, it underreported ~1%; at half tread, dead accurate, and by the tires are worn out, I expect it to be slightly optimistic again.

[Paul In Australia]

This isn't a BMW thing. As far as I am aware, NHTSA has a compliance formula, and can fine manufacturers for excessive speedometer error, with a very low tolerance on under reporting speed, with a much larger tolerance for over-reporting speed/mileage because of its impact on mileage-based warranty. With those constraints, everybody aims to report a higher than actual speed. I can't ever remember owning a vehicle that under reported. I have a 2009 Honda Fit, which was ~3-4% optimistic with the OEM tires; I went one size larger, and the speedometer/odometer is now 99.99% accurate, compared with readings from a GPS. When the tires were new, it underreported ~1%; at half tread, dead accurate, and by the tires are worn out, I expect it to be slightly optimistic again.

 

In Australia it is part of the design regulations which govern legality of imports and registration that the speedo indicates higher than actual. I think quite a few countries stipulate this.

 

[ADulay]

This morning the bike speedo said 100 the gps 94.

Mine was 100 on the speedo and gps 97.

 

AD (TPI readings are incorrect. They were at 40/41 in reality)

 

[Bill_Walker]

This isn't a BMW thing...

 

Yup. My KLX250S and my Mini Cooper both read about 10% high. I don't recall for sure what the error is on my RT since I usually have the GPS mounted and use that, but I think it's close to that.

[CoarsegoldKid]

Curiosity got the best of me. I'm glad this was about speedometers. For the record my RT's analog gauge is about 4mph low at 60mph against the GPS. The digital gauge is about 2 low. My Subarus are about 1mph low compared to the GPS.

 

[tallman]

So you wetheads actually look at the speedometer?

 

Speedo accuracy dated, but accurate.

 

Down Under

Australian Design Rule that requires that the speedo must not indicate a speed less than the vehicle’s true speed or a speed greater than the vehicle’s true speed by an amount of more than 10 per cent plus 4km/h.

 

Speedo lies

 

Sorted by price, luxury cars are the least accurate, and cars costing less than $20,000 are the most accurate. By category, sports cars indicate higher speeds than sedans or trucks. Cars built in Europe exaggerate more than Japanese cars, which in turn fib more than North American ones. And by manufacturer, GM's domestic products are the most accurate, and BMW's are the least accurate by far

 

So why would we worry about speedo accuracy?

Most are optimistic, some a little, some a lot.

 

Engineers do it so the car ahead of you thinks they are going 72 in the left lane while you're behind them showing 69mph and fuming.

Funny guys.

[lkraus]

Is the RT-P speedo accurate?

[greiffster]

This morning the bike speedo said 100 the gps 94.

Mine was 100 on the speedo and gps 97.

 

AD (TPI readings are incorrect. They were at 40/41 in reality)

 

 

Clipping along at 100....listening to opera. I think you made my day.

[Asymmetrical]

Heads up -- rear tire low.

[bwr]

This morning the bike speedo said 100 the gps 94.

Mine was 100 on the speedo and gps 97.

 

AD (TPI readings are incorrect. They were at 40/41 in reality)

 

 

Clipping along at 100....listening to opera. I think you made my day.

 

,,, in a 45 MPH speed zone!

[ADulay]

Heads up -- rear tire low.

 

Nah. I checked them about 4 hours earlier and both were showing 40/41 on an accurate gauge, like usual. Sometimes that TPI just has a mind of its own I think.

 

Funny thing is they didn't even work for the first 6000 miles!

 

AD

[ADulay]

 

,,, in a 45 MPH speed zone!

 

Well, I just happened to be on that particular stretch of road so that I could catch the 100 mph and 20000 mile turn at the same time. Luckily it's on a road between counties and close to the middle of nowhere.

 

That's also the road I took the 100,000 mile speedo video a few years back. Sometimes a little planning rewards you with a good photo or video as needed!

 

AD

[Kathy R]

All I saw was a subject line: Speedos Off

[AndyS]

All I saw was a subject line: Speedos Off

 

Haha. (The old Budgie smuggler joke).

[EffBee]

All I saw was a subject line: Speedos Off

 

Oh, sure, young lady. It's fine for YOU to be curious. But when I clicked to open the thread, I was MORTIFIED by what I feared I would find.

[Coinneach]

All I saw was a subject line: Speedos Off

 

Oh, sure, young lady. It's fine for YOU to be curious. But when I clicked to open the thread, I was MORTIFIED by what I feared I would find.

 

And yet, you clicked anyway. Oh the perils of being an admin!

[AndyS]

All I saw was a subject line: Speedos Off

 

Oh, sure, young lady. It's fine for YOU to be curious. But when I clicked to open the thread, I was MORTIFIED by what I feared I would find.

 

And yet, you clicked anyway. Oh the perils of being an admin!

 

Its his job, he has a responsibility to, for the sake of the rest of us.

[EffBee]

Its his job, he has a responsibility to, for the sake of the rest of us.

 

yeah. YEAH! Responsibility. That's the ticket.

[Asymmetrical]

The TPM is pretty useful (assuming it works). I'd expect the dealer to make it right under the warranty. Love your style with Met Opera and cruise control at 100.