Speedo Drive

[swamper]

My Speedo reads about 5MPH high at 70 MPH. The Drive is a 2.6 stock size tires and I believe this is probably the drive which came standard. Does anyone know which drive I need to get for the speedo to be closer????? I remember my 96GS, I had the same problem and I replaced the drive and corrected it, however the wheels and tires are different sizes and don't know what numbers I used.

[michelsmith]

people can change clusters around all day, even to jdm ones, and will read the original vss install the original cluster and if it corrects the issue, you know where the problem is

[MIXR]

Can't do it Swamper. The 2.6 is already the lowest stock ratio.

The R1150GS has a 3.0 ratio, so you drop it to a 2.9 off an R1100 spoker to get it near to correct. The GS has a bigger error than the R to start with. Same with the R1100GS as I understand it. There is nothing under 2.6 in the BMW lineup that I am aware of that fits. My R was reading 6 kph high with normal road tyres. It was spot-on with Avon Distanzia tyres in the same (correct) size, because the tyre had a different (height) profile. My GSA was almost 10 kph high with the stock 3.0 hub. The 2.9 (or more correctly, the 2.875) means it is less than 2 kph high now. Lovely. The 2.6 would have made it 3 or 4 kph low (bad idea to have the speedo reading low).

Your only option is an aftermarket change to the speedo mechanism or the hub itself. No idea where you get them done, but they are available. Check ADV Riders site as well. Or you could run an Avon Distanzia front. Good tyre. Good wet and dry grip, good life, and much better speedo accuracy.

[swamper]

Thanx Mixr, I have a gps on most of the time just wouild have been nice to have the speedo read right.

[sweatmark]

...have a gps on most of the time just wouild have been nice to have the speedo read right.

The R1150R Roadster and Rockster - with OE tires - have 5-10% speedometer error, when compared to GPS speed measure. Same for R850R and R1100R. That's been our experience, having owned each type, checked against GPS, and then attributed the consistent speedometer errors to "conservative BMW engineering".

[NoRRmad]

I believe it's corporate policy across all manufacturers to have the speedo read several percent high. That's to protect themselves against lawsuits from people who get speeding tickets.

[f4tweet]

The GS's have a 3.0 drive. I checked and the parts guy said the speedo will be slow. The RT guys can put an authority drive on and a calibrated speedo. The easy thing is to have your speedo calibrated.

[MIXR]

The GS's have a 3.0 drive. I checked and the parts guy said the speedo will be slow.

The speedo isn't slow with the 3.0 ratio hub. It reads high.

That means that at 100 kph genuine off the GPS, the speedo is reading 110. The lower ratio (2.875) speedo drive hub drops the error to only 2 kph high. Either way, you can rely on not getting booked for speeding because the speedo is always 'optimistic'.

The 2.6 ratio hub in the R (and other bikes) is too extreme in lowering the error to the point where the speedo would be under-reading by almost 4 kph at 110. I tried the one from my R before I sold it.

I did the math on this a while back as well. What the GS needs is a genuine 2.8 ratio instead of the 2.9 (2.875).

I have the GS Adventure, but I think the error is the same as the cooking-class GS.

[Martyn]

I believe it's corporate policy across all manufacturers to have the speedo read several percent high. That's to protect themselves against lawsuits from people who get speeding tickets.

You are correct - it's built into EU legislation that any error has to be overread e.g 60 mph on the speedo will in reality be in the region of 57mph or so.
Personally, I just mentally allow for it; certainly cheaper than the alternatives mooted above.

[sjbmw]

Pretty much every combustion engine vehicle that is manufactured for road use has a "under reporting" speedo.
I think it's standard for the industry to show you are travelling faster than you really are.

This begs the question: Does this affect odometer readings also?

How many "less" miles does a auto/bike with 100k miles on it really have?
If the speedo is high by 3% does that mean 100k is really 97k?



The only solution is to get a GPS.
(My friend took his GPS on a plane and set his GPS max speed to 487 mph and never erased it.)

[Mr. C]

My observation is that, yes, it does affect the odometer readings as well.

I have an 05-R1200RT, the speedometer matches the GPS up to at least 85.

I have an 02-R1150R, the speedometer under reports the speed compared to my GPS. I.E. Bike speedo reads 70, GPS reads 65. Bike is running the appropriate sized PR2's. I have a friend with the exact same year bike running the appropriate PR3's.

We went for a ride today, reset the odometers at a gas fill and again later in the day. At the gas station he mentioned that his odometer read 122.7 miles, where mine read 117.9 miles. I'll have to see if there's a GPS odometer I can reset for the next time.

-mc

[Dr. Strangelove]

yes, it does affect odometer readings and the odometer on a gps will show the difference

they all do that

[CycleRob]

The GPS odometer will not be accurate if there are many curves in your trip. GPS measured distances are only accurate when you are going straight. That's because it takes readings many, many times a minute that become straight line data point cords around a corner, effectively not measuring the true circular distance traveled.

The most accurate speedometer/odometer is a very inexpensive but potentially very accurate one you install and precisely calibrate yourself like this one installed on my 2+ years gone R1150R. The perfect calibration involves a starting point of using 4 turns of the front wheel to find a more accurate 4x rolling circumference, then fine tuning the calibration number by the odometer reading as it compares to the (very precise) U.S. divided highway mile markers. You then re-adjust the programmed in calibration number +/- by one digit, at a temporary stop, until it agrees with the mile markers for over a 3--5 mile stretch of data points one mile apart. Patience and some creativity required to install it on a M/C.