BMW R1200R R1150R/T F800 K1200R R1100R/T R1250R RnineT Message Board

Hi all,

This is cross posted in the Rockster section too.


I have 2004 Rockster and every time I rode it, it seemed like the speedo is off. So I get a speedo app for my phone and go for a drive. My speedo is off by 8 miles an hour fast. I have looked over the bike and I can find no indication that it was an ABS model with the ABS removed. The rear gear is stamp 31/11.

Anyone give me an idea on how to true up the speedo or get it in the ballpark?

Thanks,
Dan...

That's about right for the average machine. The rockster has the speedo drive on the rear drive ala r1100s. It is sensitive to the tire diameter. All 180/55 tires are not exactly the same. A little diference will make a difference. Having said that most speedos read a bit high on motos as a general rule. From 4% to 10% high.
Most Rocksters have a .7 ratio of 6th gear soo...
engine rpm in top gear X .7 / 2.82 = wheel rpm X circumference of wheel (pi X dia.) in inches / 12 = feet per min / 5280 =miles per min X 60 = mph.
4000 rpm X .7=2800/2.82=993 rpmXdia 6.55 feet/5280=1.23 miles per minX60=73.9 mph

Play around with that and you can see the difference a couple inches makes!



cheers

I've had a few of these Speedo Healers and they work great. https://www.healtech-electronics.com/products/sh/
Check to see if they have a model for your BMW.

kirby wrote:That's about right for the average machine. The rockster has the speedo drive on the rear drive ala r1100s. It is sensitive to the tire diameter. All 180/55 tires are not exactly the same. A little diference will make a difference. Having said that most speedos read a bit high on motos as a general rule. From 4% to 10% high.
Most Rocksters have a .7 ratio of 6th gear soo...
engine rpm in top gear X .7 / 2.82 = wheel rpm X circumference of wheel (pi X dia.) in inches / 12 = feet per min / 5280 =miles per min X 60 = mph.
4000 rpm X .7=2800/2.82=993 rpmXdia 6.55 feet/5280=1.23 miles per minX60=73.9 mph

Play around with that and you can see the difference a couple inches makes!

Had to read that last line a few times....

I'm a fan of 12oclock labs SpeedoDRD: http://shop.12oclocklabs.com/index.php? ... duct_id=59

The Roadster's mechanical speedometer drive limits tweak-ability. IIRC someone found a BMW front wheel speedo drive with cable:axle ratio different from OE R1150** part, and was able to improve veracity of the speedometer output via change.

The problem with Rockster speedometer is the signal requirement. Well, that plus speed signal generation.

But very accurate Rockster speedometer output can be done with some tinkering.

Its hard for me to understand why anybody would be so concerned about Exact speed onthemeter. Tolerances are fairly large on the rural roads these days so 5 mph fast, nothing but a little buffer.
I run 170/60 rear on my rockster and have measured the dia very precisely and I know at 4400 rpm I am about 80 mph. +- 1
Why spend money and effort to get the instrument modified to give an exact speed?

I guess there are allot of type A's out there, I feel for you but your worrying over nothing really.

No worries, as they say.

After removing iABS, I rode the Rockster 1st year without speedometer. Used a GPS to learn the gear-RPM-MPH relationships.

Later I amplified engine RPM (ignition noise) as speedometer input and discovered that RPM is a good proxy input for speedo in 5th gear.

Later still, I used an arduino as fixed frequency signal source for speedometer, with constant speedo reading of 55MPH as Sammy Hagar tribute.

Now I have a GPS-based signal for speedo that's accurate, but I never look: that gear-RPM-MPH thing is still stuck in my head.

kirby wrote:Its hard for me to understand why anybody would be so concerned about Exact speed onthemeter. Tolerances are fairly large on the rural roads these days so 5 mph fast, nothing but a little buffer. I run 170/60 rear on my rockster and have measured the dia very precisely and I know at 4400 rpm I am about 80 mph. +- 1
Why spend money and effort to get the instrument modified to give an exact speed? I guess there are allot of type A's out there, I feel for you but your worrying over nothing really.

I fully agree Kirby.

If this is the biggest problem you have in your life. Man oh man, what a wonderfull troublefree life you must have.

I'm with "sweaty"

I find myself looking at the tach way more often.

In fact.... my phone mount partially obscures the speedo. Which i use for GPS, a blue tooth radar(which has a GPS speedo within it If I want) and music.