92 R100RT odometer woes...

[revorg]

I've been driving myself nuts contemplating the low fuel economy of my relatively new to me R100RT as it runs like a top and only delivers in the low to mid 30's MPG no mater how I drive it. I posted this here once and the speedometer/odometer was mentioned... but I never gave it a thought because the speedometer actually seems a bit optimistic to me. Then a week or so ago, after a fresh fill up, I road the bike a known distance... one I had had driven many times in other vehicals... and noticed the trip odometer was off by quite a bit. :scratch Naturally I started taking note of the odometer readings from that point on. I still believe the speedo is a bit optimistic, but the odometer is low by close to 30% :confused:

Obviously, this explains my perceived low fuel economy. ;)

1) Has anyone had a similar problem ?
2) What can I do about it ?

[Guenther]

The older BMW speedometers are known to show ca. 10% more mph. The odometers are usually pretty accurate. Are you sure you have the correct instrument on your RT? What does the little number at the bottom of faceplate say?

/Guenther
(replaced my speedo at 45'miles on my '88 GS with the odometer rings moving loosely back and forth)

[revorg]

Guenther,

Thanks for the input.
The number at the bottom of the unit is 'W-1.112'

This seems very odd to me... :scratch:dunno:scratch

[razz2234]

The size (diameter) of your tires can also change your odometer readings. If the diameter is smaller than the recommended size, or the original tires, your odometer will read that you are putting in more miles than you actually are and are going slower than the speedo is saying.
Good luck. Check your tire size...

[revorg]

Rear tire is a Conti Blitz 120/90 18

30% though... got to be the wrong unit or just plain broke. :dunno

[wecm31]

Can you tell if the odometer is always rolling up mileage or is it intermittently stopping and then restarting? It is a classic problem of internal gear slippage on the shaft that could be at fault here. Here is a link to the Airhead repair for the slippage repair:

http://www.airheads.org/content/view/160/98/

If the odometer keeps turning all the time, you have other issues. But if it starts & stops, this could be your answer. A bit tricky to disassemble and repair, but the repair guide has great photos and step by step advice.

[535is]

30% is far too much for a tire size difference. It could be a slipping gear or a gear with broken teeth. Either way, the Odometer Gears guys have your solution. Nice new gears and a nice evening doing very fussy small work that you might well prefer magnifying glasses to do. :laugh But it is not hard. BT, DT. :thumb

[revorg]

Thanks for the input guys... :thumb

It would seem some exploratory surgery is in order. That link to the airheads forum was very helpful in understanding the problem. I'm thinking that the worm gear may have swiveled itself back.

If I find damaged gears are replacements available ?

[paulfinney2]

Perfect timing. My odo and tripo have been going slipo, and I was about to go looking for the link to the speedo repair. 8 pages. Not bad. Now for some patience and steady hands.

[Guenther]

For a W1112 speedo the matching rear drive ratio is 33/11. You find the rear drive ratio behind or next to the vent nipple on the rear drive.

Just to be sure that someone did not swap-in a rear drive with a different ratio w/o changing the speedometer. In which case your speedo and odometer would be off. But 30%?...hm, I donno.

/Guenther

[88bmwJeff]

I've been driving myself nuts contemplating the low fuel economy of my relatively new to me R100RT as it runs like a top and only delivers in the low to mid 30's MPG no mater how I drive it.

From what I've read, mid 30's (average) is typical for the late R100's. I have an 88 R100 RT, and typically get in the mid 30's. The older bikes do get better gas mileage than the newer ones. At least, that's what I've been able to tell.

[ccolwell]

FWIW, I always got mid 30's from my '84 R100 in usual back road riding with a one time max of 50 mpg on a highway trip.

[osbornk]

Can you tell if the odometer is always rolling up mileage or is it intermittently stopping and then restarting? It is a classic problem of internal gear slippage on the shaft that could be at fault here. Here is a link to the Airhead repair for the slippage repair:

http://www.airheads.org/content/view/160/98/

If the odometer keeps turning all the time, you have other issues. But if it starts & stops, this could be your answer. A bit tricky to disassemble and repair, but the repair guide has great photos and step by step advice.

I had this problem on my 86 80RT. I attempted to self repair but the gears were catching and I would have broken the cable if I had done so. I sent the spedo to a repair shop in Texas (much cheaper than the California one) and they repaired it for just over $100.

[535is]

If I find damaged gears are replacements available ?

I didn't capitalize it for no reason ... Odometer Gears. (http://www.odometergears.com/) :rolleyes

Look under the E30 applications for the motorcycle applications. Call and tell Jeff that I sent you.

[paulfinney2]

Osbornk, do you have contact info on the company in Texas?

[revorg]

From what I've read, mid 30's (average) is typical for the late R100's. I have an 88 R100 RT, and typically get in the mid 30's. The older bikes do get better gas mileage than the newer ones. At least, that's what I've been able to tell.

Jeff,
Only thing I know is on my 25 mile round trip commute to work the odometer is showing 17 miles... and by the odometer I've been getting around 32-33 mpg. It took me half the summer to notice because I tend to take the long way home. ;)
My other bike is a snorting oil leaking hulk of a '77 Electroglide that gets between 40 and 50 mpg depending on how hard I push it and I have been having trouble with the idea that this fine machine was less efficient.
:dunno

[revorg]

I didn't capitalize it for no reason ... Odometer Gears. (http://www.odometergears.com/) :rolleyes



In my defense I have learned not to pay a lot of attention to grammar, punctuation, spelling and even double negatives on the internet... but I should have caught that. :blush

[BubbaZanetti]

would a bouncy speedo needle have any correlation to the inaccurate odometer?


my needle sometimes stays on zero at slow speed, at that point, the odometer doesn't turn. usually, above 45, the needle "springs" to life (although bouncy) and the odo starts turning again (inaccurately)

speedo was going to be a winter project.

[osbornk]

Osbornk, do you have contact info on the company in Texas?

I think it was http://www.speedometer.com/ I sent them an e-mail describing the problem and they gave me an estimate that was very close to the final cost.

[88bmwJeff]

Jeff,
Only thing I know is on my 25 mile round trip commute to work the odometer is showing 17 miles... and by the odometer I've been getting around 32-33 mpg. It took me half the summer to notice because I tend to take the long way home. ;)
My other bike is a snorting oil leaking hulk of a '77 Electroglide that gets between 40 and 50 mpg depending on how hard I push it and I have been having trouble with the idea that this fine machine was less efficient.
:dunno

I think a lot has to do with emissions. Fuel economy and performance for cars dropped significantly in the 70's due to emission controls. From what I've read, the late 70's R100's get fuel economy in the mid 40's; however, the fuel economy and performance dropped in the 80's as emissions, on BMW's at least, were tightened. I do not know if fuel economy dropped for other manufactures, but I'd be surprised if they didn't.

[535is]

In my defense I have learned not to pay a lot of attention to grammar, punctuation, spelling and even double negatives on the internet... but I should have caught that. :blush

I'm generally ruthlessly accurate because it's my nature and habit. Although I didn't provide a link in the first message (Sorry!), I did in the second.

Why I like Jeff Caplan's company is that he did it about the same way I did if I'd had the skills. VDO would not provide parts - only rebuilding services. Jeff knows how to cast plastics, so he does that to produce copies of the gears that commonly break.
He leaves it to you to do the work replacing them. As a result, if you can do reasonably fine work, it will cost you well under $100 to replace the gears you have likely broken.