70/75 mph all day long

[GrimReaper]

Thanks Barry.My speedo reads the same till 4k rpm but above that reads lower.Anyway the speedo start shakin a bit aroun 65 mph mark and reads about 5mph lower.Will try GPS and see the results

[Adamastor]

Hi there!

Just got to test the bike against a GPS and found my speedometer is spot on!
I also confirmed that:

at 120 km/h | 75mph  -> 6.000rpm
at 100km/h | 62mph -> 5.000rpm
at 80 km/h | 50mph -> 4.000rpm

My final drive has the 31/9 inscription outside.

I counted the number of revolutions of the shaft at the rubber boot (from outside counting the number of times the bolts touched y fingers (4 per turn)) and got 6.80 full revolutions for one wheel revolution.

I saw no serial numbers on the back of my rev-counter...

Is this really odd? What can be wrong/different?

Regards,

Sergio

[Adamastor]

I have been doing some math and it looks like I might have a R45 final drive (although it says 31/9 outside)
According to the number of rotations per wheel turn the math is very close (my measure was not very scientific)

Looks like I might want to search for a spare final drive that fits better on my engine..  :-?

[Barry]

I might have a R45 final drive (although it says 31/9 outside) Sad
According to the number of rotations per wheel turn the math is very close (my measure was not very scientific)

Are you sure you didn't count the bolts twice ?  Half of 6.8 = 3.4 or a 31/9 final drive ratio.  Even an R45 drive would be approx. 3.8 rather than 6.8

Also your speedo wouldn't be accurate if you had the wrong final drive internals. I would still think it more likely that your tachometer is reading high.

[Adamastor]

I felt the bolts touch my finger 27 times and 1/4 ... I will go to the garage confirm again... brb

[Adamastor]

Oh, sorry... I counted two complete wheel turns before... sorry for my mistake..
But this measure is too un-certain to achieve any conclusion... isnt it?

[GrimReaper]

Looks like I might want to search for a spare final drive that fits better on my engine..

 What is the point to change the final drive.At 5k rpm different ratio makes 2mph difference :-?

[Barry]

But this measure is too un-certain to achieve any conclusion... isnt it?

Well I think you can conclude it's probably a 3.44 (31/9)and certainly not a 3.89 from the R45.

[Adamastor]

Hmmm.. is there a easy way to test our Rev-meter? (with a multimeter or something like that)



edit:

Looks like there's a way to test the tachometer calibration:

http://bmwmotorcycletech.info/tach.htm

[Barry]

Looks like there's a way to test the tachometer calibration:

This method does work but may not with modern fluorescent fittings that use high frequency starter gear. You want the old fashioned type with a simple starter and choke.

[Adamastor]

If you discover with this method that there is an error with your tachometer, how can you calibrate it? Is there a calibration screw?

Regards,

Sergio

[Barry]

If you discover with this method that there is an error with your tachometer, how can you calibrate it? Is there a calibration screw?

Fundamentally you can have two sorts of errors :

A zero error where the instrument reads either high or low by the same amount at any point in the range. This can be easily fixed by removing the needle and repositioning it.

A span error where the error changes - increasing or decreasing as you go up the scale. There is usually an adjusting screw to fix this type of error but I've never calibrated an airhead Tacho. Maybe somebody else will know where it is. It may be internal.      

[Adamastor]

Thanks Barry,

I believe, if this error exists, it should be teh second case.. an error that increases as revs go high. I believe this because my idle (1250rpm) seems fine, the charger light goes out at about 1.500rpms, so there shouldnt be anything wrong there. If there is an error it must happen up there..
 :-/

[fmriguy]

It looks as though others are helping with your tach readings, but just a comment on highway cruising on the R65.  I get a lot of engine vibration around 60-65 mph, so it is actually more comfortable for me to ride faster (e.g., 70+ mph) or below 55 mph.  Others might know whether this varies depending upon year and final drive, however.  Either way, being such a light bike, I feel a little fragile being buffeted around at 70+ mph for more than a few hours.  Could be that I'm just not up to the challenge

[Ed Miller]

"Either way, being such a light bike, I feel a little fragile being buffeted around at 70+ mph for more than a few hours.  Could be that I'm just not up to the challenge"

Or you just don't have a Windjammer.    

Yeah, on my Triumph I get beat up a bit by the wind.  I put my feet on the passenger pegs if it's safe to do so, and tuck down.  It's way more tiring than on my R65.