1981 CX100 Speedometer error

[lomax]

My new to me Le Mans CX100 speedometer reads 80 Mph when I am actually doing 60 Mph. That is just a bit of an error. I don't think it is the stock speedometer and maybe the wrong one was used as a replacement, But that is a mute point. Is there anything I can do ??  I guess just find a good speedometer shop and see if they can help.

[jcctx]

Buy a bicycle speedo for less than &20 and be :>)

[Tom H]

I think there are at least two speedo drive gear ratios that fit in the trans.

I'm guessing it's off at all speeds?

Tom

[lomax]

Thanks for the replies. I am going to check into a bicycle one for the mean time and check with MG Cycle and see if i can find a local speedo shop.

[Moparnut72]

As far as I can determine the speedometer on my V100 is off by 9 percent. I use a speedometer app on my phone. I believe European motorcycle manufacturers have to be careful with speedometer error due to regulations however the 4 wheelers we own are spot on. I would think they could do a bit better.
kk

[lomax]

Thanks all. MG Cycle has one but it is in KPH so not so useful for me. I have ordered up a Bicycle Speedo in the mean time and will ask my local speedometer shot to see if he will even touch an Italian clock. I could put my phone on the bars but that is just tacky. 

[wirespokes]

 I work on speedometers, mostly airhead BMWs, but have worked on a bunch of Veglias. Do answer the question of whether it reads 20mph high all through the range or much less at slow speeds.

The reason that's important is because there are two possibilities - the needle slipped and it's out of calibration, or it's either the wrong speedo or the speedo drive gearing is wrong.

Up to this point I haven't had a problem swapping speedos, all of them I've gotten have been the same drive ratio. What I mean by that is that they've all needed the same input RPMs to read a mile/minute. I have heard there are some speedometers that require a different RPM and that there are different gears in the transmission driving them. Those gears can be replaced without taking the transmission apart.

If the speedometer acts normally, just way off, then there's probably nothing a speedo shop can do. Or it would be major work to change it since the internal gearing would need  to be changed to record mileage correctly, plus adjust the balance of forces driving the needle, which can be a tedious process.

[Antietam Classic Cycle]

https://www.thisoldtractor.com/moto_guzzi_loopframe_gauge_repair.html

FWIW: My '76 Convert reads 3 mph fast at 30 (actually 27) and 4 at 60, the '90 Cal III FF was 3 mph fast at all speeds. My brother's 2010 VW Jetta is off by 2 mph - 58 mph indicated is actually 60. 

[lomax]

Thanks for the info. The guy I bought it from said it was not the original Speedo so I can only assume it has the wrong gear ratio in it. It seems to be off all through the range but the faster you go the worst it gets. It does go to zero so I don't think it is a slipped needle. From past lives I recall somewhere you can see the trans ratio and the speedometer ratio and make sure they are the same. I don't know if this information is possible on this bike or not. BTW I have a K1 Dash you can have 

[Kiwi_Roy]

Ho does the Oddometer line up, that will be out as well if the gear ratio is wrong.
You could replace the speedo with one from Speedhut, they operate off pulses and can be calibrated quite easily
Press Start, drive a set distance (2 miles from memory) then press End, its done.
Speedhut will even preload the Odometer to match your existing unit.

[lomax]

Thanks for the Speedhut Idea. I already ordered up a cheap GPS Speedo that will work just fine to actually let me know the speed. Is it really that important  Yes I am sure the mileage is way off also but I have no idea of the actual mileage on the bike, it is titled as zero, so that is kind of a mute point anyway. I just have to figure out what it reads in order to keep track of fill-ups. Great information in this thread and I thank you all.

[Mayor_of_BBQ]

My 79 CX100 has a speedo that says MPH on the face, but registers speed and odo in KPH

I have no idea how that is possible, and assume the PO switched some gears to accomplish this (bike was owned/ heavily modded in Canada)

I've asked on here a bunch of times but no one has every been able to share much clarity

[lomax]

Maybe it is a KPH speedometer and someone put a MPH face on it ??

[pehayes]

Not sure if this has a relationship to your error.
There was a time in the 70's-80's that the USA was on a great effort to save fuel.  They established a national maximum speed limit of 55mph.  Manufacturers were required to produce speedometers that had a display of "55" in larger font or alternate color.  Also, the speedometer was not allowed to display or indicate a speed higher than 80mph.  My '87 SPII had such a speedometer.  The needle could sweep past 80 but there were no more numbers or arcs on the display.  I once got the needle ALL THE WAY around to touch the ZERO pin on the back side.  :-)

Here's a pic of the rare speedo display.  Factory original from 1987 and only for USA sale machines.  The CX-100 was produced at about the same time and likely had the same stock speedometer.  You might compare the dial on your speedo.  Does your indication for 80mph show in about the same relative arc position as mine does at 60?

Patrick Hayes
Fremont CA

[Kiwi_Roy]

My 79 CX100 has a speedo that says MPH on the face, but registers speed and odo in KPH

I have no idea how that is possible, and assume the PO switched some gears to accomplish this (bike was owned/ heavily modded in Canada)

I've asked on here a bunch of times but no one has every been able to share much clarity

This might explain it
https://en.wikipedia.org/wiki/Metrication_in_Canada
BTW most guys my age can still think in mph or kph, 160 is the new target