Discussion in 'Norton Commando Motorcycles (Classic)' started by highdesert, Dec 21, 2010.
That's a speedo for a 143mph bike!
It came off a crashed bike, and had sat outside in the weather for a couple of years.
I just cleaned it up now, it polished up quite well (not the rusty bits)(the glass is broken too).
Still nice and clean inside, from what is visible.
It was replaced back then for a nice new one, for a whole $20 I seem to recall.
HOWEVER, there is NO adjustment screw on it.
More misinformation on this forum. ?
Thanks for your 'contribution' too.
Yes there is adjustment. You can get to the adjustment screw through the lamp hole.
I use the rubber dust cover/weather bottom boots on Smiths which are like loose socks to keep pulling up by does protect from most dust grime and moisture. I want to see my needle touch 150 end scale someday, so only digital can keep up after that but not much real Norton Commando left to do so.
Did you ever sit on your bike and have someone measure the rolling tire radius, i.e., with you seated on the bike, the distance from the ground to the rear axle centerline, and if so, what is the distance?
I can do it tomorrow...if I don't forget :mrgreen:
I think you will find that commandos which run at very high top speeds have high overall gearing combined with a close ratio gear box. Getting to 100MPH is not difficult regardless of the gearing, the next bit from 100 to 140 MPH probably depends on riding the torque curve. With a wide box it is easy to drop off the bottom on gear changes as the wind resistance builds up. Getting back onto the stronger part of the curve can be a slow process. A bit must depend on how much room you have to do it - difficult on most race circuits.
Someone is going to have to explain/show how then, there is nothing visible inside the lamp hole that looks moveable or adjustable in any way.
There might be something brass down a bit of a hole, but its barely visible, up high, and with very little room above it to get any sort of tool into it ?
Its also well offset from the lamp hole.
Anyone got a view of the internal workings of a speedo.
I'm reluctant to take this one apart
It's a little (brass?) toothed wheel which you use a small screwdriver, or something similar, to move. it's perpendicular to the face of the speedo so is a bit difficult to manoeuvre, and I take the speedo off to give better access, which isn't a real chore on a Commando, but, it's there.
Even the best learn something new every day.
You may find this helpful. If anything there is a picture that is almost on the bottom of the page. It shows the adjustment screw and it's relationship to the 3 screws that hold the case to the working parts. Not sure if this is applicable to all Smith's or not..
Thanks Pete, that was helpful.
Showed a lot of stuff there.
I did note this sentence theough -
"The adjustment screw has a serrated edge, and should be held in place with a punch mark just to the right of the white line in this photo. You will need to do the same, after adjustment."
I would defy anyone to do this through that lamp hole, given its so far offset from the action ... ??
I had a look at a speedo, you can see the adjustment screw but its not possible to adjust it thru the lamp hole,
the screw is punched to lock it from turning. if it wasnt punched then 3 or 4 small screwdrivers bent in an S shape with the flat at different angles may have some hope of turning the screw, easier to pull the bezel.
There is real skill putting that bezel back on so that it doesn't look like its been in a bad accident.
I tried it with the tacho that was paired with this speedo, some years back, and short of spinning in back on on a lathe,
it was tricky not to get any crimp marks at all in the process AND keep it perfectly smooth.
Chronometric speedos are a step back in time - the bezel screws on and off, and short of it vibrating off while out and about,
are a quantum leap back in 'progress'.
According to my Smith speedo the bike is doing 10 mph even before it is started.
That has got to be confidence building for claiming speeds achieved (if you believe it because you saw it on your own gauge with your own eyes then it is not a lie).
GPS tracking of the bike's movement relative to the earth surface is the current 'gold standard' for road bikes.
The confidence interval is much greater with 20 satellites tracking your progress on a slightly curving surface.
The faster you go with a gps the more accurate they become. when you are standing still the position is pinging around a point. Once you move in a direction and gain speed the gps is spot on.
Can we ask what your speed is there, nothing especially stands out..
3 satellites is enough for a fix.
If some is good, more must be gooder ??
I worked on Sat Nav software for four years a few years ago. Your statement is only partially correct.
"Pinging around a point" has a couple causes.
When stationary, a GPS nav system/speedo knows nothing of your heading. This can cause a GPS nav system to "rotate".
There is also a bit of error in civilian based GPS systems. The United States government currently claims 4 meter RMS (7.8 meter 95% Confidence Interval) horizontal accuracy for civilian (SPS) GPS. Vertical accuracy is worse. Mind you, that's the minimum. Some devices/locations reliably (95% of the time or better) can get 3 meter accuracy. 3 meters is just about 10 feet. This can cause a position to "jitter" about a point.
This becomes worse in an urban environment, where you have a lot of high rise buildings. Here, you will get reflections of signals off of the glass buildings, causing systems (with typically smaller GPS antennae chip sizes in mobile devices having worse "reception" and more prone to error vs. inbuilt car systems or airborne systems with larger and more accurate chips) to become confused as there are multiple time-position signals simultaneously for a given satellite. This alos causes "pinging around a point".
This positional accuracy and errors do not change with vehicle speed.
GPS devices are positional speedometers, based on how far the device has moved since the last measurement. The algorithm also uses the doppler shift in the pseudo range signals from the satellites. It should also be noted that the speed reading is normalized, and is not an instant speed.
Speeds are updated at short intervals to maintain accuracy at all times. It uses frequent calculations to determine the vehicle’s speed. For example, using a standard movement per time calculation, if you have covered 80 feet in one second, the GPS device works out and converts that to MPH, which in this case is 55MPH.
Depending on the device, and how it was designed (Note for pete.v: specified), speed update periodicity can be very different. For example, mobile devices (as opposed to in-car Sat Navs) have a strong bias for battery life. In this application, one of the compromises I have seen made is in how many times the software controlling the GPS module asks for an update on position. The fewwer times the GPS module asks, the greater the potential normalization error.
A system needs 3 for a fix in the horizontal plane, and 4 for a 3D fix. Most systems will only pay attention to 3 or 4 satellites at one time (depending on specification - if you have an altimeter function, for example), and these are the first ones "locked on". Again, this is for computational and power savings.
Oh, and I forgot a major reason why you see positional jitter: map data. All GPS companies buy their map data from one or two global providers, and a number of smaller regional providers. (Not all road data is created equal, nor is it all accurate - after all it is captured by vans driving around with cameras, and GPS receivers...). Then they have to take the data format and build it into a format that their devices' SW can understand, and then they have to match that to real world use. In most cases, that will result in a SW bias for "road lock" - in other words, the data and the position may say one thing, but the visual map may be saying something else. So, the device will show the vehicle as "locked" to the road when moving - you wouldnt want to be on the road and see yourself "driving" down the river, or on a service road now would you? No confidence in the GPS system then... So, when stationary the road lock is weaker - and the device will hunt for a location - "pinging" as you call it.
Yep as I said, a fully fettered Smith speedometer is as good as it gets for general public so if yours is not oh well keep bashing Smiths but hobot knows to praise and trust his two. I am still up in air on what data logger to buy to send around to hot shots and track days. I am speed conditioned enough that I do not feel like pressing speed until over 120 mph when ereo dynamics must be compensated for, my poor ole SuVee650 does not reach that unless dropping off cliff, Trixie can get close on long down hills but if pressing Peel thats about threshold where she had to snic 4th to keep the revs passing red zone and still on 2S power band to make the steady Smith needle rise more unbelievably. The fast original poster dared to pull 7800, so why not the rest of you with hot rods?
I was being very general in my statement on gps systems all of what you state I do not dispute. The JPEG that needing posted reminded me of my first gps which was a Lowrance globemap 100. …Very primitive! It was one of the first to use maps in a handheld unit… these were set at a much larger error factor on accuracy than you state in your reply with today’s GPS Systems. Also the altitude was varied greatly during the initial introduction to this technology due to Military concerns with civilians using this technology for wrong intentions…As other countries introduced there own satellite systems the errors were reduced. We have come a long way since then.
Separate names with a comma.