30 replies to this topic

[Tomf]

I have read in a few places that you can use a mountain bike speedo in a mini.

My first question is, can you get these in 12v so they will turn on when the ignition is on? if not how would the be poseders, because i cant see the little watch battery lasting long, as i would have to leave it on constantly because i will be mounting it inside an old gauge...

My second question is, how would you mount it in place i know it works with a magnet and a sensor, but how would this work? do i just mount the magnet on the wheel and then the sensor on to where ever i can find that looks suitable?

And finally, surely because some wheels are different sizes the travel of the magnet will be different so how does the speedo work properly?

[Udo]

Most have auto turn off I think but dont know about staring again you may need to press a button to wake it up

you wont find a bike one in 12 v as they are meant for a bike and so run off the watch style batteries may get a motorbike one thou?

mounting is basically as you have put

the issue with different wheels is covered by the settings on the unit which you can alter for bike wheel sizes

[Tomf]

Ok well i guess ill just have to run one off batteries then. Ill go down to halfords tomorrow and see what they have got and how the turn on/off...


From what i have read and heard it seems quite easy to do, but im just woundering why not many people have done the conversion, as from the minis i have had so far none of the speedo's are very accurate. and from other mini owners i have spoken to their speedo's arent very accurate either.

[nag1_uk]

In our GTM we put a bike speedo inside an old smiths 52mm dial body.

Mike

[Tomf]

Yea thats what im planning on doing, how did yours turn on and off? I think i know how to sort it all out now but just unsure on how to turn it on and off?

[nmt_oli]

could you make a plastic face for the gauge with a hole in it so you could press the buttons, to replace the glass?

Also, if you solder wires to the watch battery holder in the rear of the unit, and hook them up to a a single AA battery holder, you shouldnt have any problems with batteries! lasts much longer, and easier to change!

[James_1]

couldn't you just use a resitor and run it from the cars electrics?

[Tomf]

OH i like the battery idea. i think ill do that but ill have to make sure that i can find one that runds on the same voltage, not to keen on a plastic screen, ill have a think, i might be able to rewire it so that i can have a switch somewhere else.

[Tomf]

I guess i could use a resistor but i dont really know much about how to work out what resistance values to use etc.... just a thought but if i bypassed the on/off switch, that would mean that its constantly on so i could have it wired in off a resistor and then it would turn on/off with the cars ignition.

[Gazman]

Sounds like a plan......my speedo cable is screwed so anything you do decide please please please keep me/the site up to date! I'm already thinking along those lines but not enough knowledge in my head!!

Cheers

[minipip]

but if they have no power in them they loose the settings so ud have to set it up every time?!

[Gazman]

This is similar but says it has automatic on/off. If you can wire it into a live feed it would still switch off when t=not being used....??

http://cgi.ebay.co.u...1QQcmdZViewItem

[biggav]

I removed the ashtray from my top dash rail, cut the hole a bit wider and fitted a road angel in there as a supliment to my speedo.

[James_1]

I guess i could use a resistor but i dont really know much about how to work out what resistance values to use etc.... just a thought but if i bypassed the on/off switch, that would mean that its constantly on so i could have it wired in off a resistor and then it would turn on/off with the cars ignition.

just find a constant supply as used by stereos and clocks

[dklawson]

You do not want to turn it off. REPEAT, do not turn off the bicycle speedometer.

Bicycle speedos include memory bits to store your odometer readings, units, and scale factors. If you interrupt the power you'll have to reprogram it every time you power up.

The solution is to buy a Sigma bicycle computer. It's powered by a common Lithium coin cell (CR2032 ?) which will last several years ( I think the manufacturer says 3 years). The display automatically wakes up and goes to sleep. The remaining electronics are always powered by the coin cell to retain the program variables.

Sigma units are probably the best speedo choice because they can read and display high speeds. Many bicycle computers can't display high-speeds... when was the last time you saw a bicycle go 65 mph or more? Sigma speedos also allow you to VERY accurately program the scale factor (this matches your speedometer to your tire size very accurately). Lastly, Sigma units allow you to enter an odometer value. You don't have to start with an odometer that reads zero (0) miles, you can set it to match your exiting odometer.

To install the speedo you'll need to extend the wire leads between the display and the pickup (which is a reed switch). You'll need to mount the magnet to a rotating component on the drivetrain. I suggest the OD of the inner driveshaft joint. You'll have to fabricate some form of mounting bracket for the pickup so it is close to the magnet and doesn't vibrate much. The bracket needs to be fairly stiff.

An issue with bicycle speedometers is that they have no internal lighting. Your idea to mount the unit in a Smiths 52mm housing would work as it will allow illumination from the back. However, mounting it like that will make battery replacement difficult and will make it impossible to access the pushbutton switches that toggle between display modes such as odometer, trip meter, fastest time, etc.

Google Sigma and use other keywords like motorcycle. The Sigma BC800 (which I used) is a common choice of motorcycle owners who want a digital speedometer.

EDIT: See these links for a little more Sigma info.
http://www.geocities..._toys/bc80.html
http://www.strangely...comp/index.html
http://www.kartingte...om/tech/mph.htm

Edited by dklawson, 27 April 2007 - 07:59 PM.