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MG Midget and Sprite General - Bike computer speedometers

I use one of the bike computer thingies to supplement my "normal" speedometer. It works triggered by a magnet fixed to a rear wheel brake drum. Only it isn't - fixed that is.
For the 4th time I have lost the magnet. I have been glueing it there with epoxy resin but it keeps flying off off the drum. I have cleaned a patch on the drum back to bare metal so the glue should hold but it doesn't seem to last.

Anyone else got a good solution to this or is it just an on-going maintenance problem?

Guy
Guy Weller

There's an iPhone ap for that ... ;)
rachmacb

just use your sat nav and set it on speedo.any sat nav worth having has the speed setting and iv tried mine in a few cars and its correct to within 1mph.
roy judd

Probably. Does it involve gluing an i-phone to my back wheel?
Guy Weller

Roy - ! don't have a sat nav.
Guy Weller

LOL nope - but it does help if you've got someone else to sit and hold it - I did try on myself ......!
rachmacb

Guy,
On the one I fitted the magnet had a threaded pin to use with a clamp over the spokes. I drilled and tapped the brake drum and screwed it in. I cant work out why but it works perfectly up to 65MPH and then goes completely haywire, the sped dropping to about 45MPH and them wandering about all over the place. However it spot on at 30MPH and 40MPH which I find very useful

Mike
M J Pearson

Perhaps it thinks that you're dead and your legs are just dying - like a fly:)
rachmacb

My TOM_TOM is accurate at most speeds.
Sandy
SANDY SANDERS

Guy, probably the epoxy is too brittle. We use a product called Sikaflex - a one part polyurethane glue - sticks almost anything to anything - you just need to be sure that you wont need to take it apart in the future. I can drop off the end of a used tube for you next time I am home if you like - its £12.50 a tube and I guess you only need a dab?
David Banks

what type of glue are you using?

Id try a long cure time (24 hour +) 2 part
epoxy like JB weld original...but I have to warn you thats a permentant solution...Ive figured out over this past week that the 4-10 minute epoxys are way to grainy and dont have the locking secure power as the long cure time epoxys...good in there own right for the right job .... just not your project

another thought...maybe a screw down cover of some type, where you can place the magnet and have a cover with a window in the middle an 4 screws on the courners

If its just a magnet and nothing more, get a magnet on a stick ...the ones I have are incased and have a screw on the back, you could revamp it and screw the magnet on to the area you want

my guess if your getting the surface good and clean...use acetone before the glue to take any unknow/unseen residue off .... Its most likely the glue has a low "shear" tolerance in other words it cant hold on in high centrifical applications

another trick... use the tile setter procedure ...when applying the glue make sure the glue on both surfaces is rough textured with groves that oppose each other on the mating surface...this makes a lock bind, if the 2 glue surfaces are smooth its easier to pull them apart.

Hope that helps

Prop...I phone App for "This is your magent calling Ive fallen, and cant find my sticky"
Prop

Mike,
It sounds to me as if the speedo you are using is only designed to handle a limited number of pulses per second. Not uncommon, if you think about the rpm of a car wheel compared to that of a bicycle and the relative speeds involved. My Sigma Sport BC1200 (now discontinued) and the 1606L do not have too much trouble with this. The guarded terms of that statement are because I have tried it with a magnet on the driveshaft and found that, although the current speed readings were still fine, the "calculated" functions like odometer, average speed, etc were reading very low. 3.9 times the pulses exceeded its limits.

Guy,
I tried several mountings unsuccessfully and wound up with a scenario like yours, but using JB Weld. Has held for several years now.

Sat Nav might be ok, but I find that there is an unacceptable lag in the readings which contributes a vagueness I can't deal with. Likewise for the iPhone apps I have tried.
David "me likey Sigma" Lieb
David Lieb

Flag down a windscreen fitter and ask him to fit it with screen glue!!! ;-)
Mick - trying to sort the wiring

Flag down a cop and get him to test you :) I'm SURE he'll not let you go over the speed limit and charge you .......
rachmacb

I have used five minute epoxy for mine

it came away eventually, as I expected it to, but since it always dropped off the drum onto the inner wheel rim I have only lost one once

BUT that was ages ago

I have it fixed close to the outer rim, in the angle between the rim and the drum surface and after filing the spot it was going on to with a "flat-bastardİ" file

This last time I used the old style "takes a while to set" Araldite instead and let it go off and harden well before using it. I faired it in with excess epoxy and have made a smooth job of it

seems OK now

it's a Sigma 1200

marvellous

unlike the inaccurate Smiths jobbie

bill sdgpm

I dont know bill?

your new odometer is reading 852.32 miles an hour in that photo

what brand of condensor are using...I got to get me one of those...LOL

Prop
Prop

Prop,
It is a trick! He has one wheel off the ground so it is going twice as fast with no load. Notice how careful he was to minimize the scenery so you wouldn't ask how fast of a shutter speed he used to freeze the motion? Also note that the Smiths is pegged out with nothing on the odometer. Those Brits are tricky!

I forgot to mention that the Sigma 1606L adds the ability to push a button to light it up for a few seconds. With the 5-speed and a 3.9, my road speed in 5th equals rpm/50, which is an easy calculation to do in ones head, so have not bothered to illuminate the BC1200.
David "no offense, right?" Lieb
David Lieb

I use a cheepo 25 quid Garmin satnav. It has a trip computer built in and a speedo, nice colour display too.

N Sayle

Oh goody, now we get to over-analyze your driving, too ;-)

Let me see... A six and a half hour trip, but stopped over half of it... Pub crawl? a moving average of 23.9 with a burst to 66.3? Musta bin a drag race in there, too. I guess that at the third pub, someone bet that he could go faster on his bicycle than you could in that Spridget. Who won?
David "over-active speculator" Lieb
David Lieb

HOLY CRAP!!! THATS NOT FAR OFF!!!!
N Sayle

Quite an interesting range of advice there - ignoring the Irish answers! I think the general advice is that using my quick setting 2-pack epoxy is the wrong stuff for this application - I need a slower setting or a slightly more elastic adhesive.

Apart from the centrifugal force (which I vaguely remember learning doesn't actually exist!)I wondered if the drums get too hot under heavy braking, but it seems unlikely.

First thing is to find myself a new magnet!
Guy Weller

"Irish answers"??? Is there some form of racism here?
Me sainted granny was Irish, I'll have you know! I have noticed a dearth of folks posting here from Ireland, were they proscribed from owning Spridgets?
David "new magnets are not hard to find" Lieb
David Lieb

Guy,

The drum temperature under heavy braking is a very good point. IIRC common epoxies have a temperature limit of around 150C, I would expect the drums to get hotter but don't know how hot.

Anyone got some temperature telltale stickers they can fit to find out?.
David Billington

David,
My Grandmother was also Irish. I thought everyone had an Irish Grannie!

The Irish Answer is a reference to a well known fact that if you ever ask directions in Ireland, the answer always begins "well, if I were you I wouldn't be starting from here" So, I ask how to attach a magnet to a wheel drum and get advice on sat navs. Go figure! ;-)
Guy Weller

Ahh, Thanks, Guy! I did try to google the phrase and found nothing. My conjectures ranged from Jonathan Swift to explosives, but I guess I missed that one.
David "now as to the lack of Irishmen on this bbs..." Lieb
David Lieb

hmmmmmmmmmm

Irish Answers!!!!

Use a potato :P
PeterJMoore

I use the same one as what Bill posted, has worked very well until 'someone' drove with the E brake slightly on the other day - something seems to have warmed up a wee bit and the poor thing is just reading out current time and no other info.

I'll have to remove the wheel and take a look at the damage. Fortunately I still have brakes!
Rick Bastedo

i used one on my mini
drilled it an the tywraped to the cv joint.
you could try to ad a tywrap and sika (black tar kind of kit) combination.

but that was all before i decided speedo's were useless anny way
Onno Könemann

Rick, That is what mine is doing. Tells me the time, that's all. Its because the magnet has gone walkabouts.

I had thought of either drilling or grinding some surface grooves into the drum to give something for the adhesive to "key" into. But I thought that might create a stress fracture in the drum when I stomp on the brakes. I really need to find a magnet pre-housed in some sort of bracket or mounting
Guy Weller

Very common in burglar alarms, the magnets are in plastic with the ends made to be mounted to the tops of doors. Also gets the magnet a little bit away from the steel. I spent a couple decades working with that stuff, among other things...
Rick Bastedo

To be honest I did think of drilling the side flange to wire the magnus in place, wasnt entirely sure if it would throw up an outabalance situation if I did, so I didnt

yet!

I paid 30pence for a replacement magnet at my local bike shop (not Halfords they dont like to sell bike pooter spares) then took the wheel off and found the original stuck inside the rim of the Rostyle

I still have the spare (just in case you see)

I reckon everyone everywhere has at least one Oirish granny or great grandad, it seems that both my Scots dad and my Brummie mom had Oirish in their distant families

I bet even America's Prez has some too, its sorta mandatory unless you have Polish ones they say


Prop, that is mileage not mileanhourage

852.32 miles since last battery change for the sigma

:-)
bill sdgpm

Bill, In your photo I was most impressed by the acceleration indicated! O to 107 in less than a furlong!

Guy Weller

Could you just magntise a bit of the drum, it is steel. Don't know how though.
MarkDJ-glos

Guy

that was taken when the three of us were decelerating from 110

Mark the trigger is a simple reed switch so it needs a "close once to count" signal from the magnet, a magnetised drum would hold the switch closed all day and night

I had considered getting one of those superstrong rare earth magnets to do the job but wasnt sure that residual magnetism would allow the counting circuit to work. The magnet would certainly stay stuck to the drum

still, so far I'm fine with it still stayed on even after the last track day including braking from 113 to go through the slow hairpin many times didnt damage the grip of the Araldite
bill sdgpm

Hi Nick - what model of Garmin SatNav are you using - yours has a lot more useful info than my £300 TomTom!!!

David Banks

my magnet is cable tied and glued, 2 big cable ties all the way round the drum and through the little bit that's s'posed to join to the spoke :)

mine goes mental over 62mph - i've worked out that it's probably 'cos it only goes to 99 kph (it's only got 2 digits), then gets all confused. Next job is to engage my brain to make it read mph when it thinks it's kph, so I can get up to 99 on the thing. Doesn't have a light in it so no use for night time stuff, but it was only £3.99...
Rob Armstrong

my first effort was with a three quid cheapo one that could only read up to two figures, fine enough at 99mph (ish) but when I converted it to read in KpH it dropped down to about 60MPH... Dohhhh!

took it to France with me cos I had it just to avoid potential zealous flics on trips through the small towns en route to and back from Le Mans (long straight road downhill into Sees (?) springs to mind for those in the know)

It was an absolute packet of sh.... er rubbish

that was why I went in search of the Sigma unit after reading some good reports on here of them, apart from its lack of backlights which would cost a bomb in batteries anyway, it has been brilliant

I thought of cable tying it but thoghts of potentially melting the cable tie at speed when braking always stopped me
bill sdgpm

Guy,

I used bike computer for similar purpose; I bought extra strong magnets from Maplin, they have different shape and "thickness", I stuck two round one together and they stayed on for over a month before I manage to refurbish the speedometer. The downside is, I couldn't see the speed in the dark.
A Lo

hi Alan

how are you doing?
bill sdgpm

When I used to run one on my Mini I stuck the magnet to the inside of a wheel with double sided tape, and covered with another bit of tape. That way centrifugal force only makes it stick harder.
Only required a small bracket to place the sensor near enough to it.
G Hawkins

Guy, I would have suggested the metal tie-wraps that are used to hold CV boots on (similar to Rob's solution). I would have thought you could get some big enough from a HGV parts place. If I remember I'll call in at my local supplier and see if they've got any.
Tarquin

ive been driving without a connected speedo for a year and a half now, not really missing it.
I now drive on revs only and drive the speed others do when i enter a average speedcheck.
Arie de Best

And Arie what do you do when you're sneaking home from the farm at 3.00am and you are going through an average speed but there are no other vehicles about?
Gary Lazarus

Hi David, It is a Garmin StreetPilot c510, these are so last week that they can by found on eBay for under £30. I only discovered the trip computer section the other week by mistake trying to reset it on the move. The speedo display is spot on.
N Sayle

Thanks for the offer Matt. I need to find the best magnet. I had been using the smallest I could find - about 1/4" across - as I thought this would give less momentum trying to rip it off. But at this size there would be nothing much to fasten a strap like that around!
Guy Weller

Cheers Nick.
David Banks

Hi Bill, I am good, just my tools are a bit too clean and shinny, need something else to do otherwise I will have to take up Yoga to relief the stress (not having car to play with).

Guy, the magnets from Maplin are really strong and only cost a few quid.

http://www.maplin.co.uk/Module.aspx?ModuleNo=26348

A Lo

Try ordinary silicone sealant. once cured, it will not let go
neil munn

The service I received from this company, for a different application, was excellent so maybe they can help:

http://e-magnetsuk.com
Doug Plumb

last week's sat-navs are cheap! so are sigma bike computers... does anyone who has one know if it would fit inside a smiths 2" housing? Obviously it would have to come out if it wanted any of its buttons pressed but i'd be happy with speed and distance. easier to light it as well if it's in a gauge housing :)
Rob Armstrong

Lots of bike computers used here in France for regularity rallies,nearly always operate from front wheel on rear drives (no wheelspin).On my frog I used a wee bracket from disc backplate.
Alistair
A.G Peters

Apart from having had two Irish grannies...


Bill, your 'Smiths' was probably inaccurate as it wasn't a Spridget one! 120MPH looks like MGB
Dave O'Neill 2

It is a B speedo Dave

I couldnt find a Midget speedo that looked "early" style and read almost enough for the car...

The gearing of the B speedo keeps it within a reasonable span of the real speed

The Midget speedo stops reading at least 13 mph before the car stops accelerating
bill sdgpm

This thread was discussed between 19/04/2010 and 21/04/2010

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