Speedo Help Needed.

[elliotsdaddy]

Evening all.

In an attempt to make my Sherco 100% road legal I have fitted a speedo to keep Mr and Mrs Plod happy.

It's just one of those mountain bike ones from that ever popular auction site -

http://www.ebay.co.uk/itm/DIGITAL-CYCLE-MOUNTAIN-RACER-BIKE-DIGITAL-WIRELESS-SPEEDO-COMPUTER-SPEEDOMETER-/290960376715?pt=UK_SportGoods_CyclAcces_RL&hash=item43be97038b#ht_2800wt_1141

Has anyone else fitted one of these?

It does work, after a little modification to the little magnet...motorbike spokes are a little bigger than mountain bike ones...but it does read a little erractic.

There is a chart to allow you to insert a code based on the wheel size. This chart doesn't go up to motorbike sizes so I was wondering if that could be the issue, and what can be done to make it work better?

Basically can anyone who has fitted one of these tell me how and where they fitted it, and what wheel size to go by?

I'm happy for it to be on there and continue to read as it is. I mean if I get stopped at least I can say "tadah...here is my speedo Mr Officer", but it would be nice if it would read more accurate.

Thanks in advance,

Chris.

[2stroke4stroke]

If you think that one's erratic you obviously haven't tried an original one :-)

A normal 700c cycle wheel is close to a 21 inch front I think so the scale does go that far up. If you measure how far the wheel goes in one revolution using the valve as a reference point you can plug that in to the computer. Most instructions detail how to do this.

Edited October 27, 2014 by 2stroke4stroke

[graham66]

Hello, 2stroke is correct but remember that for accuracy one wheel rotation must be measured exactly (to the mm) when you are on the bike with the usual tyre pressure. The circumference of the tyre will be different without your weight etc. The help of a mate is essential.

I have always found that "radio" speedo's are rubbish and that the only decent ones are those with a wire which connects the sensor with the display unit.

regards

[naichuff]

Agree with GRAHAM66 the radio one can pick up signal of the ignition system Wired ones are best Had one a BSA B31 for years Ok up to 55mph them flashes ( use it mainly for the time)The proper speedo has the wrong gearing Had others that did not like a knock If set right they are ok Have one fitted on the Beta just for recording distance and time run between services

[copemech]

Not sure if it helps you, but I use a handheld GPS for ref on speedo calibrations on cars. Most widgets like that are based upon revs per mile so one is able to tune accordingly based upon your percentage of error calculations from the GPS. Take readings at 20, 30,40 mph indicated and compare to actual on GPS which is quite accurate.

[the_italian]

I hope this will help.

I have professional experience with push bikes.

99 % of the times the "code" you input is the same accross different computers and it is the measure in mms of the wheel circumference.

if it is very cheap yes it gets erratic.

if the distance between magnet and reader isn't right ( 1mm) again it will get erratic.

Sometimes a new battery helps a lot.

[sean65]

I have come a cropper with my insurance company underwriters wanting me to fit a speedo. I'm unclear. Its an MTB one acceptable or even just the use of a mobile with GPS. Like most things I guess it is just to appease the company. You can swap things after an MOT if one was so inclined. So daft really to insist on one.