Speedo Talk :/

[guest1406]

Hi all,

Long story short ive completely stripped and rebuilt and modified my GN250. I bought an old speedo and am wondering how on earth I match it up? i.e. i can get the cable and drive, yet someone spoke to me about ratios and matching things up? Not as simple as just plugging it on as i thought

Thanks for any help,

Mackenzie

[guest1406]

Right, researching on the internet and talking to various people Ive found that I will need to get the drive and cable (easily got) the try and have the speedo gear changed to 'match' the gear set in the Suzuki's hub. So research into the Ducati Bronco speedo drive ratio(Thats what i salvaged it from) will be needed.

Also was told that it may be easier to match the speedo to the wheel rather then the wheel to the speedo. I'll need to find out my wheel drive ratio and the speedo ratio, then research into a few other head units to match.

Technical stuff!

Mackenzie

[SteveC#222]

You could always use a digital - pushbike type - speedo/computer, a lot of customs use them and you can alter them to suit almost any wheel/tyre combination......cheap too!

[themoudie]

Agree with SteveC#222,

Mount the wee dodger on a flap of trials number plate rubber with a bit of padding, so that the 'vibe' doesn't destroy the innards. Calibrate as per instructions. You can either get senders that are wired to the display or 'BlueTooth' type senders requiring no wire.

I used one on a Duke single for 4 years in the late '90's and early 2000's. Model: Sigma Sport 800. When the screen played up after 3.5 years, I returned to Sigma asking if anything could be done, but I realised that I was outwith any warranty period. Result, new replacement and a letter of apology, to which I politely replied , thanking them for their generosity. Probably old technology now. The only drawback was the lack of illumination after dark! Still it's amazing what a Tia Maria can do for you!

My regards, Bill.

[guest1406]

Steve and Bill I just cant do a digital. The only time a digitial suits a bike is when its on a motorcross style type bike. Ive now found a researched everything I have to do, it will be long, hard and mathmatical but to me it will be worth it!

Mackenzie

[themoudie]

Aye Mackenzie,

C'est la vie! 

I hope you acheive the affect you are looking for.

My regards, Bill.

[guest1406]

Bit of an update on the quest. I have now researched that I only need the speedo gear ratio. I think ... .. .

So just a few questions now.

Will any speedo drive fit any front end? I.e. are they different shapes and sizes?

How can I get the ratio that the speedo works on? Do i need the ratio or can I find the speedos sprocket tooth size and whatever drive fits and have a new ratio

So once I have the ratio, a speedo cable and drive that all fits what do I do with it? I.e. how do I physcially calibrate it all to read correctly.

Thanks for any help,

Mackenzie

[johnr]

you dont! you cant calibrate a modern speedo. theyre a mechanical device. the wheel turrns the speedo drive, which turns a worm gear which spins the cable and that in turn drives the speedo. theyre all set. you dont adjust them, if you fit a different speedo, then in order for it to read true, you need the speedo cable to spin at the same speed at a given road speed as the original one for the speedo you have. so, if you have a ducati speedo and you want it to read true, then you need the cable to be spinning at the same speed at say, 30mph on your bike as it was at 30 on the ducati. this is why folk suggest digital speedos, cos it doesnt matter what wheel size you have, you just punch  the right numbers into the speedo and press set! a mechanical speedo if it doesnt read true cant be calibrated unless you fancy manufacturing specially matched drives.
of course you could just buy a mountain bike speedo for a fiver or so, fit it after putting the new speedo on your bike and coupling it to your existing speedo drive, and then run it and see if it is in any way accurate. by some quirk of fate, it might just be something close to accurate. if it is, just remove the digi speedo, and revel in your good luck.

[guest1406]

Cheers John!

Gotcha. Well Ill keep my fingers crossed as i have fallen for the little speedo sadly.

What about if I got the speedos cable and drive and it all fitted. Would it still read true regardless of my wheel cirumfrance?

Mackenzie

[johnr]

depends on the ratios used. old speedos used to have their drive ratio written in tiny numbers at the bottom of the dial. imagine a small 10 inch scooter wheel connected to a speedo, now for the sake of simplicity, lets say that at 30mph the front wheel is spinning at 5 times a second, now put a 21 inch trials wheel on the front at 30mph the wheel is obviously going to turn fewer times, and so your speedo might only say 15mph even though you are doing 30, thats the complication, manufacturers fit speedos wheels and speedo drives as matched sets, and unless you have the right ratios, swapping components from one bike to another will give wild variations of speedo readings.