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Author: Subject: Sender unit for Racetec Speedo

posted on 4/10/19 at 10:47 AM Reply With Quote
Sender unit for Racetec Speedo

Hi, I'm looking at buying a Racetec Digital Speedo but the standard unit does not come with sender. The sender is very expensive at aroound 70. There are other senders on the market for around 20. My understanding of these type of sensors is that they are simply a magnetic proximity sensor which provides a pulse to the Speedo. With that in mind does anyone know if the cheaper senders can be used with a Racetec speed?



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Mike Wood

posted on 6/10/19 at 08:30 AM Reply With Quote

Merlin Motorsport list this:

As an aside, nice looking Locost in your pic. Did you make the ali scuttle and is that a Caterham screen and frame (which model please?). Any tips on hillclimb prep for that car as I am building somthing similar, noted the scrutineering tockets in the roll bar and guess you are also an Uphill Rcaers forum poster too.


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posted on 6/10/19 at 12:33 PM Reply With Quote
Thanks Mike,
Yes I book built my Locost from scratch and registered it in 2004. I competed with it for a couple of seaons with an Xr2 cvh in, but it wasn't competitive. Installed a Redtop but then bought an OMS single seater (currently for sale). I made all the ali bodywork - largely by trial and error, it was great fun. As far as prepping for hill climbing I would say that a Quaife LSD is a must to give good traction out of tighter corners. Anti roll bars are helpful to enable a bit of handling tuning. Engine power and tyres are what it's all about though and at present in the road going classes Extreme are the flavour of the moment I believe. Oh and before I forget make sure your front mudguards have the leading edge well down the front of the wheel to prevent drag.
Good luck and have fun!


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posted on 6/10/19 at 12:35 PM Reply With Quote
Sorry mike forgot to mention, yes it's Caterham screen...not sure which one. I made the screen stays as they needed to be wider at the base than a Caterham stay due to wider scuttle.
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posted on 8/1/20 at 07:47 PM Reply With Quote
I have a Racetech speedo but analogue, i.e. circular dial with pointer. This is far more effective than digital as you can get an idea of how fast you are going in a glance instead of reading digits. Humans have been recognising shapes far longer than reading numbers.

Anyway if you want a digital readout of speed then so be it.

How do you plan to get a signal for the speed?

The best option is to get that from the gearbox so next question is what gearbox is fitted in the car?

If Ford, you can buy an electronic sender or like me make your own because I did not want to spend the money and perhaps more importantly there would not be enough space.

I made mine from aluminium tube and sheet using lumiweld to hold it together. There is a brass spindle in a 5mm roller bearing, one end filed square by hand to engage in the gearbox drive with a slotted disc spinning between a magnet and hall effect sensor. I think there are 4 or 6 slots, more slots being more accurate but the pulse rate must be within spec. for the gauge.
There is a simple electronic circuit to take the signal from the sensor to the Racetech gauge.

I cannot remember what signal the gauge requires but from memory it is switched to ground, done by a transistor.

I am not sure if the Ford sender can be connected directly or would require a simple electrical circuit.

Alternatives are reed switches and magnets on prop shaft or inductive sensors for drive flange bolts, neither of which are as good as gearbox driven implementations.

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