Rear Driven Speedo?

[yowsaboss]

I have a Cup bike, race track only. They don’t have a working speedometer/ odometer because there are no ABS rings on the wheels, no associated sensors or wiring connected the the ECU. As a consequence the ABS light on the dash is always lit. This is normal, as there is no ABS. I’d sort of like to have an odometer, just to keep track of mileage. It would be easy enough to connect a bicycle speedometer/ odometer, but if I can easily make the existing one work, it’s one less complication. A plus being that the speedometer on the dash will work, not that I’m going to spend much time looking at it.

My understanding the the street bike’s speedometer is driven by the front wheel’s ABS ring. The next time my wheels are off, if I were to install an ABS ring on the rear, and connect the sensor to the connection where the front sensor is ordinarily connected, would this give me a reasonably accurate odometer?

I know the rings front and rear are different sizes. I assume this is to account for the different tire diameter. So my assumption would be that having the speedo driven off the rear wheel would give the exact same reading if it were driven off the front. The different sized rings give the ECU a 1:1 reading, the software isn’t factoring in that the rear wheel’s rotation is 104% (a guess) of the front.

True?

As it is I am running a (standard) 140 rear instead of a 150, so there’s going to be some error anyway. But I’m not interested in absolute accuracy, as most factory speedos read a few percent high anyway. As long as it’s accurate within a few percent, no problem.

Will this work?

 

[Fasteddy]

On the 15 /16 MY bikes the ABS tone rings supply a signal to the ABS module that is at a much higher frequency then what is sent to the combo instrument, the ABS module divides it down and supplies a cleaner lower frequency pulse train for the speedo. The wheel circumference can be adjusted in the combo instrument. There was one version of RC, I believe the RC200 that was non ABS which used a more standard KTM style speedo pickup on front but had a module that went between the wheel sensor and the combo interments

Short answer, no will not work, but, with some software and a micro controller.....

 

[B7ACKTHORN]

On the 15 /16 MY bikes the ABS tone rings supply a signal to the ABS module that is at a much higher frequency then what is sent to the combo instrument, the ABS module divides it down and supplies a cleaner lower frequency pulse train for the speedo. The wheel circumference can be adjusted in the combo instrument. There was one version of RC, I believe the RC200 that was non ABS which used a more standard KTM style speedo pickup on front but had a module that went between the wheel sensor and the combo interments

Short answer, no will not work, but, with some software and a micro controller.....

Correct me if I'm wrong, the VSS picks up the pulses and sends to the ABS first as opposed to the ECM?

 

[Fasteddy]

Just did a quick check of the signal paths on 2015 wiring diagram, magneto pickups front and rear go direct to ABS unit, pulses varying in frequency representing speed leave ABS module on pin 8 / Blue/White wire then feeds LSU (mis labeled in diagram) ECU and combo instrument. 2018 is similar but different pins / colors.

RC200, Asia only market, has no ABS. Although it is not shown in it's wiring diagram it uses the same type of pickup on front wheel as KTM bikes like SD990 etc that develops pulses from reluctance of disc brake bolts going past it, this sensor goes into a module that I have not found documented anywhere but have seen in some photos on the web.