Rally Computer Installation

Update by Per Schroeder to the Saab 99 project car
Dec 12, 2007

We finished up the installation of our Brantz 2 tripmeter last night. The system uses a sensor that can measure anything that’s spinning relative to road speed. Axles, hubs and driveshafts are typical measurement points. We chose the rear hub and particularly, the backs of the rear studs. We get four increments per wheel rotation and since we’re using the rear wheels, we don’t have to worry about wheelspin on the fronts affecting our mileage counts.

The sensor is mounted on a stainless steel bracket that was actually leftover scrap from a MINI exhaust system. We bolted the bracket to one of the ears that the original dust shield attached to, and then attached the sensor to the other end. It’s adjusted so that the head of the sensor is just one millimeter away from the back of the studs and just barely tucks inside the rear brake rotor hat.

The unit itself is screwed into the glove box door (which was attached permanently to what is left of our dashboard.) The wiring for the Brantz, like the Terratrip isn’t all that self-explanatory. The wiring color, for example, doesn’t follow the normal convention of Brown=Ground and Red=12v+. In this case, Brown=12v+ and Yellow/Green=Ground. What makes it even more confusing is that the sensor wiring is different still, with Brown attaching to Blue for one of the leads. Anyway, the point is, read the directions!

To calibrate the Brantz, you punch “100” into the calibration setting and drive one measured mile (or kilometer if you’re running a rally elsewhere). The distance shown in the display then becomes your new calibration factor. For example, our buddy Luke Sorensen’s Brantz has a calibration factor of 297 for tall rally tires and 323 for smaller ones.

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