The reed switches work fine at the 1-2 pulses/second but they are bouncy I'm a bit worried about the 20-30 wheel revs a second the MC will do.
I ordered an Optek OHN3019U Hall Effect Sensor from Jameco to try as a replacement for the wheel reed switch. I'm pretty impressed. In a typical three lead package you get the whole deal: The Hall element, a linear amplifier, a threshold amplifier, and Schmitt trigger, along with an onboard regulator allowing it to run on a range of voltages. It's also wicked fast with operation up to 200 KHZ – So I could handle speeds up to just under one Million MPH.
Trying it out on a proto-board it seems much more sensitive than the reed switches, with the same magnets it reacts at almost 1/2 in. vs 1/8 in for the reed switches. The down side is that it means running three conductors out along the MC swingarm vs. two for the reed switches. One of those leads would be VCC so if something goes wrong I'd risk the power supply. The reed switches are just connected to inputs and pullups so if they short there's no big deal.
For the moment I'm going to stick with the reed switches. If I run into a speed or geometry problem on the motorcycle I'll know what I can do with the hall effect sensor.
http://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?jameco_page=42&langId=-1&productId=1871908&catalogId=10001&freeText=OHN3019U&storeId=10001&search_type=mfgr&ddkey=http:StoreCatalogDrillDownView
I'm interested in your comment about the tach being driven by a hall-effect sensor. The wiring diagram shows it coming from something called the "igniter" which sounds exciting but I need to look into voltages and waveforms,
What's your overall project? If my fabrication and coding skills were up to it I'd be doing a whole control panel display for the motorcycle.