I'm looking to buy a bike computer, and preferably wireless, all of the models I've seen use a magnet and sensor that are attached to the fork and front wheel of the bike. I have a trispoke front wheel and therefore cannot mount a magnet to any spokes so I want to attach it to my rear, but I'm wondering if it will still be in range with the head unit to send information. I also don't want to spend too much, just something simple. Currently looking at the sigma sport 8.12 BC. Thanks.

Cateye Double wireless CC-RD400DW or CC-RD410DW. We've got the CC-RD400DW on our tandem , works well, uses one cadence/speed sensor mounted on the chainstay.

If you chainstay is unusually contoured or thick, you might have a problem mounting it though.

Yes I was aware of that and realize that it may be my best bet, but I wanted to know if there are any cheaper models(let's say sub $50) whose range would be sufficient, would just any wireless computer have enough range

Our tandem chainstays are huge, no problem mounting it although it can and does get kicked out of alignment occasionally.

I have a riding buddy that has a Cateye Strada Double Wireless and has the cadence sensor on the chainstay and the speed sensor on the seatstay as high up as he can get it and still keep the magnet within range. He doesn't have any problems with it not connecting to the computer head. But it's slightly more than $50.00 unless you can find them on sale.

You can glue on any old magnet to one of the three spokes, or use the same type of magnet that is used for a cadence sensor; a magnet that attaches with a zip-tie.

Nashbar Double Wireless reads speed off the rear wheel. It also has cadence with both cadence and speed reading from a sensor/transmitter on the left chainstay. I use one of the "super" magnets for the cadence magnet, it allows for an exceptional range and makes adjusting the sensor lots easier.

I used a Planet Bike Protégé wireless computer on the rear wheel of my gravel bike for a few years without issues.