I'm looking into purchasing a bike computer, primarily to track distance and speed. Is it worth it to go up a notch and get a computer that also tracks cadence? How accurate are bike computers at doing this? I'm not interested in wireless computers - I hear too much about interference, and they are much more expensive (thus targets for thieves) -- so is it worth it to hook up more cables to the bike in order to get cadence info?
I also think the answer is "it depends", but for slightly different reasons to Daniel. I think it depends on why you're cycling.
If you are training, then measuring cadence can definitely be useful. In fact, there are training programmes that are based around cadence. (You're basically looking for a high value, and a steady value.)
Otherwise, the information has more-or-less interest value only, although you could still argue that the "steady" side of the value could be used just to improve your technique.
As regards accuracy, cadence is measured using a magnet, just like speed and distance. So there's no reason why cadence should be any less accurate than speed and distance. It depends on the hardware of course but I'd expect computers these days to be pretty accurate.
As regards your reservations regarding wireless technology, again its going to depend on hardware but wireless is the way all the high-end computers have gone, so there is certainly not any inherent problem with this technology. It is possible to measure things like speed, cadence, power and heart rate, even I believe gearing info, all simultaneously, all wirelessly and without interference.
You're correct that there is extra cost and hassle involved in collecting cadence. The question you need to answer for yourself is: does the benefit outweigh the cost. Since you don't seem to see any benefits, the answer is obviously no.
You should buy things when they fill a need, rather than buying things because they are available.
As far as accuracy goes, they're all accurate enough as makes no difference. Modern electronics can easily generate clocks accurate to parts per million and your variation in pedalling speed is much greater than that.
It's only worth going up a notch if it's a feature you'll use.
I use cadence all the time. It's the primary information I use on a bike computer while I'm riding.
Accuracy is just fine. Awesome in fact. 99% of the time I'm using my Shimano Flight Deck, which does it the "poorly implemented" way, as Dan says (I think).
I'm also using a Garmin now that has a crank sensor so it calculates it the right way. Still, the biggest number on the screen is always my cadence. Both screens.
Don't worry about interference. Never experienced it. Even in road race bunches and group rides. Never had a problem establishing and keeping wireless connections.
This in over a decade using Specialized and Shimano bike computers, and now a couple years on a Garmin using ANT+. Pretty sure the old Polar coded HRM never had trouble either that couldn't be explained away by my chest hair being a bigger source of interference than the wireless.
Wired computer cables can break. I may be paranoid there since I've avoided them for longer than I used them (and I did use them for a while).
I always remove computers and lights before locking a bike (I am certainly paranoid there), but have never worried about somebody wanting to steal the mounts and sensors. Just don't park by the jr high. There's always some jerk there who just wants to break other people's stuff and won't care how cheap it is to fix.
Summary: I used it a lot for a while getting started. Now I never look at it.
Cadence was one of the primary features I was looking for when getting a computer for my road bike. I bought one of the nice Bontrager wireless models where the speed sensor and cadence sensor are all in one piece on the left chainstay. (not advocating wireless, it's just what I have).
I found it to be absolutely essential when I first started riding road. I'm tall and have strong legs so on a MTB I'm a "masher". When I moved over to the road I had a tendency to pedal far too slow. I'd constantly need to look at my cadence to remember to bump it up. 80-90 on flat, 100ish up hills.
After a few hundred miles, I got very used to those rhythms, and I'm able to stay in my target areas without the counter. I'll check from time to time, out of curiosity, but I find I almost never use it any more.
So, If decide if you think you'd be the same way. Maybe use one for a bit and remove it later, or borrow one for a while.
It depends on the unit. Cadence is good to have, if you want to do any sort of training, but cadence is often poorly implemented. In fact, I'm not aware of ANY good computers with cadence at present. The old Cateye Micro was excellent, but it's not been available for 15 years or so.
If you get a unit with cadence you want to be sure it has a SEPARATE cadence pickup, not a combined pickup for both cadence and rear wheel speed. (The current Cateyes use a combined pickup that is impossible to keep aligned.)
As to "extra hassle", the cadence pickup, being near the crank and the foot, is slightly more apt to be knocked out of alignment than the speed pickup, but it's really not that much of a "hassle" (so long as it's not combined with the speed pickup). The main reason for not having a cadence unit is that there aren't many good ones (if any at all).
(I was making use of cadence on my bike trip last week, to help me keep my RPMs up when I got tired. It was a definite asset in that case.)