offline access to maps. better battery life for long rides. better screen visibility in dark and bright light. better resistance to heat from direct sunlight. keeping my phone in a safe, unexposed location in the event of a minor MTB crash and being confident i'm not burning through the phones's battery in case of emergency

Thanks for your answer @PaulH. "Offline access to maps" --> Here again good apps take care of that, e.g. Komoot. "Battery life" --> I feel it's really sufficient and you can recharge even during the ride. "Heat from direct sunlight" --> In my experience, never a problem, as the phone is simultaneously cooled by the wind. "Keeping the phone safe" --> I've been in crashes with my phone mounted on top of the handlebars and this is a pretty secure location, plus the good mounting cases protect the phone pretty well.

I might give you that the visibility poses a problem sometimes, again in my experience daytime visibility is really sufficient on good phones (if the mount allows adjustment of the angle of viewing), but during night time, it's easy for the maps displayed on the phone to blind me momentarily sometimes.

This ultimately opinion based. None of the apps with "offline" maps have been satisfactory to me with my custom tracks that I've created. Having even an iphone SE mounted to my handbars sounds like an absolute nightmare

Not to mention, carrying an external battery and connecting to the phone while I ride -> no thanks.

Battery life, mostly that, especially when paired with external sensors (cadence, speed, cardiac); when riding, I want to keep my phone as fully charged as possible.

@PaulH offline mapping works well for me using ipbike with mapsforge. It also supports sensors. I've got a dynamo setup for lighting so can charge the phone during daylight hours (and at night need minimum backlight so the battery lasts a long time). This is a cheap rugged phone (it came off at 30km/h when the plastic mount failed, and only got slightly dented). Works for me.

@ChrisH do you have a good mount now? I remember that you had issues with vibrations and retention and experimented a bit. That is, beyon the rain screen you made.

@ChrisH of course it works for you. having a dedicated unit works for me. i tend to keep my phones for a long time and battery life is an issue. My 9 year-old Garmin 800 on the other hands, lasts 10 hours easy and leaves my phone nice and fresh.

also, saying "it's fine, I have a dynamo" is pointless to the broader community. It hardly makes sense to purchases and new wheel (or rebuild an existing one with an expensive hub) solely to skirt around a $200 head unit

@PaulH I go into a bit more detail below, but I also keep phones until they break. My issue is more that I couldn't bring myself to afford a GPS I actually want and the cheap ones would be frustrating. This is improving all the time.

@gschenk a cheap aluminum one from ebay does the trick - the weight of my phone revealed weak spots in plastic brackets, even those marketed for phablets. I've remade the windshield in 2mm polycarbonate to fit the new bracket, but it's essentially the same

@ChrisH That's worth a question on its own.

@PaulH (re dynamos) dynamo lighting is essential for the amount of dark riding I do, the phone charging is an added benefit. Long run time battery lights with decent do exist but they're bulky and heavy and the cost rapidly approaches that of a dynamo setup - which still wins for multi day stuff. On the length of rides I do, people have to top up garmins anyway. Conclusion: even on similar rides, different tools suit different people.

@ChrisH Frankly I don't see the point of having a dynamo recharge the phone - or (to PaulH) any objection to a power bank - when a small power bank that can recharge a phone twice weighs about 150g and can be easily taped under the stem or the top tube...

@ttarchala given that I've got the dynamo for lights anyway, it may as well do something during the day. A power bank is another useful tool especially when days are short or you've got an overnight stop without power

@gschenk you could be right. Much of it is covered in my answer to a loosely related question and some of the rest is close to recommending an (unbranded) product

@ttarchala ... [too late to edit my previous comment] I wouldn't buy a dynamo specially for charging. I did choose which front light to buy on the basis of being able to charge.

@PaulH consider making your comment an answer - remember everyone, comments are for clarifying and improving the question/answer, not for chatting about it.

I think you're downplaying the heat issue too much. I work outside a lot and if I put my phone in the wrong spot (direct sunlight), it gets very hot quickly.

Hi @JPhi1618, I'm speaking from first-hand experience here, I've been using my phone in various hot places for years and when I'm riding, it never gets hot because it gets cooled by the wind at the same time. That's provided you have it in an open case. If you put it in an airtight/waterproof pouch and ride in direct sunlight, that's a different story.

I'm impressed no one mentioned security as a concern. Sometimes bikes can be expensive and it might be risky to ride in some places of the town. Attaching a phone and showing it means jackpot to those guys who happens to be fond of someone else's stuff.

Hi @gmauch, I can see how it might be a concern riding in countries with high crime. I guess most people in this thread, including myself, write from Western Europe or the USA where the level of violent crime isn't so high at the moment, although certainly you can have your bike stolen if you leave it unlocked and/or ouf of sight.