I want to be able to go on unplanned, winding rides without getting lost. All I really need is a map and a "go home" button. I don't care to have route planning, biometric feedback, etc.

I'm looking at a flyer from a big-box electronics store that shows nav systems for cars. I can get something in the $100 to $150 price range, and most seem to have handlebar mounting systems available on the web for less than $10. The models in this flyer are the Garmin nuvi 205W and 255W, and the TomTom XXL540S.

Are there drawbacks to this approach that I haven't thought about? If you have done this, what model(s) have you used, and are you happy with the choice?

Thanks in advance for any feedback.

I got a Tom Tom 130 for Christmas, and wanted to use it on the bicycle for the same reasons you do, I haven't tried it that way yet, but figured I'd keep it in the trunk until I needed it and then get my bearings to figure out how to get home. Mine has spoken directions, and I'm wondering if the GPS could get a signal in the trunk and allow me to avoid mounting it on the handlebar.

Works fine, but there are two things to check - battery life and waterproofness. Most car units are built with the assumption that they'll usually be plugged into 12 VDC power and therefore only need the internal battery to operate for a short time. And most are not waterproof so you may need to keep them covered (ziplocks work ok) if you might find yourself riding in the rain. You can usually solve the battery life problem by adding an external battery pack.

Also check to see if the unit you have in mind lets you specify that you're using it on a bicycle (the Garmins you mention above do) so when you push the 'go home' button it doesn't direct you to the nearest freeway onramp.

I use a Garmin Oregon 550T as my bike computer and it works great.. The best choice now is the Garmin Dakota 20 series, a full featured gps but supports garmin bike options like HR and Cadence.. A little smaller form factor over the Oregon series but still much bigger than the 305 or 500 bike garmin series.. aa batteries and long runtime..

https://buy.garmin.com/shop/shop.do?cID=145&pID=30926

The 20 series has a microsd card slot so you can load anytype of maps..

here is a review: https://www.gpsinformation.org/penrod/dakota/dakota.html

I tried it with a Nuvi 360 but the various mounts I tried didn't seem like they would hold over some of the stiffer bumps. The lack of waterproofing is also a problem as someone mentioned, as is daylight (and night visibility). In the end I sold the Nuvi and got a 705. $323 and that includes HR strap and cadence sensor, plus two bike mounts so it doesn't end up being that much more expensive than a car GPS. The 705 GPS is also a lot more sensitive than the 360 was, so more likely to be able to hold signal in an enclosed or hilly area.

You are going to be happier with a bike GPS, or even a mapping hand held such as the Oregon line or an Etrex (all by Gatmin by the way).

If you really want something you can also use in the car, there us ONLY one good choice from Garmin and that is the Nuvi 550. Why the 550? It is waterproof to IPX7 standards. I have a 550 and I use it in my truck and on my Waverunner. The Waverunner really puts the waterproof claim to a test. So far it has held up, even in the saltwater. Try that with any other automotive GPS.

The 550 also has a user replacable battery, giving a solution to short battery life. Buy a second battery. When number 1 gives out, insert number 2.

But on my bike, the 550 is clunky. Too big. And not really protected in the event of a spill.

Get a bike specific GPS with mapping ability, or a less expensive mapping handheld that is waterproof.

For what it is worth, a lot of phones have GPS these days (iPhone and Android come to mind).

I use a Mio C320, which is hacked and running MioPocket (makes it a true CE-based PIM). The unit cost around $100. I've got text-to-speech enabled, which is as nice for the bike as the car. Most importantly, since my unit is running MioPocket, I can use other CE-based navigation programs. I've got Ozi-Explorer CE installed on my MIO, which enables me to use the USGS topo maps for the forest I live in--the forest roads don't appear on commercial software. I wouldn't bike or hike without my GPS. If the weather is dry, I will sometimes mount my GPS on the handlebars. It's important that you use auxiliary straps or bands of some kind to help hold the unit in (most manufacturers will warn you that you need to do so if you use a bicycle or motorcycle mount). Here's a picture of my unit in it's handlebar mount. This day, I wasn't using GPS software but playing MP3s using the built-in speaker (I won't wear earbuds on a bike, I think it's dangerous). I've got an auxiliary battery pack plugged into it as well.

The one Garmin I have used did had options for car, walking or a bike. I guess because if you are on a bike or walking you can easily turn around on a two way street and if you are walking you can legally walk the wrong way on a one way street.

The only draw back is if you go off road or take trails that wouldn't be in the system like a hiking unit may have. The unit may always want to put you on a road.

You should be able to put it in offroad mode. Also, if you turn on logging and then go ride, when you get home, if you connect the GPS (if compatible) to a computer with Google Earth, you can upload your route. Haven't had a chance to really get a reliable test offroad with this, but I know the two functions are available and both work, and I think they will work together.

Yes, it works fine. My Garmin GPS was marketed for car use but I mainly use it for bicycling and some for hiking. Here's an example of using it for hiking to show that it tracks fine when off roads:
https://www.everytrail.com/view_trip.php?trip_id=552952

and here's a recent bike ride example:
https://www.everytrail.com/view_trip.php?trip_id=548964