I am using Easton Attack aero bars with an aero bar mounted waterbottle cage so the only place I could see placing my 305 was on the stem. But while riding yesterday I noticed that the GPS may not be all that accurate being mounted there. I would look down and see 18mph and sit up and see 23. Has anyone else experienced this issue? Any other good mounting techniques for this device? I really like the bottle cage where it’s at. It will make it more convenient going through aid stations and not having to fill up an aero drink.
Sounds like when you’re in the aero position you are blocking the GPS receiver which would cause a delay in the satellite signals. It’s hard to find a good spot for the 205/305 on a bike because that flat area should really be pointed at the sky. I had the same issue too, and I ended up just wearing it on my wrist. Just a flick of the wrist and I could check out the data and it also made T2 easy.
What did you use to put it on your wrist?
Are you using the Edge or Forerunner 305?
There have been a few threads where people showcased how they invented a mounting bracket between the aerobars. With the Forerunner, you should have room to have both the bottle and the 305. With the Edge, I’m not so sure.
edited to add this link: http://forum.slowtwitch.com/gforum.cgi?post=1723056;search_string=305%20mount;#1723056
I wear a basic waterproof watch on my wrist so I dont race with anywhere but the bike. I have the quick release kit and I wear the wrist strap when I train but not on race day.
Looks like you are more aero/faster sitting up. Just race in that position! Kidding.
I have my FR 305 mounted to a horizontal mount attached to the aerobar. The 305 hovers over the stem and I have never seen a loss of signal, in any position. I do have my 305 screen angled down toward the front of the bike for better viewing when aero. A side benefit of this is that the antenna is more exposed.
Can you use one of these mounts to put the 305 farther out, maybe between your hands?
I use the stock mount for the Edge 305 that puts it on top of the stem and use an NXT waterbottle in front of it. The only time I have issues with GPS reception is on a particular section of the bike path that has pretty heavy tree cover. Any other time it works pretty much perfect. You could use the computer mount attached to the side of the aerobars out front of the bottle, it might be a bit less coverage except that your hands may be in the way most of the time. I made a bracket similar to the one in the above-mentioned thread:
http://forum.slowtwitch.com/gforum.cgi?post=1723056;search_string=305%20mount;#1723056
I don’t use it for the 305 but have been considering it. I drip sweat directly on the 305 all the time so it might be good for longevity to have it out front a bit further…
If you get the forerunner, when training if you aren’t using the between the aerobars water bottle, you can strap the watch to the bottle cage. works great for me.
or just wear it on your wrist!
I also have mine mounted on the stem. I’ve never noticed abrupt speed changes, except
when I’ve slacked off. 
-Jot
Ok question for all. How easy/hard is it to use the Garmin 305 on 2 different bikes. And if I use the 305 on my bike, does it give me speed without the cadence sensor, or do i have to get the cadence sensor in order to get accurate speed on the bike. Also, when you go running with the 305, all you need is the unit itself to get speed and distance on runs? You dont need that footpad sensor do you?
I’m looking to get one for my gf, as she is really needing someont that will help her with pace and distance.
It’s easy to swap it between bikes. You can use it fine without the cadence sensor and it
will use GPS. I have the cadence sensor so I can also display, well, cadence. 
I heartily recommend the quick release kit.
As for running, yes, it’s GPS and so no need for the foot pod.
As for instantaneous speed accuracy, remember it’s pretty accurate, but measuring every
6 seconds (normally). So if you surge a lot or change directions a lot it’s not as accurate.
For me those differences just don’t matter that much.
-Jot
I swap my FR 305 between my tri and road bikes all the time. It is my only bike computer. You can get a second quick release off the internet for ~$12.
One caveat, though. I only use the cadence sensor on my tri bike. I did some research and apparently it is difficult to get the 305 to work with 2 different sensors. Since I’m not that concerned with cadence on the road bike it’s not a big deal to be without it. If you are going to use either bike on a trainer then put the sensor on that one.
Not difficult to use a FR305 or Edge 305 on 2 different bikes with cadence sensors. When switching between bikes you just need to go to settings and get the cadence re-synching again. Takes only a few seconds. Just make sure that you are not in range of the other cadence sensor - around 10m away, just in case the unit detects both sensors.
Ok, good to know.
Yeah, it’s fairly easy. I have a Forerunner 305 and an Edge 305. On some days I am running and my GF is biking, so I’ll use the Forerunner and she just goes into the menu and rescans the cadence sensor. One tip is that the sensor goes to sleep if it hasn’t been used in a while. So if you leave that bike stationary and spin the wheel on the one you want it to link to you should be able to do it without having to have the bikes 10m apart. The one that’s a kicker is switching HRMs when I’ve been using the Edge and she wants to use it at the same time I am going out on a run with the Forerunner…then it gets confused on which one it’s on since both are active. “Honey go over to the other side of the house and stay there for 30 seconds!” “WHAT? Oh ok gotcha…” Makes for some strange conversations…
Works flawless for me here…
I just wear the Forerunner 305 on my wrist with the screen on the inside of my wrist. I simply roll my arm slightly and I can see everything I need to while on the bike. In T2, while I am running out of T2 to start the run, I switch to run mode. In T1, I’ve got the GPS rubber banded to my arm rest, turned on, and reset so it’s ready to record. It only takes a few seconds to put the GPS on before I head out on the bike.
Hi Can you explain a little more what you did or some more pictures.
thanks
chris
Here is how I have it set up. I bought the quick release kit and ran 2 zip ties through the mounting holes and pulled them tight. Then I ran 2 zip ties in the opposite direction to attach it to the stem.
or just wear it on your wrist!
I just wear the watch on the inside of my wrist – really easy to see when in the aero position.