To get the best results, the selection and fitting of clip-on aerobars is a process that should be done with the assistance of a trained professional and true fit expert, preferably at a high-end bike shop.
There are so many factors involved that I consider myself fortunate that my total ignorance when I purchased mine didn't make it a waste of time and money.
Some of the factors involved include:
- Upper arm length: Selecting bars with the wrong pad height can be a big mistake, if the pad height isn't adequately adjustable. Otherwise, you'll need to adjust your road bar height, which can negatively affect your road ride.
- Forearm length: Proper positioning of the pad near the elbows with the hands on the bars means the pad-to-grip positioning has to be correct, preferably adjustable.
- Elbow separation: Many amateurs can't ride with their elbows tight together like the pros. While this is most efficient for reducing drag, it can restrict breathing and make riding uncomfortable if the fit isn't precise. Pad separation must be adjustable to be as wide (or narrow) as needed.
- Wrist angle: Some folks like to bend their wrists and point their thumbs into the wind. While this is highly aerodynamic, most pros do it because it makes shifting easier. But since clip-on aerobars don't have shifters, many other, more comfortable, wrist angles are possible. Personally, I like the wrist angle with the Profile Design Airstryke (no bend at all), but others hate it.
- Upper body weight: Elbow pad 'give' needs to be balanced. Too much, and control is affected. Too little, and you can be vibrated to bits. My bars initially came with plastic elbow supports that flexed too much: Fortunately, aluminum replacements were available.
It is also the very best investment you can make to reduce road bike drag. Nothing else comes close. Personally, I view aero helmets as a waste, unless you routinely ride at over 30 mph for hours at a time. And that's the #2 factor after clip-on aerobars and a good aero fit. A very distant second.
The best way to buy clip-on aerobars is to put them on your bike, get them adjusted by an expert, then go for a test ride. This process takes time, and is well worth the investment.
This is why bike shops seldom discount clip-on aerobars like the online retailers do: They know that some one-on-one time is needed to select and fit the right bars. Please don't ask for this level of service then walk out without buying the bars that fit best: Be sure folks get paid when they do custom work for you.
Again, the best pre-purchase step is to first get a tri bike fit. If you don't know what the "real thing" feels like, you may have great trouble getting any clip-on aerobars to be both effective and comfortable. Be sure you get your tri bike "fit numbers", so you can use them to see how close you can push your road bike + clip-on aerobar fit.
In my case, my amazing dumb luck still wasn't perfect. My Airstryke bars came with spring-up elbow pads that permit the road bar tops to still be used. At first I thought this was an advantage, preserving all the things I like about my road bars, until I rode in my first time-trial with my clip-on aero bars. When in aero and needing to shift, the pad would pop up when I moved my arm to reach the shifters. This made it VERY awkward to get my arm back on the aerobar! My solution was to lock the pads down with tie-wraps.
Even the ideal clip-on aerobar may turn out to be less than perfect. Mine only came close after I replaced the elbow supports and strapped them down, and then experimented with my bike fit for a year.
My dumb luck got even better after I purchased my Garmin Forerunner 305: The closed front of the Airstryke bar gave me the perfect location for my Garmin bike mount, putting my 305 in an ideal position to read while in aero. All the other solutions I've seen aren't nearly as elegant or as visible. Dumb luck rocks!
For this age-grouper, the net result is that I presently have no intention of ever getting a tri bike. The investment in clip-on aerobars and finding my best fit have provided me 90% of a tri bike ride for 5% of the cost. I wish all my investments paid like that.
YMMV, of course!
Me, I'm planning to invest my savings in a Di2 gruppo for my current bike: That will permit me to add electronic shifter buttons to my clip-on aerobars! Plus, I've broken 2 chains during steep uphill shifts (I applied power before the shift completed), and I'm told that the Di2 shifts so quickly that it eliminates this problem.