Inviscid Design Speedfil Z4 – Review

When Inviscid Design launched the Speedfil Z4 they promised us a product that would change—possibly even revolutionize—how we setup our bikes. We shared our first look at the Z4 in July – and came away thinking that they may have nailed it. For those looking to mount a bottle (or even an Inviscid Design Speedfil A2) while retaining easy access to a computer, the Z4 may be everything you are looking for. But final impressions can never be made on press releases and photos alone, time must be spent getting to know a product in order to determine where it excels and where it may fall short.  And so we began our journey with the Z4.


The Z4

The Z4 is a cage, albeit it a very smart cage. Weighing in at 62g, the Z4 is designed to be mounted with either standard cage screws or via 4 zip ties.


By supporting both zip tie and screw mounting options, the Z4 opens up a range of mounting options for any triathlete. You can mount it up front in a BTA setup or hang it off the saddle with zip ties. You can even choose to mount it to any of your frame’s standard locations. Speedfil’s Facebook page demonstrates the versatility of the Z4 with this Blue Triad SL with no less than four separate Z4s.


We have tested the Z4 in both the front and rear locations (the rear in conjunction with a Speedfil R3). While we typically steer away from zip tie solutions (for our purposes we usually use Velcro because it simplifies removal and allows for on-the-fly adjustments), we chose to use them up front for this test since that was the recommended solution. And we have to say that, in this case, it really worked. The provided zip tie mounting locations hold the Z4 securely in place over even the hardest bumps. We have not launched a single bottle from the front of the bike throughout our testing.


Up top you will find the detachable arm, which is designed to hold the quarter-turn mounts that come with all Garmin cycling computers. The arm places the computer far enough forward that it’s in easy line of sight. The quarter-turn mount snaps and locks into place inside the arm. If you use a 910xt with its unique orientation, you can easily setup the mount to support it.

The Z4+

The Z4 will set you back $39.95, but for $10 more you get the Z4+ model designed specifically for the A2. While the Z4 is built with the more generic BTA setups in mind (single 20-24oz bottle), the Z4+ adds a non-slip strap and tube clip that is designed to be used in conjunction with the A2. In fact we already feel that if you are considering an A2, go ahead and purchase the Z4+ along with it – it’s the perfect companion.


The non-slip strap is designed to hold the bottle in a single orientation throughout even the longest ride. And the tube clip holds the bite valve out of the way until you need it. In fact, this is easily one of our favorite bits of engineering with the Z4+. In an earlier Week in Review we called the tube clip “brilliant,” and we still stand by that assessment. It’s a small detail, but one they got absolutely right. Once we placed the straw into the clip, the straw never dislodged. Many have looked at the AeroGeeks site banner and noticed the giant straw hanging in front of the Quintana Roo. But with the Z4+ that is no longer an issue.

Riding with the Z4

We have been using the Z4 to carry both standard bottles and the A2 (in conjunction with the added strap from the Z4+). During this time we have found that the Z4 lives up to its billing – it really does change the BTA cage game. The Z4 is both a solid cage and computer mount rolled into a single package. It holds the bottles (no launches!), and more so, is the cage the A2 was always looking for.

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When we first reviewed the A2 we mounted it via a series of Velcro straps. The same straps which—much to our dismay—catastrophically let go in the middle of a race. We searched in vain for a better solution. And while many worked, the Velcro had been the best at holding the bottle in place and preventing it from rotating (even at risk of another major launch). Needless to say, the Z4+ was the solution we desperately needed. It consistently holds the A2 in place and holds the straw out of both our face and the wind.

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Because the Z4 is meant to be a cage for all needs – we have also used it as a saddle based cage. And while it worked extremely well (never launched a bottle), we found it to be a bit more clunky than some of the other options out there. The base of the Z4 is pretty thick and if you use it with a rear mount, make sure to use extra-long screws or you may not be able to tighten everything down.

Final Thoughts

We’ve said it once and we’ll say it again—brilliant! The Z4 delivers exactly as advertised – it provides a secure and easy to setup solution for holding bottles in a BTA position with an integrated computer mount to boot. With the Z4+ we get the missing piece of the puzzle that the A2 needed from the very beginning. Our biggest complaint to Inviscid Design is they don’t yet offer an A2/Z4+ bundle – but that is the kind of complaint any company is going to welcome and one we think they can rectify pretty easily!

4 responses to “Inviscid Design Speedfil Z4 – Review

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  4. I was looking for a BTA solution, and bought a Z4 after reading your review.

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