There is about 37mm of stack difference between the lowest pad mount position (widest pad position for either clamp width configuration) and highest (narrowest pad position for either clamp width configuration). From Zipp's data you are at 93mm of cockpit stack and the pad width is 180mm. If you flipped the extension clamps to the narrow configuration and moved the pads out to the second from narrowest position (what they call 12.5° facet) you would drop the cockpit stack to 79mm with the armrest width at 177mm or about the same pad with and 14mm pad stack reduction.

Zipp also has low stack extension clamps that drop pad stack about 12mm. The limitation is that they only allow the pad width/height adjustment with the wide pad mount position. So the lowest pad stack you can get at the 180mm pad width is 81mm. If you flip the extension clamps it will give you a 143mm width, but won't go lower than the 81mm pad stack.

Lots of adjustability with these bars, but they only allow you to go so low if you want the pads narrow.

If your bike allows it, you can gain same more drop with a slammed headset cap.

Since you seem to know about the Vuka Stealth, can you please help me out. I have a Felt IA16 coming in this week and ordered a Vuka Aero to go with it. The new Vuka Aero has the same set up as the Stealth but used a stem. The frame has a stack of 537 and I want to get to a stack of 627. Will it be able to get me to 527? How will it be set up?

Thank you

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''Sweeney - you can both crush your AG *and* cruise in dead last!! 😂 '' Murphy's Law

http://www.zipp.com/...rt/vukafit/index.php

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Favorite Gear: Dimond | Cadex | Desoto Sport | Hoka One One

t


I was totally confident about this until I messed with that thing yesterday. That's what caused all my worries.

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''Sweeney - you can both crush your AG *and* cruise in dead last!! 😂 '' Murphy's Law

How does that cause concern? It will literally output the exact setup you need to hit your numbers.

Whats your pad stack and reach? Input it into the calculator. (Measure to the back of the pad for reach per the Vuka calculator)

Whats the frame stack and reach? Input into the calculator.

How much headset/spacers will be below your steam? Input into the calculator. (Assuming less than 10mm total since I believe the fork comes precut from the factory on the IA16 to work with the Felt stem.)

Whats your pad width measured center to center? Input.

Select your extensions.

Calculate.

Done.

Are you having trouble reading the output? If so, screenshot the output and post here and someone will explain.

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"One Line Robert"

Fitting my wife with a low stack target on the Dimond required a lot of research on the Vuka Stealth and Aero. Ben Waite @ Zipp was very helpful. He posted a great stack and reach chart graphic in one of the past Vuka threads.

The posts above on the Vuka Fit app are correct, if you have one set of pad coordinates to hit. It is more difficult to work out if you are aiming for a range of targets or trying to build in some stack adjustability. These bars and the hardware allow for almost unlimited pad reach adjustment. But with pad stack you are limited by the clamp extension risers - new 5mm, 10mm, 25mm and 50mm. This hardware does not allow for stacking the risers, you have to pick one height and use the associated bolts. The other limitation is that that incremental pad stack adjustments (at the pad mounts) all result in a change in pad width. In comparison, the Speed Concept type hardware allows you to set pad width and height independent of each other. But as long as you aren't looking at an extremely low pad stack (over frame stack) target, these bars give you plenty of options.

The Zipp Aero2 will give you as little as 62mm of pad stack from the center of the stem clamp using the regular extension clamps. And same as with the Vuka Stealth, it will go 12mm less, or to 50mm with the low stack extension clamp kit.

Assuming you meant getting to the 627 pad stack, you have 90mm of cockpit stack to play with on your new Felt. At first glance this should allow you plenty of room, but stem selection plays a part, as does the headset top cap. I haven't seen a lot of info out there on how this works out on the new Felt. If you're using the Felt stem, it actually rises rather than extending flat or down. The VukaFit app only includes the stems Zipp offers so you'll have to approximate using those or another stem calculator.

How you intend to mount the extension clamps (narrow or wide) and your pad width will set most of the cockpit height on your bar. Use the stem info to get the other part of the stack dimension. If there is much difference you can make it up with a steerer stem spacer or use one of the extension clamp risers. You should be receiving bars that include the 5mm riser. One piece of advice learned through installing several sets of these bars is that if you mount the extensions in the narrow position, adding at least a minimal extension riser can be helpful for easier extension adjustment. This is because the contour of the bar makes accessing the torx extension clamp bolts (facing inwards) difficult. A ball-end torx would help, but I don't have one in my toolbox yet...

Thanks, now I feel confident again. I started messing with the Vuka Fit App yesterday and it got me thinking the this was going to be tight. There is no adjustment at the stem. It's one size fits all o n the IAx. So we can mount the base bar and take it form there. I can be pretty adaptable width wise, as long as I get the right drop from saddle to pad.

Thanks again, it's looking good again.

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''Sweeney - you can both crush your AG *and* cruise in dead last!! 😂 '' Murphy's Law

Since you are using the Felt stem you could try messaging SuperDave here on ST to ask him to confirm the stack dimension from the bottom of the stem to the center of the handlebar clamp. Slowman's "Felt downstreams the IA" article lists 10° rise or -7° and 90mm length. This would be about 16mm of stack over the stem rise. If you assume 20mm additional stack for half the stem clamp height, the Felt stem would put the center of the clamp at 36mm over the frame stack assuming the stem sits flush with the TT.

36mm of stack from the stem plus the minimum Vuka Aero2 cockpit stack of 62mm could push it over your 90mm pad stack target. You can always get some additional drop with a different stem if that works with the IAx, but it definitely won't be as clean a match as the proprietary stem.

Thanks. This is extremely helpful. One more question for you. I currently have the armpads mounted to the wide position via the bracket pointed outward, and the armrest bracket is in the middle position for the fore aft adjustment. I need to move it one position rearward, so that the bracket will "straddle" the extension mount. However, I already have everything cabled. Is there any way to make this adjustment after running cables? The cables are Di2, and to a junction box inside my Vuka Stealth. I would have to disassemble quite a bit if this cannot be done while it is cabled.

Is this a trick question? lol.

I just swapped my Vukas from short to medium and must have mine wired similar to yours. It took half the Superbowl to re-fish the wiring to hide most of it internally. So I can sympathize with you.

I wondered about having to make this same reach change when I routed the Di2 wiring this way. I thought it would require a teardown. After looking at it tonight, I think maybe it can be done without rewiring. For it to work assumes: 1) there is enough cable slack to allow sliding the extensions out the front of the extension clamps while wired; 2) that both the extension clamps and armrest clamps can open enough to slip the e-tube wire through when the clamp screws have been removed completely. Puzzle challenge! Let me know how it goes.

Tricky to me ;)

Before I posted I was able to get the Di2 cable out of both slips so that everything was removed from the routing. I was also able to place the armrest pad in the rearmost position. However, I am not able to solve the puzzle of how to move the armrest mount to the next position forward, which would straddle the extension mount. If you can figure that one out let me know!

It looks like you've got answers to all your questions, but if there's anything else that's vague let me know.
Thanks WSRobert and SummitAK for the help!

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Ben Waite | Zipp Senior Design Engineer | The Power of Bicycles: Please contribute to World Bicycle Relief | Zipp | SRAM | Quarq |

The only part I am still fuzzy on, is how to move the armpad bracket from the center mount, to the -20 Straddle postion AFTER cable routing has been completed (if it is possible).

Thanks

Bad news - not possible.
Maybe a good excuse to buy etap? ;)

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________________________________________________________
Ben Waite | Zipp Senior Design Engineer | The Power of Bicycles: Please contribute to World Bicycle Relief | Zipp | SRAM | Quarq |

Thanks for the update.

I have a question for someone over in the Felt IA thread. He asked me; what is the minimum stack for the Vuka Stealth from the center of the basebar to the top of the pad?

Thanks

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''Sweeney - you can both crush your AG *and* cruise in dead last!! 😂 '' Murphy's Law

The stack from the center of the basebar to the top of the pad isn't really useful since the center of the basebar is an arbitrary point in space.
From the bottom of the stem clamp (where it attaches at the steerer) to the top of the pad is the measurement that should be most useful. For the Vuka Stealth, that is 93mm with the normal extension clamp and 81mm with the low stack extension clamp. Does that help you out?

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Ben Waite | Zipp Senior Design Engineer | The Power of Bicycles: Please contribute to World Bicycle Relief | Zipp | SRAM | Quarq |

Thanks, I will pass it along.

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''Sweeney - you can both crush your AG *and* cruise in dead last!! 😂 '' Murphy's Law

If you were looking for a bar pad stack of 91 could you use the low stack clamp with a 10 mm riser?

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''Sweeney - you can both crush your AG *and* cruise in dead last!! 😂 '' Murphy's Law

Yes, you could use the low stack and 10mm riser.
The normal clamp with no riser gives a stack of 93mm. To get within 2mm, that is probably good enough. The stackup of tolerances for cockpit measurements is probably a few millimeters. Example: our measurements include an assumption on weight for pad compression of a new pad. An older one will be millimeters less.

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________________________________________________________
Ben Waite | Zipp Senior Design Engineer | The Power of Bicycles: Please contribute to World Bicycle Relief | Zipp | SRAM | Quarq |

Whilst on the Vuka Stealth topic - does anybody have any suggestions how best to attach/conceal a di2 junction box to the Vuka stem?

When I had mine I put internal junction boxes in the extensions and ran a long etube back through the frame and up the seatpost. Mounted my charging external junction to the back of the seatpost. It's a little bit of extra work but well worth it. I did the same with my Triad.