Zipp SL Speed stem weirdness

Discuss light weight issues concerning road bikes & parts.
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billspreston
Posts: 370
Joined: Tue Jun 30, 2009 7:40 pm
Location: CA

by billspreston

I've got Zipp wheels on my bike most of the time so I figured I'd try and match up with the newer Zipp carbon seatpost and speed stem. The seatpost is quite nice, but the stem has induced some serious handling issues like nothing I've experienced before. I swapped an Easton EA90 stem out for the equivalent length Zipp stem and the handling with the Zipp stem became incredibly twitchy at low speeds to the point where I can't ride the bike hands free. At high speeds the bike was very slow to turn-in and would develop a disconcerting wobble tracking a straight line. I'm sure it sounds like I'm exaggerating here, but I'm not. I remounted the stem and double-checked headset preload and the problem persisted. I've since swapped in an Enve stem and the handling is back to normal. Anybody have any experience with this weird Zipp stem?

The main thing that strikes me is how beefy the dimensions are when compared to an Enve stem (photo below) and I wonder if that has something to do with it? I also notice they don't make the stem over 120mm which makes me think flex is an issue, but I can't say the stem felt flexy to me - quite the opposite really. In any event, it looks like I'll be riding the Enve stem and I can't say I'd recommend the Zipp SL Speed stem at all. And just to provide some WW content, the stem is 123g in 110mm so a bit heavier than the Enve as well...

Image

billspreston
Posts: 370
Joined: Tue Jun 30, 2009 7:40 pm
Location: CA

by billspreston

Sorry should have been more clear. That photo above was just to show how beefy the zipp stem is compared to another carbon stem I had on hand (Enve).

This is the stem that was replaced. Went from 110mm Easton EA90 to 110mm Zipp SL Speed. A 6mm shorter headset cone spacer was used to accomodate for the different stem angles (10 vs 6 degree). Then I replaced with a 110mm Enve stem which handled exactly like the Easton stem, with some added vibration dampening.

The handling differences I'm describing are much more pronounced than a 20mm difference in stem anyhow. The bike was borderline unrideable with the Zipp stem. Bizarre.

Image

by Weenie


NiFTY
Posts: 1193
Joined: Sat May 26, 2012 11:26 pm

by NiFTY

I can only imagine it is a preload issue. No hands on bars and unstable cannot be a stem stiffness issue as there is no load on a stem riding handsfree other then the preload.
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billspreston
Posts: 370
Joined: Tue Jun 30, 2009 7:40 pm
Location: CA

by billspreston

That was certainly my impression as well NiFTY, but after resetting the preload several times and experiencing the same issues I had all but ruled that out in my mind. Both the Easton and Enve stems were preloaded in the same manner as the Zipp stem without any handling abnormalities. I will say that preloading a headset is something I've done hundreds of times, but tonight I'll actually check the torque setting I'm using to preload the Enve/Easton stems and then replicate that value using the Zipp stem for an exact comparison before I bin it.

wingguy
Posts: 4193
Joined: Thu Mar 08, 2012 11:43 pm

by wingguy

Did you use the shorter headset cap on the other stems as well as the Zipp? Mostly likely cause is something wierd happening with that.

Definitely though, you're doing omething wrong. It has to be. A) Stems don't cause this to happen. They just can't, there's no physical mechanism by which they have this effect. What could possibly be the explanation for it? B) This stem in particular doesn't cause this to happen. SL Speed stems have been out for a while now, lots of people are riding them, people I know are riding them, and I've never seen or heard any reports of them magically making bikes want to fall over!

eric01
Posts: 545
Joined: Mon Feb 06, 2006 1:06 am

by eric01

Are you sure you aren’t bottoming out the top cap/ preload after switching to the shorter spacer?

Just to eliminate a variable, stick an extra spacer above the stem and then preload.
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spud
Posts: 670
Joined: Sat Feb 07, 2009 5:52 am

by spud

no way the physical properties of the stem are causing this - there's not enough weight difference to change resonance in the front end. Either the set up was bottomed out (as per above) and you weren't actually preloading the bearings appropriately, or (less likely) the top and bottom surfaces of the stem on the steerer clamp are are not parallel/perpendicular, causing uneven preload on the bearings.

alcatraz
Posts: 1234
Joined: Mon Aug 29, 2016 11:19 am

by alcatraz

As previous poster mentioned. Check that you are not bottoming out. If you are you need to add a spacer between the stem and top cap.

It happens when swapping stems with different height.

/a

by Weenie


billspreston
Posts: 370
Joined: Tue Jun 30, 2009 7:40 pm
Location: CA

by billspreston

Thanks guys for pushing me towards the headset. I put some new bearings in last night and lightly preloaded things up again with the Zipp stem. Smooth sailing! I'm sorry to Zipp for not diagnosing the issue properly and the mean things I said :mrgreen:

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