slamthatstem headset top cap dust cover spacer

How low can you go?

If you’re a fan of, probably not low enough.

The brain child of Ian Schon, an engineering student, and Ryan Kelly of, the Slam That Stem headset bearing cover drops the top of your headset down to just 0.075″ (1.9mm) for that low, sporting look while saving a few grams, too.

” We had been talking about how to get that look,” said Schon. “We’d seen so many user submissions of top caps that had been grinded down or pros just running the stems directly on the bearings, which isn’t very good for longevity.

“We both race Cannondale CAAD 10’s and thought it would be fun to make something for ourselves and friends. It’s made for that bike and the SuperSix EVO and newer CAAD8 in particular, but it’ll fit any bike that has a 1.85” top cap.

“I know they’ll work on some Specialized and Cervelo bikes with a few of FSA’s micro shims underneath the dust cap. We’re working on making them for a few other models of bikes, too.”

slam that stem headset top cap dust cover spacer

It’ll also drop a few grams, even if you’re not trying to get as low as possible they could replace your standard headset cap if they fit.

slam that stem headset top cap dust cover spacer

Blanks are cut in Michigan, then they’re die stamped out of 6061-T4 aluminum in Boston, Massachusetts.  They’re just $15 including shipping. Add $2 for international orders. Colors are black, red, blue and green and this early batch is laser etched with V.1 so everyone’ll know you’re an early slammer.

“We’re just a two-man operation trying to help people slam that stem,” said Schon.

More of the story behind it on Ian’s website.


  1. breadandbits on

    not that this will stop anyone, but there are very specific reasons why this, as pictured, deserves to explicitly void the warranty on your fork and headset. immediately coming to mind are two seals that most headset covers have, and the stress distribution in the steerer tube that results from having the stem extremely close to the top bearing…

  2. Zap? on

    “Low sporting look”?

    Is this something that a roadie would worry about? I’ve never worried about how my stem looks on my mountain bike, I just want to make sure it is strong.

  3. Pancakes on


    Can you explain how moving the stem closer to the top bearing would cause the steerer tube to snap, or are you just being a hater?

  4. Ian Schon on

    In response to breadandbits-

    Thank you for your concern. Any bicycle warranty can be void by alteration from the original assembled condition. This does fall under that category, but so do many common alterations.

    Lowering the stem shouldn’t have any adverse effects on stress distribution in the steerer tube, but I will keep this in mind as I continue with future iterations.

  5. breadandbits on

    I don’t care how it looks, but am otherwise a proponent of being able to put the stem lower than is often possible on a road bike, for aerodynamic reasons (rider position). More race organizers seem to be disallowing TT bikes in stage races in order to “level the playing field.” This is good, imho, but is also a good reason for frame manufacturers to keep shorter head tubes on some of their bikes.

    Regarding a mechanical explanation, if someone asks in a genuinely curious and reasonable manner, I would respond.

  6. Gillis on

    Nick Legan, former pro wrench and tech writer at VeloNews, recently answered a question in part with this statement:

    “Not all decisions in the pro peloton are made based on anything scientific or methodical. As an example, many pros run their stems slammed down on the headsets, but not because that’s what’s best for them, but because it looks cool. Peer pressure is a very real thing.”

  7. Pancakes on

    Since you’re not offering a response to a question which didn’t have nearly as much hostility as your initial post, I’ll assume you don’t have a good answer.

    The stem has less leverage on the steerer tube since it’s closer to the top bearing, this would put no more undue loads on it than having a taller spacer stack. There are limits on (maximum) spacer heights with carbon steerer tubes because of this leverage. The most recent limit I saw was somewhere around 20mm, though that number varies from one manufacturer to another.

    Are you talking about a scenario where 3cm of spacers are put above this top cap to take the place of an OE “tall cone” spacer below the stem? That would indeed be unsafe, but that’s also missing the point of this part in the first place.

    Another recommendation regarding carbon steerers is to put a spacer above the stem (as in the picture) so that the compressive forces of the stem clamp are entirely supported by the steerer tube, rather than having it spread above the top. I don’t think your concern relates to that though.

    Please tell me if I’m misinterpreting your assertion, breadandbits, because at this point, I don’t buy it.

  8. Isaac cross on

    Does anyone remember when Hincapie’ steer tube broke at Paris-Roubaix? I was working at a trek dealer at the time, and we received a memo from stating that we must maintain 5mm ar something above the bearing shield. Apparently this was the reason for Hincape’s failure and a few more in the pro ranks. Interesting these treks were all aluminum steerer’s. What i gather from this is that the stem and the top bearing are going to move a small amount no mater what. A few spacers will alow for your steer tub to bow a little. By slamming your stem and minimizing your bearing shield you creat a focal point for this stress and intern a stress riser. Maybe this only applies to aluminum were fatigue is a concern, carbon no fatigue no problem.
    I haven’t paid any heed to this warning as I am always fighting my stack. My caad7 has been slamed since i bought it in 2001, On my cross bikes I raced two seasons without a bearing shield, just went through a few bearings.
    Now if only it didn’t have that dumb writing. Guess I’ll buy the black one and use my trusty sharpie.

  9. law&order on

    there is no void of guarantee to run your stem all the way down, it´s the way it´s suppose to be. The shims are there because people are to fat and lazy to ride their bikes the right way. I sell cannondale and we just get really happy when people wants to slam! the old bikes like the systemsix has alternative topcaps, shims add flex.

  10. bbb on

    i dont see whats wrong with spacers except for carbon steerers … and there is actually no problen even with carbon steerers cause you can put spacers above the stem

  11. Darren on

    Stupid arguments aside, this is a great idea. There are so many new road bikes coming out that have tall head tubes, and again, come with 30mm top bearing cover, the front end of road bikes is getting higher. This suits most riders, however those after a sporting, or racing position find it harder to do so. Aside from purchasing a new headset, it is quite hard to find a lower bearing cover.
    Well done boys.

  12. Alex Webster on

    Truly the most important new cycling product in living memory. Thinking of all the would-be fred sleds saved from a life of contemptible ignominy bring a tear to my eye.

  13. incognitus on

    You don’t have to look very far to find the reason for breadandbits concerns:

    “Use spacers above and below the stem- always. This is not as obvious as over torquing, but riders must have a minimum of 5mm and maximum of 40mm of spacers between the stem and the headset. In addition, a 5mm spacer is required above the stem. These spacers prevent the stem from creating a stress riser on the steerer. Racers must factor in these spacers when sizing their bike.”

    The reason is that you create a specific point load if you don’t have any space between the bearing and the stem, which might cause catastrophic pfailure with most carbon steerer tubes.

    Try this: take a pencil and hold it with both hands so that your two thumbnails are immediately next to each other. Now try to break the pencil. Try the same with a littlespace between the thumbnails. The latter is harder, because it is missing the pinching effect, besides having more “leverage”.

  14. breadandbits on

    @ Ian Schon

    regarding voiding of warranty, i agree – people do it all the time.

    it seems that you’re neglecting the lateral loads on the steerer tube, from the top headset bearing (which is responsible for very little axial constraint). trek indicates that 10-40mm should separate the bearing from the stem ( i think that this is to avoid combining the two loads.

    depending on the nature of the failure mode, a possible solution could be for you to sell glue-in steerer sleeves that are threaded for a top cap bolt (like the ones that come with alpha-q forks). a few sizes would probably fit most fork manufacturers’ specs.

  15. incognitus on

    Curious: Any reason why my post explaining the reasons for leaving a minimum space between stem and bearing was deleted?

  16. Pmurfdesign on

    Are you freaking kidding me? I just dropped $30 on a cane creek 40.IS42short top assembly for my CAAD10 (which, btw, contrary to to many blog posts I read, does NOT completely match the outer diameter of the headtube – it’s a tad smaller) because the stock cover is a ridiculous 20mm tall. Wish I’d known about these guys a week and a half ago. Looks like a killer product, not to mention the OD being a perfect match. I’m not after the look of the pro peloton, but I do love a good tuck and a flat back. The lower the better – it may be all mental but I can feel a difference in speed the lower I get.

  17. greg on

    i have one possible idea for the REAL reason some companies recommend at least one spacer below the stem: the stem clamp deforms the steerer tube. it makes the thing non-round (slightly), therefore putting extra stress on the compression ring, and making failure at that point slightly more possible. with a bonded-in reinforcing insert (cervelo, 3t) i would not worry one bit. im not sure i would worry anyway.
    the thought of “combining two loads” is a load in itself (sorry, couldnt resist), breadandbits seems to forget that there are other companies with other recommendations/guidelines besides trek.
    for instance, both cannondale and specialized recommend running ZERO spacers above the stem after the initial fitting period- their compression plugs/reinforcements support the top of the steerer very well though.

  18. BBB on

    law&order – 04/28/12 – 4:57am
    The shims are there because people are to fat and lazy to ride their bikes the right way. I sell cannondale and we just get really happy when people wants to slam! the old bikes like the systemsix has alternative topcaps, shims add flex.

    No wonder there are so many people ride ill-fitted bikes.

    The shims/spacers are there so people can adjust the handlebar height the way that suits their riding style, flexibility and aspirations, not the way that suits some clueless (bike fitting wise) and patronising shop assistants with racing background.

  19. BRVTAL on

    Ken at Zodiac Engineering has been doing a 1.5mm stack height dust cap for some time now. The Zodiac ones are made from 7068 aluminum and include three heat treated stainless steel shims.

  20. IdeaStormer Jorge on

    OK, some people (not me) keep anywhere from 5mm to 20mm above and below the stem. Why? Well I actually ask these people and most do that because they don’t want to slam it then attempt to sell the frame/bike later and not be able to satisfy some Fred down the road who might want to buy it.

    Yes, there’s a few who who have some issue with their backs, shoulder or other and can’t ride so low.

    I don’t get that pencil analogy as a carbon steer tube is nothing close to a fragile pencil. Lowering or slamming it actually keeps it from breaking because there is no leverage force or the leverage force is greatly reduced when you slam it. Those people with anywhere from 10mm and above gaps from the top cap are creating a leverage force when braking, etc. and we know how good a leverage force can be, well some of us.

  21. Dennis the Mennis on

    A lot of you guys have some really specific, relavant and important things to say. But many of you are a bunch of Bloody Idiots who know nothing of what you are talking about. First of all if you commented on this as a MTB’er (as am I- but view this as a roadie issue) – you were right this is a road thing so comment on MTB s*** and leave this talk to the adults. Second, all of you dorks are worried about warrany- i doubt this will come into play but do you have to spill your soul in a warranty replacemen? Put it back as it was and shut the hell up to get her fixed. If it concerns you be honest and cough up the cash- LAMO! IF people want to drop their stem lower for looks they will loose power and are lame posers (pro or not) . But some of who are flexible and can do more than 20 pushups or more ( hopefully- but not Likely) often want to drop the stem more than the bike will allow. So, this will work great for some and give negative benefit for others. Which is prob most of the people asking stupid questions and worrying about warranty. Ride the bike as it fits you best ( which most have no idea what fits them best). But those of you who do know what I mean. I often need a few more mm of drop to get where I need to be to be in the best aero position on my road and tri bike in which I also produce the most power. If you cannot touch much lower than your toes this would not apply to you. This requires flexibility- so go ahead and raise your stem as high as you can if you cannot touch you toes- You have no flexibility- sorry! Try a Hybrid.

  22. Veloflyte on

    It’s unfortunate how some people with no engineering background and no mechanical ability can express opinions thinking they are somehow correct. The truth concerning George HIncapie’s famous steerer tube break is that he had crashed at least once earlier in the race. His steerer tube simply gave way under extreme abuse. There is absolutely nothing wrong with clamping your stem directly above the upper bearing. It will Not cause your steerer tube to break or to experience any more stress than it normally would. I personally produce the Veloflyte Carbon Dust Shield that is even thinner than the Slam That Stem brand. There is absolutely no adverse effect upon steerer tube longevity or strength. Both my Veloflyte product and the Slam That Stem product are perfectly acceptable alterations to any bicycle.

  23. Zen on


    The pencil analogy is spot on. Ironically, a pencil is made mostly from carbon too, in fact the cellulose is carbon fiber, but not held together by resin and of course the graphite component has almost no structural contribution… but I digress. Whether the shear created by moving the stem closer to the top bearing race will actually cause a carbon, aluminum or steel steerer to fail is debatable. What is not debatable is the physics of moving these two structures closer together brings the pivot point at which they apply torque to the steerer closer. Thus, the load is distributed over a smaller length of the steerer.

    If you slam your stem to look cool, you better be able to drop, outsprint, outclimb and outhandle all those uncool guys with a few cm of spacers. I’ll be looking for you.

  24. Echo on

    Anyone who want to look cool, confidence & wanna gain more aerodynamic benefit drop that sh*t! Cause If you don’t want, just don’t do it.. why always be followers?


COMMENT HERE: (For best results, log in through Wordpress or your social media account. Anonymous/fake email comments may be unapproved or deleted. ALL first-time commenter's posts are held for moderation. Check our Comment Policy for full details.)

This site uses Akismet to reduce spam. Learn how your comment data is processed.