Open Mountain Bike O1 29er hardtail from Gerard Vroomen and Andy Kessler

Gerard Vroomen and Andy Kessler are unveiling their Open mountain bike brand today at Sea Otter. Fortunately, they invited me to give it a spin yesterday and take a few photos.

Called the O-1.0, the name refers to it being model number one for the Open brand. It’s a UD carbon fiber 29er hardtail, and it’s light. It’s also pretty stiff with tight handling, and they put some unique features on the frame to help set it apart.

Their geometry is done by stack and reach rather than top tube length. Vroomen says this tells you that if you’re on one frame and you want to go with a 10mm shorter or longer stem, you’re probably on the right size bike. If you want to change stem length 20mm, you need to go to the next size bike. It’ll be offered in four sizes, Small thru XL, each with 20mm changes in reach from 395mm to 455mm (reach is the horizontal distance from the BB center to the top of the headtube).

Now for the good stuff…

Open Mountain Bike O1 29er hardtail from Gerard Vroomen and Andy Kessler

Paint finish is a simple matte clearcoat with clean white logos and their four logo colors painted around the bottom of the tapered headtube. They said it’ll become a little more opaque to hide some of the carbon layers. Personally, I thought it looked great the way it was.

Open Mountain Bike O1 29er hardtail from Gerard Vroomen and Andy Kessler

The bike come with mechanical cable stops and ports, shown above. But the frame is designed to accommodate electronic shifting like the K-Edge conversions (until Shimano introduces something) and the Acros hydraulic group. For mechanical shifting (aka: cables), the housing stops right here at the headtube and run directly to a guide at the bottom bracket:

Open Mountain Bike O1 29er hardtail from Gerard Vroomen and Andy Kessler

Shown on the right, a cable guide plug holds the cables inside the frame. During install, you run the cables through the guide and out of the bottom bracket shell (front der.) or though the chainstay (rear der.), then pop the guide into the BB shell. Once that’s done, you run the cable into the derailleur clamps and set it up.

At left, a good view of the asymmetric BBright bottom bracket.

Open Mountain Bike O1 29er hardtail from Gerard Vroomen and Andy Kessler

BBright because it gives you the most stiffness for the weight by using the extra space not used on the non-drive side to flare out the downtube and add diameter for improved strength and stiffness. Kessler says there are other brand cranks that should have something on offer for mountain bikes soon. SRAM makes a road BBright crankset, just nothing for mountain. Yet.

Open Mountain Bike O1 29er hardtail from Gerard Vroomen and Andy Kessler

Seat tube is square at the bottom where the side loading forces are greater (reminiscent of Cervelo’s Squoval shape, no?) then rounds off at the top.

Open Mountain Bike O1 29er hardtail from Gerard Vroomen and Andy Kessler

Chainstays are somewhat flattened toward the rear. Nothing like Scott or Cannondale’s flex stays, but noticeable. Shift cable exits into a small piece of housing to the rear derailleur. The derailleur hanger bolts onto the carbon dropout.

Open Mountain Bike O1 29er hardtail from Gerard Vroomen and Andy Kessler

The post mount rear brake section is reinforced to provide strong braking, and all of the material and mounts are on the chainstays. This lets the seatstays flex as intended.

Open Mountain Bike O1 29er hardtail from Gerard Vroomen and Andy Kessler

“Most seatposts have a minimum insertion, but that tells you nothing about what’s safe for the frame,” said Vroomen. “So we put a small hole on the seat tube and i you can see the post through it, you’re safe.”

Monostay seatstay design is thin and flat. He said they could get good torsional stiffness with very little material in the seatstays, and adding more would have reduced vertical compliance. Speaking of which, Kessler says the built-in frame compliance is more for vibration damping than to act as a mini suspension.

Minimal material was also used in the seat tube. Vroomen said when the seatpost is loaded (aka sitting on it), the seat tube bows forward slightly, and slightly more under impact. They’re not making any claims as to total axle movement, but on my ride it seemed to take the edge off without any discernible bounce.

Open Mountain Bike O1 29er hardtail from Gerard Vroomen and Andy Kessler

All models use the Rotor crankset because it’s the only brand offering something that fits the 84mm BBright standard used on Cervelos. To keep the matte color theme, they had Rotor do custom cranksets with a mild gloss on matte crankset without their otherwise bold graphics.

Open Mountain Bike O1 29er hardtail from Gerard Vroomen and Andy Kessler

I heard 890g being tossed arpund, but Vroomen says a large frame with all hardware is just under 900g, without any bolts or the derailleur hanger it’s around 850g. The large bike built up with all ENVE cockpit and rims, the Rotor cranks and full XTR brakes and drivetrain otherwise came in at just 19lbs 5oz.

Vroomen said the low weight is achieved simply by choosing the right materials and the right layup. For example, he used ultra high modulus carbon fibers, which are more brittle, running alongside the flat sections of the downtube and used stronger materials where they’re needed.

Passes the German EFBe tests, which add about 20% to 30% to the EN standards. Vroomen says this is the lightest mountain bike frame to ever pass it.

“The light weight is nice, but it’s just a by product of building the frame right,” said Vroomen. “It was more important to us to get the stiffness and strength right, but it’s nice that we got both.”

Frame is $2,700 alone and $3,400 with the custom Rotor cranks, BB and chainrings. At launch, they’ll also offer an X0 build with 3T stealth components and DT Swiss wheels and Magura MT6 brakes. Fork will be Rockshox, they’re still deciding why model. Pricing will be about $6,500, but not finalized until fork spec is decided. They’ll also offer a limited edition model with Acros A-GE hydraulic shifting and ENVE wheels ad cockpit. Pricing on this is likely to be around $12,000.

Interestingly, Kessler said another limited edition they’re thinking off will be a 1×11 SRAM build. Hmmm…


Kessler and I rode the flowing singletrack around Laguna Seca for a little more than half an hour. The section we rode had plenty of climbs and descents, corners and straights. As lightweight as the bike is, it didn’t feel flimsy or feathery. It climbed well, feeling stiff under power both seated and standing. The headtube angle is a somewhat steep 72º across all four sizes. I didn’t get the bike into any super tight and twisties, but it felt quick in some of the corners without being twitchy or unstable. Vroomen hinted that it’s designed to be a very quick handling bike, I just didn’t get a chance to really test that.

Overall, it rode well and I can see it appealing to racers looking for something a bit different and super light. The build I weighed was light, but there are lighter wheels out there, and XX still edges out XTR in total group weight, which should make weight weenies super happy.


  1. Gerard Vroomen on

    Thanks for the review Tyler. One note on the handling, while it is quick this does not preclude neon stable. There is this misconception that you need slack head tubes and floppy front wheels for stability, but you don’t. We’ll get you on he bike some more in the future to prove it! Cheers.

  2. Tom on

    The frame looks nice. Weight is even better. Seat stays look really nice on the frame. Weight weenies will love the blacked out look; playing it pretty safe I think. I am not sure I am the target market for this frame and don’t want to be totally negative, but I still don’t get the push for all these BB standards, it never ends. Make…it…stop. The benefits always seem marginal at best and it just limits the selection of equipment.

  3. Topmounter on

    Do you have to remove the BB to replace the internally routed cables?

    We’ve come a long way from square tapered bottom bracket spindles, but things have really gotten out of hand with all the (mostly fleeting) “standards” for shells, BB’s and cranks.

    Regardless, it is definitely a very nice looking, tasteful frame and sounds like it should be a nice riding frame. That being said, I’m not a sponsored “new-bike-a-year” racer, nor am I sufficiently “aspirational” to drop $3.4k on a hard-tail race frame, so this frame is definitely not targeted at me.

  4. Will on

    Great looking bike. . . maybe in a year or two “Open” will make some bikes more akin to the R3 or RS. . . price wise

  5. Will H on

    @ Steve M
    I’m pretty sure “Neon stable” is a reference to the stability of the Neon element given that it is a Noble Gas. But that is just an assumption.

    As far as the bike goes, I would really like to get my hands on one. I love the way their road bikes feel and would love to see how this bike feels.

  6. Samuel J. Greear on

    Window in the seat tube? Seriously? Yet another place for debris to infiltrate the frame and cause all manner of problems. A mark/line printed on the frame, great idea — but a window, really? And this after they were smart enough (from what I can tell of the photos) to move the split in the seat tube to the front, which helps prevent infiltrates.

  7. Gillis on

    @ Samual J. 1) a line on the outside isn’t going to do you much good, 2) that hole isn’t going to catch much from that location, and 3) if you’re using it right the seatpost should be closing it the whole time as it is the minimum insertion point, keeping out any debris.

  8. greg on

    lots of specialized bikes have a little hole in the seat tube that the post must pass. it’s fine, it does not take in dirt. if youre worried, stick some chewing gum in it.
    my guess is that “neon-stable” = “non-stable” or “not stable”. typo.
    not a big fan of BBWhy, until a crank truly maximizes the chainring spider space instead of just putting a spacer there.

  9. Samuel J. Greear on

    Gillis, if you can’t figure out how to make sure your seatpost is far enough in the frame from a line on the outside I pity you. Here’s a hint, it involves installing the seatpost to depth then removing to check. That hole will have no kind of “seal”, even a well-greased seatpost will let a bunch of crud infiltrate the first time you ride on any dirty surface in the rain.

    This feature is totally idiotic. As it is I remove the seatposts from my bikes at least once or twice a year to try to clean out all the crap and re-grease them. Any bike that I have neglected to do this the seatpost has become siezed inside the seat tube. I do not know what kind of pristine surfaces the rest of you folks ride on, or maybe you just aren’t putting enough miles on — but this “feature” makes this bike a total non-starter for me, it doesn’t matter what else is good about it.

  10. MaLóL on

    I love this frame for asian vendors to copy and sell. Hong-FU just copied the cervelo rca and are selling it around 800g and 520$ shipped. From craddle to craddle, from catory to owner, saving lots of peoples unnecesary salaries… Cycling frames can’t be high tech anymore. Over 1000$ for any hardtail frame is just sick.

  11. Gerard Vroomen on

    Hi Samuel, thanks for your point of view. But a few things:

    1) You say even a well-greased seatpost will get a bunch of crud infiltrate. Why are you greasing a seatpost, I hope you’re not talking a carbon post. You should use assembly paste instead. Anyway, regardless of this, if your frame is properly made, the fit between seattube and post is such that noting will go through
    2) You may think it’s an unnecessary feature, maybe for somebody like you who properly checks the insertion depth it is. But anybody who works at a bike company producing carbon frames knows that insufficient insertion depth is probably the biggest cause of seattube cracks, and people always claim “but I inserted it to the limit shown on the post.” And as a frame maker, how do you tell your customers they need to insert it to a specific depth? By putting it in the manual that nobody reads?

  12. Gerard Vroomen on

    craigsj wrote: “I always wanted a 29er hardtail with a 5 year old geometry…but I wanted to pay more for it.”

    Hi Craig, you’re in luck. I’m at SeaOtter, so I’ll look around for you and if I find a bike that matches that description, I’ll let you know. Cheers.

  13. road and dirt on

    I lLOVE that Gerard Vroomen, the engineer that has made so many amazing bikes (including this one) has come to the bikerumor forum to a big cup of “shut the f*** up” to all the haters. That being said, this looks like and amazing XC bike that could handle some light trial work if you actually know how to ride it. Hopefully there will be a distribution network forthcoming, and hopefully Cervelo dealers get first dibs.

  14. Samuel J. Greear on

    Gerard, paste on carbon and grease on alloy and steel frames. They serve the same function in keeping stuff out — that is, the grease or paste will trap it near any potential infiltration points, for a while. Eventually it works its way down the seat tube. Ride and race several thousand off-road miles every year in dry, dusty and occasionally wet conditions and I don’t know how you could not see this problem on any bike with a typical seat tube and post design. I’m not talking big infiltrates, they are microscopic, but they accumulate and they cause problems. Not greasing a seatpost at all hastens the buildup and shortens the time until the post becomes un-movable.

    It would be hard to miss that printed indicator on the side of the seat tube — even sans hole.

    This is probably a great feature on a road bike, mountain bikes get dirty.

  15. greg on

    many companies use a little hole to confirm there is enough post in the frame. here’s a link to a Venge (road bike, i know, but most of their mountain bikes have it too) showing the hole. it’s covered with a clear sticker that doubles as a warning label. hey! dirt problem solved with a sticker!!

  16. Samuel J. Greear on

    Greg, hey guess what dude! Stickers get wet and fall off, get scraped off in crashes and suffer from wear to a much greater extent than the frame! To my knowledge Specialized mountain bikes do not have this, there is a 2012 Fate sitting less than 10 feet from me, no random hole in the seat tube. Please do share what models those are that have compromised themselves in this fashion and I will be glad to talk those down as well.

    Gerard, if you want to do it right — mold some polycarbonate or similar into the frame and make it an actual window, not a hole.

  17. Joshua Murdock on

    Considering Vroomen has developed more successful bike brands than most of us, I’d say just might know what he’s talking about.

    Personally I think this frame looks excellent, seems to be well thought out and I would love to race it. It’s expensive enough that it’s not going to happen on a shop mechanic’s budget, but someday… someday… Maybe an Open Factory Team??

  18. Gregg on

    Gerard – Would you also please provide standover and effective top tube lengths for the bike? I realize stack and reach are the most important for fit; however, I consider standover also critical on an off road bike. Especially since the likelyhood of a quick dismount is much higher on the trail.

  19. olek k on

    hi, my m5 epic 29 2012 HAS a tiny hole “for inspections” drilled in the seattube (right side facing SE direction). anyway I wouldn’t mind one of those being delivered to my place. really dig the looks.

  20. Adam on

    Great looking bike! I’m excited to see the technology and bike construction experience Vroomen is bringing to mountain bikes! I’m even more excited to see him on here intelligently defending against those with FAR less knowledge and experience.

  21. Spencer on

    The guy that reasoned neon stable is one or two notches above the negativity surrounding this bike. New bikes are great- for everyone. Even clown-hilllers are reaping the benefits that the gram-counting, leg-shaving front-wipers of yore pioneered. I’m probably not going to own this bike because I don’t live where this bike could be rallied; however many people do. If you don’t think it fits you, don’t buy it. Props to Vroomen for being responsive and feisty. He could just ignore the t***-waffles out there.

  22. satisFACTORYrider on

    I bet most of us couldn’t tell on an unmarked frame test the brand ht 29er we were on. Nothing original going on with this sled. Next.

  23. craigsj on

    “Nothing original going on with this sled. Next.”

    Exactly. Nothing innovative here, not that there’s much room in a hardtail for it. All the “features” are really about getting the job done with minimal material which is ultimately about making a light frame despite rhetoric to the contrary. It’s really about smug exclusivity and appeal to the more-wealthy-than-informed customer. Why else design for internal routing of shift solutions that don’t exist or are grossly over-priced? A “limited edition” 11 speed cassette? Yeah, loud and clear. This is a bike for wealthy posers.

    Open is shooting to be the new Versace of mountain bikes. No doubt they have the lineage.

    The minimum post insertion “problem” would be solved best by choosing a frame insertion requirement less than that of the post. Can’t be pretentious about that, though. Just another example of “innovation” targeted at the ignorant.

    Gerard, thanks for the offer to look around for me at Sea Otter. You and I both know you aren’t leaving money on the table, though. 😉

  24. satisFACTORYrider on

    @craigsj – amen brother. there’s usally a hint of truth in hator-ade. atleast it’s better than knowingly slammin roofie cocktails.

  25. Gerard Vroomen on

    Hi Samuel, we fully agree on the grease vs paste there. Obviously this is a carbon post and carbon frame, hence paste. The thing is, eventually stuff will get in regardless, simply through the top. No seattube collar can prevent that in the long run despite the fact that you’re seriously clamping down there. As Greg suggests, a sticker would solve any problem people have with that for the inspection hole, but I fear that won’t solve the issue of stuff getting in on the top.

  26. Clint on

    Is it possible to get actual seat tube (C to T) and effective top tube measurements for the XL size? Competitive Cyclist listed 17.9 inches for this size and just wanted to verify. That seems very short (typically around 21″) for the long legged (6’4″ XL) rider. Thanks!

  27. Samuel J. Greear on

    Gerard, your willingness to entertain negative feedback in a public forum is commendable. You sir are a gentleman and a scholar and for that reason if no other I will definitely keep an eye on your future products. Best of luck with the new enterprise.

  28. SeanA on

    Now that’s a sweet frame, with clean lines and no cables not even break housing dangling outside.
    Its expensive but worth saving for even if you don’t sponsor no name pros.
    I have been waiting for a couple of years for some of the big names to step up, but they just change one little thing and hold back the rest of the upgrades till next year.
    For what it’s worth I think all the details are a pretty huge change from the current mindset of most big name companies and that makes it future proof (at least more so than others in the same category). In a sport where several grams are considered extreme weight savings and people win and loose in mere seconds this frame could make a difference if it rides the way it’s designed.
    I have been racing for more than 5 years on epics s-works and HT 29ers and I can tell you that all pros (even those of us bringing in the rear) wash our bikes (or get it washed if youre lucky) every week and dry clean the chain and wipe off fork seals and seat post collar after every ride.
    Just my two cents.
    Thanks Gerard, so now maybe do the same thing with a sweet cross bike with disc bakes with all internal routing.

  29. SeanA on

    BTW dig the 1×11. I race in Texas mostly and have been riding 1×10 for two years now (39, 11-36) and have my HT, S-works 29er down below 18lbs. 16.5 wih a Niner rigid carbon fork (for CX).

  30. Brian on

    Hey Gerrard,
    GREAT bike! Congratulations on the new company too. Also, welcome to the world of mountain biking, where innovation is ONLY acceptable/tolerated if it has NOTHING to do with road biking. 29ers?? OMG AWFUL!! crabon fibres?? WHY NOT SHAVE YOUR LEGS TOO!! 650b?? NO, JUST NO NO NO. In MTB land, cross-country is barely tolerated, only because the guys who race xc wear (get this) LYCRA!!!!


    Anyway, this is an astonishingly well designed, well executed bike. A bike that, unfortunately I’ll never be able to afford. I have to agree with “craigsj” in that regard. Unfortunately, REAL, passionate cyclists and die-hard racers won’t be your target market. it will be the 911-driving dentists from Dallas and San Diego who probably won’t even notice all the subtle refinements and nuances going on with this frame.

  31. Gerard Vroomen on

    Hi Bazookasean, the two are not related. But of course one does not exclude the other either. We’re looking for just a small number of stores, because there is only so much time in the day to support them, but we will be adding a small number in the next few months.

  32. Brandon on

    Since this is coming from a guy who designed tri bikes for the dorkiest of triathletes, before I get one of these frames I have a few questions:

    Do I need to pee while on my bike?
    Do I need to leave my shoes clipped in all the time, even when not on the bike?
    Do I need to let every liquid nutritional supplement run amok and harden all over the frame?
    Where do I mount the straw?
    Where is the wind tunnel data?
    How much time will it save me over 40k?

  33. Mason on

    This reminds me of a bunch of D&D playing zit-faced fat guys talking about how there’s no way they’d entertain the idea of seeing Kate Upton naked in person because in one of her pictures once something didn’t look completely perfect.

    I’d love to ride one of these. Looks awesome. Also pretty cool to see an industry heavyweight talk to a bunch of dorks whining about his cool new bike. Kudos, Gerard.

  34. Adam on

    My favorite part of all of this is that Vroomen is on here ANSWERING YOUR QUESTIONS AND CRITICISMS!

    Where is Mike Sinyard when a new Specialized model drops?
    Or the owner of Dorel?
    Or Pivot?
    Or frankly, anyone.

    You might not dig the bike, but at least the creators are here getting your input and responding.

    Plenty of road bikes have that little hole on the frame for seatpost depth, and it’s a non-issue.

  35. Me on

    Any reason why the bike pictured has an offset post? The website says specifically that the frame is designed for a zero offset post.

    Also, what about making something (potentially interactive) to demonstrate the different ETT’s of the frame allowing people to compare sizing easily to their current favourite bike. ex: If the seat tube angle is 73, the ETT is 630. If the seat tube angle is 73.5, the ETT is 625. etc.

  36. craig on

    In reference to: Samuel J. Greear – 04/19/12 – 11:15pm “Gerard, paste on carbon and grease on alloy and steel frames. They serve the same function in keeping stuff out” .Actually Samuel J. Greear, you are wrong, paste is required to increase friction between carbon parts, or any two parts that may be sensitive to compressive forces. It allows a reduction in clamping pressure. Also the function of grease on a seatpost or in a seat tube is not to “keep stuff out”, in metal frames it is to prevent galling or seizing, in which case an anti-seize compound should be used. As a frame designer I agree with Vroomen for all of his stated reasons, it is a great feature on the frame. Additionally I suggest you do some research and check the tolerances of some seatposts and frames. Once you learn of the variation in manufacturing tolerances, then I suggest you calculate the gap in surface area between a typical frame and seatpost due to variations in cylindricity. From here, factor in the surface area of the small hole on the Open frame’s seat tube, and you most likely will realise how much of a tw_t you have sounded like.

  37. ginsu on

    Gerard, do you set temperature limits on your carbon bike frames? I have been wondering because there are lots of high/low temperature limits for high-performance carbon equipment like bats and tennis racquets where the product will fail outside of these temperature ranges.

    I haven’t heard much of this about carbon bicycles, but I think it is because the early carbon bikes weren’t really light enough for it to become an issue, but I think if I were designing these bikes it would be a concern for me (I’m a ME). I would think as you approach the lighter weight frames you start running into factors like the carbon becoming brittle at low temperatures, and then the carbon can loose a lot of strength in high temperature conditions as well, especially in flat black. Do you warn your customers about this?

    I have worked with a lot of carbon fiber in automotive racing and it astounds me how poor the durability is any time you get something that is actually lightweight and has to undergo stressful conditions such as temperature extremes with high-frequency vibrations. Of course, you can add a ton of layers and you will get something very durable but then it doesn’t actually save any weight.


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