d.fender spacer boost 142 148 Unboost-3 (2)

What do you do if your new frame uses Boost spacing, but your wheels don’t? Before you shell out for a new rear hub, D.Fender might have a simple solution. There are a number of factors to consider before you mount up that 142mm rear hub, but it’s worth a look…

d.fender spacer boost 142 148 Unboost-3 (3) d.fender spacer boost 142 148 Unboost-3 (1)

The premise for the UN-Boost spacer kit is pretty simple – two 3mm spacers are placed on either side of the hub over the 12mm axle. This centers the 142mm hub in the 148mm dropouts allowing you to keep your current hubs. However, in order to make this work, first you will have to shim out either the rotor or the brake caliper. This shouldn’t be too hard using products like the Syntace rotor shims, or various washers under between the brake adapter. Above, Jarrod Bunk is using one pack of Syntace shims and a small shim on the brake and he says the set up is completely solid. It probably goes without saying that this is likely to void some sort of warranty somewhere, so take that in consideration but I’ve had to do similar things to fat bike forks over the years without issue.

The use of the spacers will also change the chainline of the cassette and move it inward. But if you’re using a non-Boost crankset this won’t be an issue, as the chainline is the same as non-Boost. Finally, it will also probably complicate wheel changes slightly, but if it’s saving you from buying a pricey King hub to replace your old one, it might be worth it. Best of all, the kit is priced at just $8.00 and is made in Pennsylvania. Shipping isn’t included, but it would be a good chance to order up one of their D.Fenders and double up on shipping. Jarrod tells us that UN-Boost spacers for the front are currently in the works along with a few other exciting products coming soon!



  1. Colin on

    why does this have to be a thing? Everyone knows that 145mm is the perfect happy medium and offers all of the benefits with none of the draw backs.

  2. dw on

    a collective “oh c’mon man” from bike mechanics across the world… there wasn’t a second shooter on the hill, they did land on the moon. Engineers aren’t part of a conspiracy to get you to spend more money. Trust the industry, bro…

  3. D.FENDER on

    As a bike mechanic I was bummed about backward compatibility on most frames. This solves the problem of getting rid of my beloved Chris King hub, or having to wait and order another one in the future once they actually see the light of day. The Salsa Cycles Deadwood is too good of a bike to sit and wait to be built so I decided to do something about it. And like all of our products these are Made In The USA

  4. JBikes on

    I’m going to print this out and show it to the local shop mechanics that just would not believe one could retrofit a 148 boost frame back to 142. “too many things as its ENGINEERED for 148”. I stated “what things? 1. hub spacers 2. disc shims (which need to be done correctly)”
    “no, that won’t work. 148 is a different system, it’s better and was engineered to replace 142”.
    me: “ok”…think to myself the median IQ in here is far too low.

  5. out for a ride on


    While most people are probably OK with the retrofit (it would be cheap to find out), other things might cause problems. If you’re running a large chain ring, bringing it inboard 3mm might cause chainstay interference, for instance. Bottom line is, 3mm isn’t much but at the extremes it will make a difference.

    My take on boost is that people are paying for more tire clearance, shorter chain stays, more travel, and stiffer wheels so the industry accommodates. For people buying a complete bike, it is a selling point. Gotta start somewhere. It would be weird if technology stopped changing and nothing became obsolete anymore.

  6. WAIT FOR ME GUYS!! on

    “hold on guys, I dropped my little spacer thing in the leaves over here while I was fixing my flat… will you help me look for it?” Don’t be that guy…..

  7. DFENDER on

    I know they do, but they aren’t offering axles to retro 142 to to the 148. I asked, I called, I begged, they said no. And for the 8$ VS the cost of a new King hub I think the difference is pretty good. I already had the wheels, etc, just transferred them from my Krampus to my Deadwood.

  8. Antipodean_eleven on

    Begin my first rant of 2016

    What s@!#s me to tear is when I hear people say thing like ‘oh this has been engineered to be better, so it must be… bla bla bla…’. As @pete so kindly pointed out, 150 already existed. It was THERE, did what this Boost tosh says it does, without having to do it again and has been doijg it for a few years already. And 148 vs. 150… that’s 2mm folks. 2… TWO. Not sure how big a dif that is? Get out your Verniers and look, then think that’s 1mm per side.

    148 was absolute pure ‘Merketingerering’, that’s it.

    @JMUSuperman, no, they did not see the light, they saw a market segment they could not afford to neglect – they make hubs and 148 is a new hub. As has been said, Boost now coming on new bikes means that there will be upgrades etc. etc hence a 148 ecosystem will emerge, and that ecosystem will need ‘support’. King not offering it would have been daft, though all good modern aftermarket hubs should have the ability to be swapped back and forth with adaptors.

    I like what @DFENDER is doing, it is sticking it to ‘the man’ and keeps perfectly good frames running for as long as they should, not as long as the marketing man thinks they should.

    End my first rant of 2016

  9. Jon on

    Bikerumor, you seem pretty behind on this one. Adapter kits have been made for a couple of months now and we’ve been talking about this since Sept. on mtbr


    I applaud dfender for helping out with a solution but his is very limited to what’s already available. It’s just the 2 spacers. Others provide a solution for the disc rotor as well with their kits. And one offers custom made end caps so you don’t have to worry about losing spacers.

  10. D.FENDER on


    Thanks! And for reference I have a Ponyruslter on order that I am building with boost wheels
    But I just couldn’t justify buying a new rear hub of waiting 8months to ride my bike. It’s nice to get as much use as you can out of bike parts, since they seem to only get more expensive each year.

    I think boost 148 definitely needed to be 150/83 and all would be well.

  11. xc-fr on

    this solution is far away from being “rock solid”. its just a question of time that this solution will damage your axle. it’s impossible, that the surface pressure is always high enough & dfender is not able to guarantee it for all possible combinations 😉
    a “rock solid” solution will be to have by 3mm extended endcaps for the hub. this can make every cutting machine operator for a cup of coffee.

  12. Veganpotter on

    Anyone try putting a 150 hub in a 148 frame? I’m guessing the stays on most bikes are long and flexible enough to allow proper threading in with a small amount of care. If it works, we could forget about this boost crap? I like the idea too but yes, 148 is idiotic

  13. Jon on

    @Antipodean_eleven, @D.FENDER

    I’m not defending Boost 148 but it should be noted that it is no where close to ‘150/83’.

    150 (as used on DH bikes) is the same nomenclature as 135mm rear spacing (ie it is 15mm wider). 142mm is just the thru axle version of 135mm (ie they have the same cassette and chainline spacing.

    Boost 148 is 6mm wider (3mm wider cassette and chainline) than this 135/142 spacing but still 9mm narrower than a 150 DH bike.

  14. PDXFixed on

    @Veganpotter, 150mm hubs don’t have the 3.5mm shoulder extension on either end like a 142 or 148 hub. Since they don’t have this extension, the cassette lockring would interfere with the frame.

  15. rich on

    I like how Jon calls out bikerumor for being behind, and then links to a bikeerumor story on mtbr in the first post of the thread!

  16. Middle Jon on

    BTW this is the Jon who was talking about 148 v 150 not the other two posts.

    @other Jon

    This solution puts all the shear load through the axle rather than both the end cap and the axle. That means a weaker system and a pretty dangerous failure mode.

  17. Jon on

    @Middle Jon

    Failure in what way? That it could damage the hub bearings or axle? Or more of a catastrophic failure where the wheel could separate?
    If that latter, how so?


  18. xc-fr on

    no. its just a question of time that your 12mm axle will get roll marks in best case, in worst case deformation at the same place. in last case you will get huge troubles to remove the 12mm axle & therefore your rear wheel is more or less fixed in your frame forever 😉
    It could work, of course, but i would never trust in this backjard solution. spend some bucks for custom endcaps instead & you are on the safe side 🙂

  19. DFENDER on

    Thanks for the positivity. To the negatives I just lol.

    As far as disc spacers etc. Those are coming, but the cost of getting them produced in the USA, is higher, and thus (since I am a one man show, with limited funds) will be coming sometime after the new year. I have quite the backlog of products that between various proto stages. I also have something pretty special showing up at QBPs FROSTBIKE this year.

  20. Jon on


    Thanks for the response. I’m still having trouble picturing it though. As far as I can imagine it the spacers wouldn’t move at all – the clamping force would hold them secure between the dropouts and the end caps. So why would the axle be affected?


    What do you think? I’m sure you wouldn’t be selling these if you thought there was any risk but still interesting in hearing your reply.

    And to be clear: you should be applauded for helping out with a solution for mtn bikers hoping to keep their existing wheels – disc spacer or not.

  21. D.FENDER on

    The tolerances are pretty tight on the piece but since every manufacturer is different and we based this off of a King axle the fit could be different. As far as testing goes. We haven’t seen any roll marks. These spacers are held in place with the clamping force of the axle. The only way to a get a roll mark would be to ride a bike with loose axle. Even then, alloy on alloy isn’t that much of an issue.

    Irregardless we reccomend that these be installed by a competent and professional bicycle shop to check on initial installation.

    Endcaps are only the solution on a per hub basis. However if you use a hub (i.e. King). That uses a one piece axle then end caps cannot be made for them.

  22. xc-fr on

    as i said: you cannot guarantee that the clamping forces are sufficient for all possible combinations & that’s a fact! the 12mm axle is not designed to absorb shearing forces in anyway. what’s with the clamping forces when a lot af water is in the game? what at different temperatures? what if someone have some oil at his fingers during installing? there’s a reason why the end caps of the hub are always supported by the frame & this is not the case with this solution, cause the 3mm spacer are exactly at this place now. the hub itself doesn’t get any support from the frame anymore & therefore you’ll get shearing forces on the 12mm axle.
    reg. arising forces: think about drops, jumps or just a high speed passage with some roots. depends of course on the style of ride & the rider weight, but i’m really sure that there are a lot of troubles will coming up with this stupid solution.
    beside that: what about the warranty of the 12mm axle? it’s lost with this kind of installation 😉

  23. Jon on


    I’m still not seeing it. Not saying you’re wrong by any means, just that I don’t see the issue.

    150 hubs don’t slot into a dropout. They’re just held in place by the clamping force. In fact if you read about it one of the reasons they went to 157mm was it made the wheel easier to instal as you didn’t need to hold it in place.

    No question the dropouts make it easier to install wheels but I’m not sure how much security they add. If an axle gives way the wheel is going to come out just as it would without a dropout.

    So bottom line is I’m not sure what difference there is between a spacer (that’s been properly machined to spec) and a new, lengthened end cap. The spacer can be a pain to install for sure. But as long as the end result is 148mm and the axle is adequately tensioned, the wheel should be as secure both ways, IMO.

    Anyway, I have no idea the answer. But it’s an interesting argument here.

  24. Speed Dream on

    The 10mm “through-skewer” by DT Swiss and others has been in use for many years and has no dropout provision for shear forces (flat inside face). I have never had an issue on my bike with this setup for the last 10 plus years, a 12mm axle should be even more reliable.


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