Sure, all mountain bikers know Boost 148 spacing by now, but what about Road Boost for roadies, gravellers, bikepackers & e-bikers? Is there really going to be another new road hub spacing standard?

The answer is, Yes. Road Boost is real. It is not April 1st. It’s already here, having snuck in over the past couple years. And it’s here to stay…

What is Road Boost?

Road Boost new wider hub spacing standard, 12mm 110mm 148mm thru-axle standard for road gravel e-bikes, Focus Road Boost

c. Focus

Simply put, Road Boost is new wider thru-axles for gravel & e-road bikes. It’s another new disc brake thru-axle standard, sort of. Really, it just mixes and matches from what is already out there.

Most modern mountain bikes now use the regular widened Boost standard for stronger off-road wheels: 12x148mm rear & 15x110mm front.

Modern disc road, gravel & cyclocross have mostly settled on the smaller diameter 12mm thru-axle standard to balance stiffness and tire clearance: 12x142mm rear & 12x100mm front.

There are other mountain bike standards, but they’re irrelevant here.

Road Boost new wider hub spacing standard, 12mm 110mm 148mm thru-axle standard for road gravel e-bikes, new vs. old

c. Novatec, 12x110mm vs. 12x100mm front hub spacing

The new Road Boost standard uses 12x148mm rear & 12x110mm front thru axles, mixing accepted Boost-spacing with a smaller 12mm front axle to create wider, stiffer, and stronger wheels to stand up to more off-road use and heavier bikes & e-bikes.

Wider is stronger, but does that make it better? 

Salsa Cutthroat mountain bike Boost 148

c. Salsa

Salsa was one of the first to tease gravel bike riders with the idea of Boost for dropbars & road on their 2020 Cutthroat. The tougher, wider wheels were stiffer for more aggressive off-road riding, and would be more durable for loaded bikepacking over rough terrain.

But, Salsa really just used regular mountain bike Boost spacing, matching a 12x148mm rear end with a 15x110mm mountain bike thru axle up front.

Farr Twin-T mountain bike boost 148

c. Farr

That’s becoming more common, as we’ve seen MTB Boost bleed over from monstercross bikes like the wild new Farr Twin-T, Chiru’s titanium gravel Kegeti, or Sage’s ti Storm King adventure gravel bike, for example. This has been the simplest way forward, not requiring any new hubs.

gravel vs. mountain bike wheels

So, why do this?

First, it’s about wheel stiffness, which we’ll explain below.

But, for the rear of the bike, there are real frame and drivetrain benefits, too. By adding 6mm (from 142mm up to 148mm) of axle width, you can gain 6mm of space at the chainstay yoke (just behind the bottom bracket), too. Which means more tire clearance.

When mountain bikes switched to Boost spacing, many cranksets ended up getting a bit wider, too, or using 3mm offset chainring designs. This kept the chainline straight, something that’s equally important…and increasingly important as drivetrain makers add more cogs into the rear.

RELATED: Check out our complete Boost explanation to see why the chainline matters and more graphics that explain how all these axle widths work.

So, it’s really only fork spacing that differs…

Why not just use Boost MTB thru axles in the front?

Road Boost new wider hub spacing standard, 12mm 110mm 148mm thru-axle standard for road gravel e-bikes, Roval hub

That’s the million dollar question, and there’s no perfect answer. Going to the wider 110mm spacing up front was a logical step paired with the wider 148mm move out back – more strength & stiffness for better handling & durability. So why not just go for the existing 15mm MTB axle diameter?

Road Boost new wider hub spacing standard, 12mm 110mm 148mm thru-axle standard for road gravel e-bikes, DT Hybrid Gravel

c. DT Swiss

Basically, because it’s overkill. Using the larger 15×110 would add weight compared to a 12×110 axle. And a narrower 12mm thru axle allows for smaller diameter hub shells, which are more aerodynamic…and also lighter.

And since the 12mm has proven successful for road & gravel, simply making it wider should provide the desired improvements without the downsides.

Road Boost new wider hub spacing standard, 12mm 110mm 148mm thru-axle standard for road gravel e-bikes, DT stiffness test

c. DT Swiss

DT Swiss say that comparing their 12×100 road wheels to otherwise identical 12×110 hybrid road wheels, the wider Road Boost setup is 12% stiffer laterally, and able to support 10kg (22lb) heavier bike+rider combos.

Maybe it’s just for e-bikes?

Focus Paralane2 prototype with Road Boost spacing

It was actually e-bikes that really took off with this new Road Boost standard, specifically for e-road & e-gravel. Focus was one of the first with their Fazua-powered Paralane² that brought their Project Y concept bikes to market. In fact, we weren’t able to test ride that first prototype because the proper front hub wasn’t ready yet.

Shimano EP8 mountain bike eMTB motor

c. Shimano

The most common e-bike motors hang at the center of the frame, and need as much width as they can get. They were already pushing out to wider MTB bottom bracket widths, and this is really what led to creating the Road Boost standard. Adopting Boost for e-road & e-gravel essentially means compatibility with all the same e-bike motors as any eMTB. And Q-factor seems to be less of an issue when you get electric pedal-assist.

Specialized S-Works Turbo Creo SL with Road Boost spacing

c. Specialized

Specialized joined in, using the extra width to make room for their own drive system on the e-road/all-road/gravel Turbo Creo SL. Canyon did the same with their Bosch-powered Grail:ON electrified gravel e-bike.

Canyon Grail:ON with Road Boost spacing

c. Canyon

As usual (because they provide hubs to sooooo many wheel brands), DT Swiss had wheels to make it all possible, offering the DT Swiss HG Hybrid Gravel wheels were the first developed for those Focus concept e-bikes all the way back in 2017. And Specialized added their own Roval version for the Creo SL.

Which bikes are using Road Boost axles?

Focus Atlas gravel bike with Road Boost spacing

c. Focus

So far, Focus might be the first to bring Road Boost to bikes that you have to pedal for real. The recent alloy Atlas gravel bike has opted for the same wider wheels as their e-road bike range. No longer limited to e-bikes, Road Boost appears here to stay and is likely to spread to more gravel bikes in the near future.

Focus Atlas gravel bike with Road Boost spacing

c. Focus

It is worth noting that all of the Atlases use wheels specifically built for them – pairing low profile gravel-ready alloy rims to new DT or Novatec hubs, plus a new Road Boost-spaced Shutter Precision PL-7 dynamo front hub.

How does Road Boost affect Q-Factor? Wheel selection?

Canyon e-road bike with Fazua motor

c. Canyon

One upside is that you can now use a really nice set of XC mountain bike wheels on your gravel bike (with axle reducer end caps for the front) on your gravel bike…although there are good reasons not to do that.

Unfortunately, all your current road disc wheels & hubs won’t fit your new Road Boost bike.

Road Boost also makes a wider Q-factor likely. It won’t need to be as wide as the average mountain bike Q territory, though, since frame manufacturers aren’t trying to clear 2.6″ tires or anything crazy like that.

But, because road and gravel chainstay lengths are generally shorter than mountain bike chainstays, they will need the front chainring(s) to be set wider to maintain proper chainline. So, you can expect Q-Factor to increase by ~6mm.

That’ a 4% Q increase over an average road setup, which will probably be fine for many off-road-oriented gravel riders, but will certainly bother some cyclists.

Road Boost new wider hub spacing standard, 12mm 110mm 148mm thru-axle standard for road gravel e-bikes, robert axles

While it’ll be a while before you need to upgrade your Road Boost thru axle, it’s worth checking our “Everything you need to know about Thru Axles” video to see how thru axles themselves differ, and a quick history of their size changes.

DT Swiss Gravel road wheel lineup, 650b & 700c, 24mm internal width, GRC 1400 Spline 42 aero carbon gravel bike wheels

As for regular roadies, it’ll be interesting to see if pure road bikes, or even all-road bikes, make the switch. We could see this becoming the next performance advantage, but also not worth the aerodynamic losses or weight gain. What do you think?

39 comments

    • Briain O'Shea on

      Absolutely, particularly the 12mm front axle. It’s just a way to make frames obsolete. What’s the weight difference between a 15mm and a 12mm axle. Also if you add the weight of hub adaptors(which most companies are using as they are giving you mtb hubs) I’d guess the 12mm axle standard is heavier. As far as boost spacing goes do you really need it? The claimed reason on mtb is is allows shorter chainstays on full sus bikes again not really an issue on a gravel bike that takes maybe a 2.1 tyre.

      Reply
  1. ATBScott on

    Something here makes me think that the latter comment about eBikes having a Q-factor similar to a MTB is a big part of the play here… Making new frame configuration(s) that work for eBikes and forcing that into the road arena so that those who need the ‘latest and greatest’ must upgrade more than just the frame. When you think about the powerhouse riders who rode frickin’ QUICK RELEASE axles successfully and didn’t complain about stiffness – and now they are changing the latest 10mm thru-axle to 12mm to get additional stiffness? Sorry, sounds like there is a lot of marketing in this new advancement. Gravel bikes don’t need the microscopic aero advantage this 12mm front hub will have over the 15mm MTB standard, and an eBike would probably benefit from the larger axle… I’d personally rather have a bike that would potentially let me use the same hub spec as my MTB so I could potentially swap wheels or at least build a new wheel using an existing hub if I wrecked a rim on one of my bikes. Still riding QR on my 23-year-old Salsa road bike. I’m sure that the gravel bike I plan on adding to the quiver will have thru axles, but now I guess I have to look for one with 15mm front axle standard.

    Reply
      • JBikes on

        I also think journos can straight up call certain things BS, and call OEM marketing BS.

        Nothing is saved on a bike needed this extra stiffness by not using MTB standard axle dia. of 15mm. These are not lightweight or aero bikes.

        The comment about 6mm width equally 6mm at the yoke. Nope. Not true. The only thing that helps that is the wider crank spindle, and as someone mentioned this seems to be done to match MTB width e-bike motors. Which brings me back to….why 12mm?

        Not surprised to see Focus adopting this. Their engineers developed the RAT thru axle. An absolute POS piece of engineering and manufacturing.

        Reply
    • ed llorca on

      Don’t blame the jurnos they have no part in this other than to inform us. This BS is up to large bike corporate offices who are so disconnected from riders that they send us these overpriced non standard bike and parts.

      Reply
  2. Chris on

    I know why they went with a 12mm front axle. To prevent you from being able to share wheels between your mountain bike and your gravel bike. Guess you will have to buy more wheels. How convenient.

    Reply
  3. OriginalMV on

    110×12 spacing can go die in a dumpster fire. Asking me to believe the 15×110 standard (before it has even reached total market acceptance amongst MTB brands) is unacceptably heavy in comparison is a bridge too far. This is nothing short of egregious.

    Reply
  4. venmi on

    Why? I get incremental gains but at some point 3mm on a front axle bolt isn’t going to matter – and at the cost of being compatible with absolutely nothing.

    Reply
  5. Jman on

    I’m all for boost spacing on adventure bikes as I have two with this configuration. I find it disappointing the industry is making a case for the 12×110 axle for e-bikes and gravel bikes because the axle is slightly lighter and slightly more aerodynamic than the common 15×110. Do these two benefits really make a noticeable difference when you have battery power or gravel/adventure 40-55mm tires? Seems another excuse to make it more complicated for the consumer.

    Reply
  6. Dude On Bike on

    Sorry, but this endless desire to upsell is getting old. And just think of in about 15 years how much of a pain in the ass it will be finding replacement parts for whatever drivetrain your bike happens to have. And if you have multiple bikes? It’ll be a disaster.

    The average (first-world) consumer will either give it away or toss it in the bin, only to buy the NEXT latest fad.

    So much for cycling having anything resembling “environmental awareness!” Carbon footprint? Who cares! Move units! Change standards to ensure planned obsolescence. Mine that aluminum & rare earth metals! Produce those epoxy resins! Keep the product development moving in endless motion, forever convincing the consumer what they ALREADY own is junk and needs immediate replacement!

    For shame!

    Reply
  7. mudandmoremud on

    So, to continue using road groups with road boost, a 68 mm BB is necessary (or PF30 and the like). How do they compensate for the wider chainline? Won’t new cranks be required with less offset? For 1x cranks with direct mount rings, not a problem. But what about Shimano and Campy, who don’t use direct mount on their road groups?

    Reply
  8. Ol' Shel' on

    You fell for it with mountain bikes, so now they’re going to fleece you on road bikes. Oh, and just like with MTBs, they’re not going to go straight to the number that will get you the best chainline right away. No, they’ll inch up on it, changing every 3 years or so, just to make sure you open your wallet to avoid feeling left behind.

    Who knows, as material technology advances increase wheel strength, perhaps -no, absolutely- they’ll start narrowing those axles again…

    Reply
  9. Mr Pink on

    So, in reality this isn’t “road boost” if everything stayed the same except the front axel is 3mm small in diameter than a standard MTB thru axel. Its’ just a front boost hub with a new axel option.

    I get the benefit for e bike cranks with silly wide q factors. But for everyone else, an increase in Q factor is rather significant at 6mm and I’d bet it’s even more as those making such statements usually compared worst case (low end) width scenarios….especially when they choose to leave out exact Q factor of the cranks in question. My guess is could be up to 10-12mm vs a Dura Ace/SRAM RED/Rene Herse crank….maybe more.

    In the end, if you’re gonna go boost go boost and do boost MTB cranks and get that tire clearance up. But for the love of God let’s not have a “road boost” nomenclature over a different diameter axel. That’s just ridiculous Fox News kinda logic. 😉

    Reply
  10. Calvin on

    *facepalm…

    Same old ‘stiffer by X% bull dust but in reality creating a graveyard of incompatible bicycles and parts. Roadies only just started jumping on board disc brakes and thru axles. I think I’m going to revert to team rim brakes if this goes on.

    Reply
  11. Shafty on

    So, what have we learned since the last hub spec was developed and released? It doesn’t really matter how compatible it is, since new specifications rely heavily on OEM implementation. It’s a mildly interesting addition to the current crop of hubs, but for rigid forks, even DT Swiss agrees, the difference is minor. You can read that “12% stiffer laterally” as 12% less lateral deflection. That’s almost nothing. If they were truly worried about it, they’d push 15mm axles and simplify things. Can’t do that though–roadies will whine that their 23lb disc all- road bike would be heavier.

    When will 15mm rear axles become a thing? Most bearings already fit those. Then road can have 12mm and mtb can have 15mm.

    Reply
  12. bikeengineer on

    Two aspects missing:
    – Boost doesn’t necessary lead to a wider Q-Factor. Boost is only about the chainline
    – Shimano GRX groups do have a wider chainline by 3,5mm, so it makes sense to match this by a wider hub to get a better chainline

    Reply
    • TheKaiser on

      Yeah, I’ve been having that issue off and on over the past week as well, or sometimes it will say 4 comments but only 1 shows up. Right now it seems to be working though, as I see yours and all the other 20+, so hopefully its fixed for good.

      Reply
  13. herrbman on

    There has to be a way to tell bike/hub companies that we do not want this.

    All their talk comes across as tone deaf. More lateral stiffness, but we need to keep it aerodynamic.. what?? Support heavier loads? People have been loading up old QR wheels with 100s of pounds forever. I would be curious what the weight limit is being increased from.

    Wider hubs MIGHT make sense for e-bikes, but in that case just use the MTB standard since an e-bike isn’t worried about weight or “aerodynamics”.

    Reply
  14. John Caletti on

    Q factor is in the cranks, not the frame. With boost rear spacing, it seems we should use a crankset that is made for that. Current road cranks are not ideal for existing gravel bikes. GRX and Force Wide are slightly wider, maybe they’ll work ok. It would be helpful for frame design (fitting big tires with shortish chainstays) to have slightly wider cranks than the current road cranks (including Ekar).

    Reply
  15. ed llorca on

    Effing ridiculous. The industry is flipping their finger at the consumer. What a pile of crap. Life was better when you bought a new part for damage or upgrade reasons and put it on you bike just like that. Now impossible or wickedly expensive. This is not progress. Two minutes from now there will be 15mm to 12mmx110 sleeves to at least get one way compatiblilty to work around this lunacy.

    Reply
  16. JBikes on

    6mm at the rear hub doesn’t automatically give you 6mm at the chain stay yoke. Crank geometry and BB width do that.

    Nobody is hurting for tire clearance in the road/gravel world.

    I hope educated consumers put a foot down and just don’t buy it and tell their non-bike friends not to buy it either.

    I hope bike journalist also flat out say these bikes are not recommended because of this.

    Reply
  17. satanas on

    This is s terrible idea, serves no purpose except planned obsolescence, and anyone promoting it should be boycotted immediately. I’m starting now. 🙁

    Reply
  18. Chris Kwok on

    I care more about expensive consumables, chains, brake pads, tyres etc than new bikes that come with different standards and measuring than my old bikes.

    Reply
  19. David F on

    Oh my god guys.. I just went out on my road bike which only had quick release wheels and it was literally so un-enjoyable…. One woman even picked up her child as I went past and said, “look at that man on his silly noodle bike”. Livid.

    Reply
  20. carlos on

    Wider forks and hubs are actually weaker – need to strengthen the forks and hub axles to make up for it – that’s more weight. Remember all the hoo-ha when fat bike hubs started breaking. Going from 135 mm to 177 without strengthening the axles and hubs was a lousy idea.

    Reply
  21. renewasabi on

    I agree, the weight argument is not valid. Both 15 and 12mm front hubs from DT (240 straightpull) are 104g.

    Perhaps it does have to do with production. Because it is easier to get bearings for a 12mm thru-axle in combination with Center-lock. DT modifies 6903 bearings (ID Ø18mm instead of 17) so that the axle is 1.5mm thick instead of 1.
    Bigger ID (20) comes in OD32 (too big for CL) or OD27 (not able to withstand the pressure). I once suggested to use 2*6704 (20-27) back-to-back.

    Reply

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