What's the deal with Boost?

In the past couple of weeks we’ve seen both SRAM/RockShox and Fox release some new standards to the mountain bike market. SRAM are calling it Boost, and it’s a collection of products that are running a greater width. SRAM have introduced wider rear hubs in 148mm wide, 110mm front hubs, and cranksets that also allow for wider bearing stances and better chain line. There are also select fork models to suit. Fox also released their 27.5+ range of Fox 34 forks, which use the 110mm front hub standard. So what is there to gain? I spoke to US bike racer, engineer, and the man who is half the grey matter behind boutique hub and rim brand, Kappius components. Brady Kappius took a pretty level view at the new standards, and what might be holding back bikes from an engineering point of view. Is “Boost” really the answer for better riding bikes?

AMB: As an engineer, what are the limitations you see to making the most mechanically efficient bike.

BK: Oh wow, limitations… I think it will always be a battle of compromises. Some wheel sizes might be better for certain applications but will be limited by sizing and rider fit. External drivetrains are a very efficient and simple power transfer mechanism but they have their limitations in maintenance and vulnerability. Suspension systems will continually battle efficiency for plushness and feel. There have been great strides with these issues in the past 10 years and I expect to see more. I’d love to see internal gearbox systems become more mainstream. I think it’s just a matter of time before they become lighter and more durable.

AMB: SRAM have just launched their Boost range of hubs, moving the flanges, and no doubt bearings, further out for added stiffness. Is this what you were hoping to achieve with the Kappius KH1 hubs?

BK: The KH-1 hub was designed to create a more durable and reliable hub system by utilising the wasted space in current cassette designs. Creating a stiffer hub was a way of increasing the reliability of the wheel bearing system. We were still limited on the spacing of the flanges by the cassette on the drive side and the disc brake on the non-drive side. The Boost range of hubs has addressed the flange spacing issue by giving us 6 more mm of room to space the spokes out (on the rear). This increases the triangulation of the spokes overall creating a stiffer wheel. The KH-1 design allowed us to move the drive side wheel bearing substantially further out but we were still restricted on the flange spacing.

The original Kappius KH-1 rear hub.

AMB: Will the 10 and 6mm movements (front and rear respectively) make a marked improvement for riders – what sort of changes will they notice?

This is quite speculative at this point. I’d have to do some theoretical and real-world testing to prove this, but in principal this should create a stiffer wheel overall. If the average rider could feel these, only time will tell.

AMB: As a XC (and CX) racer, do you think this is relevant technology, or are you more concerned about the changes in Q-factor with the matching Boost crank sets?

BK: My engineering mind says these are relevant changes are worthwhile. From what I’ve seen, the chain line can be compensated by different spiders without changing Q-factors. Overall, I have a positive outlook on things.

Brady has helped engineer the 30mm wide, 360gram 29er KR29 rim. The internal bead just doesn’t seem to burp. So, is wider always better?

AMB: The Boost format will work for 27.5+ wheels as well as 29. Could 27.5+ be the happy medium for trail riding, without needing to be so niche like fat biking is?

BK: I think the push to Boost will bring good benefits to trail riding and even XC riding. I expect to see the vast majority of bikes going this way in 5-10 years. Fat bike frames struggle with lots of spacing issues due to their extreme tyre size. That segment of the industry has struggled with chainline issues related to tyre clearance and bottom bracket width. I don’t expect to see the Boost standard to have this issue.

Chainlines on fat bikes. Not pretty.

AMB:As an engineer, do you see the Boost concept being something that should be adopted industry wide (for MTB) or do you think there are other parts of the bike that need to be optimised first?

I’m a bit partial because I design hubs but honestly, I think there are at least two other issues that are a much bigger priority: tyres and chains. Tubeless tyres have made a big progression in tire reliability but flats, burping and overall installation are still an issue. I think there is significant progress that can be made here in terms of overall reliability. Chains can be complicated, especially with increasing the number of cogs in the rear, chains are getting more and more narrow. Chain suck can be an issue, breaking chains can happen, chain suck can stop you in your tracks. As I said before, a light, reliable, wide range internal gearbox with either a chain or belt drive would be awesome!

Our Say

So it’s fair to say that Boost has the tick of approval from an engineer, pro cyclist, and boutique component manufacturer – all in one guy! But does that mean it will please consumers? Adding width to hubs means new forks and frames. And it hasn’t taken a huge leap in technology to do so. There is a good chance that this move will be highly unpopular, right as riders have settled on what wheel size they want, and frame manufacturers have adopted 142×12 as a good standard. And all of a sudden, your bike is ‘obsolete’ again?

We’ll wait to hear the reaction from larger bike brands, Shimano, and other industry professionals, but there is the wonder as to whether this was held off until SRAM had their line of wheels up to speed. There was no need for this to not have happened when 27.5 become popular, or even 29ers. Much like oversized/tapered steerers. Gary Fisher and Klein were doing that decades ago. Going to tapered steerers wasn’t due to technological advancement, it was just when the industry chose to shift. It’s a shame to not see some shifts happen concurrently.

Brady