Boost: The Hows, Whys and What Fors

Boost. It’s the latest buzzword in the mountain bike world. But what is it, and will we all be clamoring to upgrade our bikes with it? Is it a must-have, a gimmick or somewhere in between?

We asked Wheelworks’ Tristan Thomas to give us a rundown and his impressions on the Boost system… here’s what he had to say
 

What is Boost?

Boost refers to front hubs which are 10mm wider and rear hubs which are 6mm wider than ‘standard.’ Boost front hubs use the same diameter 15mm front and 12mm rear axles.

By making the hubs wider wheels can be built which are stiffer, and more clearance is available for 11 speed drivetrains. The wider Boost rear hub means that cassette is moved outboard by 3mm and so Boost-specific cranks and chainrings are needed to retain good chainline.

Does Boost make a stronger wheel?

No, not really. All things being equal there will be only a marginal increase in wheel strength and possibly an equally marginal increase in the resistance to taco-ing in a really big crash. We’re talking tiny amounts though.

Does Boost make a stiffer wheel?

Yes. The wider Boost hub flanges allow the spokes to make a wider triangle and better support the rim. This increase in wheel stiffness was the primary driver for the development of Boost.  Many new wheelsets use straight-pull hubs and these have a decrease in flange width of approximately 3mm so moving to Boost reclaims what was lost by using straight-pull.

This may go against what the Industry tells you but straight-pull hubs will decrease the wheel’s stiffness because of the extra room needed to lay the pulling and pushing spokes side by side.  If the Industry had stuck with J-bend spokes there wouldn’t be much need for Boost, but the cost-savings of wheelbuilding with straight-pull hubs have driven their adoption.

The driveside spoke bracing angle on a typical rear wheel is around 4.3* and Boost will increase this by 0.6*.  That’s not a whole lot.

Is Boost the same as 27.5+

No. Boost refers to the hub with, the + refers to tyre width. It’s worth mentioning that many + bikes use Boost hubs though.

Do I need to move to Boost?

No. You could buy Boost forks but you can’t retrofit a Boost rear-end to your bike, and even if you could the advantages aren’t enough to justify the cost.

What compatibility is there with my current wheels and crankset?

None. A Boost frame requires a Boost hub, and unlike the move from 135mm quick release to 142×12 the actual hub has widened meaning that it’s not possible to run a Boost frame without Boost wheels, or to run Boost wheels in a non-Boost frame.

There might be some front wheels which are adaptable but this will be a hack and they won’t be true Boost so you won’t have any of the advantages. To run the correct Boost chainline you’ll need either a new chainring or a new crankset, depending on what make and model you’ve currently got.

My head hurts

Mine too. Just like cell phones or laptops the cycling industry is constantly looking for negligible improvements on products.  Anyone who has compared a 5 year old bike to a modern one will notice the sum of many small improvements.

Should I factor Boost into a new fork / bike decision

Yes and no. I don’t think the advantages of Boost are enough to justify picking one bike or fork over the other – I’d argue that a ‘good’ bike without Boost is better than a ‘bad’ bike with it. 

However Boost looks to be the new ‘standard’ so if you’re upgrading then it would make sense to get the most current ‘standards’ possible.