In part 4 of our series on Wider is Better, we’re going to look at Hubs. “What, why would they make hubs wider?”, you may be asking, and you’re not wrong. For decades hub width has been nearly static, however recently some companies have been pushing hubs wider for certain applications, so we’ll look at why and if it makes sense for your application.
In road bikes the hub rear width has been 126mm to 130mm for decades with the front hub unchanged at 100mm, however recently the advent of disc brakes on road bikes has introduced 135mm rear hubs to the mix. Moving from rim brakes to disc brakes meant new hubs, and mountain bikes with disc brakes were already using 135mm hubs, so many manufacturers opted to use that standard instead of trying to source 130mm disc hubs. In the early days of road discs you would see some in each size, but it appears now the argument has been settled with major wheel companies like Mavic producing wheelsets like the Ksyrium Pro Disc in 135mm spacing.
In mountain bikes there have been a few new hub widths released over the last decade for a few different reasons. The traditional 100mm front and 135mm quick release hubs first gave way to 15x100mm front and 12x142mm rear through axle systems like the Hope Pro 4 hubs. While having nearly the same dimensions and flange spacing for an equivalently strong wheel, moving to this hub standard allowed increased axle stiffness over the traditional quick release system brought over from road bikes 30 years ago. Frequently there are conversion kits for the frames to switch between these standards as they are relatively similar.
In 2015, Trek and SRAM introduced a new hub standard called Boost. The boost front hub is 110mm wide, moving the hub flanges outward 5mm, and the boost rear hub is 148mm wide, moving the hub flanges 3mm outward and chanline 3mmm outward as well. The reasoning here was as wheel diameter had grown from 26” to 27.5” to 29” the wheels had grown weaker as the bracing angles of the spokes were too narrow. Going wider here necessitated new frames, hubs, and forks which caused many riders a great deal of frustration knowing that their existing bikes were not compatible with this new standard. Aftermarket companies like Chris King quickly jumped on board with their ISO Disc hub in boost sizes. This wider hub flange spacing helps build a stronger wheel, so you can get some of the advantages of carbon rims with an aluminum wheelset.
The newest standard along this line of thought is called Super Boost 157mm. Effectively it is a standard 157mm Downhill hub shell that has existed for a decade, with the hub flanges pushed out to help build stronger wheels. Unlike the move from 142mm to 148mm boost, the Super Boost 157mm hubs and frames will be mostly interchangeable with older 157mm applications. So no need to fear that all of your existing wheels are headed for the dumpster, but if you’re building a new DH bike you may want to consider these wider Super Boost 157mm. These are so fresh, they’ve barely hit the market, but we’ll update here when they do!
So, is wider better with regards to hubs? There are definitely advantages in wheel strength for some applications, but maintaining compatibility with your existing bikes and wheels can be important if you’re racing and need to consider the cost & availability of spares on race day.