As the FatBike market matures a bit and more forks recognize their versatility we get more questions about riding narrower rims and tires within FatBike frames when the conditions warrant (typically summer, semi technical trail conditions or touring, or somewhat ironically icy winter conditions when narrower studded tires are desired).
Put simply, 29er wheels are definitely an option for your FatBike (except a Moonlander), so you can ride narrower rims and rubber without any problem on either the Surly’s or the Salsa’s that we sell (again, except the Moonlander – more on that further below). Specifically we’re recommending 29er wheels as opposed to 26 inches because a FatBike tire outer diameter is pretty much the same diameter as a cross country 29er tire (of course this depends a bit on the exact model of both tires you’re comparing, but it should be fine no matter what you choose).
However, we recommend building up a pair of 29er tires specifically for your FatBike as opposed to using a stock set. If you’re riding a Salsa you really have no choice in the matter because you’ll require a 135mm hub in the front and a 170mm or wider (depending on model) hub in the rear, and stock 29er wheels come with 100mm in the front and 135mm in the rear. In some cases you could use a stock 29er rear wheel as the front wheel of your FatBike because it would have a (possibly) matching 135mm width but it would also be heavy and more expensive (everything else being equal) because it would have a freehub which is of no use to you when installed in the front.
If you’re riding a Surly Pugsley you’ll require a 135mm hub front and rear (unless you happen to have the less common 100mm Puglsey front fork), but we recommend you build up a set specific to your FatBike so that it’s properly dished. The most common Pugsley set up has an offset front fork and they all have an offset rear end. The frame and sometimes the fork (depending on model) is offset to the right (drivetrain side) in order to push the hub to the right and help with chain line clearance of the fat rear tire, so the wheel needs to be dished back to the left so that the rim is still in line with the rest of the frame. The dish is even more radical on a 29er rim compared with a FatBike rim because the 29er rim is narrower and the spokes are centred on the rim (whereas the spoke holes offset on the FatBike rim) and they therefore have to be dished more in order to cross from the right hub flange to the centre of the rim. Despite the extreme dish angle we can still build strong 29er wheels specific to the Puglsey.
Moonlanders are the exception to the info listed above. They can’t roll with 29er wheels because their wheel dish is even more radical than the Pugsley, in order to accommodate even wider tires, and a narrow rim with centred spokes can’t be built strong enough to be ridden in this case – the rim is just too far to the left of the hub.
Aside from the hub width and dish considerations you also of course need to think about whether your frame and fork is using a quick release or a thru axle and then buy the ‘matching’ hubs for your 29er wheelset.
Obviously there’s more than enough width clearance between the frame and 29er tires, and because the tires have roughly the same outer diameter there’s virtually no change to the rest of the bike’s geometry or handling.
Well, the handling of your FatBike with 29er wheels will feel a bit different in as much as it will be lighter and therefore have quicker acceleration, but at the same time it will have less traction, and of course less floatation. Many FatBikes have fairly ‘neutral’ geometry so a 29er wheel spec’d ‘neutral’ FatBike won’t be as nimble as a standard cross country racing 29er with racier geometry, but it’ll still get you through the same terrain in pretty much the same fashion.
Two more things to consider while we’re on the subject:
1) Pugsley’s are not suspension corrected, so if you want to use your FatBike as a suspended 29er with standard 29er front suspension this is not the option for you – you’re stuck with rigid if you get a Pugsley. Salsa’s ARE suspension corrected, so you can fit a 29er suspension fork on a Mukluk or Beargrease frame, use specifically built 29er wheels, and pretty much you’ve got a conventional 29er with a slight weight penalty and a crazy amount of mud clearance.
2) The RockShoks Bluto is the first mass produced suspension fork for the FatBike, so it can be used with your FatBike tires and rims instead of having to use 29er wheels to get some suspension on your Fattie. There are however other considerations with th Bluto, like yet another hub width requirement, so come and talk to us if this is a route you want to go.
3) Some folks out there are using conventional 29er rear wheels for both the front and rear of their Pugsley. This means the wheels aren’t dished appropriately for the frame and fork and the rims are not in line with the main frame of the bike. That seems messed up to us but there are people out there who swear this set up does not cause any handling problems, so if you’re interested in trying this go right ahead. Oh, and because the tires are so much narrower in most cases there is still enough seat and chain stay clearance and no chain rub issue even though the tire is skewed to the right side of the frame.