Fat Bike Full Suspension?

Salsa Cycles Fat Bike prototype: (Image courtesy of Salsa Cycles blog)

Unless you were off the grid yesterday, this Salsa Cycles fat bike full suspension prototype is no news to you. The reaction to this development was wide ranging, enthusiastic, and rather surprising to me.

Of course, I love riding my fat bike, I think the idea of year-round fat biking is already proven, and I think it definitely has a place in off road/mountain biking. A full suspension fat bike? Sure! Why not? That said, there are several things that would need to be addressed before a full suspension fat bike becomes a reality from any company.

First and foremost is the question, "What sort of suspension does a fat bike need?" Obviously, Salsa is well on their way to answering that for themselves, and need no advice from the likes of me. My way of thinking about this question is as follows though...

A fat bike tire is a big, voluminous air spring. Race car drivers have been wrestling with this aspect of large volume tires for years. Altering air pressures causes the spring/tire to react differently, much like the spring in a traditional shock. Traditional mountain bike tires don't really have enough volume to affect overall suspension performance, but fat bike tires would. How that figures into overall suspension kinematics and design is not well known at this point for bicycles. My guess is that the suspension design would necessarily have to be more focused on damping the tire/spring than anything we've seen for a suspension fork for a mountain bike thus far.

There is a big air spring in this image!

"Where do you get the parts?" Then you have to source a fat-bike compatible suspension fork. Fat-bikers have long been employing Maverick SC-32 forks and more recently, the German Answer "Flame" fork. Trouble is that the Mav is flexy and the Flame fork is limited to using narrower rims. Wide rims and fat bike tires don't clear very well, according to reports I've read, between the stanchions on the Flame.

Added to this are the difficulties with small productions, costs, and distributions that are inherent with smaller manufacturers. Don't forget wider crowns require more down tube clearances as well. That complicates matters a bit. Oh yeah.....fat bikes with front suspension will also suffer from tall front ends, just like 29"ers do.

One other thing not talked about much is weight. Fat bikers are somewhat weight obsessed, and I see guys trumpeting their "under 30lb" bikes all the time. Obviously, adding suspension puts you back up there a ways again in weight. Whether most riders would find that worth the trade off for the suspension is not known.

"How Much Travel?" Just what works best for travel on a fat bike is another unknown quantity. Some feel more is better always. But there are limitations. Pointing at the difficulties within the 29"er suspension designs, one can see where fat bikes, whose tires are 29-30" in diameter depending upon tire model and rim combination, are going to quickly run up against the same issues. Front derailleur clearance, tire clearances, and chain stay lengths are also going to figure heavily here. Ideally, I think four inches or less, (most probably less), is going to be the target. Talk about unsprung weight too! Holy cow! Designing a rear damper to deal with all that mass getting thrown around back there is going to be a big challenge.

That doesn't even touch upon through axles, pivots that may need to be beefed up, and swing arm design to contain it all.

I have to hand it to Salsa Cycles and the Crew there. They bit off a "big one" with this project. Now we'll all get to see if they can chew it up, and spit out something worthy. Whether they can or not, I'm betting it will take a while to come to fruition, if it does at all.

Update: Some more information regarding the prototype fat bike FS from Salsa has been posted by "Dirt Rag". See here.