Ron

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If you are in the market for a new fat bike, you have undoubtedly seen a few new bikes featuring 27.5 wheels. Which is better: 27.5 or 26? Hopefully, this article will help with the buying decision. I did a ton of investigation and interviews, including an interview with Why Cycles to get to the facts. Before the review, read on for the advantages of 27.5-in. wheels and information on tires and tire pressure (PSI).


  • Fat bikes have only been designed around 27.5 wheels for a couple of years. The advantages to a 27.5 are the ability to run a narrower fat tire and get the same or greater diameter with increased tire patch contact for increased traction, decreased rolling resistance, and lower PSIs for more comfort. The sidewalls on a 27.5 tire are lower and stiffer, improving handling and cornering. The 27.5 also has a improved attack angle, reducing resistance in deeper snow or loose conditions.
  • 26-in. wheels are claimed to be better in deep snow or loose conditions, but that claim is based on comparing a 26x4.6/5.0 tire to a 27.5x3.8 tire. That's true, however, 27.5x4.5 tires are taller, have the same or greater footprint, and, due to lower sidewalls, have improved handling ability.
  • 26-in. wheels claim to "spin up" faster. This isn't true unless the tire radius is less than a 27.5-in. wheel and tire!
  • "Can you run a 27.5 on a 26 frame?" Even if you can fit the wheel and tire on your 26 bike, a few things can occur to the geometry of a frame designed around a 26 wheel: the bottom bracket height changes as well as the head tube angle, wheel flop, and Trail. All of this adds up to a bike that wasn't optimized for that wheel size.
  • You can run a 26x4.5 or 5.0 tire on a 27.5 frame. If you so desire, you can easily run a 26, but why?
  • The real issue comes down to tires. 27.5 wheels for fat bikes are relatively new. There are only a handful of tires available and all but the Bontrager Barbagazi 4.5 are 3.8 or 4.0. To date, Trek, Farley, and Why Cycles Big Iron are the only companies that specify their bikes can accommodate tires wider than 4.0 in Why? A 26x4.6 tire (about the max width of 26-in. tires) is about the same height as a 27.5x4.0 tire, so the rear triangle, fork, bottom bracket, and head tube must be designed for taller tires. Manufacturers will need to radically modify frames' geometry to accommodate tires larger than 27.5x4.0. That costs a lot of money for R&D.
  • Tire selection will have the biggest effect on your fat bike. Most riders on 27.5 wheels are running their 3.8s at 8-14 PSI on dirt and as low as 1-3 PSI in the snow. Even 0.5 lb of pressure can make a difference. For winter riding, you may want studs or stickier rubber compositions. Tread design and height are also important factors. So, if you demo a bike, make sure you get the pressure dialed as well as the right tire for the right temperature and terrain you are riding. Ride with a pump and gauge. And go tubeless!


The Big Iron

I toyed around with the idea of getting a fattie for about 2 years and finally pulled the trigger on a Why Cycles "Big Iron." Why Cycles is based in Carbondale, CO. They offer three tiers of build levels but what's really cool about Why Cycles is that you can customize your bike around your wants and needs. Since the company sells direct to consumer, it offers a 30-day money-back return policy. All Why Cycles frames are titanium. The Big Iron comes with a Bontrager Haru Pro full carbon fork and is designed around a 27.5-in. wheel. The build weight of my large frame without pedals is 25 lb 10 oz. For comparison below, I used the Trek Farley, 19.5-in. frame and the Salsa Beargrease in large. I also used the Otso Voytek and Rocky Mountain Suzi Q in my research.



Some comments on geometry where it pertains to fat bikes:
  • Tire size. After riding the Barbagazi, I strongly recommend a bike that can run a 4.5 tire. The Barbagazi is seated at 4.45 in. on the I9/HED, 82mm internal width rims and measure 31 in. tall.
  • Head tube angle. 68.7°. Modern fat bikes are going to slacker head tube angles, making them more stable and allowing a better angle of contact in snow. You may think that's too steep, but If the head is too slack, it will increase the trail and wheel flop to the point where the bike is unstable and ponderous. I found a range of 69° down to 68° across the field.
  • Chain stay length. Like the Farley, the Why Cycles also features an adjustable rear to allow for tire space as well as tweaking your ride. For riding in rocky terrain or deeper or loose snow, or touring with weight and bags, you might want a longer chain stay. Shorter will make it snappy and quick.
  • Trail. The Big Iron's trail of 98 is a nice blend of stability and quickness. Since you are pedaling a ginormous front end, how it reacts to inertia and input is very important! Trek Farley is 91. A lower number tends to make for quicker turning but can be less stable.
  • Standover height. When wandering off a packed trail and sinking into deep snow, you want a bike with a slanted top tube with plenty of standover. It also provides more room in the frame to stow gear.

How I Spec'd My Big Iron
  • I9/HED Carbon 825 "Big Rig" wheels (see wheel image here). There is no better upgrade than a good set of wheels and hubs. I9 Fat Bike hubs come with grease that is rated down to -40°F!
  • Bontrager Barbagazi 4.5-in. tires. Although marketed for snow, these babies roll with gobs of traction!
  • Revive 160 dropper post. You need to buy a dropper that is weather- and temperature-appropriate.
  • The drive train is a SRAM Eagle-based mix with GX rear, XX1, 30t cranks paired with a 10-50 cassette.
  • SRAM XO1 RS brakes. According to many articles, for cold weather, DOT or Mineral will work but DOT is preferred, especially below -15°F. Riding in super cold, below -30°F? Go mechanical.
  • Enve M6, 780mm handlebars. Wider bars with short stems and a long reach make for stability.
  • Diety stem and "bits" in lime green to match; super short stem pairs with the wide bars.

Initial Observations

I have to say, this bike is beautiful! The overall shape of the frame, badass HED I9 wheels, and green accents look awesome. I own a Moots (handmade Ti frames in Steamboat), and I was skeptical about the welding and frame build, but the welds are clean and precise -- not up to the same level of the Moots, but close enough, IMHO, Why Cycles has a more advanced geometry. Just look at the images below. Beautifully shaped Ti tubing most notable in the down tube where it's "ovalized" for vertical compliance and horizontal stability, and the rear and chain stays have a noticeable double S curve, allowing tire clearance and ride compliance. There is some really well-done etching on the frame, too.

Ride Impressions

The one word to sum the bike is FUN! I rode an 8-mi loop that has a bit of everything from a 14% section of climbing (and descent) to rock gardens to fast hard pack. I set the tire pressure at 10 PSI. On pavement you can feel the drag of the monster-sized Barbagazis, but once you get onto the trail, you lose the majority of the drag and feel the incredible traction and unstoppable rollover power. The titanium has a very nice feel; it really helps to mute vibration; combined with the big tires, I never felt the need for a suspension fork.

The trail starts with a moderate climb and goes into several switchbacks. I was laughing on the first climb; the tire traction seemingly pulls you up the hill. Going into the switchbacks, I was shocked how nimble the Big Iron was in the corners. I was expecting the front tire to wander or want to go straight but it handled much like my Yeti SB5. Continuing up, I went through a section of irregular jagged rocks where I would normally thread my tire through; with the Big Iron, you just roll over it! No problems and super fun. On the way down, the dropper worked flawlessly and comes with a great remote trigger. You just point and roll with the bike. I was flying down sections letting the tires soak up the hits and the Big Iron was plenty stable. Part of the stability is the 68.7° head angle, which is slack enough for descending and provides stability at slow speeds. Descending switchbacks was unreal. Due to the tire width, you could stand on the outside pedal and tilt the bike more than on my Yeti. The Big Iron just slithered through almost effortlessly. I don't think I will be adjusting the chain stay from the factory setting from midpoint, where the bike feels very balanced.

Overall, the Big Iron was a total blast and I am sold! I will be testing different PSIs, and in spring I will test 3.8 tires to see how they differ from the 4.5s. I encourage riders to get on a fattie to see for themselves that these bikes aren't ponderous, lethargic beasts only for snow but are rather super fun, quick, and agile. No, they wont replace your 150mm full suspension bike, but they are far more versatile than you might think.

Please click below for full-size images of frame details.
 

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Jersey Skier

aka RatherPlayThanWork or Gary
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No, they wont replace your 150mm full suspension bike, but they are far more versatile than you might think.

Please click below for full-size images of frame details.
Throw a Manitou Mastodon on the front and you might take that statement back.
 
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Tom K.

HRPufnStf
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@Tom K. Seems like Trek is "all-in" on 27.5 Fatties. The Haro pro carbon fork is sweet and their tires are really nice. The Barbagazi is amazingly light, ~1230 for a 4.5 is incredible.
IIRC, that's been the case for awhile, now. I came close to a fat bike a few years back, but it would be a silly indulgence in the PNW. There is seldom a period over 10 days where I cannot go on some kind of "regular" bike ride, and when that happens, it usually means exceptional skiing!
 

Jwrags

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While I like the look of your fun on the new bike I like the look of snow on Mt. Werner in the background better:daffy:
 
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Ron

Ron

Seeking the next best ski
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My Friend was riding on 26x40 tires. I jumped on it to feel the difference. It was like riding a kids bike. The wheels felt tiny. Yep, it spun up fast, but too fast, I much preferred the traction and roll of the 27.5x4.5's. You would finesse the bike better especially on the climbs.
 

Blue Streak

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Do you have studdable tires for the winter?
They make them, right?
Or are the stock tires safe for icy and snowy roads?
 
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Ron

Ron

Seeking the next best ski
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