27.5" fatbike bottom bracket drop makes no sense to me

schnee · Jan 18, 2024

Been looking at all sorts of different frames, in an effort to replace the Mukluk I'm tired of.

The thing that's strange about 27.5" fatbikes to me is that the BB drop isn't any different than 26" ones - if not even less. Bikes like Mukluk and Arctodus have 80mm, but Kona Wo, Trek Farley, RSD Mayer have between 55-60mm. So, with tires that are up to 1" taller, the bottom bracket is dropped even less.

That makes no sense to me - shouldn't they have more drop, to counter / go with the taller tire sizes?

Or is this a difference in purpose, i.e. they're optimized for different things, so the height of the BB off the ground is just higher and that's OK? Or there are bigger handling issues that come up that I'm not thinking of?

Anyone who can shed light on this?

mikesee · Jan 18, 2024

26 x 4.8" tires and 27.5 x 4.5" tires are basically the same overall height.

HEMIjer · Jan 18, 2024

I very rarely get snow but questions maybe should be asking is 27.5 vs 26 inch fat bike really matter? Gonna be different for some, I just cant justify it with the amount I use my FB and still have ton of fun rolling 26x4.3s

schnee · Jan 18, 2024

mikesee said:
26 x 4.8" tires and 27.5 x 4.5" tires are basically the same overall height.

Huh. I guess I missed something in the videos I've seen, the 27.5" wheels with those measurements looked significantly taller. That said, all I've seen are videos. Not many fatbikes in Stockholm to compare to.

HEMIjer said:
I very rarely get snow but questions maybe should be asking is 27.5 vs 26 inch fat bike really matter? Gonna be different for some, I just cant justify it with the amount I use my FB and still have ton of fun rolling 26x4.3s

I'm an American football-player sized clydesdale, so I need all the float I can get. I'm in the process of swapping out my frameset so I can fit Johnny 5 and Snowshoe 2XL tires, and my curiosity was piqued during my research.

serious · Jan 18, 2024

My fat bike has 70mm BB drop and I simply cannot understand why the hell does one need a low bottom bracket for fat biking in freaking snow. After a few centimetres of snow, my pedals are hitting the snow. In rocky areas (and where I ride it is really rocky) I have to constantly pay attention to pedal strikes, ratcheting constantly.

A low bb might make sense for a trail bike or enduro bike, but not for a fat bike. And even for trail bikes, I constantly see complains about pedal strikes and now everyone is talking about 160mm cranks. 🙄

Luke Bikewalker · Jan 18, 2024

schnee said:
I'm an American football-player sized clydesdale, so I need all the float I can get. I'm in the process of swapping out my frameset so I can fit Johnny 5 and Snowshoe 2XL tires, and my curiosity was piqued during my research.

In this case, you might want to check out the max float option paired with a frame from your neighbor's country brand

https://www.mtbr.com/threads/may-the-float-be-with-you.1226346/

serious said:
My fat bike has 70mm BB drop and I simply cannot understand why the hell does one need a low bottom bracket for fat biking in freaking snow. After a few centimetres of snow, my pedals are hitting the snow.

Initially, I was also skeptical of a rather tall BB on my end: "only" 60 mm drop and 337 mm BB height with Snowshoe 2XL tires on 128 mm rims. But after quite a bit of snow-only riding, I don't find it as tall or uncomfortable as I feared it would be. I would go a few mm lower even with 2XL, but with Johnny 5 tires, it's quite close to the sweet spot.

schnee · Jan 18, 2024

Luke Bikewalker said:
In this case, you might want to check out the max float option paired with a frame from your neighbor's country brand https://www.mtbr.com/threads/may-the-float-be-with-you.1226346/

I saw it, I'd be down for one, but unfortunately, titanium + 'surprisingly light' (as per the review) isn't a good mix with my size. I'd break it.

Jayem · Jan 19, 2024

serious said:
My fat bike has 70mm BB drop and I simply cannot understand why the hell does one need a low bottom bracket for fat biking in freaking snow. After a few centimetres of snow, my pedals are hitting the snow. In rocky areas (and where I ride it is really rocky) I have to constantly pay attention to pedal strikes, ratcheting constantly.

A low bb might make sense for a trail bike or enduro bike, but not for a fat bike. And even for trail bikes, I constantly see complains about pedal strikes and now everyone is talking about 160mm cranks. 🙄

Well, to help getting on the bike possibly. When you are standing in deep snow and trying to get back on the bike, low BB on the bike helps.

But, yeah, they should have been specing 165mm cranks OEM and if they weren't, they deserve a punch in the face.

BansheeRune · Jan 19, 2024

serious said:
My fat bike has 70mm BB drop and I simply cannot understand why the hell does one need a low bottom bracket for fat biking in freaking snow. After a few centimetres of snow, my pedals are hitting the snow. In rocky areas (and where I ride it is really rocky) I have to constantly pay attention to pedal strikes, ratcheting constantly.

So they can high center the bike any time it is taken off of a paved roadway!

serious said:
A low bb might make sense for a trail bike or enduro bike, but not for a fat bike. And even for trail bikes, I constantly see complains about pedal strikes and now everyone is talking about 160mm cranks. 🙄

In what regard? Offroad is going to relegate either pedalkicking the entire ride or hike-a-bike the entire ride! Lowriders get stuck on the speed bump in front of the local package store all the time.
Frankly, trails where I live and ride are not in any way going to be rideable with a low BB rig since the pedals are stuck to the terrain. My custom frames all have zero drop BB's so I can go Jeepin on two wheels.

jonshonda · Jan 19, 2024

mikesee said:
26 x 4.8" tires and 27.5 x 4.5" tires are basically the same overall height.

And even if the 27.5 is taller overall, the physical bb height is half the difference of the wheel diameter.

Luke Bikewalker · Jan 19, 2024

schnee said:
I saw it, I'd be down for one, but unfortunately, titanium + 'surprisingly light' (as per the review) isn't a good mix with my size. I'd break it.

One way to find out

For reference, all my enduro frames in the past have cracked (stays and mainframes), and I also had to repair the carbon Bucksaw mainframe ... so after a season or two, it should be a pretty good indicator of how the light titanium hardtail is holding up. That's despite the "normal" weight (80-85 kg range) and smooth riding style, but the amount of riding might contribute to material fatigue.

BansheeRune said:
My custom frames all have zero drop BB's so I can go Jeepin on two wheels.

Zero BB drop, wow. Just curious: what's the BB height from the ground on those frames? What crank lengths are you running?

BansheeRune · Jan 20, 2024

Luke Bikewalker said:
Zero BB drop, wow. Just curious: what's the BB height from the ground on those frames? What crank lengths are you running?

170 & 175. My inseam is long so I can easily use big block stroke for torque provided by a nice loong reef bar instead of a stubby wrench!
A little insight on BB elevations. My trials bike is +35mm, later models are as high as 120mm. One of my custom B+'s is -25 and BB center is up where it needs to be for off piste jank.
Yus, it lightens the front end however, I am capable of biasing weight. That translates to being able to float the front end at will without being Super Man! Also like a slack STA since it works for my riding style and needs. The last career choice in my view is becoming a pedalstrike manufacturer!! Trials is the basis of riding for my entertainment.

27.5" fatbike bottom bracket drop makes no sense to me

schnee

mikesee

HEMIjer

schnee

serious

Luke Bikewalker

schnee

Jayem

BansheeRune

jonshonda

Luke Bikewalker

BansheeRune

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