New Fat Bike - Wheels, Climbing, Geometry, etc.

one piece crank

Well-Known Member
So I’m almost 4 weeks into fat bike ownership of a 2019 Specialized Fatboy. It does have the carbon fork, but I specifically went for the M5 aluminum frame. The parts pick is nice, with little touches I would have skipped had I built it myself, which make the overall package really nice. The wheels are the new Stout XC80 rims, no lightening holes, 80mm wide (76mm internal) and 4.6” Ground Control tires. Everything sets-up tubeless simply by removing the rim strip and adding sealant (and in my case drilling the rim for a Schrader valve!). I’ve converted the rear due to three thorns in the first 5 days, but I have yet to convert the front (too much fun riding).

Tire pressure - yeah, I’m still figuring that out. Started at 12psi, dropped it down as low as 7psi, and now currently back up to 10-11/rear and 9/front. On my local single track the lower pressures ride REALLY nice, but most places have so many rocks, and when I see a fun line I take it (Trials background)! I find it a very tough balance - soft enought to deform on irregularities, without my 240lbs causing rim strikes - and often change it up right at the trailhead.

Out on the trail (and even sections of road) I don’t notice much loss or weight penalty, but I’m coming from ten years on a burly SS with DH tires that weighs a good deal more than the Fatboy. On the trail it carves up the turns and flow sections with the added benefit of increased roll-over. The front-end feels a bit long and requires more effort to lift, but the bike as a whole is super stable and the rear is dead simple to lift and flick. It's really comfortable out of the box and climbs great. The 1x11 gearing is awesome. The stock seat not-so-much (that was my first change).

Which brings me to my only complaint, all this big-wheel modern geometry crap drops the BB height to the floor! I feel like even aggressive ratcheting puts the pedals within reach of rocks and roots (and it has!) I did a LOT of reading on modern Geometry trends, and specifically chose the Fatboy. With most Fat bikes within 5mm of BB drop, there is no getting away from the low BB’s. I am certainly NOT used to it yet, so I’ll just have to wait until I have significant time in this saddle.
 
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Juggernaut

Master of the Metaphor
So I’m almost 4 weeks into fat bike ownership of a 2019 Specialized Fatboy. It does have the carbon fork, but I specifically went for the M5 aluminum frame. The parts pick is nice, with little touches I would have skipped had I built it myself, which make the overall package really nice. The wheels are the new Stout XC80 rims, no lightening holes, 80mm wide (76mm internal) and 4.6” Ground Control tires. Everything sets-up tubeless simply by removing the rim strip and adding sealant (and in my case drilling the rim for a Schrader valve!). I’ve converted the rear due to three thorns in the first 5 days, but I have yet to convert the front (too much fun riding).

Tire pressure - yeah, I’m still figuring that out. Started at 12psi, dropped it down as low as 7psi, and now currently back up to 10-11/rear and 9/front. On my local single track the lower pressures ride REALLY nice, but most places have so many rocks, and when I see a fun line I take it (Trials background)! I find it a very tough balance - soft enought to deform on irregularities, without my 240lbs causing rim strikes - and often change it up right at the trailhead.

Out on the trail (and even sections of road) I don’t notice much loss or weight penalty, but I’m coming from ten years on a burly SS with DH tires that weighs a good deal more than the Fatboy. On the trail it carves up the turns and flow sections with the added benefit of increased roll-over. The front-end feels a bit long and requires more effort to lift, but the bike as a whole is super stable and the rear is dead simple to lift and flick. It's really comfortable out of the box and climbs great. The 1x11 gearing is awesome. The stock seat not-so-much (that was my first change).

Which brings me to my only complaint, all this big-wheel modern geometry crap drops the BB height to the floor! I feel like even aggressive ratcheting puts the pedals within reach of rocks and roots (and it has!) I did a LOT of reading on modern Geometry trends, and specifically chose the Fatboy. With most Fat bikes within 5mm of BB drop, there is no getting away from the low BB’s. I am certainly NOT used to it yet, so I’ll just have to wait until I have significant time in this saddle.

Those are still 26” rims on the fatboy right? You could go to 27.5 rims and as fat as you can fit in the frame. That’ll raise it up. With the bigger diameter rims you can use a narrower tire and still have the same float so it’s a valid swap. Unless you happen to be a short 240 lb. then shorter cranks are an option too.

Good luck.
 

one piece crank

Well-Known Member
Yes, the Fatboy is 26-inch. The reason I avoided B-Fat is that it takes away the primary attraction of a fat bike, and that is the fat carcass of the 26-inch tire. Its kind of like modern 4-wheel-drives with low profile tires on large(er) diameter wheels - you lose the higher tire aspect ratio, lose the usable inflation range, and wind up with something only good on pavement.

My quick math tells me I could gain about 0.85 inches (27.5x4 vs. 26x4.6 wheel), cut that in half for theoretical static BB gain at 0.425 inches. I don’t think this is the solution for me. If B-fat at the higher pressure rides better than 26-Fat at the lower pressure, could I just run higher pressure?
 

Juggernaut

Master of the Metaphor
Yes, the Fatboy is 26-inch. The reason I avoided B-Fat is that it takes away the primary attraction of a fat bike, and that is the fat carcass of the 26-inch tire. Its kind of like modern 4-wheel-drives with low profile tires on large(er) diameter wheels - you lose the higher tire aspect ratio, lose the usable inflation range, and wind up with something only good on pavement.

My quick math tells me I could gain about 0.85 inches (27.5x4 vs. 26x4.6 wheel), cut that in half for theoretical static BB gain at 0.425 inches. I don’t think this is the solution for me. If B-fat at the higher pressure rides better than 26-Fat at the lower pressure, could I just run higher pressure?

Not B-Fat, Full-Fat. I only mentioned it because I have 3 fatbikes, a 2013 Mukluk, 2015 Beargrease (both 26”) and a 2018 Farley. The Farley is the one running 4.8’s on 27.5 BHD’s. I’m 255 and at Allaire I run 6.5/7.5 and Jungle 8/9.
 
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Karate Monkey

Well-Known Member
165s are great when you're rolling with multiple speeds.

Even with 175s, I only wind up smacking crap when I'm tired.

Not B-Fat, Full-Fat. I only mentioned it because I have 3 fatbikes, a 2013 Mukluk, 2015 Beargrease (both 26”) and a 2018 Farley. The Farley is the one running 4.8’s on 27.5 BHD’s. I’m 255 and at Allaire I run 6.5/7.5 and Jungle 8/9.

Yeah, your numbers seem (?) a bit high, op. 29x3 for cross country use at 180, I'm running 9.5/11
 

mattybfat

The Opinion Police
Team MTBNJ Halter's
Yup your gonna need to adjust. I run 26" hoops 5 inch tires. I have also been using flats after 20+ with clipless on all bikes but still get my hits. Being once a dominant SSer ratcheting is ingrained in the brain hence why I have I9 rear hub. Always felt rear hubs are one of the most important parts of any bike.
 

Juggernaut

Master of the Metaphor
Thanks, those are good comparison points. I'm not really liking my 9/11.

Another way to play with Ride feel is with the sidewalls. If rocks are still causing rim hits, a thicker/less supple sidewall Can act as a damper, so to speak. Rigid fat-bikes have suspension, but they do not have damping. Which is why if you miss on the pressure you feel like you’re riding in a “bouncy house”.

Anywho, People like @fidodie are more equipped to speak on this from a science/math standpoint... but in “keep it super simple” terms, some of the force from the tire/rock collision is eaten up by the effort needed to deflect the sidewalls.

A thicker/less supple sidewall requires more force to deflect whereby Increasing the time it would take the rock to make it all the way to the rim. Unless it’s one of those run in to a square ledge kinda hits, you’re forward motion might get you past It before it makes contact with the rim....

2c-
 

one piece crank

Well-Known Member
I have thought about the tire sidewall contribution, but I do not know how my Cound Controls compare to something like a Maxxis EXO casing, or even any fat tire for that matter. For reference, I was looking at the Maxxis Colossus as my next tire.
 
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SmooveP

Well-Known Member
Until someone comes up with a lightweight tire with flexible and durable sidewalls, you have to live with the fact that the pressure that feels the best is not conducive to riding the rockier trails in NJ. Been riding fat (4") since 2011, and lived through the era of very few tire choices at all and no tubeless tires or rims. I personally hate the feel of heavy tires and stiff sidewalls, but I'm a scrawny 150lbs, so your experience is probably different. I've been pretty happy with the Jumbo Jims. The handling and traction is perfect for me, and they've held up great - no torn casings or failures of any kind in 3 years.

I don't recall hearing many complaints about pedal strikes on fatbikes, though. My (fully rigid) fatbike's BB height is right around 12.25", and I'm pretty happy with that. My 27.5+ Yeti is a different story in that department - pedal strikes galore.
 

one piece crank

Well-Known Member
My fat bike is about the same (12.25"), with 5" below the pedal at its lowest point. My old SS was 13.25" BB and 6" below the pedal. Even though one inch is a lot, I'm starting to feel that it isn't so much the BB/pedal proximity to the ground, as much as it's the overall size of the fat bike. I"m 6'4" riding an XL, and with the bigger wheels, taller-stack & longer-reach I find I get trapped on the bike if I get stopped in technical terrain. If I spin the rear wheel or slightly slip a pedal I cannot seem to recover like my old bike. I never thought about it before, but I may look into a dropper post.

Last few rides at 9/10psi were uninspiring. On trails with roots, logs, shot/steep climbs, but a distinct absence of rocks, I really wanted to be a few psi lower. Overall I like my Ground Controls, I just need to learn the new bike...
 
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SmooveP

Well-Known Member
My fat bike is about the same (12.25"), with 5" below the pedal at its lowest point. My old SS was 13.25" BB and 6" below the pedal. Even though one inch is a lot, I'm starting to feel that it isn't so much the BB/pedal proximity to the ground, as much as it's the overall size of the fat bike. I"m 6'4" riding an XL, and with the bigger wheels, taller-stack & longer-reach I find I get trapped on the bike if I get stopped in technical terrain. If I spin the rear wheel or slightly slip a pedal I cannot seem to recover like my old bike. I never thought about it before, but I may look into a dropper post.

Last few rides at 9/10psi were uninspiring. On trails with roots, logs, shot/steep climbs, but a distinct absence of rocks, I really wanted to be a few psi lower. Overall I like my Ground Controls, I just need to learn the new bike...

Yeah, 1" difference in BB height is a lot. I think your brain gets used to whatever BB height once you ride it often enough. Switching back and forth between multiple bikes with different BB heights makes it difficult to adjust. The secret formula for adjusting tire pressure is to keep lowering it until you destroy a rim, then add 1 psi ;).
 

one piece crank

Well-Known Member
Another way to play with Ride feel is with the sidewalls. If rocks are still causing rim hits, a thicker/less supple sidewall Can act as a damper, so to speak. Rigid fat-bikes have suspension, but they do not have damping. Which is why if you miss on the pressure you feel like you’re riding in a “bouncy house”.

Been riding fat (4") since 2011, and lived through the era of very few tire choices at all and no tubeless tires or rims. I personally hate the feel of heavy tires and stiff sidewalls, but I'm a scrawny 150lbs, so your experience is probably different. .

My first tire epiphany was back in 1988. I built a new rear wheel for my Trials bike, upgrading from the 20x2 Pirelli tire to the massive 19x3. As much as the small Pirelli ruled, the new, wider, soft-n-thick sidewalls where simply unbelieveable! It was 10+ years until anything remotely similar would be available for DH bikes. I've been riding DH tires exclusively because I can get low psi AND rim protection from the sidewall (even tubed). The lighter fat bike sidewalls (yes, I did write that) are unusual - the width says go low, but sidewall flexibility says add few psi. I'm a big guy and I like that dampened DH-esque sidewall at lower pressures.

The secret formula for adjusting tire pressure is to keep lowering it until you destroy a rim, then add 1 psi ;).

Well, I didn't destroy a rim, but to avoid doing so I'm sticking around 9-10psi when I know rocks are present, or if I'm not familiar with the terrain.
 
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Dajerseyrat

Well-Known Member
I think the pedal strikes is simply the lower bottom bracket trend for a lower center of gravity. I have come off a Scalpel 3 29er and rarely strike pedals on features however when I tested 3 different newer 27.5 plus bikes, I would strike pedals at least 3 to 4 times a ride. I tried playing with tire pressures and sag but it still happens. Looking at the 29er tire right next to the 27 plus tire, there is a negligible difference in overall height. The dropping of the bottom brackets in the newer designs is just something we need to get used to.
 

one piece crank

Well-Known Member
Pedal strikes - haven’t had any more, but haven’t really hit any rock gardens either. I *think* I’m getting to know the bike. I also installed an internal routed dropper post, something I have not run for 25 years:
IMG_0983 copy.JPG

(My 1989 Hite-Rite)

Although I have yet to test the dropper on seriously technical terrain, a minimal drop makes the bike a lot more maneuverable in tight twisty stuff and I stand more (which feels good coming from a SS).

Overall the bike is beyond awesome. I absolutely love it. The geo, wheels and rigid fork are perfect for me and my riding style. No desire to ride a different bike.

The 1x drivetrain still leaves me speechless. Nice, smooth shifting, and not even a slap or hint of a dropped chain. I’m coming off 10-years of SS-only, and I simply forgot what it’s like to always have the right gear to hit your cadence. All my riding has improved, and my fitness is getting dragged upward as well.
 

one piece crank

Well-Known Member
This weekend was my first real snow ride, pushing up to 4 inches of relatively fresh snow. So, I got schooled a little on tire pressure. I found if I ride lightly, being extra careful with weight distribution, spinning in a very low gear, I can basically control bottoming down to about 5psi. I’m still super paranoid about rim damage as I typicallly ride a lot of roots and rocks, but I never really experienced snow Fat. At 230lbs, and the fact that this isn't really very much snow (meaning ultimately I'm still riding on the ground), I'm sticking withe 5-6psi in slow snow, and 9psi on dry trails.

Very interested to see how much snow we get tonight. If the snow machines hit the farm fields by my house I'll be out for couple hours...
 
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