[FishMan473]

I'm curious what people who feel knowledgeable enough to share think the ideal geometry is for a fat bike who's sole purpose is riding in snow? Around here, we have groomed trails, but I also spend a fair amount of time making tracks in ungroomed surfaces. A couple issues that I see as important are:

• stable handling as very low speeds
• being able to track in a straight line in deep snow, resisting snow pushing the tire to the side
• climbing on loose, steep surfaces
• being able to get my body in a position that produces power well
• evening out weight distribution on the tires for better 'float' (this is probably contrary to the above though)
• offsetting issues like self-steer that come up with large tires at low pressures

Curious what other things people think are important for snow riding, and how folks think good geometry can address these.

....

This came up as I am starting to look into new bike options, as I'd like to upgrade from my 2013 Beargrease in the next couple of years. Comparing to the 2022 model, very little has changed:

• The head tube is 1° slacker
• The seat tube is 0.5° slacker (as opposed to industry trends)
• The chainstay is 15mm shorter. Not sure if they wanted the '13 model to have longer stays or they just could not achieve shorter stays with the original Al frame, and having built around a 2x drivetrain

But overall, not a lot has changed! Many other fat bikes have similarly 'old school', shorter, steeper geometry compared to 'modern' standard MTB's. I don't think we need or want real slack HTA's on fat bikes, but I really do prefer a longer TT.

Its not clear to me if there is a reason for the current geometry of fat bikes, or if there just hasn't been much development with them as the demand for fat bikes has died down.

 

[prj71]

...but I really do prefer a longer TT.

The stack and TT is a little larger on this one vs. most other fat bikes. My GF has this one.

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The Woo continues to be one beloved fat beast! Its ability to carry massive amounts of gear with its three-pack cage mounts aboard its carbon disc fork make it a sand and snow bikepacking favorite. With geometry derived from the Honzo, ultra-powerful hydraulic disc brakes and a 12-speed...

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I think 68-70 HTA is the sweet spot for a fat bike solely riding snow. Slacker HTA makes it harder to handle in the snow.

 

[Jayem]

Yeah, on a snow-bike, you spend so much time on flat terrain, vs. bikes that climb and descend more, you don't want or need an excessively steep STA IMO. It's not ALL flat terrain, but as a %, it's higher IME. You don't want that increased pressure on your wrists. Since it's a hardtail, it already doesn't sink back in the travel like a long travel FS bike (where they steepen the STA to make up for this). Then there's HTA, IME, too slack washes out in turns too easy. If you are having issues rolling over stuff on a wheel as big as a 26" fat wheel, with effective diameter greater than 29", you need a dropper post and some skills. Most likely, you are just letting the front end dig in to stuff, not holding the bars straight (possibly due to real narrow bars), not un-weighting the bike properly. Get the TT length you prefer. It's also nice to have a larger frame for a bigger frame bag. Don't go to a too-large frame just for this, but there are decades of programming that make people think they should downsize when in-between sizes, which leads to cramped riders, again, on most of the terrain/time that they ride.

 

[Flyer]

I think that 68-69 HA is great for fatties. I would not want to go above that since (for me) it wold be much harder on steep switchbacks. That whole super short stem and stretched out front would just cause a ton more washouts in corner, I think. I did sell my Fatboy and got a slightly slacker (I think) 27.5 Farley and it is certainly nicer rolling with the taller wheels. I have not tested out the tight cornering yet, where the Fatboy did really well, since the steeper HTA dug into the ground harder.

 

[FishMan473]

That whole super short stem and stretched out front would just cause a ton more washouts in corner, I think.

Would it though? What's the difference if you have a 600mm top tube with a 100mm stem vs a 640mm TT with a 60mm stem?

 

[Overkill]

Would it though? What's the difference if you have a 600mm top tube with a 100mm stem vs a 640mm TT with a 60mm stem?

wouldn’t you have a longer front centre and therefore have a less weighted front? I would assume this would make create a situation where less weight on the front decreases traction and increases washouts.

 

[Traktor]

The head tube angle discussion seems valid but my humble opinion is that shifts in rider weight fore and aft are far more significant than bar position or chain stay length. You skootch forward to weight the front wheel or slide back for traction. Add to that the infinite snow variables of density and depth and it seems like trying to design a perfect snow bike is just internet chatter. Any reasonably designed fat bike will work.

Going from 3.8 to 4.8 tires is something to be grateful for.

 

[prj71]

The head tube angle discussion seems valid but my humble opinion is that shifts in rider weight fore and aft are far more significant than bar position or chain stay length. You skootch forward to weight the front wheel or slide back for traction. Add to that the infinite snow variables of density and depth and it seems like trying to design a perfect snow bike is just internet chatter. Any reasonably designed fat bike will work.

Yup. Agree. The only thing I needed to adjust on my fat bike when I bought it was the fore / aft of the seat to balance my weight.

Given the variable condtions of snow...Most snow only riders should plan on the front tire washing out a few times a year.

 

[Flyer]

I like getting more weight up front naturally without having to move around as much an I do on a regular bike. I like the 75mm stem I use on the fattie. It may be 80. It feels super planted.

 

[Jayem]

The head tube angle discussion seems valid but my humble opinion is that shifts in rider weight fore and aft are far more significant than bar position or chain stay length. You skootch forward to weight the front wheel or slide back for traction. Add to that the infinite snow variables of density and depth and it seems like trying to design a perfect snow bike is just internet chatter. Any reasonably designed fat bike will work.

Going from 3.8 to 4.8 tires is something to be grateful for.

This is something I have to do a LOT more on my fat-bike, it helps with my normal bike skills too. There are so many little inclines, humps, bumps, where you can't pedal up them because the traction doesn't exist. What you have to be able to do is loft the front with your weight rearward, have the front wheel go over, then throw your weight forward, so you'll have momentum and an un-weighted rear, to follow the front. CG bias basically has to shift from wheel to wheel. While this happens in most all riding, this becomes very exaggerated on fat-bikes in snow IME.

 

[rth009]

The head tube angle discussion seems valid but my humble opinion is that shifts in rider weight fore and aft are far more significant than bar position or chain stay length. You skootch forward to weight the front wheel or slide back for traction. Add to that the infinite snow variables of density and depth and it seems like trying to design a perfect snow bike is just internet chatter. Any reasonably designed fat bike will work.

Going from 3.8 to 4.8 tires is something to be grateful for.

I'm no expert, but this is consistent with my experience. The right tire size and pressure and the right body english at the right time makes a lot more difference than a couple degrees of head tube/seat tube angles and mms of reach and chainstay length. Snow is so variable ...

 

[Flyer]

I'm really liking the 27.5 Farley over the 26 Fatboy. The Fatboy was maybe a lb lighter and did have a slightly steeper head angle. The only place it had an advantage was steep and tight slow turns where the front was more planted. The Farley needs a little more planning and weight shift in those scenarios but I am getting used to it as well. Other than that, the rollover and speed of the Farley is nicer. It is also more stable and fun to ride. The DHs are a lot nicer and I can enjoy the ride more since the rocky DHs needed more focus on the Fatboy. I do have the wheelbase on the longest setting but will shorten it as soon as I get my new studded tires on the new wheelset. I will have a wheelset with studs and one without.

I'm shifting my weight around less on the Farley as well, in 90% of riding. I have primarily been testing it for setup since we only got a couple of snows. The real test is yet to come as well get a real base around here. I think Trek nailed the geometry in general. I do run a longer stem and 780mm ENVE bar that don't have a of of sweep and it feels really good, though my 800mm Ibis bar (on the Ripley) feels perfect. I could go to 800 but will prob just leave it as-is since the Farley is mainly for snow. In some ways, I prefer now snow (I love my dry trails and dry gravel routes) but since it is probably inevitable and sorely needed, I'm looking forward to snow-packed trails.

 

[Cdal1770]

It's unfortunate that fat bikes haven't experienced the same R&D as "normal" bikes. I think this is due to market demand. Regardless, I own a LaMere fatbike (27.5 x 4.5 on 75 mm rims) and it has a, wait for it, 70.5 deg HTA. It's a wonderful climber, but on steep descents.....ugh: worrisome. It's built for groomed single track racing and it shows. I have taken it everywhere though so a more well-rounded and active fat bike would be most welcome; queue the Skookum.

I purchased one a few months ago and will transfer the components of my LaMere to the Skookum (bikes and bike parts are pricey!) sometime in January. I'll miss the luxury of changing out the carbon rigid fork for a suspension fork, depending on the season, but I think it'll be a good compromise. Best of all, it'll be a more playful and better all-around fatbike with greater squish in front.

I'm very curious to see how different it'll feel on groomed snow trails. I'm going to run it with 85mm rims and 26 x 5 tires.

 

[ZX11]

Since it matters what the snow is, figure out your bike then match it to the snow it is ideal for. Be sure to go out on those days that snow is present. Expect to struggle where the conditions aren't ideal. Then expect to have more fun because not ideal and a bit of struggle is a better time. At least for me.

Person asked, "do you have ideal pressure in your tire?"
Someone who just rides replies, "It seems to have pressure."

 

[BansheeRune]

Ideal is that which works for you! It is akin to trying to install an Audi water pump on a Ford...
There is not really a one angle fits all.

 

[singletrackmack]

I'm curious what people who feel knowledgeable enough to share think the ideal geometry is for a fat bike who's sole purpose is riding in snow?

This is like asking “what is the ideal geometry for a bike who’s sole purpose is riding on dirt?” More information is needed to answer the question. Mainly, what type of terrain you’re talking about.

So, what are you asking then?
Ideal geometry for riding snow on flat rolling terrain on wide groomed trails?
Ideal geometry for riding snow in mountain terrain with lots of elevation gain, narrower trails with corners and tight turns, steep ups and downs and a lot more speed?

Just like on dirt, the terrain you ride effects what type of geometry you want. Riding dirt on wide flat rolling double track has a different ideal geometry from riding dirt in the mountains on singletrack, with corners and steeper terrain. So, what type of terrain are you asking about for ideal geometry riding a fat bike in the snow?

 

[Jayem]

This is like asking “what is the ideal geometry for a bike who’s sole purpose is riding on dirt?” More information is needed to answer the question. Mainly, what type of terrain you’re talking about.

So, what are you asking then?
Ideal geometry for riding snow on flat rolling terrain on wide groomed trails?
Ideal geometry for riding snow in mountain terrain with lots of elevation gain, narrower trails with corners and tight turns, steep ups and downs and a lot more speed?

Just like on dirt, the terrain you ride effects what type of geometry you want. Riding dirt on wide flat rolling double track has a different ideal geometry from riding dirt in the mountains on singletrack, with corners and steeper terrain. So, what type of terrain are you asking about for ideal geometry riding a fat bike in the snow?

Does "snow bike" speak for itself? This implies travel on mostly-snow and that said snow will have to replenish itself from time to time. This should introduce enough variability into the situation...

 

[singletrackmack]

Does "snow bike" speak for itself? This implies travel on mostly-snow and that said snow will have to replenish itself from time to time. This should introduce enough variability into the situation...

Well, I live and ride on the backside of a ski resort with, um, snow that is at a sharper angle I guess (since terrain doesn’t seem to matter )? Not much horizontally angled snow, so I prefer slacker and longer because of this. However, I don’t think this is ideal for everyone, but if all riding in the snow is the same regardless of terrain, then I guess this will work for all, so slacker and longer it is

But really, terrain and where you ride matters a lot. Just think about skis, completely different if your riding flat or steep terrain, so why wouldn't you want your fat bike to better fit different terrain types with snow? Many of the groomed trails I ride on I also snowboard down. Parts are steep and fast and having a slacker and longer front end really makes for a better ride here. Off groomers and it is steeper with more turns.

I think ideal geometry for snow is:
-68-66 degree HTA
-Longer reach to allow shorter stems for better control.
-Adjustable chainstays for varying conditions and types of ride.
-BB that are in the -50mm drop range.
-shorter seat tubes to allow for long droppers.

A longer bike as I like shorter stems for better control. I don’t like the sketchy feeling of trying to weight the front tire with a flag pole of a stem. On snow, being able to properly weight the front tire is a big deal to help avoid wash out, and this is much more controlled and steering is way more direct with a short stem.

For HTA, I think between 68-66 degrees seems to be the sweet spot with going 66* if you have steeper terrain and 68* if flatter. Maybe 69 if only riding rigid, but over 68 degrees on a hardtail gets too steep with the dynamics of a sus fork, fat bike or not imo. Also, weighting the front tire with a steep HTA is sketchy and as I mentioned, being able to properly weight the front tire is a big deal on snow.

Chainstay length, I would say adjustable for sure. I definitely notice the difference between 465 to 450 or 450 to 435. It is nice to be able to adjust this according to conditions and the type of ride I am doing. If conditions are making traction more difficult, then the shorter position is ideal getting more weight on the rear tire. If I am going on a ride with steeper terrain, then the longer setting is nice for more stability and weight on the front wheel.

For BB drop, I think a little higher is better just for the simple purpose of ground clearance in deeper snow.

Finally, shorter seat tubes to be able to run longer droppers. This is so nice for so many different scenarios riding on the snow from wanting to get your weight low as possible for better control in slippery conditions at speed to simply being able to put your foot down without tipping over in deeper than you thought snow. I also really like being able to lower the seat height a little for steeper, slippery climbs as it allows me to shift my weight around more and quicker to the tire that needs traction.

 

[Jayem]

So do you want a modern trail bike with fat tires?

 

[mikesee]

Some grub for thought:

Snowbike geometry.

A few weeks back I shared some pics and minutia relevant to my new snowbike. For years I've been meaning to write out the pe...

lacemine29.blogspot.com