Well, since you asked …

I’m looking at a similar project, but with a Pinion gear box.

The problem with running a gearbox or a motor with a large wheel is you end up with really long chainstays.

The way around that is to use a high pivot suspension.

I have a Kavenz VHP Pinion on order, it should be here next month. If this bike works out, my next “ask” is a fat Pinion.

If I wanted a full suspension e-fat bike, it would make sense to use the Pinion e-gearbox that combines a motor with a gearbox.

 

Thank you for the feedback.

I have asked both Pinion DE and NA about their fat bike compatible MGU, and short answer is, not in the immediate future. Individual motor units and batteries for independent bike builders won't be available until 2025-ish

I'll look into Kavenz if they are willing to make a normal fat-fs. The only high-pivot bike I know is the Cannondale Jekyll. I can feel that the bike wants to surge forward after a full compression, and I don't know if I want that.

Foes e-fat is also another option, if they ever open their pre-orders. The other fs-fat with modern geo is Huraxdax ELS X2.

 

Hi guys,

I need feedback on, what I hope to be, my one and only bike. My main reason is to combine fat bike with e-mtb.
I wanted to see what a full-suspension e-fat bike will look like if it can fit 27.5x4.5 Cake Eaters mounted on Nextie 89mm ID rims.
Geometry is based on my current 2022 Norco Sight VLT (small). I'm 165cm with 74mm~ inseam. T-rex arms.

Chain stay length +51mm to accommodate the massive rim + tire combo.
Head tube length +67.4mm to offset lengthen rear-end since I can't lengthen the reach.
Seat tube length matches top of tire so even when in full compression, you won't buzz your butt.
View attachment 2075923
*This is the only fat e-bike frame from XACD catalogue with a straight seat tube.
*If you know an OEM frame with almost same fit, please let me know.

My hope is to use this as my all-season sled here in the Canadian Prairies.
Cheers and I appreciate your feedbacks!

What are you going to do for front fork? CEs are so massive on 27.5 that it will really limit the travel of a Mastodon. I guess that's ok if you are only going for 3-4" of travel in the rear. All the DC forks limit the tire size to basically "not really fat".

 

Yeah, he’s trying to have his cake and eat it too 🤣

The bigger the tire, the more undampened the suspension, so it doesn’t really make sense to have more that 4-5” of travel.

My Fatillac is 120/140 on 27.5 x 4 Studded D4’s, not the greatest flotation, but it works for all but the softest snow; we don’t get much snowpack where we live.

If the OP really wants big flotation tires, I’d keep the bike more moderate, like Jayem suggested, 100/120, then have three sets of wheels (27.5 x 3, 27.5 x 4.5, 29 x 3).

 

Whereas, with 26" tires, I can go a little bigger and use the bike as a 150/150 enduro 29er rig in the summer pretty easily, but CEs are just giant. I have them on my hardtail with 95mm rims. But I'm thinking running CEs on a FS bike is going to mean pretty limited travel.

Which reminds me that I just want a gooddam 80-100mm headshock type front fork, able to accomdate fat tires without all the extra metal structure required for an 8" wide fork like the mastodon.

 

Whereas, with 26" tires, I can go a little bigger and use the bike as a 150/150 enduro 29er rig in the summer pretty easily, but CEs are just giant. I have them on my hardtail with 95mm rims. But I'm thinking running CEs on a FS bike is going to mean pretty limited travel.

Which reminds me that I just want a gooddam 80-100mm headshock type front fork, able to accomdate fat tires without all the extra metal structure required for an 8" wide fork like the mastodon.

This is new to me. Why they stop making this? This is perfect for me

I'm also looking at Dengfu E55 frame. It's 26x4.8 and has kinda modern geo but long reach. Made me feel like riding a scooter.

 

Yes, I do intend to have my cake and eat it, too!

The way I was thinking of running the bike as my only, and all-season bike is by:
using low pressure CE's with suspension locked out or stiffened up for winter.
use 29+wheelset with 160mm Mastodon EXT for summer time.

My question is how soft and flexy would the rear end be with 197mm fat spacing, aggressive MTB tires, and 150mm of travel. Haven't experienced that before.

 

Ain’t no such thing as a Mastodon EXT 160mm fork, best you’ll get is 140mm.

More travel will increase your RC.

Bigger tires will increase your RC.

Adding a motor will increase your RC..

You are going to end up with an RC of 480mm, which is no bueno unless you just like going straight.

You’re gonna need to compromise: less travel, less tire, or no motor.

It’s just math.

 

My hope is to use this as my all-season sled here in the Canadian Prairies.
Cheers and I appreciate your feedbacks!

Just curious, where at in the prairies?

 

I roam the free ranges of Kananaskis(?), AB to Wascana trails, SK. I'm a land developer accountant, so I get dragged around.

You can easily spot me on a local sidewalk, toppled over by high winds. And so I hide in the woods.

 

Have you actually priced out what a custom FS would cost? Are you actually building it yourself or hire someone? Do you have any building experience? I like the idea of Jack of all trades .... until you learn about the "Master of none" part.

Fat FS kind of disappeared for a reason. Fat bikes already are more expensive and heavy, and FS just adds even more weight and cost. And a hone-designed suspension, designed by someone inexperienced and without design software likely won't be great. No offense, I don't know your skills. Look on YT at the "Vorsprung Suspension" and other videos to learn what all plays a role

Fat bike FS also will be hard to tune. You have an undampened spring (large tire) and dampened spring. Lots of adjustments. I'm no expert, but assume there is a reason long travel FS have small tires.

I'm not discouraging you. Kudos for thinking about it. One-bike-for-everything sounds great till you have carrying riding styles and seasons.

 

Have you actually priced out what a custom FS would cost? Are you actually building it yourself or hire someone? Do you have any building experience? I like the idea of Jack of all trades .... until you learn about the "Master of none" part.

Fat FS kind of disappeared for a reason. Fat bikes already are more expensive and heavy, and FS just adds even more weight and cost. And a hone-designed suspension, designed by someone inexperienced and without design software likely won't be great. No offense, I don't know your skills. Look on YT at the "Vorsprung Suspension" and other videos to learn what all plays a role

Fat bike FS also will be hard to tune. You have an undampened spring (large tire) and dampened spring. Lots of adjustments. I'm no expert, but assume there is a reason long travel FS have small tires.

I'm not discouraging you. Kudos for thinking about it. One-bike-for-everything sounds great till you have carrying riding styles and seasons.

The bike design is from the XACD catalogue and will be built by them. Main point of the build is to have one bike.

As someone has already pointed out, the latest 160mm Mastodon fork (non-EXT) doesn't fit the rim/tire combo I had in mind for winter. As the geo I used is based off of a Norco Sight VLT which is a 160/150 F/R. It is better to use 26x4.8 for tire clearance, even at full squish. At this point, a custom build is no longer needed as Foes Mutz/Lenz Fatillac already exist.

 

My point was to not underestimate the size of CE “4.5”s. These are one if the few exceptions where the tires actually exceed the claimed size. They are massive and much bigger than say D5s on even the same rim. Im going to mount up D5s (27.5) this week on 75s and ill put them next to my CEs on 95s for you. Not the exact same thing, but youll get an appreciation for how much bigger the CEs are in width and diameter.

 

My point was to not underestimate the size of CE “4.5”s. These are one if the few exceptions where the tires actually exceed the claimed size. They are massive and much bigger than say D5s on even the same rim. Im going to mount up D5s (27.5) this week on 75s and ill put them next to my CEs on 95s for you. Not the exact same thing, but youll get an appreciation for how much bigger the CEs are in width and diameter.

Thank you, please do! I'll post mine mounted on a BR2250 (I think this is 79mm ID?). I never underestimated CE's size as I stumbled upon them as the tallest (I don't know if widest) 27.5+ tires there is. Another reason for a custom bike is I can't fit them on my Canyon Dude. The Dude gets an OEM FBR because I don't want to commit to another tire that might not fit.

If you need deep snow, high flotation, then a hardtail is the way to go, full suspension won’t really benefit that use, and it just complicates things.

I have five miles of single track in my backyard, tight, trees, some tech, flow, a jump line, and a few drops.

The most snow we get is 24” and the trails don’t get much deeper than 12” packed. I can do all my climbs, even with ice.

The Fatillac 120/140, coil/coil set up with D4 studded is perfect. My second wheelset is 29 x 3, which I use during the warm months.

That seems to be the general consensus. Hardtails for max float and short travel if going FS. If only Fatillac have a straight seat tube, I'd have gone for it. I need max drop for my short legs, hardtail or FS.

I think that a 140/130 f/r would be most realistic with current available parts. I'll try aping Norco VLT Fluid's geo but I'm sure this'll still be sled regardless. I just noticed the 513mm CS length T.T

For now, this build is on pause. I'll research more into parts that actually exist and can fit together.

Thank you for the feedback and guidance @Jayem and @Donkeeboy.

Also, is there a collection or database of actual fat tire height/width sizes here w/ pictures mounted on Mastodon STD/EXT? That would be helpful.

 

Also, is there a collection or database of actual fat tire height/width sizes here w/ pictures mounted on Mastodon STD/EXT? That would be helpful.

You'll have to dig a bit. There's a spreadsheet on Hayes' site with which tires fit which fork config (STD or EXT). No photos.

Then there's Mike's blog with a useful visual: Testing one, two: Simple visual.

And I can confirm that Manitou Mastodon and Snowshoe 2XL on 128 mm DR rims work well. Tight, but without rubbing. https://www.mtbr.com/threads/drunken-rhinoceros-widest-carbon-rims.1219614/page-8#post-16079583 (with pics). 140 mm EXT.

You also have the electric Maxx fatbike as you already mentioned, but it's limited to 26 x 5 tires. MAXX Huraxdax ELS (EP8) - The Offroad Monster

In your case, the geo from the first post, I'm concerned that a long wheelbase, extra long chainstay, and quite slack HTA won't be particularly fun or nimble to ride, except on high-speed or steep terrain. Those geo numbers more resemble a DH rig. Depending on your body build and height, it might be a bit of a bike to handle and maneuver. If there would not be a motor and/or gearbox, it would be slightly easier to make a compromise on wheel fit/clearance and geometry.

+5 cm chainstay length and +8 cm wheelbase is a massive difference compared to the Norco VLT.

 

Manitou Mastodon Pro Fatbike Fork (2024)

80mm to 160mm travel Tire clearance for 27.5 x 4.5"/26 x 5" A single external compression adjuster simultaneously adjusts HS and LS damping characteristics Features a fixed shim stack and a secondary shim stack that is preloaded by the external adjuster. The resulting wide tuning range combines the benefits of a low-speed platform and high speed progressive tune suitable for any terrain Incremental Volume Adjust (IVA) modifies the volume in the positive air chamber with self contained spacers dictating the position of the IVA piston E-Bike compatible

 

Here's my current bike build with 140mm EXT fork, CE's 27.5x4.5 mounted on BR2250's. The CE's are so massive that they almost off-set the 20mm decrease in front travel.

Fork tire clearance. Currently pumped up to 10 PSI for commute use.

 

How much travel is that fork running? Looks like maybe 100mm?

 

It could just be sucked down, which happens with the Mastodon, you have to attach a pump and pull it apart (that's the only way the negative chamber can equalize).

 

An inherent design flaw...