MacFatro - Fatbike news and builds thread

[epicyclo]

How fat do you need to go to get good flotation.....

Nah, no mudguards...

Actually it looks like one of my boatie mates in Oz, Troppo Bob, who is known for deviant boats*. If it wasn't for the tyres, I'd think it was him.



*Also his courtship procedure. He used to pick up middle-aged female tourists with gifts of hand made jewellery featuring coproolite** and take them aboard his yacht for some amorous jousting. The whole harbour would know of his success because of the ensuing ripples emanating from his boat - that's if the vocals didn't give the game away. His exploits once got as far as being featured in the middle pages of the Australian Financial Review. He didn't appreciate the publicity because he reckoned it almost completely cut off his supply...



**Lovely amber looking stone, but actually kangaroo shit encased in epoxy resin.


Edit:

My wife reminded me that the final name for this was "Hopperite".

 

[velomaniac]

Took delivery of my new fat bike rims from Robsson, what a typically efficient German organisation.
I know fat rims are fat but I still find these ones 'FAT', blimey 65mm seems so wide even when you know most folk are using 80-100mm. My coleague George at work will build these for me, he has more patience and greater attention to detail than me, I want these wheels built well, not just adequately as I'd do.
I'm currently rebuilding the Gruffaloe, my test rig, to try out my planned new rear end which will sport 150mm OLN dropouts (plan so far but might change) using a flip flop screw on freewheel hub and a band brake I've been itching to fit to something. Front will be conventional 100mm OLN disc hub.
Deadline is FatForth 14, I must get it built by then !

 

[clubby]

Deadline is FatForth 14, I must get it built by then !

No, get it done a month before so you're not test riding it on the day.








Again.

 

[velomaniac]

Where would be the fun in that ?

Anyhoo only technical issues I've ever had with my bodged fat bikes have been the tyres and inner tubes. Surly ones attract thorns like magnets attract iron. My 24 x 3" ones were suspiciously cheap which should have caused alarm bells. The bead was damaged and wouldn't stay on the rim plus my inner tubes were too small which was definitely my fault.
Nope this time proper fat rims and sealant filled tubes attached to a properly bodgineerd frame.

End of March is my completion target if not before so I have at least a week or two to tinker.

 

[keithyr]

thanks to FFTC i do like the look of them 9zero7's.

so first advice / questions:
for a bit of summer general trail riding with lots of winter snow/mud and some beach work (did aberdour to burntisland on the anthem when the tide was out which was a hoot) whats the consensus on best rim/tyre widths ?

im not gonna singlespeed it so thinking 2x9 or 2x10 gearing - im confused over rear hub width 135/170/190mm - is wider better ?

feck all riding to do so dreaming about bikes lol.

 

[velomaniac]

65-80mm seems to be the preference for width with 4" wide tyres. The wider the rim the lower the psi you can run giving a bigger foot print and thus more float. On-One's Fatty uses 70mm rims and is aimed as an all rounder fat mtb as opposed to floatation bike so for general purposes around there is probably best.
80 - 100mm for 4.8" wide tyres.
On-Ones Floater tyre is a good all rounder with a more round profile than much of the Surly range, good for trail but not outstanding on soft going but good VFM.
Is wider better, jury is still out but currently I'd say no, just another option.
135mm rear only works with offset frames as the hub has to be built with undished spokes to push the freehub out to the right to allow the chain passed the tyre. Cheap option from parts point of view but not upgradeable to fat specific parts. 170mm allows the frame to be normal ie non offsett to the right but requires either a 170mm specific hub or an adapter to fill the 35mm on the left with a 135mm offset fat wheel. 170 I would say offers the best compromise currently via said adaptor for using 135mm parts yet being upgradeable to specific parts in the future. 185/190 is fatbike specific no compromise but can lead to issues of feet clearance often having a high Q factor, distance pedals are apart. I think 170 could be the VHS solution and everything else becomes Beta Max.

 

[clubby]

Personally, I would ignore rear spacing as an issue. Pick the frame you want and whatever spacing it has, it has. All it affects is the initial build.
Rim width does affect tyre profile, but in UK conditions the difference is very little. I've been on group rides with all mix of bikes and nobody struggled more than others. For maximum ability you'd go for 100mm clown shoe rims and 4.8 Bud and Lou tyres but for trail riding they are not the best.
My black ops started on 80mm rims and 3.8 tyres. I now run the same 80 mm front with a 4.8 and the rear is 65mm with a 3.8 (lightweight) to save weight. The new rear is nearly 2lb lighter than before and gives a rounder profile to the rear. This feels better on trails and I've yet to notice a difference on the beach. Yes I'm at a theoretical disadvantage in deep snow or long sections of soft sand but the type of riding I do, I don't encounter these very often. Us Scots have very varied conditions compared to the Yank and generally don't need the ultimate float you might over there.
And for the record, the Floaters may seem cheap but they last nowhere near as long as Surly tyres in the long term. Salty has had thousands of miles out of Surly's but I've seem Floaters looking really rough after less than 500.

 

[epicyclo]

If it was summer use only I'd go for narrow rims.

For general stuff, including snow I use 80mm rims.

I'd go to 100mm rims if I had enough clearance for the bigger tyres, but that would be for soft going only.

My opinion is that the best rear end is the 135mm offset. It allows the use of a wide range of hubs, including hub gears. If you're a weight weenie, there is also the advantage of lighter hubs, but best of all, it is stiffer.

I don't like many of the current crop of wide rears because I think that for an axle of 170mm or 190mm, the axle should be at least 12mm for stiffness. Fatbike tyres are capable of feeding a lot of load into the axle and our axles were designed for a fraction of that. We're using motorbike size tyres on axles originally designed for road bikes with 1" tyres and smooth surfaces. Leaving the axle the same diameter and widening it seems like a real bodge to me.

Much the same applies to the front. I've tried a few 135mm forks and there is a squirm under heavy braking I don't get with the 100mm. A Jones style truss fork is probably the ideal for a fatbike because its structure removes some of the reliance on the axle for stiffness.


(I do know that there are thicker axle designs around now, and if I was going to buy into a wider rear that's how I'd go)

 

[velomaniac]

How can an offset rear frame be stiffer/better, your bending the frame in an area of stress ?
Surely a straight or nearly straight tube will be stronger, but I do agree a stronger axle is a good idea.
I'm not criticising your opinion but I do want to be informed.

 

[kaiser]

Lots of great info above , I can only add the the 907 now to my eyes looks horrible, hydroformed alloy bleugh, could even be a rebadged GT for all I know The best 'affordable' option as I see it now is the Pugsley, and I think clubbys Black Op's (also another reason to buy Black Ops' FFS ) is a fantastic bike with some very cool upgrades. I'd even tout my own which I still think looks quite cool. Thats where I'd be going I think.